Recoverable Bismuth-Based Microrobots: Capture, Transport, and On

Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Recoverable Bismuth-Based Microrobots: Capture, Transport, and On-Demand Release of Heavy Metals and an Anticancer Drug in Confined Spaces Seyyed Mohsen Beladi-Mousavi,† Bahareh Khezri,† Ludmila Krejčová,† Zbyněk Heger,‡ Zdeněk Sofer,† Adrian C. Fisher,§ and Martin Pumera*,†,∥

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Center for the Advanced Functional Nanorobots, Department of Inorganic Chemistry, University of Chemistry and Technology, Technická 5, 166 28 Prague, Czech Republic ‡ Department of Chemistry and Biochemistry, Mendel University in Brno, Zemedelska 1, CZ-613 00 Brno, Czech Republic § Department of Chemical Engineering and Biotechnology, University of Cambridge, New Museums Site, Pembroke Street, Cambridge CB2 3RA, U.K. ∥ Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea S Supporting Information *

ABSTRACT: Self-propelled microrobots are seen as the next step of micro- and nanotechnology. The biomedical and environmental applications of these robots in the real world need their motion in the confined environments, such as in veins or spaces between the grains of soil. Here, self-propelled trilayer microrobots have been prepared using electrodeposition techniques, coupling unique properties of green bismuth (Bi) with a layered crystal structure, magnetic nickel (Ni), and a catalytic platinum (Pt) layer. These Bi-based microrobots are investigated as active self-propelled platforms that can load, transfer, and release both doxorubicin (DOX), as a widely used anticancer drug, and arsenic (As) and chromium (Cr), as hazardous heavy metals. The significantly high loading capability for such variable cargoes is due to the high surface area provided by the rhombohedral layered crystal structure of bismuth, as well as the defects introduced through the oxide layer formed on the surface of bismuth. The drug release is based on an ultrafast electroreductive mechanism in which the electron injection into microrobots and consequently into the loaded objects causes an electrostatic repulsion between them and thus an ultrafast release of the loaded cargos. Remarkably, we have presented magnetic control of the Bi-based microrobots inside a microfluidic system equipped with an electrochemical setup as a proof-of-concept to demonstrate (i) heavy metals/ DOX loading, (ii) a targeted transport system, (iii) the on-demand release mechanism, and (iv) the recovery of the robots for further usage. KEYWORDS: micromotors, bismuth, drug delivery, water purification, heavy metals, microfluidic channel

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INTRODUCTION Self-propelled nano/microrobots have been at the cutting edge of multidisciplinary research.1,2 They are often referred to “motors” because of their ability to transform external fuels, for example, light or chemicals, into mechanical motion. However, a simple propulsion is not their only function, and an exciting future for these tiny robots to advance different applications is expected. This is based on the notable achievements in the recent years in the fabrication3−5 and application6−9 of robots with different functions for environmental monitoring and water purification,10,11 imaging,12 drug delivery,8,12,13 nanosurgery,14 lab-on-chip devices,15 and sensors.7,8 Particularly, the recent progress in targeted drug delivery and efficient water purification systems is very promising. However, the application of these robots in actual environments, for example, in veins or between the grains of soils, is still challenging and needs great efforts. © XXXX American Chemical Society

The challenges of implementation of targeted drugs in clinical praxis are as follows: (i) to find the target in a particular disease, (ii) to find a drug that could treat it, and (iii) to have a drug carrier that can safely transfer the drug to the targeted sites.16 Nanomaterials such as liposomes,17 carbon derivatives,18,19 metals and metal oxides,20,21 black phosphorus,22 and dendrimers23,24 have shown good performance as drug carriers when linked with targeting ligands.25,26 However, these represent passive systems that are transported by fluxes of blood and diffusion. Nano/microrobots can function as an active self-propelled platform for drug delivery.27 These machines combine the benefits of the traditional carriers such as drug protection, selectivity, and biocompatibility with Received: December 12, 2018 Accepted: March 7, 2019

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DOI: 10.1021/acsami.8b19408 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

process often requires addition of selenide and sulfide (e.g., Bi2Se3 and Bi2S3)59−61 that are not biocompatible; and thus harmful. Therefore, using pure metallic bismuth could eliminate the hazardous substrates, which is an obvious advantage for biological applications.62 Bi microrobots were synthesized via template-assisted electrodeposition of bismuth as an outer layer on the inner wall of a polycarbonate membrane (PC), followed by electrodeposition of nickel (Ni) and platinum (Pt) as middle and inner layers, respectively (i.e., Bi/Ni/Pt microrobot). The loading capacity of the robots for the anticancer drug, that is, doxorubicin (DOX), and heavy metals (As and Cr) was remarkable. Notably, an electrochemical release mechanism was performed in this work, which allows on-demand release of cargoes within only a few seconds.63 This is extremely important regarding the often-limited fuels of microrobots in contrast to the time-consuming process of drug release using conventional methods, that is, the pH-triggered release mechanism.64,65 The magnetic properties coupled with the on-demand release mechanism allow the recovery of the robots (in the case of water purification). Remarkably, the mentioned processes such as load, navigation, and on-demand release of cargoes were performed in a microfluidic system equipped with an electrochemical setup. This is an important step toward realization of the autonomous self-propelled microrobots with direction-specific driving, which has been intensively studied in the past few years.66 Coupling the favorable surface characteristics of bismuth with their excellent performance in loading and unloading DOX and heavy metals, recyclability of the robots, and their application in a microfluidic channel makes these high-performance tubular microrobots accessible for advanced drug delivery and water purification applications.

their function to swim and penetrate into tumor tissues and release the drug at the desired time and location. Moreover, these machines can be carefully controlled by external sources, for example, light, ultrasound, and a magnetic field. For example, the in vitro studies confirmed their application to deliver drugs, to sense protein or ligands, to isolate cells, to perform microbiopsies, or to assist sperms with motion deficiencies. The quality of water is rapidly worsening. This is mainly due to population growth, reinforcement of agricultural activities, and increasing industrialization and urbanization.28 Heavy metals, particularly chromium and arsenic, are extremely dangerous and threatening to living organisms and human beings. These elements are very toxic and nonbiodegradable, and they accumulate via the food chain. The maximum permissible limits in drinking water, recommended by the World Health Organization, for chromium (Cr) and arsenic (As) are 50 and 10 μg L−1, respectively.29−31 Therefore, removal of these heavy metals from sources of drinking water using efficient and cheap methods is extremely important. Among different technologies such as chemical precipitation, gravity separation, ion exchange, reverse osmosis, membrane filtration, electrodialysis, and adsorption, new findings in nanotechnology revealed the effectiveness of adsorbent materials.32 In spite of all the efforts, there are only a few reports on the removal of As and Cr, which is due to their preferable occurrence in the anionic form (arsenates and chromates).31,33,34 Although there are successful reports on the treatment of As and Cr using metal salt, metal oxides, and hydrous metal oxides, collection and recovery of the adsorbent material are still challenging, which significantly limits their realization for industrial applications.29,35,36 Recently, promising results from the application of self-propelled nano/ microrobots in the environmental field have been shown. These artificial swimmers combine different functions such as (i) active motion in solution resulting in enhanced (micro)mixing,7,37,38 (ii) surfaces with different functionalities designed for adsorption or degradation of the desired pollutant,11,39−50 and (iii) transfer of the pollutant (and robot) to the selected location.41,51 There are also reports on designing robots to analyze water quality (detection of metals)52 to evaluate pH53 or to sense other materials.54 Herein, we present the fabrication of new self-propelled Bibased tubular microrobots and detailed a proof of concept of their performance for smart drug delivery and recovery of heavy metals (arsenic and chromium) from contaminated water. The desirable properties of bismuth, such as (i) its chemical stability in aqueous solution, (ii) its excellent biocompatibility (known as “green element”),55 (iii) its high surface area provided by the layered rhombohedral crystal structure,56 and (iv) its ability to strongly interact with hazardous heavy metals, make it an ideal candidate for the fabrication of advanced microrobots. Moreover, the Bi layer will be partially oxidized after insertion of robots in the water, which have additional effects on binding with ions of heavy metals. Recent studies have shown the promising performance of bismuth derivatives for biological applications including imaging, photothermal therapy, and drug delivery.57,58 This is due to the large X-ray attenuation coefficient of the bismuth element, low toxicity, low cost, and no residue in the organism, which provide higher flexibility in the clinical setting. Despite the mentioned benefits of Bi-based agents, the synthesis

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RESULTS AND DISCUSSION Fabrication of Bi/Ni/Pt Microrobots. The fabrication of tubular microrobots using Bi as an outer layer, Ni as the middle layer, and Pt as an inner layer, via a template-assisted electrodeposition protocol is demonstrated in Figure 1a. The bismuth layer functions as a carrier to adsorb the demanded objects. The nickel layer provides magnetic properties to navigate the microrobots to the desired location by an external magnetic field. The Pt layer decomposes hydrogen peroxide (H2O2) into water and oxygen bubbles, and the self-propulsion of robots is based on the force provided by the ejection of the bubbles from one side of the tubular microrobots. The fabrication of Bi/Ni/Pt microrobots is explained in detail in the Experimental Section. In summary, at first, Bi was electrodeposited on the inner wall of a PC membrane with 5 μm diameter pore size from a 4 mM aqueous solution of Bi(NO3)3·5H2O (pH = 2.7) using cyclic voltammetry with a scan rate of 20 mV s−1 over the 0.0 to −0.8 V potential range (vs Ag/AgCl) for two cycles (Figure 1b).67 The electrical conductivity of the Bi layer allows consecutive electrodeposition of the other layers. The Ni layer was electrodeposited using amperometry at −0.9 V with a cutoff charge of 4C (Figure 1c and Figure S1), and the Pt layer was electrodeposited by a galvanostatic technique, that is, applying −10 mA for 600 s (Figure 1d).50,68 Finally, the Bi/Ni/Pt microrobots were released by dissolving the membrane in dichloromethane (DCM). The Bi/Ni/Pt microrobots were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and X-ray powder B


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Propulsion of Bi/Ni/Pt Microrobots. Figure 2a−e and the corresponding videos (Videos S1−S5) show movement

Figure 2. Propulsion of Bi/Ni/Pt microrobots in the presence of different concentrations of the fuel: (a) 0.5% H2O2, (b) 1% H2O2, (c) 2% H2O2, (d) 3% H2O2, and (e) 5% H2O2. (f) Impact of fuel concentration on average speed. Presented speed is the average of 20 independent experiments. Error bars represent the standard deviation for speed measured at each concentration of fuel (H2O2). All motion analyses were carried out at a constant sodium dodecyl sulfate (SDS) concentration (0.5% w/v). Movement pattern of Bi/Ni/Pt microrobot (g) without magnet and (h) in the presence of a magnet; experimental conditions: 3% (v/v) H2O2 and 0.5% (w/v) SDS.

Figure 1. Synthesis and characterization of Bi/Ni/Pt tubular microrobots. (a) Template-assisted electrodeposition of bismuth, nickel, and platinum layers, in the PC membrane (connected to conductive copper foil from one side), followed by dissolution of the membrane and isolation of tubes. (b) Electrodeposition of Bi during two CV cycles at ν = 20 mV s−1 using 4 mM Bi(NO3)3·5H2O solution, pH = 2.7. (c) Amperometric electrodeposition of Ni via applying −0.9 V up to 4C charge. (d) Potentiometric electrodeposition of Pt at −10 mA for 600 s. Copper foil, Ag/AgCl, and carbon foam were used as working, reference, and counter electrodes, respectively, in panels (b)−(d). (e) SEM image of a Bi tube on copper foil. (f) SEM image of the side view of a Bi/Ni/Pt tubular microrobot; length 10 μm. (g) Homogeneous distribution of Bi, Ni. and Pt as determined by EDX spectroscopy. (h) Raman spectrum of the Bi layer illustrating the characteristic Eg and A1g bands of bismuth. (i) XRD analysis of the Bi layer with diffraction peaks corresponding to the lattice planes in the rhombohedral crystal structure (inset).

patterns of the Bi/Ni/Pt microrobots in the presence of various concentrations of the fuel (H2O2). The trajectories of the microrobots have been monitored using bubble tails. These bubble tails are the result of hydrogen peroxide decomposition in contact with the inner Pt layer, resulting in propulsion of the microrobots. The velocity of the microrobots was significantly increased at higher concentrations of the fuel, and the microrobots exhibited more complex motion (Figure 2f). The average speed of the Bi/Ni/Pt microrobots rose from 102 μm s−1 in 0.5% H2O2 to 384 μm s−1 in 5% H2O2. The propulsion speed is the resultant of the driving and drag forces. The drag force can be predicted precisely by Stokes’s law for any shape with a low Reynolds number.73,74 The drag force depends on the shape and morphology of the microrobot, and a correction factor can be applied to Stokes’s law to correct the influence of the shape. The drag force of the tubular Bi/Ni/Pt microrobot (40.1 pN) was calculated using the equation below in the presence of 3% H2O2:

diffraction spectroscopy (XRD). Figure 1e displays the SEM image of an electrodeposited Bi tube after removal of the PC membrane, illustrating successful deposition of a homogeneous, thin layer of Bi. A microrobot consisting of all three layers is shown in Figure 1f, demonstrating an average length of 10 μm. The EDX analysis of the microrobot reveals its components including bismuth, nickel, and platinum (Figure 1g). The Raman spectrum of the Bi tubes exhibits characteristic peaks of metallic bismuth including two modes at 71 cm−1 and 98 cm−1, which correspond to the two first-order optical bands of rhombohedral bismuth related to doubly degenerate Eg and non-degenerate A1g phonon modes, respectively (Figure 1h).69,70 To further confirm the formation of the bismuth layer of the microrobots, XRD analysis of a bismuth film, prepared according to the above protocol, was performed (Figure 1i). The sample shows a bismuth phase with clear diffraction peaks corresponding to the lattice planes in the rhombohedral crystal structure and crystallographic parameters of a = b = 4.55 Å, c = 11.86 Å and α = β = 90°, γ = 120° (PDF #44−1246).71 Since bismuth is prone to oxidation, another phase, that is, bismuth (III) oxide (Bi2O3), was also identified.72

F=

2πμL ϑ ln(L /r ) − 0.5

where ϑ is the speed of the microrobot, μ is the viscosity of the solution, and L and r are the length and radius of the tubular microrobot, respectively. The movement pattern of the Bi/Ni/ Pt microrobot in the presence of a magnetic field was also studied. As expected, in the presence of a magnet, the random walk of the Bi/Ni/Pt microrobot (Figure 2g) turns to a straight line swimming toward the magnetic field (Figure 2h). Use of Bi/Ni/Pt Microrobots for Drug Loading and Delivery. The Bi-based tubular microrobots present significant promise as drug microcarriers for efficient loading, C


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Figure 3. Drug delivery application of Bi/Ni/Pt microrobots. (a) Physical adsorption of doxorubicin (DOX) on the outer layer of the microrobot. (b) UV−Vis spectra of a DOX solution in the absence (black) and presence (colored) of microrobots at different incubation times. (c) Optical (top) and fluorescence (bottom) images of a robot loaded with DOX. (d) EDX spectroscopy images of a typical example of the microrobot, illustrating the distribution of N, confirming the presence of DOX molecules on the surface of the robot. The robot’s elements (Bi, Ni, and Pt) were also detected but for simplicity reason, they are not shown here (see Figure 1g). (e) Bubble/magnet-propelled swimming of microrobots loaded with DOX in the presence of cancer cells (green). (f) Optical images of cancer cells before (left) and after applying a potential (−1 V vs Ag/AgCl) (right) in the absence of robots. (g) Electroreductive release of DOX from Bi/Ni/Pt microrobots; first scan: −0.2 → −1.0 → 0.0 (red); second and third scans: 0.0 ↔ −1.0 (black); the blank is in the presence of only cancer cells. (h) Schematic illustration of the electrochemical release of DOX from robots to cells upon applying a cathodic potential (see Figure g). (i) UV−Vis spectra of the solution after drug release. (j) Optical (top) and fluorescence (bottom) images of a cancer cell after drug release. (k) EDX spectroscopy images of a microrobot, illustrating no nitrogen, confirming total detachment of DOX molecules. (l) Schematic illustration of the collection of the drug residues using microrobots controlled by an external magnetic field. (m) UV−Vis spectra of the solution after collection of drug residues. (n) Optical (left) and fluorescence (right) images of a cell and a robot after the recollection of drugs.

transport, and on-demand release of a widely used anticancer drug, that is, DOX (Figure 3).75,76 The drug loading capability of microrobots was evaluated by the UV−Vis absorbance of the DOX solution mixed with microrobots at different incubation times (Figure 3a,b). The initial absorbance of the DOX solution before the addition of robots was 0.82 a.u. In the presence of robots and after only 5 min, the absorbance of the DOX solution has significantly decreased (0.74); this shows the high affinity of DOX molecules toward bismuth microrobots. The adsorption of DOX on the surface of robots slowly plateaued in the following 720 min (abs. of 0.74 → 0.52) (Figure S2). The loading efficiency in the current case was ∼145% of the geometric surface area, which is attributed to the layered structure and roughness of the bismuth layer (eqs S1−S3). Next, the loaded microrobots were washed several times with pure water to remove the free DOX from the solution. DOX has strong intrinsic fluorescence (self-fluorescence at λem

= 580 nm), which was employed to confirm the successful loading on the surface of microrobots (Figure 3c).77 Additionally, the EDX study of the loaded robots showed the homogeneous distribution of nitrogen atoms, indicating packed loading of DOX molecules on the surface of the microrobots (Figure 3d). The conventional methods of the drug release, that is, acidtriggered release, are time-consuming processes, and the microrobots may significantly change their position during this period due to the ongoing propulsion, thus thwarting the targeted delivery of the active substance.78 For example, carbon nanotubes (CNTs) (modified with chitosan or poly(ethylene glycol)) loaded with DOX exhibit a half-life of 20−50 h at pH 5.5.64,65 The acid-triggered release is probably caused by the enhanced positive repulsive charge in the DOX/CNT environment.79 A recent work by Sadaf and Walder showed that electron injection into the DOX@CNT composite, D


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5-diphenyltetrazolium bromide (MTT) assay. As illustrated in Figure 4a, the exposure of the cancer cells to Bi/Ni/Pt

without modification of the CNT carrier, causes an ultrafast release of the DOX within only a few minutes at neutral pH.80 Therefore, we have studied this electroreductive method to release DOX molecules loaded on our robots via an electron injection mechanism, while robots are in motion in cancer cell cultures (Figure 3e). Prior to the testing of therapeutic efficiency of electrochemically released DOX on targeted cancer cells, testing of electrochemical conditions leading to the DOX release was carried out, and the behavior of cancer cells upon electron injection (without the presence of robots) was observed under an optical microscope. It was observed that applying a potential in the same electrochemical conditionas used for drug releasedoes not have any obvious impact on the cells (Figure 3f) (see the electrochemical response in Figure 3g, blank). The release procedure was performed by cyclic voltammetry (CV), swiping the potential from −0.2 to −1 V at the first scan and 0 to −1 V at the second and third scans with a scan rate of 20 mV s−1 in the presence of cancer cells (Figure 3g,h). It is noteworthy that the subunit of DOX is 1,4-dihydroxyanthraquinone (quinizarin), which can be reversibly reduced to leucoquinizarin (+ 2e−/2H+) (at approximately −0.57 V vs Ag/AgCl) or oxidized to anthracenetetrone (− 2e−/2H+) (Figure S3).80 The huge irreversible current at the first scan is attributed to the electron transfer to the outer layer of microrobots. This induces negative charges to both microrobots and DOX molecules, causing electrostatic repulsion and finally release of DOX. The irreversible cathodic current disappears after the first scan, illustrating the ultrafast release mechanism. The successful release of the drugs was further confirmed by measuring the UV−Vis spectra of the electrolyte solution after the release, exhibiting the characteristic peaks of DOX (Figure 3i). After the release of the drug and because of its adequate uptake by the targeted cells, they show representative apoptotic features, demonstrated by cell shrinkage and a change in intracellular DOX fluorescence (Figure 3j). Furthermore, the isolated tubes were analyzed by EDX and showed almost no trace of nitrogen, confirming the successful and residue-free electrochemical release of DOX (Figure 3k). Next, the ability of Bi/Ni/Pt microrobots to recollect the residue of the drugs that were not uptaken by the cancer cells was assessed (Figure 3l). This is an important step due to the high dosages that are often used in chemotherapy with a risk of development of severe side effects when nontargeted (healthy) cells interact with residue-free DOX.81 In this approach, 1 h after drug release, the robots were driven around the reservoir (14 cm3) by a magnet for 10 min. Notably, the robots collected a substantial part of the drug residues. This was confirmed by the decrease of the intensity of the peak in the UV−Vis absorbance spectrum of the solution after the recollection step (Figure 3m, compare with Figure 3i) as well as the significant DOX fluorescence (which confirms the DOX recovery) observed in the optically visualized microrobots (Figure 3n). Examination of Effects of Bi/Ni/Pt MicrorobotMediated DOX Delivery on Cell Viability. Since the biocompatibility of the drug delivery systems is a prerequisite for their biomedical application,82,83 the in vitro screening is carried out. Initially, the viability of breast cancer cells (T47D) after 24 h of treatment with different concentrations of selected therapeutic agents (Bi/Ni/Pt microrobots, their DOX-loaded variant, and electroreductively released DOX, referred to as free DOX) was evaluated by a 3-(4, 5-dimethylthiazol-2-yl)-2,

Figure 4. In vitro screening of the therapeutic effect of Bi/Ni/Pt microrobots. (a) Viability screening of T47D cells treated with Bi/Ni/ Pt microrobots (in the presence/absence of KCl) (100% corresponds to 1.75 × 106 robots mL−1). (b) Viability screening of T47D cells treated with DOX@Bi/Ni/Pt microrobots and free DOX (electroreductively released DOX from DOX@Bi/Ni/Pt). The viability screenings were analyzed upon 24 h exposure. The data are expressed as a dependence of the cell viability (%) on the concentration of the particular therapeutic agent. (c) Representative living-cell fluorescence images showing nuclei counterstaining (Hoechst 33258, blue) and nuclear internalization of doxorubicin (DOX, red) in cancer cells exposed (6 h) to the selected therapeutic agents. Scale bars for images were 50 μm. The apoptotic features (nuclei shrinkage and DNA condensation) are pointed out by white arrows.

microrobots of various concentrations (100% corresponds to 1.75 × 106 robots mL−1) led to a negligible change of the cell viability. It is noteworthy that when the cells were co-treated with 1 mM KCl (electrolyte used for electroreductive release of DOX), their viability was slightly higher, which is attributed to the supportive effect of KCl on cell growth. This finding, together with the safety confirmation about the electrochemical DOX release condition (obtained within the previous chapter), verifies the safety of the entire procedure for mammalian epithelial cells. It is noteworthy that even a small amount of H2O2 fuel has a negative impact on the viability of cells,9 and it has been used as a model system in this proof-ofconcept work. Regarding the therapeutic efficiency of DOX, namely, the toxicity of electroreductively released DOX (free DOX) and DOX@Bi/Ni/Pt microrobots toward targeted cancer cells, their viability after 24 h of treatment was compared (Figure 4b). In the case of targeted cancer cells, free DOX exhibited higher toxicity compared to the toxicity of E


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ACS Applied Materials & Interfaces DOX loaded on Bi/Ni/Pt microrobots. This phenomenon is most likely due to slower internalization and release of DOX from Bi/Ni/Pt microrobots. Overall, the exceptional in vitro biocompatibility of Bi-based microrobots is in line with other studies dedicated to application of Bi-containing materials for cancer therapy or diagnosis is confirmed.84−86 Moreover, we also found that the DOX release/recollection is a very promising approach to increase the efficiency of the protection of non-targeted cells against the negative side effects of DOX. To visualize the difference between the therapeutic effect of free DOX and DOX@Bi/Ni/Pt microrobots, living-cell fluorescence imaging was carried out (Figure 4c). The cancer cells, preincubated for 24 h, were treated with Bi/Ni/Pt microrobots, their DOX-loaded variant, and free DOX. After 6 h of incubation, the nuclei of cancer cells were stained with Hoechst 33258 with the aim of recognizing whether the DOX molecules were internalized in the cells and reached their site of action (the nuclear DNA). The highest intensity of DOX fluorescence was observed in the nuclei of cancer cells treated with free DOX. On the contrary, cells treated with DOX@Bi/ Ni/Pt microrobots exhibit a significantly lower intensity of DOX fluorescence, demonstrating the lower bioavailability of DOX when loaded on the Bi-based microrobots. Phase contrast and Hoechst micrographs (Figure 4c) show that the cells treated with free DOX present the typical apoptotic features (changes in cell membrane contrast, shrinkage, and condensation of nuclear DNA). Meanwhile, the cells treated with DOX@Bi/Ni/Pt microrobots exhibited the onset of the apoptotic features in their early stage (see cellular rounding in phase contrast micrographs). The cells treated with Bi/Ni/Pt microrobots (similar to control experiment) exhibit no evidence of apoptotic features, which highlights the biocompatibility of microrobots and verifies the MTT data. Use of Bi/Ni/Pt Microrobots for Water Purification. To demonstrate the proficiency of the Bi/Ni/Pt microrobots for water purification, their performance for removal of As and Cr from contaminated aqueous solutions is studied (Figure 5a− e). The microrobots (1.75 × 106 robots mL−1) swam either by an external magnetic field or by generating bubbles in a solution containing heavy metals (in the case of bubblepropelled motion, 0.5% (w/v) SDS and 1% (v/v) H2O2 were also added) (Figure 5a,b). At different time intervals (5 min, 10 min, 15 min, 30 min, 4 h, and 24 h), the concentrations of the heavy metals were measured by inductively coupled plasma optical emission spectrometry (ICP-OES) (Figure 5g); this determines the adsorption efficiency of robots toward different metals. Interestingly, although the bubble-propelled robots cause a stronger mixing effect, the adsorption efficiency observed for robots propelled by an external magnetic field is only slightly smaller than the adsorption by bubble-propelled robots. This is attributed to the high affinity of the heavy metals toward Bi microrobots and a fast adsorption process. Notably, after only 5 min, the bubble-propelled microrobots removed 64 and 45% of the As and Cr, respectively. The adsorption increased over time; however, the changes were not dramatically significant after 30 min. The adsorption percentages of As (5 ppm) and Cr (4 ppm) on the surface of bubble-propelled microrobots after 1 h were 92 and 67%, respectively. The removal of heavy metals after up to 24 h was also studied; however, the concentration almost did not change when compared to the value determined after 60 min (Figure S4). The Bi microrobots are more efficient in removal of arsenic from contaminated water than removal of chromium,

Figure 5. Environmental application of Bi/Ni/Pt microrobots. Schematic illustration of (a) adding of microrobots to a solution containing targeted heavy metals, (b) adsorption of heavy metals on the surface of the self-propelled Bi/Ni/Pt microrobots, (c) collection of the microrobots using a magnet, (d) electrochemical release of heavy metals from the microrobots by applying a constant potential (−1 V vs Ag/AgCl), and (e) collection of the recycled microrobots using a magnet. (f) EDX spectroscopy images of the bubble-propelled microrobots loaded with heavy metals (1 h), illustrating the presence of As and Cr on the surface of the microrobot. The robot’s elements (Bi, Ni, and Pt) were also detected but for simplicity reason, they are not shown here (see Figure 1g). (g) Inductively coupled plasma optical emission spectrometry (ICP-OES) showing the removal of As and Cr using magnet- and bubble-propelled Bi/Ni/Pt microrobots. The recovery percentage of desorbed heavy metals by electrochemical release has been shown for bubble-propelled systems (hatched columns); control experiment is after 24 h. Experimental conditions for bubble-propelled Bi/Ni/Pt microrobots: 1.75 × 106 microrobots mL−1 in water containing targeted heavy metals (As: 5 ppm; Cr: 4 ppm), 0.5% (w/v) SDS, and 1% (v/v) H2O2.

which is in agreement with the previous results.36 It was shown that arsenic adsorption is via a Lewis acid−base reaction between bismuth and As(III), while the adsorption of the Cr is explained by electrostatic interactions.36 To further verify the adsorption of heavy metals on the Bi/Ni/Pt microrobots, EDX analyses were performed, confirming homogeneous distribution of As and Cr on the surface of robots (Figure 5f). A control experiment confirmed that in the absence of robots, SDS and H2O2 do not have any major effect on the concentration of heavy metals (Figure 5g, control). The removal procedure has also been repeated using non-motile microrobots (neither external magnet nor bubble-propelled), and the removal percentages for both As and Cr were less than 15%. Trajectory and speed analyses of Bi/Ni/Pt microrobots, exposed to the solutions containing As and Cr, have been performed, and no major differences were recorded. The reusability of the carriers is considered as an important step toward the large-scale application of microrobots. This was achieved for the first time by an electrochemical mechanism, in which electron insertion into the heavymetal@Bi/Ni/Pt robots causes the heavy metals’ detachment F


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unloaded robots were guided to the next reservoir for collection. The screenshots of the self-propelled microrobots passing the working electrode are presented (Figure 6a). As discussed earlier, the electrochemical release of DOX molecules is the result of an increase in the negative repulsive charge in the DOX@Bi/Ni/Pt environment (Figure 6c). However, the electron injection into the heavy-metal@Bi/Ni/ Pt microrobots probably disturbs the complex formed between the metals (As or Cr) and bismuth/bismuth(III) oxide (Bi2O3) and thus their detachment from the robots. The possibility of magnetically guiding the robots to the desired location combined with the on-demand electrochemical release mechanism allows designing an automated system to navigate microrobots so as they perform their assigned duties.

from the microrobots. This is attributed to disturbance of the complex formed between heavy metals and Bi/Bi2O3. In this system, a constant potential (−1 V vs Ag/AgCl) was applied for 10 min through the working electrode, that is, the copper plate. The electron transfer to robots, settled on the working electrode, causes a fast detachment of metals from the surface of the robots. It was also confirmed that collision of the moving robots to the standing working electrode has a similar effect, and a comparable release was observed. After the electrochemical release, the electrolyte solution was analyzed by ICPOES, and the robots were collected by a magnet. The ICPOES results revealed that the electrochemical release caused desorption of 87 and 86% of the attached As and Cr, respectively (Figure 5g, hatched columns). SEM images of the robots after heavy-metal removal confirmed that the electrochemical release mechanism does not affect the morphology of the Bi/Ni/Pt microrobots. The heavy-metal removal/release capability of the recovered robots was also examined up to five times, and similar results were recorded. Load, Transport, and Release in a Microfluidic Channel. As a proof of concept, performance of the Bi/Ni/ Pt microrobots was verified using a microfluidic channel with a built-in electrochemical setup (Figure S5) to perform different tasks, which were explained earlier, including (i) loading of DOX and heavy metals (removal from contaminated solution) inside the reservoir, (ii) transport of the loaded robots to the desired location, that is, the microchannel equipped with an electrochemical setup, (iii) electrochemical release, and (iv) collection of recycled microrobots inside the second reservoir (Figure 6 and Figure S6). As shown in Figure 6b, DOX molecules or heavy metals are adsorbed on the surface of the bubble-propelled Bi/Ni/Pt microrobots inside the first reservoir. An external magnet was used to propel the microrobots through the channel, equipped with a threeelectrode setup, while a constant potential was applied (−1 V). This caused the release of the cargoes (Figure S6). Then, the

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CONCLUSIONS

In summary, we have studied the significant performance of bismuth-based tubular microrobots for drug delivery (DOX) and removal of toxic heavy metals (As and Cr) from contaminated water in a confined space, that is, a microfluidic channel equipped with an electrochemical setup. The tubular robots’ structure consists of multilayers of bismuth (outer layer), nickel (middle layer), and platinum (inner layer), provide different functionalities. Bismuth is chosen for the outer layer of the microrobots because of (i) its biocompatibility, which is excellent for biomedical applications, (ii) the high surface area provided by its layered rhombohedral crystal structure, and (iii) its capability to form complexes with heavy metals. The use of a green Bi outer surface facilitated the unique performance of microrobots as drug delivery carriers for clinically relevant applications. The widely used anticancer drug DOX was loaded on the surface of Bi microrobots and navigated toward cancer cells, taking advantage of the magnetic properties of the nickel layer. A new on-demand release mechanism based on an electrochemical procedure, that is, electron injection to the moving microrobots, is investigated. It was shown that this method allows an ultrafast release of the drugs upon applying low cathodic potentials. An in vitro study confirmed this efficient release mechanism in the presence of cancer cells. The unique properties of the Bi/Ni/Pt microrobots enabled the effective DOX release in tumor sites and thus enhanced the therapeutic efficiency and reduced the toxicity side effect on the healthy tissue. The Bi microrobots were also introduced for efficient removal of arsenic and chromium, as highly toxic heavy metals, from contaminated water via a simple adsorption process. We have shown the recovery of heavy-metal ions and further reusability of the Bi-microrobots. In this system, self-propelled microrobots move randomly in the contaminated water to adsorb the heavy metals and subsequently are simply collected via a magnet. We have used a similar electrochemical method, as shown in drug release, to detach the adsorbed heavy metals. Notably, the robots were reused for further removal of heavy metals. Most importantly, a proof-of-concept study confirmed the loading, navigation, and on-demand release of DOX and toxic heavy metals in a microfluidic system equipped with an electrochemical setup. In this system, (i) the drug/heavy metals were loaded on the self-propelled microrobots in the first reservoir, (ii) the loaded microrobots were guided by a magnet to the channel equipped with an electrochemical setup,

Figure 6. Load, transport, and release of DOX and heavy metals (As and Cr) in a microfluidic channel. (a) Experimental screenshots of a Bi/Ni/Pt microrobot while passing the working electrode (middle electrode). (b) Schematic illustration of a microfluidic channel with built-in electrodes (see an optical image in Figure S5). (c) Mechanism of the electrochemical release of cargoes from a microrobot upon applying a negative potential (−1 V); the release of DOX from microrobots is attributed to an increase of the negative repulsive charge in the DOX@Bi/Ni/Pt environment. In order to confirm that the release was successful, the robots were initially loaded with the cargo and then inserted into the first reservoir, followed by their transfer to the channel for the electrochemical release. G


Research Article


vertical WE to study the release from motors settled on the working electrode (no motion) or motors on motion touching the WE, respectively (see heavy-metal recovery section for more details of a similar process). UV−Vis spectroscopy was used to evaluate the detachment of DOX molecules from surface of the robots. The fluorescence images were obtained using an optical microscope coupled with a UV filter. Velocity Analysis. The velocity of synthesized Bi/Ni/Pt microrobots was measured in the presence of hydrogen peroxide of different concentrations. The video of the self-propelled microrobots was captured using an Olympus BX43 microscope equipped with a high-speed camera (Retiga R1 CCD), which is controlled by OCULAR software. Tracking and analysis of the recorded video were performed using Image Pro 9 and NIS-Elements software. Cell Line and Culture Conditions. Breast cancer cells (T47D) were purchased from the Health Protection Agency Culture Collections (Salisbury, UK). The cell cultivation was carried out in RPMI-1640 medium supplemented with 10% (v/v) fetal bovine serum with penicillin (100 U mL−1) and streptomycin (0.1 mg mL−1). The cells were maintained at 37 °C under a humidified atmosphere of 5% CO2 in the incubator Galaxy 170 R (Eppendorf, Hamburg, Germany). Prior to the in vitro screening (MTT assay and fluorescence imaging), the density of the cells was evaluated by an automated cell counter Countess II FL (Thermo Fisher Scientific, Waltham, MA, USA). In Vitro Testing of Biocompatibility of Bi/Ni/Pt Microrobots. The viability of T47D cells after 24 h of treatment with selected therapeutic agents (Bi/Ni/Pt microrobots, their DOX-loaded variant, and electroreductively released DOX) was determined by the MTT assay. DOX-containing treatments were standardized through DOX intrinsic fluorescence and analysis of DOX absorbance, while nonDOX treatments were standardized as the amount of microrobots per milliliter. Seeding of the cells in 96-well plates was performed at a density of ∼5000 cells per well, and after that, cells were incubated for 24 h, at 37 °C with a 5% CO2 atmosphere. Then, the T47D cells were treated with a series of amounts of the selected therapeutic agents. The therapeutic agent-containing medium was discarded, and the cells were washed with PBS. MTT (10 μL) (5 mg mL−1 in PBS) was added to the treated cells, followed by further incubation (4 h, 37 °C, 5% CO2). The MTT-containing medium was replaced with dimethyl sulfoxide (DMSO, 99.9%, 100 μL) and, after 5 min of incubation, the absorbance (at 570 nm) was determined using an Infinite M200 PRO Multimode microplate reader (Tecan, Maennedorf, Switzerland). The MTT assay was performed in triplicate for each of the abovementioned therapeutic agents. Fluorescence Imaging. The cancer cells were cultured in a 24well plate (24 h, 37 °C, 5% CO2). Then, the T47D cells were treated with selected therapeutic agents (6 h, 37 °C, 5% CO2). Such treated cells were washed with PBS, and for nuclei counterstaining, Hoechst 33258 (Thermo Fisher Scientific) was used. The cells were visualized using an EVOS FL auto cell imaging system (Thermo Fisher Scientific). The cell morphology was recorded under ambient light. The nuclei fluorescence and DOX fluorescence were visualized using a 4′,6-diamidin-2-fenylindol filter and a Texas Red filter, respectively. Removal of Heavy Metals. The capabilities of Bi/Ni/Pt microrobots for removal of heavy metals (arsenic and chromium) have been tested in an aqueous solution containing targeted heavy metals (As: 5 ppm; Cr: 4 ppm) and the microrobots (1.75 × 106 robots mL−1) for both on-the-move microrobots and static ones. For on-the-move microrobot, fuel (hydrogen peroxide, 1% v/v) and SDS (0.5% w/v) were added to the solution. These experiments have been carried out at different times (5 min, 10 min, 15 min, 30 min, 45 min, 60 min, 4 h, and 24 h). Control experiments have been performed to investigate the effect of the fuel and SDS on the removal of targeted heavy metals. For each time interval, microrobots were separated from the solution using a magnet due to their magnetic property (Ni layer), and the solutions were analyzed using ICP-OES to probe the adsorption capacity of the microrobots. Bi/Ni/Pt microrobots were rinsed with ultrapure water and then sampled for SEM/EDS analysis, while the rest were collected for the recovery experiment.

where the electroreductive release was performed, and (iii) the unloaded robots were guided toward the second reservoir. The bismuth microrobots have shown excellent performance for both drug delivery application and toxic heavy-metal removal. The simple fabrication method combined with excellent properties of green bismuth as well as the ondemand electrochemical release mechanism provides promise for future development of these tiny microrobots for different applications ranging from drug delivery and nanosurgery to energy and environmental applications.

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EXPERIMENTAL SECTION

Fabrication of Bi/Ni/Pt Microrobots. Bi/Ni/Pt microrobots were fabricated using an electrochemical procedure, which deposited the desired element layer by layer on a PC membrane as a template. One side of the membrane was covered by silver (Ag) using thermal evaporation techniques with a 0.4 nm s−1 deposition rate. The Agcoated membrane was attached to copper tape acting as the working electrode for electrochemical deposition. This electrode was assembled into a homemade electrodeposition cell. Electrodepositions were carried out using an Autolab potentiostat (PGSTAT 302 N) controlled by NOVA software (version 2.2). A platinum wire and a Ag/AgCl electrode were employed as counter and reference electrodes, respectively. First, the bismuth layer was deposited using an acidic solution (pH = 2.7, HNO3 acid) containing 4 mM bismuth nitrate (Bi(NO3)3·5H2O) by cyclic voltammetry from 0.0 V to −0.8 V for two cycles. The bismuth electrodeposition solution was removed, and the cell was washed several times with ultrapure water. The nickel layer was electrodeposited using a commercial electroplating solution (NB Semiplate Ni 100, NB Technologies GmbH, Germany) using amperometry at −0.9 V with 4C cutoff charge to provide the Ni layer for magnet propulsion using a simple neodymium (Nd) magnet. After Ni layer electrodeposition, the cell was rinsed with ultrapure water several times, and finally the platinum layer was electrodeposited galvanostatistically by applying −10 mA for 600 s, using a commercial plating solution (Technic Inc., USA). After deposition procedures, the membrane was polished to remove the Ag-coated layer, and then the membrane was dissolved using DCM. The fabricated microrobots were collected by centrifugation (8000 rpm for 5 min) and washed five times with DCM, followed by washing with ethanol and ultrapure water three times each and collected by centrifugation after each rinsing step. Finally, the tubes were stored in ultrapure water at ambient temperature. Loading of DOX on Bi/Ni/Pt Microrobots. Initially, 1 mL (1.75 × 106 robots per 1 mL) of microrobots was added to a DOX solution (2.8 × 10−5 M). The kinetics of loading of DOX was assessed by analyzing the UV−Vis spectrum of DOX prior to and after the addition of microrobots at different incubation times. The DOXloaded robots were separated via centrifugation (8000 rpm) for 5 min. The free DOX was removed by continuous washing of the loaded microrobots with ultrapure water. After each washing step, the supernatant solution was tested with UV−Vis spectroscopy to ensure the total removal of free doxorubicin molecules. The drug-loaded Bimicrorobots were re-suspended in PBS buffer (pH 7.4) to simulate physiological conditions. The stability of DOX on the surface of microrobots was confirmed by continuous monitoring of the solution by UV−Vis measurement. Electrochemically Triggered DOX Release from Bi/Ni/Pt Microrobots. The release of DOX from the microrobots was achieved via an electrochemical technique using a three-electrode system (electrochemical conditions: RE: Ag/AgCl, CE: carbon foam, and WE: copper foil). The electrolyte solution was 1 mM KCl aqueous solution containing DOX@Bi/Ni/Pt microrobots and cultured cancer cells. The electrochemical release, based on electron transfer from the WE to the robots and the cargo,80,87,88 was done by three continuous CV scans by swiping the potential between −0.2 and −1.0 V in the first cycle and between 0.0 and −1.0 V in the second and third cycles. The release was performed using a planar WE and a H


Research Article

ACS Applied Materials & Interfaces Heavy-Metal Recovery and Reusability of the Microrobots. (i) Electrochemical cell with planar working electrode: the electrochemical release is based on electron transfer from the WE to the robots and the cargo.80,87,88 The electrochemical release of the heavy metals (As and Cr) from microrobots was performed by applying a constant potential, that is, −1.0 V, for 10 min to the robots that settle down on the surface of the working electrode (electrochemical conditions: electrolyte, 1 mM KCl; RE, Ag/AgCl; CE, Pt wire; and WE, copper tape). The recovery solutions were analyzed using an ICP-OES to probe the heavy-metal concentrations after electrochemical release. Microrobots were collected from the recovery solutions to test their reusability. First, they were washed several times with ultrapure water, sampled to perform characterization using SEM/ EDX, and then used in the reusability test. The reusability experiment was done following the same conditions, used in the removal test, and repeated five times. Bi/Ni/Pt microrobots were exposed again to targeted heavy metals for 1 h followed by separation from solution using an external magnet, and the solution was analyzed by ICP-OES. (ii) Electrochemical cell with vertical working electrode: the same condition as discussed in (i), but in this case, the copper working electrode was standing, and the release was happening upon the collision of on-the-move robots to the negatively charged electrode. (iii) Microfluidic channel: the same condition as in (i). In order to make sure that the release was successful, the robots were initially loaded with the heavy metals and then inserted into the first reservoir. This experiment was also repeated once without any applied potential, and almost no heavy metal was detected, confirming the role of applied potential in the channel. Microchannel Fabrication. A 500 μm × 100 μm (width × height) channel mold was prepared on a clean glass wafer via a negative photoresist (Microchem, SU-8 2100). The photoresist was coated using a spin-coating method on the wafer, prebaked at 65 and 95 °C, and subsequently irradiated with UV light (Karl Suss, MJB3). After post-baking at 65 and 95 °C, the wafer was developed in EC solvent (Microposit, Rohm, and Haas) to disclose the channel mold. Then, channel was covered with poly(dimethylsiloxane) (PDMS-Dow Corning, Sylgard 184). The PDMS was peeled off from the casting mold and exposed to air plasma along with the electrode wafer. Afterward, the electrodes and microchannel were precisely aligned and were connected. The assembled device was then heated at 65 °C for 2 h to guarantee a mechanically strong seal.

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ORCID

Zdeněk Sofer: 0000-0002-1391-4448 Martin Pumera: 0000-0001-5846-2951 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the project Advanced Functional Nanorobots (reg. no.CZ.02.1.01/0.0/0.0/15_003/0000444 financed by the EFRR). Z.S. was supported by the Czech Science Foundation (GACR no. 16-05167S). Z.H. was supported by the Czech Health Research Council (AZV no. 15-28334A).

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b19408. Propulsion of Bi/Ni/Pt microrobots in the presence 0.5% H2O2 (AVI) Propulsion of Bi/Ni/Pt microrobots in the presence 1% H2O2 (AVI) Propulsion of Bi/Ni/Pt microrobots in the presence 2% H2O2 (AVI) Propulsion of Bi/Ni/Pt microrobots in the presence 3% H2O2 (AVI) Propulsion of Bi/Ni/Pt microrobots in the presence 5% H2O2 (AVI) Collection of Bi/Ni/Pt microrobots by a magnet; adsorption of DOX molecules on the microrobots; cyclic voltammetry of doxorubicin; removal of As and Cr in different time intervals; image of the microchannel setup; release of DOX and heavy metals in the microfluidic channel (PDF)

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REFERENCES

(1) Credi, A. Nanomachines. Fundamentals and Applications. By Joseph Wang. Angew. Chem., Int. Ed. 2014, 53, 4274−4275. (2) Jurado-Sánchez, B.; Escarpa, A. Milli, micro and nanomotors: Novel analytical tools for real-world applications. TrAC, Trends Anal. Chem. 2016, 84, 48−59. (3) Wang, H.; Pumera, M. Fabrication of Micro/Nanoscale Motors. Chem. Rev. 2015, 115, 8704−8735. (4) Wang, H.; Pumera, M. Emerging materials for the fabrication of micro/nanomotors. Nanoscale 2017, 9, 2109−2116. (5) Parmar, J.; Ma, X.; Katuri, J.; Simmchen, J.; Stanton, M. M.; Trichet-Paredes, C.; Soler, L.; Sanchez, S. Nano and micro architectures for self-propelled motors. Sci. Technol. Adv. Mater. 2015, 16, No. 014802. (6) Wang, J.; Gao, W. Nano/Microscale Motors: Biomedical Opportunities and Challenges. ACS Nano 2012, 6, 5745−5751. (7) Wang, W.; Duan, W.; Ahmed, S.; Sen, A.; Mallouk, T. E. From One to Many: Dynamic Assembly and Collective Behavior of SelfPropelled Colloidal Motors. Acc. Chem. Res. 2015, 48, 1938−1946. (8) Campuzano, S.; de Á vila, B. E. F.; Yañez-Sedeño, P.; Pingarron, J. M.; Wang, J. Nano/microvehicles for efficient delivery and (bio)sensing at the cellular level. Chem. Sci. 2017, 8, 6750−6763. (9) Villa, K.; Krejčová, L.; Novotný, F.; Heger, Z.; Sofer, Z.; Pumera, M. Cooperative Multifunctional Self-Propelled Paramagnetic Microrobots with Chemical Handles for Cell Manipulation and Drug Delivery. Adv. Funct. Mater. 2018, 28, 1804343. (10) Orozco, J.; Mercante, L. A.; Pol, R.; Merkoci, A. Graphenebased Janus micromotors for the dynamic removal of pollutants. J. Mater. Chem. A 2016, 4, 3371−3378. (11) Soler, L.; Magdanz, V.; Fomin, V. M.; Sanchez, S.; Schmidt, O. G. Self-Propelled Micromotors for Cleaning Polluted Water. ACS Nano 2013, 7, 9611−9620. (12) de Á vila, B. E. F.; Angsantikul, P.; Li, J.; Lopez-Ramirez, M. A.; Ramírez-Herrera, D. E.; Thamphiwatana, S.; Chen, C.; Delezuk, J.; Samakapiruk, R.; Ramez, V.; Obonyo, M.; Zhang, L.; Wang, J. Micromotor-enabled active drug delivery for in vivo treatment of stomach infection. Nat. Commun. 2017, 8, 272. (13) Gao, W.; de Á vila, B. E. F.; Zhang, L.; Wang, J. Targeting and isolation of cancer cells using micro/nanomotors. Adv. Drug Delivery Rev. 2018, 125, 94−101. (14) Srivastava, S. K.; Medina−Sánchez, M.; Koch, B.; Schmidt, O. G. Medibots: Dual-Action Biogenic Microdaggers for Single-Cell Surgery and Drug Release. Adv. Mater. 2016, 28, 832−837. (15) Kherzi, B.; Pumera, M. Self-propelled autonomous nanomotors meet microfluidics. Nanoscale 2016, 8, 17415−17421. (16) Fahmy, T. M.; Fong, P. M.; Goyal, A.; Saltzman, W. M. Targeted for drug delivery. Mater. Today 2005, 8, 18−26. (17) Sercombe, L.; Veerati, T.; Moheimani, F.; Wu, S. Y.; Sood, A. K.; Hua, S. Advances and challenges of liposome assisted drug delivery. Front. Pharmacol. 2015, 6, 286. (18) Liu, Z.; Robinson, J. T.; Tabakman, S. M.; Yang, K.; Dai, H. Carbon materials for drug delivery & cancer therapy. Mater. Today 2011, 14, 316−323.

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Corresponding Author

*Email: [email protected] I


Research Article

ACS Applied Materials & Interfaces (19) Geim, A. K. Graphene: Status and Prospects. Science 2009, 324, 1530−1534. (20) Sharma, H.; Kumar, K.; Choudhary, C.; Mishra, P. K.; Vaidya, B. Development and characterization of metal oxide nanoparticles for the delivery of anticancer drug. Artif. Cells Blood Substit. Biotechnol. 2016, 44, 672−679. (21) Sharma, A.; Goyal, A. K.; Rath, G. Recent advances in metal nanoparticles in cancer therapy. J. Drug Targeting 2018, 26, 617−632. (22) Fojtů, M.; Chia, X.; Sofer, Z.; Masařík, M.; Pumera, M. Black Phosphorus Nanoparticles Potentiate the Anticancer Effect of Oxaliplatin in Ovarian Cancer Cell Line. Adv. Funct. Mater. 2017, 27, 1701955. (23) Kesharwani, P.; Jain, K.; Jain, N. K. Dendrimer as nanocarrier for drug delivery. Prog. Polym. Sci. 2014, 39, 268−307. (24) Madaan, K.; Kumar, S.; Poonia, N.; Lather, V.; Pandita, D. Dendrimers in drug delivery and targeting: Drug-dendrimer interactions and toxicity issues. J. Pharm. Bioallied. Sci. 2014, 6, 139. (25) Langer, R. Drugs on Target. Science 2001, 293, 58−59. (26) Rubiana, M. M.; Luciano, P. S. Drug Delivery Systems: Past, Present, and Future. Curr. Drug Targets 2004, 5, 449−455. (27) Wang, H.; Pumera, M. Micro/Nanomachines and Living Biosystems: From Simple Interactions to Microcyborgs. Adv. Funct. Mater. 2018, 28, 1705421. (28) Ali, I. New Generation Adsorbents for Water Treatment. Chem. Rev. 2012, 112, 5073−5091. (29) Liu, G.; Zhang, X.; Talley, J. W.; Neal, C. R.; Wang, H. Effect of NOM on arsenic adsorption by TiO2 in simulated As(III)contaminated raw waters. Water Res. 2008, 42, 2309−2319. (30) Wang, X. S.; Chen, L. F.; Li, F. Y.; Chen, K. L.; Wan, W. Y.; Tang, Y. J. Removal of Cr (VI) with wheat-residue derived black carbon: Reaction mechanism and adsorption performance. J. Hazard. Mater. 2010, 175, 816−822. (31) Beladi-Mousavi, S. M.; Pourrahimi, A. M.; Sofer, Z.; Pumera, M. Atomically Thin 2D-Arsenene by Liquid-Phased Exfoliation: Toward Selective Vapor Sensing. Adv. Funct. Mater. 2019, DOI: 10.1002/adfm.201807004. (32) Hua, M.; Zhang, S.; Pan, B.; Zhang, W.; Lv, L.; Zhang, Q. Heavy metal removal from water/wastewater by nanosized metal oxides: A review. J. Hazard. Mater. 2012, 211, 317−331. (33) Ö nnby, L.; Kumar, P. S.; Sigfridsson, K. G. V.; Wendt, O. F.; Carlson, S.; Kirsebom, H. Improved arsenic(III) adsorption by Al2O3 nanoparticles and H2O2: Evidence of oxidation to arsenic(V) from Xray absorption spectroscopy. Chemosphere 2014, 113, 151−157. (34) Alemayehu, E.; Thiele-Bruhn, S.; Lennartz, B. Adsorption behaviour of Cr(VI) onto macro and micro-vesicular volcanic rocks from water. Sep. Purif. Technol. 2011, 78, 55−61. (35) Lazaridis, N. K.; Bakoyannakis, D. N.; Deliyanni, E. A. Chromium(VI) sorptive removal from aqueous solutions by nanocrystalline akaganèite. Chemosphere 2005, 58, 65−73. (36) Zhu, N.; Yan, T.; Qiao, J.; Cao, H. Adsorption of arsenic, phosphorus and chromium by bismuth impregnated biochar: Adsorption mechanism and depleted adsorbent utilization. Chemosphere 2016, 164, 32−40. (37) Sánchez, S.; Soler, L.; Katuri, J. Chemically Powered Microand Nanomotors. Angew. Chem., Int. Ed. 2015, 54, 1414−1444. (38) Paxton, W. F.; Kistler, K. C.; Olmeda, C. C.; Sen, A.; St. Angelo, S. K.; Cao, Y.; Mallouk, T. E.; Lammert, P. E.; Crespi, V. H. Catalytic Nanomotors: Autonomous Movement of Striped Nanorods. J. Am. Chem. Soc. 2004, 126, 13424−13431. (39) Guix, M.; Mayorga-Martinez, C. C.; Merkoçi, A. Nano/ Micromotors in (Bio)chemical Science Applications. Chem. Rev. 2014, 114, 6285−6322. (40) Jurado-Sánchez, B.; Sattayasamitsathit, S.; Gao, W.; Santos, L.; Fedorak, Y.; Singh, V. V.; Orozco, J.; Galarnyk, M.; Wang, J. SelfPropelled Activated Carbon Janus Micromotors for Efficient Water Purification. Small 2015, 11, 499−506. (41) Mushtaq, F.; Guerrero, M.; Sakar, M. S.; Hoop, M.; Lindo, A. M.; Sort, J.; Chen, X.; Nelson, B. J.; Pellicer, E.; Pané, S. Magnetically

driven Bi2O3/BiOCl-based hybrid microrobots for photocatalytic water remediation. J. Mater. Chem. A 2015, 3, 23670−23676. (42) Teo, W. Z.; Zboril, R.; Medrik, I.; Pumera, M. Fe0 Nanomotors in Ton Quantities (1020 Units) for Environmental Remediation. Chem. − Eur. J. 2016, 22, 4789−4793. (43) Orozco, J.; Cheng, G.; Vilela, D.; Sattayasamitsathit, S.; Vazquez-Duhalt, R.; Valdés-Ramírez, G.; Pak, O. S.; Escarpa, A.; Kan, C.; Wang, J. Micromotor-Based High-Yielding Fast Oxidative Detoxification of Chemical Threats. Angew. Chem., Int. Ed. 2013, 52, 13276−13279. (44) Li, J.; Singh, V. V.; Sattayasamitsathit, S.; Orozco, J.; Kaufmann, K.; Dong, R.; Gao, W.; Jurado-Sanchez, B.; Fedorak, Y.; Wang, J. Water-Driven Micromotors for Rapid Photocatalytic Degradation of Biological and Chemical Warfare Agents. ACS Nano 2014, 8, 11118− 11125. (45) Guix, M.; Orozco, J.; García, M.; Gao, W.; Sattayasamitsathit, S.; Merkoçi, A.; Escarpa, A.; Wang, J. Superhydrophobic AlkanethiolCoated Microsubmarines for Effective Removal of Oil. ACS Nano 2012, 6, 4445−4451. (46) Seah, T. H.; Zhao, G.; Pumera, M. Surfactant Capsules Propel Interfacial Oil Droplets: An Environmental Cleanup Strategy. ChemPlusChem 2013, 78, 395−397. (47) Mou, F.; Pan, D.; Chen, C.; Gao, Y.; Xu, L.; Guan, J. Magnetically Modulated Pot-Like MnFe2O4 Micromotors: Nanoparticle Assembly Fabrication and their Capability for Direct Oil Removal. Adv. Funct. Mater. 2015, 25, 6173−6181. (48) Singh, V. V.; Martin, A.; Kaufmann, K.; DS de Oliveira, S.; Wang, J. Zirconia/Graphene Oxide Hybrid Micromotors for Selective Capture of Nerve Agents. Chem. Mater. 2015, 27, 8162−8169. (49) Wang, H.; Potroz, M. G.; Jackman, J. A.; Khezri, B.; Marić, T.; Cho, N.-J.; Pumera, M. Bioinspired Spiky Micromotors Based on Sporopollenin Exine Capsules. Adv. Funct. Mater. 2017, 27, 1702338. (50) Wang, H.; Khezri, B.; Pumera, M. Catalytic DNA-Functionalized Self-Propelled Micromachines for Environmental Remediation. Chem 2016, 1, 473−481. (51) Vilela, D.; Parmar, J.; Zeng, Y.; Zhao, Y.; Sánchez, S. GrapheneBased Microbots for Toxic Heavy Metal Removal and Recovery from Water. Nano Lett. 2016, 16, 2860−2866. (52) Moo, J. G. S.; Wang, H.; Zhao, G.; Pumera, M. Biomimetic Artificial Inorganic Enzyme-Free Self-Propelled Microfish Robot for Selective Detection of Pb2+ in Water. Chem. − Eur. J. 2014, 20, 4292− 4296. (53) Dey, K. K.; Bhandari, S.; Bandyopadhyay, D.; Basu, S.; Chattopadhyay, A. The pH Taxis of an Intelligent Catalytic Microbot. Small 2013, 9, 1916−1920. (54) Moreno-Guzman, M.; Jodra, A.; López, M.-Á .; Escarpa, A. SelfPropelled Enzyme-Based Motors for Smart Mobile Electrochemical and Optical Biosensing. Anal. Chem. 2015, 87, 12380−12386. (55) Mohan, R. Green bismuth. Nat. Chem. 2010, 2, 336. (56) Beladi-Mousavi, S. M.; Pumera, M. 2D-Pnictogens: alloy-based anode battery materials with ultrahigh cycling stability. Chem. Soc. Rev. 2018, 47, 6964−6989. (57) Briand, G. G.; Burford, N. Bismuth Compounds and Preparations with Biological or Medicinal Relevance. Chem. Rev. 1999, 99, 2601−2658. (58) Li, Z.; Hu, Y.; Howard, K. A.; Jiang, T.; Fan, X.; Miao, Z.; Sun, Y.; Besenbacher, F.; Yu, M. Multifunctional Bismuth Selenide Nanocomposites for Antitumor Thermo-Chemotherapy and Imaging. ACS Nano 2016, 10, 984−997. (59) Li, Z.; Liu, J.; Hu, Y.; Howard, K. A.; Li, Z.; Fan, X.; Chang, M.; Sun, Y.; Besenbacher, F.; Chen, C.; Yu, M. Multimodal ImagingGuided Antitumor Photothermal Therapy and Drug Delivery Using Bismuth Selenide Spherical Sponge. ACS Nano 2016, 10, 9646−9658. (60) Mao, F.; Wen, L.; Sun, C.; Zhang, S.; Wang, G.; Zeng, J.; Wang, Y.; Ma, J.; Gao, M.; Li, Z. Ultrasmall Biocompatible Bi2Se3 Nanodots for Multimodal Imaging-Guided Synergistic Radiophotothermal Therapy against Cancer. ACS Nano 2016, 10, 11145−11155. (61) Wang, Y.; Wu, Y.; Liu, Y.; Shen, J.; Lv, L.; Li, L.; Yang, L.; Zeng, J.; Wang, Y.; Zhang, L. W.; Li, Z.; Gao, M.; Chai, Z. BSAJ


Research Article

ACS Applied Materials & Interfaces Mediated Synthesis of Bismuth Sulfide Nanotheranostic Agents for Tumor Multimodal Imaging and Thermoradiotherapy. Adv. Funct. Mater. 2016, 26, 5335−5344. (62) Lei, P.; An, R.; Zhang, P.; Yao, S.; Song, S.; Dong, L.; Xu, X.; Du, K.; Feng, J.; Zhang, H. Ultrafast Synthesis of Ultrasmall Poly(Vinylpyrrolidone)-Protected Bismuth Nanodots as a Multifunctional Theranostic Agent for In Vivo Dual-Modal CT/PhotothermalImaging-Guided Photothermal Therapy. Adv. Funct. Mater. 2017, 27, 1702018. (63) Khezri, B.; Beladi Mousavi, S. M.; Krejčová, L.; Heger, Z.; Sofer, Z.; Pumera, M. Ultrafast Electrochemical Trigger Drug Delivery Mechanism for Nanographene Micromachines. Adv. Funct. Mater. 2018, 29, 1806696. (64) Mo, Y.; Wang, H.; Liu, J.; Lan, Y.; Guo, R.; Zhang, Y.; Xue, W.; Zhang, Y. Controlled release and targeted delivery to cancer cells of doxorubicin from polysaccharide-functionalised single-walled carbon nanotubes. J. Mater. Chem. B 2015, 3, 1846−1855. (65) Liu, Z.; Sun, X.; Nakayama-Ratchford, N.; Dai, H. Supramolecular Chemistry on Water-Soluble Carbon Nanotubes for Drug Loading and Delivery. ACS Nano 2007, 1, 50−56. (66) Ariga, K.; Mori, T.; Nakanishi, W. Nano Trek Beyond: Driving Nanocars/Molecular Machines at Interfaces. Chem. − Asian J. 2018, 13, 1266−1278. (67) Yang, F. Y.; Liu, K.; Hong, K.; Reich, D. H.; Searson, P. C.; Chien, C. L. Large Magnetoresistance of Electrodeposited SingleCrystal Bismuth Thin Films. Science 1999, 284, 1335−1337. (68) Khezri, B.; Sheng Moo, J. G.; Song, P.; Fisher, A. C.; Pumera, M. Detecting the complex motion of self-propelled micromotors in microchannels by electrochemistry. RSC Adv. 2016, 6, 99977−99982. (69) Mitch, M. G.; Chase, S. J.; Fortner, J.; Yu, R. Q.; Lannin, J. S. Phase transition in ultrathin Bi films. Phys. Rev. Lett. 1991, 67, 875− 878. (70) Trentelman, K. A note on the characterization of bismuth black by Raman microspectroscopy. J. Raman Spectrosc. 2009, 40, 585−589. (71) Bedoya Hincapié, C. M.; Pinzón Cárdenas, M. J.; Alfonso Orjuela, J. E.; Restrepo Parra, E.; Olaya Florez, J. J. Physical-Chemical Properties of Bismuth and Bismuth Oxides: Synthesis, Characterization and Applications. DYNA 2012, 79, 139−148. (72) Myung, N.; Ham, S.; Choi, S.; Chae, Y.; Kim, W.-G.; Jeon, Y. J.; Paeng, K.-J.; Chanmanee, W.; de Tacconi, N. R.; Rajeshwar, K. Tailoring Interfaces for Electrochemical Synthesis of Semiconductor Films: BiVO4, Bi2O3, or Composites. J. Phys. Chem. C 2011, 115, 7793−7800. (73) Gao, W.; Sattayasamitsathit, S.; Orozco, J.; Wang, J. Highly Efficient Catalytic Microengines: Template Electrosynthesis of Polyaniline/Platinum Microtubes. J. Am. Chem. Soc. 2011, 133, 11862−11864. (74) Li, L.; Wang, J.; Li, T.; Song, W.; Zhang, G. Hydrodynamics and propulsion mechanism of self-propelled catalytic micromotors: model and experiment. Soft Matter 2014, 10, 7511−7518. (75) Steiniger, S. C. J.; Kreuter, J.; Khalansky, A. S.; Skidan, I. N.; Bobruskin, A. I.; Smirnova, Z. S.; Severin, S. E.; Uhl, R.; Kock, M.; Geiger, K. D.; Gelperina, S. E. Chemotherapy of glioblastoma in rats using doxorubicin-loaded nanoparticles. Int. J. Cancer 2004, 109, 759−767. (76) Kuerer, H. M.; Newman, L. A.; Smith, T. L.; Ames, F. C.; Hunt, K. K.; Dhingra, K.; Theriault, R. L.; Singh, G.; Binkley, S. M.; Sneige, N.; Buchholz, T. A.; Ross, M. I.; McNeese, M. D.; Buzdar, A. U.; Hortobagyi, G. N.; Singletary, S. E. Clinical Course of Breast Cancer Patients With Complete Pathologic Primary Tumor and Axillary Lymph Node Response to Doxorubicin-Based Neoadjuvant Chemotherapy. J. Clin. Oncol. 1999, 17, 460−460. (77) Motlagh, N. S. H.; Parvin, P.; Ghasemi, F.; Atyabi, F. Fluorescence properties of several chemotherapy drugs: doxorubicin, paclitaxel and bleomycin. Biomed. Opt. Express 2016, 7, 2400−2406. (78) Heister, E.; Neves, V.; Tîlmaciu, C.; Lipert, K.; Beltrán, V. S.; Coley, H. M.; Silva, S. R. P.; McFadden, J. Triple functionalisation of single-walled carbon nanotubes with doxorubicin, a monoclonal

antibody, and a fluorescent marker for targeted cancer therapy. Carbon 2009, 47, 2152−2160. (79) Ali Mohammadi, Z.; Aghamiri, S. F.; Zarrabi, A.; Talaie, M. R. A comparative study on non-covalent functionalization of carbon nanotubes by chitosan and its derivatives for delivery of doxorubicin. Chem. Phys. Lett. 2015, 642, 22−28. (80) Sadaf, S.; Walder, L. Doxorubicin Adsorbed on Carbon Nanotubes: Helical Structure and New Release Trigger. Adv. Mater. Interfaces 2017, 4, 1700649. (81) Housman, G.; Byler, S.; Heerboth, S.; Lapinska, K.; Longacre, M.; Snyder, N.; Sarkar, S. Drug Resistance in Cancer: An Overview. Cancers 2014, 6, 1769−1792. (82) Yang, H.; Yuan, B.; Zhang, X.; Scherman, O. A. Supramolecular Chemistry at Interfaces: Host-Guest Interactions for Fabricating Multifunctional Biointerfaces. Acc. Chem. Res. 2014, 47, 2106−2115. (83) Naahidi, S.; Jafari, M.; Edalat, F.; Raymond, K.; Khademhosseini, A.; Chen, P. Biocompatibility of engineered nanoparticles for drug delivery. J. Controlled Release 2013, 166, 182−194. (84) Staedler, D.; Passemard, S.; Magouroux, T.; Rogov, A.; Maguire, C. M.; Mohamed, B. M.; Schwung, S.; Rytz, D.; Jüstel, T.; Hwu, S.; Mugnier, Y.; Le Dantec, R.; Volkov, Y.; Gerber-Lemaire, S.; Prina-Mello, A.; Bonacina, L.; Wolf, J.-P. Cellular uptake and biocompatibility of bismuth ferrite harmonic advanced nanoparticles. Nanomed.: Nanotechnol., Biol. Med. 2015, 11, 815−824. (85) Yang, S.; Li, Z.; Wang, Y.; Fan, X.; Miao, Z.; Hu, Y.; Li, Z.; Sun, Y.; Besenbacher, F.; Yu, M. Multifunctional Bi@PPy-PEG Core−Shell Nanohybrids for Dual-Modal Imaging and Photothermal Therapy. ACS Appl. Mater. Interfaces 2018, 10, 1605−1615. (86) Song, Q.; Liu, Y.; Jiang, Z.; Tang, M.; Li, N.; Wei, F.; Cheng, G. The acute cytotoxicity of bismuth ferrite nanoparticles on PC12 cells. J. Nanopart. Res. 2014, 16, 2408. (87) Beladi-Mousavi, S. M.; Sadaf, S.; Walder, L.; Gallei, M.; Rüttiger, C.; Eigler, S.; Halbig, C. E. Poly(vinylferrocene)−Reduced Graphene Oxide as a High Power/High Capacity Cathodic Battery Material. Adv. Energy Mater. 2016, 6, 1600108. (88) Beladi-Mousavi, S. M.; Sadaf, S.; Mahmood, A. M.; Walder, L. High Performance Poly(viologen)−Graphene Nanocomposite Battery Materials with Puff Paste Architecture. ACS Nano 2017, 11, 8730−8740.

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