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3D Printed Microfluidic Device with Microporous Mn2O3 Modified Screen Printed Electrode for Real-Time Determination of Heavy Metal Ions Xiao-Chen Dong, Ying Hong, Meiyan Wu, Guangwei Chen, Ziyang Dai, Yi-Zhou Zhang, and Guosong Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b10464 • Publication Date (Web): 17 Nov 2016 Downloaded from http://pubs.acs.org on November 21, 2016

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ACS Applied Materials & Interfaces

3D Printed Microfluidic Device with Microporous Mn2O3 Modified Screen Printed Electrode for Real-Time Determination of Heavy Metal Ions Ying Honga,c‡, Meiyan Wua‡, Guangwei Chen,d Ziyang Daia, Yizhou Zhanga, Guosong Chenb*, Xiaochen Donga* a

Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM),

Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, China. b

College of Chemistry and Molecular Engineering, Nanjing Tech University (NanjingTech),

30 South Puzhu Road, Nanjing 211816, China. c

Nanjing Entry-Exit Inspection and Quarantine Bureau, 1 Guojian Road, Nanjing 211106,

China. d

College of Electrical and Computer Engineering, Purdue University-West Lafayette, Indiana

47906, United States. E-mail: [email protected]; [email protected] ‡

These Authors contributed equally

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Abstract Fabricating portable devices for the determination of heavy metal ions is an ongoing challenge. Here, a 3D printing approach was adopted to fabricate a microfluidic electrochemical sensor with the desired shape in which the model for velocity profiles in microfluidic cells was built and optimized by the finite element method (FEM). The electrode in the microfluidic cell was a flexible screen-printed electrode (SPE) modified with porous Mn2O3 derived from manganese containing metal organic framework (Mn-MOF). The microfluidic device presented superior electrochemical detection properties towards heavy metal ions. The calibration curves at the modified SPE for Cd(II) and Pb(II) covered two linear ranges varying from 0.5 to 8 and 10 to 100 μg L−1, respectively. The limits of detection were estimated to be 0.5 μg L−1 for Cd(II) and 0.2 μg L−1 for Pb(II), which was accordingly about 6 and 50 times lower than the guideline values proposed by World Health Organization. Furthermore, the microfluidic device was connected to iPad via a USB to enable real-time household applications. Additionally, the sensing system exhibited a better stability and reproducibility compared with traditional detecting system which offered a promising prospect for the detection of heavy metal ions especially in household and resource-limited occasions. KEYWORDS: 3D printing, microfluidic device, microporous Mn2O3, screen printed electrode, heavy metal ions detection

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1. INTRODUCTION In recent decades, while global electrical and electronic industry has brought increasing convenience and benefits to the human society, it simultaneously entailed severe environmental pollution to the biosphere. Heavy metal ions are recognized as one of the cancer-causing agents on account of their high toxicity, high stability and tendency of accumulation through food chains.1-3 Consequently, it is a serious urgency to tackle the pollution problems posed by electronic products, which is the main source of heavy metal ion pollution. For instance, the European Union has issued the Restriction of Hazardous Substances (RoHS) directive to limit certain hazardous materials entering the European market, which involves nearly all electronic devices used in daily life. Accordingly, effective detection methods for heavy metal ion are urgently needed, especially for Cd2+ and Pb2+, which commonly co-exist in various environments.4 At present, the microwave digestion method is the standard method and is suitable for the treatment of 10 to 100 samples in batch for local field detection. However, the great challenge still remains in building up portable, low-cost and highly efficient field testing devices for heavy metal ions. Anodic stripping voltammetry (ASV) is a traditional detection method for heavy metal ions, which presents relatively high sensitivity and low cost. Traditional ASV, especially in terms of designing devices and modifying electrodes, suffers from huge consumption of sample solution and, long lasting pre-electrolysis procedure and poor reproducibility. With the growing need for rapid and accurate analyses and portability, screen-printed electrode (SPE) based sensors are required.5-9 Meanwhile, the mass production and miniaturization of the instrumentation can also be realized by the employment of SPE. However, SPE based sensors

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normally suffer from problems including poor sensitivity, stability and reproducibility. To address this challenge, a novel sensing system integrating a microfluidic cell with SPEs modified with nanomaterials was designed and fabricated in this work. The microfluidic system was designed and optimized using the finite element method (FEM)10. FEM is currently the most widely used and reliable numerical approach to solve various practical problems of engineering and sciences. FEM was employed to optimize the parameters of the microfluidic cell. To facilitate the optimization of the sensing system, three dimensional (3D) printing was adopted as the fabrication tool for the microfluidic cell. 3D printing is an economical and environmental-friendly technology, which holds great promise for the standardization and mass production of devices.11-17 Recently, 3D printing has been employed to fabricate analytical devices such as electronic sensors,18, 19 injection valves,20 portable fluorescence microscopes,21 reaction ware22 and microfluidic devices23,

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. The

increasingly affordable printing system is also allowing the extraordinary freedom to design and fabricate devices with desired shape and materials without intermediate manufacturers. Here, a transparent ASV microfluidic cell with smooth surface was fabricated using 3D printing approach based on the FEM result. The introduction of nanostructured materials has been of great significance to improve

detection limits, sensibility, selectivity, reproducibility and miniaturization of sensing devices.29 Also, the unsaturated atoms on the surface of nanomaterials will potentially bind with other atoms and lead to high chemical activity.30 Metal-organic frameworks (MOFs), as a kind of multifunctional material, have been used as precursors for the preparation of highly ordered porous functional materials with high specific surface area.25-28 MOFs have also been

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documented as superior materials for modifying electrodes in terms of simultaneous electrochemical detection of dopamine, ascorbic acid and uric acid in aqueous solution.26 Mn2O3 obtained via Mn based MOFs (denoted as Mn-MOF) as sacrificial templates, is a kind of nanomaterial with unique thermal, mechanical, electronic and biological properties.31, 32 Furthermore, the interesting chemical and magnetic properties, along with various valence states and high biocompatibility of manganese enable its application in electrochemical- or bio-sensing.33, 34 In this work, a real-time injection system was created for the determination of heavy metal ions by integrating the MOF-derived Mn2O3 modified SPE, portable 3D printed microfluidic cell, universal serial bus (USB) interfaces, peristaltic pump and tablet such as iPad, which could solve the problems of poor reproducibility, dissipation of sample solution and time consumption in traditional ASV. And the resulted microfluidic device presents superior electrochemical detection properties towards heavy metal ions of Cd(II) and Pb(II), including high sensitivity, excellent selectivity, outstanding stability, reproducibility and real-time detection. This new portable electrochemical sensor will keep tracking of real-time results and update them to an iPad which is connected to the sensor via a USB cable. This method shows a great potential of this design which extended the applications for the determination of trace heavy metal ions into a wide range.

2. RESULTS AND DISCUSSION A model of the microfluidic cell for the electrochemical detection of heavy metal ions was built and solved by using finite element method (FEM) with COMSOL Multiphysics. Considering the fluid characteristics and electrochemical reaction of the electroactive species,

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Navier-Stokes (NS) equation (eq.1) and Convection-Diffusion equation (eq.2) were employed here.

 u   u  u   p  2u  f  t 

 

c  D2c  u  c t

(1) (2)

Where  is the fluid density,  is the dynamics viscosity, p is the pressure, u is the flow velocity of fluid, f is the external force, D is the diffusion coefficient of species and c is the concentration of species. The velocity profile of the microfluidic cell at different injection angles was investigated. As shown in Figure 1a, three directions (A) 90º, (B) 45º and (C) 0º for sample solution injection were simulated in numerical model. The maximum velocity appeared near the top of the channel in the microfluidic cell at the injection angles of 90º and 45º, while the maximum velocity was observed at the center of channel at the injection angle of 0º. This phenomenon may come from the inertia of fluid. Furthermore, willow type velocity profile induced by sample injection along the tangential direction has the longest flow path in the microfluidic cell, which facilitates deposition of more reactants on the electrode surface. Therefore, the injecting direction of 90º was chosen as our experimental condition. Figure 1b shows the corresponding curves of stripping voltammetry obtained by detecting the solution containing Pb2+ (80 μg L−1) with three modes (A), (B) and (C), which confirms that injection angle A (90º) is the optimal choice for the microfluidic device. The influencing factors of the diffusion layer thickness were investigated by FEM simulation. The thickness of diffusion layer is defined as the length of the concentration varying from 0 to bulk concentration. Firstly, the thickness of diffusion layer of different height was studied 6


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under the same current velocity (0.037 m/s). As shown in Figure 2a, with the height of microfluidic cell decreasing from 1.5 to 0.3 mm, the thickness of diffusion layer decreases from 0.1 to 0.027 mm respectively. Contrarily, the effect of velocity on the diffusion layer thickness was evaluated at the same channel height (1.5 mm). In Figure 2b, the length of diffusion layer decreases from 0.12 to 0.03 mm with the velocity increasing from 0.018 to 0.37 m/s respectively. Consequently, the velocity has much larger effect on the thickness of diffusion layer than the channel height. Although Figure 2 shows the tendency that low height of the microfluidic cell and high velocity are beneficial to the diffusion, the height of 0.8 mm and the velocity of 0.037m/s were picked for further experiments by considering the results of practical testing. The structure of the resulted 3D printed microfluidic device with 34 mm length × 24 mm width × 8 mm height is shown in Figure 3a (Figure 1S gives the 2D orthographic views of the microfluidic device). As we can see from Figure 3b, the microfluidic device has a highly transparent and smooth surface, which makes it easy to observe what is happening inside the device. Then the screen-printed electrode (36*14 mm) was inserted into the device with all the three electrodes (Ag, Ag/AgCl and working electrode) included in the cavity. Moreover, as shown in Figure 3c, the SPE made of flexible material can be bent easily, which broadens its application range, especially in flexible electronics. The numerical solution of the Navier-Stokes equations and the Convection-Diffusion equation above with a computational domain in COMSOL Multiphysics and the boundary conditions (BCs) were described in Figure 3d and Table 1. The fluid velocity at the inlet is designated. The specified no-slip boundary condition was employed at the walls (CD, BC, DE and AF). Representative values

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of diffusion coefficients were selected from the reported values in literature.35 The numerical solution of the steady-state NS and Convection-Diffusion equations in the laminar regime with constant boundary conditions is shown in Figure 3e. The side view of the mock flow distribution diagram was given by the microchannel simulation of COMSOL Multiphysics 3.5a software, which shows a wide area for ideal working. Since the reference electrode and counter electrode hardly have any influence on the electrochemical simulation, we focus on the area of working electrode in the numerical model. Figure 4 shows the schematic of the detecting system. The sample solution was pumped into the saddle-shaped cavity through the inlet hose by a peristaltic pump and then drained through outlet hose. The negative voltage (-1.2V) was applied when the peristaltic pump started to drive the solution into the microfluidic cell for pre-electrolysis. After 180s, the peristaltic pump was shut down, and the whole system was settled for 60s. The USB interface enabled the device to connect with the electrochemical workstation which is linked to the iPad. The microfluidic technology was employed in the design of the device, which can effectively overcome the defects existing in the traditional ASV detection. In addition, the microfluidic technology integrates operations of the chemical analysis into one system and miniaturizes the detecting device. Here, the object picture of the assembled device was given and the simulation picture of hexagonal prism structure of MOF-tempted Mn2O3 is presented on the left of it. It is worth noticing that once the related controllers were configured, this system would easily achieve automatic detection. In addition, the 3D printed transparent device allows the full-time observation during the whole detecting process. Figure 5(a) displayed the XRD patterns of the Mn-MOF precursor and Mn2O3. The red curve

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exhibited the typical pattern of Mn-MOF, which was similar to the previous report.36 Mn2O3 was formed after annealing, and all the diffraction peaks shown in the pattern could be indexed to the product-Mn2O3 perfectly without any other peaks. It can be seen that two notable peaks are presented, which can be attributed to Mn2O3 at 2θ = 32.9° and 55.2°, corresponding to the (222) and (440) reflections of Mn2O3, respectively (JCPDS no. 41-1442). In addition, diffraction peaks of Mn2O3 are well indexed to the (211), (400), (332), (431) and (622) phases at 2θ = 23.1°, 38.2°, 45.2°, 49.3° and 65.8°, respectively. The surface chemical composition and the valence state of Mn2O3 were analyzed by X-ray photoelectron spectroscopy (XPS). In the survey spectrum of the Mn2O3 (Figure 5b), the characteristic peaks of O and Mn coexist in Mn2O3, which is well witnessed by XRD analysis. The asymmetric peaks shown in the O 1s spectrum indicates that crystal lattic oxygen (OM-O, 529.85 eV) and surface hydroxyl groups (OH-O, 532.15 eV) are presented simultaneously in the manganese oxide, indicating that pure Mn2O3 was successfully synthesized.31 The deconvoluted spectra of Mn 2p are shown in Figure 5d, wherein binding energy values of Mn 2p1/2 and Mn 2p3/2 are observed at approximately 641.1eV and 653.4 eV respectively. The splitting energy difference between Mn 2p3/2 and Mn 2p1/2 core levels is 12.3 eV, indicating the presence of Mn3+ in the nanomaterial. Figure 6a shows the surface morphology of the working electrode without modification. Figure 6b and Figure S5 are the SEM images of Mn2O3 modified electrode, showing the porous structure of Mn2O3 due to the release of gas molecules37 from the Mn-MOF precursor. In Figure 6c, the lattice spacing of 0.384 nm for Mn2O3 nanomaterials is consistent with the d value of (211) plane. Figure 6d gives the illustration of the polyhedron around the Mn3+,

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showing the octahedral coordination arrangement. That is to say, Mn3+ is in an octahedral coordination arrangement surrounded by six oxygen atoms or an irregular rectangle surrounded by four oxygen atoms, respectively. Figure 6e shows the nitrogen adsorption-desorption analysis for the porous structure of Mn2O3. As shown in this curve, a point of inflexion (B) appeared at first, which represents the saturated adsorption capacity of mono-molecule. Then a hysteresis loop was observed after multilayer adsorption, which is typical for mesoporous materials. The surface area of the MOF-templated Mn2O3 calculated by Brunauer-Emmett-Teller (BET) method is ~708 m2 g-1, which is much larger than the traditionally fabricated Mn2O3 nanomaterials.38 The narrow pore size distribution (Figure 6f) in a range of 3.71-4.71 nm was given by Barrett-Joyner-Halenda (BJH). The electrochemical behavior of the electrode was measured by differential pulse anodic stripping voltammetry (DPASV) method as described in Figure 7. The DPASV behavior of 40 μg L−1 Cd(II) at carbon, carbon/Nafion and the modified electrode were detected in 0.1 M NaAc-HAc buffer containing 500 μg L−1 Bi3+ (pH = 4.6) at -1.2 V for 180 s. The stripping peak was obtained at the carbon and carbon/Nafion electrode for the Cd ion, while enhanced peaks were observed at the C/Nafion and C/Mn2O3/Nafion electrodes. Nafion film was considered as an ideal polymer for preconcetration. The -SO3-Na+ groups in Nafion film will be of benefit to capture Pb2+ or Cd2+ because of the selective ion-exchange.39 Furthermore, with the presence of porous Mn2O3, higher stripping peak could be obtained due to the adequate electroactive surface area provided by the porous structure and higher electrical conductivity of C/Mn2O3/Nafion. Moreover, the nanosized Mn2O3 could be served as a great adsorbent to metal ions, which made it proposing in the detection in trace metal ions.40

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Compared with the C electrode, the stripping signals of the C/Mn2O3/Nafion were increased by about 2.33 times for Cd(II). The voltammetric behaviors of Cd(II) at the C/Mn2O3/Nafion had been tested (Figure 7b, c). The correlation equations were fitted as y = 0.11844c-0.02138, R2= 0.995 in the range of 0.5 to 8 μg L−1, and as y = 0.09c+0.20967 with a correlation coefficient of R2= 0.999 in the range of 10 to 100 μg L−1. In addition, the analytical curves for Pb(II) (Figure S6) covered two linear ranges varying from 0.5 to 8 μg L−1 and 10 to 100 μg L −1

, demonstrating the good linearity in these two linear ranges. The correlation equations were

calculated as y = 0.1148c+0.1253, R2= 0.998 and y = 0.0813c+0.302, R2 = 0.997, respectively. Moreover, the limits of detections (LOD) were calculated to be 0.2 μg L−1 for Pb(II) and 0.5 μg L−1 for Cd(II) (S/N = 3), which was, respectively, 50 and 6 times lower than the guideline value for drinking water required by the World Health Organization.41 As shown in Figure 7d, two well-defined peaks for Cd(II) and Pb(II) were observed at around -0.84 V and -0.60 V. The presence of Cd(II) or Pb(II) would slightly affect the standard deviation of the stripping peak potentials for another ion, which is negligible.42 Therefore, Cd(II) and Pb(II) could be detected and distinguished by different position of the stripping peaks at the prepared C/Mn2O3/Nafion electrode. Furthermore, the other interfering metal ions had been added into the electrolyte, which presented excellent selective responses for Cd(II) and Pb(II) (Figure S7). The interfering metal ions were added into the solution of 50 μg L-1 Cd(II), the range of the percentage for Cd(II) peak currents was 94.7% ~ 102.2% (Figure S7a). The similar result (range of 93.2% ~ 101.9%) was obtain for Pb(II) (Figure S7b). In addition, the fabricated microfluidic was used to detect the Cd(II) and Pb(II) in plastic samples from the electromechanical products. Table S1 was the comparison of the detection results of Cd(II)

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and

Pb(II)

by

Microfluidic

sensor

and

ICP-OES.

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The relative deviations of the

measurements are less than 5%, which demonstrates the promising future of the sensor for practical applications. Last but not least, the reproducibility of this system with optimized conditions (Figure 7e) was proved here by comparing with the traditional ASV method (Figure 7f). The C/Mn2O3/Nafion electrode had exhibited superior performances than the carbon and carbon/Nafion electrode in the determination of Pb(II) and Cd(II), showing great promise of this detection system for practical applications in the near future.

3. EXPERIMENTAL SECTION Fabrication of the 3D Printed Microfluidic Cell and Synthesis of Screen-Printed Flexible Electrode. The PolyJet 3D printing system Eden260vs with size of 870×735×1200 mm from the Object Company was used for manufacturing the microfluidic cell. The photosensitive resin was used as the raw material of 3D printing from Stereo lithography Appearance (SLA) prototyping. The microfluidic cells with delicate construction, smooth surface (surface roughness: 16) and relatively high transparency were therefore fabricated for detecting metal ions (see specific sizes and structure in Figure S1, 2). The screen-printed flexible electrode (details available in Figure S3), which employed three electrodes, was produced by the screen printing technology for electrochemical sensor. A silver electrode acted as the counter electrode, while the reference electrode was made of a solid-state silver-silver chloride (Ag-AgCl) electrode. Synthesis of MOF-Templated Mn2O3. MnCl2·H2O (5.35g, 10.82 M) and 1.35g of 2, 5-dioxidoterephthalate (26 mM) were added into 80 mL solution (EtOH : DMF = 1:15). After

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stirring for 30 min, the above solution was heated at 135 °C for 2 days with stirring. A bright orange solid began to form after several hours. Upon completion, the solids were cooled to room temperature and quickly rinsed with clean DMF. Then the solids were freeze-dried and annealed at 500 °C for 3h. Finally, the MOF-templated Mn2O3 was prepared. Fabrication Process of C/Mn2O3/Nafion. The as-prepared Mn2O3 (5 μL, 1 mg/mL) was dropped on the surface of the working electrode. After the electrode was dried in air, 5 μL Nafion solution (0.5 wt%) was cast onto the surface of the Mn2O3 modified GC electrode and dried for 30 h at room temperature. Nafion was added here to serve as an antifouling coating since permselective Nafion membrane can decrease the interference of the surface-active compounds as well as improving the mechanical stability of the electrode. Characterization of the Mn-MOF Derived Mn2O3. The morphology of the electrode was observed with scanning electron microscopy (SEM, Hitachi S-4800). The X-ray diffraction (XRD) was carried out on a Bruker D8 Advanced Diffractometer employing Cu Ka radiation with a scanning rate of 2°/min. X-ray photoelectron spectroscopy (XPS) measurements were performed using a Kratos Axis Ultra DLD spectrometer equipped with a monochromatic Al Ka X-ray source operated at 150 W. The specific surface area of the Mn2O3 was measured by a surface area analyzer (Tristar 3020). Electrochemical Measurements of the C/Mn2O3/Nafion Electrode. Electrochemical measurements were performed on a CHI 660C electrochemical workstation (Chenhua Instrument, Shanghai, China). Peristaltic pump was obtained from Shanghai LingDe instrument Co. Ltd. (Shanghai, China). The pH meter was purchased from Shanghai YiDian scientific instrument Co. Ltd. (Shanghai, China). The peristaltic pump was turned on with the

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modified electrode inserted into the cavity. And the electrolyte (0.1 M NaAc-HAc) containing the target analyte (Cd2+ or Pb2+) was pumped into the cell with a current velocity of 0.44 mL min-1 for preconcetration at a defined concentration with -1.2 V applied for 180 s. Anodic stripping was carried out by square wave voltammetry at the frequency of 25 Hz, amplitude of 25 mV and potential increment step of 5 mV.

4. CONCLUSIONS In this paper, a 3D printed microfluidic sensing device based on Mn2O3 modified flexible screen printed electrode has been successfully fabricated for the real-time stripping analysis of heavy metal ions (Cd2+ and Pb2+). FEM simulation was applied to optimize the parameters of the 3D printed device and found the injection angle at 90º, channel height of 0.8 mm and 0.037 m/s for the velocity of the fluid to be the optimal conditions. The Mn-MOF was successfully fabricated and used as the precursor for the porous Mn2O3, which greatly improved the active electrochemical surface and the real-time stripping detection behavior of Cd(II) and Pb(II). The system showed a low detection limit of 0.5 μg L−1 for Cd(II) and 0.2 μg L−1 for Pb(II), as well as good selectivity and excellent reliability. Furthermore, when connected to an iPad via a USB, real-time detection can be achieved. All these results indicate that the 3D printed microfluidic device with nanomaterials modified SPE represented by Mn2O3 in this work has a promising future in analytical applications especially in household and in the field. A SSOCIATED CONTENT Supporting Information The specific size of the 3D printed device, 3D exploded view of the microfluidic device,

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assembly drawing of the detecting devices, the diagram of the process for fabricating the screen-printed electrodes, curves of the effect of inlet diameter on the thickness of diffusion layer, SEM images of the as-prepared Mn2O3 with different magnification, DPASV curves of C/Mn2O3/Nafion, C/Nafion and C electrodes, the calibration plots of C/Mn2O3/Nafion electrode, selectivity of the electrode, the comparison of the detection results of Cd 2+ and Pb2+ in real samples by Microfluidic sensor and ICP-OES.

ACKNOWLEDGEMENTS The work was supported by the NNSF of China (61525402, 21275076), Key University Science Research Project of Jiangsu Province (15KJA430006), QingLan Project, Research Project of General Administration of Quality Supervision, Inspection and Quarantine (2015IK129, 2016IK138, 2016KJ24).

REFERENCES (1) Sud, D. ; Mahajan, G. ; Kaur, M. P. Agricultural Waste Material as Potential Adsorbent for Sequestering Heavy Metal Ions from Aqueous Solutions – A Review. Bioresour. Technol. 2008, 99, 6017-6027. (2) Cui, L.; Wu J.; Ju H. Electrochemical Sensing of Heavy Metal Ions with Inorganic, Organic and Biomaterials. Biosens. Bioelectron. 2015, 63, 276-286. (3) Elizabeth, M. N.; Stephen, J. L. Tools and Tactics for the Optical Detection of Mercuric Ion. Chem. Rev. 2008, 108, 3443. (4) Ouyang, R.; Zhu, Z.; Tatum, C. E.; Chambers, J. Q.; Xue, Z. L. Simultaneous Stripping Detection of Pb(II), Cd(II) and Zn(II) Using a Bimetallic Hg-Bi/Single-Walled Carbon Nanotubes Composite Electrode. J. Electroanal. Chem. (Lausanne) 2011, 656, 78-84.

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(5) Moreno, M.; Rincon, E.; Perez, J. M.; Gonzalez, V. M.; Domingo, A.; Dominguez, E. Selective

Immobilization

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Oligonucleotide-modified

Gold

Nanoparticles

by

Electrodeposition on Screen-printed Electrodes.Biosens. Bioelectron. 2009, 25, 778-783. (6) Schuler, T.; Asmus, T.; Fritzsche, W.; Moller, R. Screen Printing as Cost-efficient Fabrication Method for DNA-chips with Electrical Readout for Detection of Viral DNA. Biosens. Bioelectron. 2009, 24, 2077-2084. (7) Nascimento, G. A.; Souza, E. V.; Campos-Ferreira, D. S.; Arruda, M. S.; Castelletti, C. H.; Wanderley, M. S.; Ekert, M. H.; Bruneska, D.; Lima-Filho, J. L. Electrochemical DNA Biosensor for Bovine Papillomavirus Detection using Polymeric Film on Screen-printed Electrode. Biosens. Bioelectron. 2012, 38, 61-66. (8) Xiong, L.; Batchelor-McAuley, C.; Goncalves, L. M.; Rodrigues, J. A.; Compton, R. G. The Indirect Electrochemical Detection and Quantification of DNA Through Its Co-adsorption with Anthraquinone Monosulphonate on Graphitic and Multi-walled Carbon Nanotube Screen Printed Electrodes. Biosens. Bioelectron. 2011, 26, 4198-4203. (9) Taleat, Z.; Khoshroo, A.; Mazloum-Ardakani, M. Screen-printed Electrodes for Biosensing: A Review (2008–2013). Microchim. Acta, 2014, 181, 865-891. (10) Zienkiewicz, O.C.; Taylor, R.L. Butterworth-Heinemann, Oxford, 2000. (11) Ambrosi, A.; Moo J. G. S.; Pumera M. Helical 3D-Printed Metal Electrodes as Custom-Shaped 3D Platform for Electrochemical Devices. Adv. Funct. Mater. 2016, 26, 698-703. (12) Gross, B. C.; Erkal, J. L.; Lockwood, S. Y.; Chen, C.; Spence, D. M. Evaluation of 3D Printing and Its Potential Impact on Biotechnology and the Chemical Sciences. Anal. Chem.

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Valves Enabling Online Monitoring of Extracellular Calcium and Zinc Ions in Living Rat Brains. Anal. Chim. Acta 2014, 838, 58. (21) Wei, Q. S.; Qi, H. F.; Luo, W.; Tseng, D.; Ki, S. J.; Wan, Z.; Gorocs, Z.; Bentolila, L. A.; Wu, T. T.; Sun, R.; Ozcan, A. Fluorescent Imaging of Single Nanoparticles and Viruses on a Smart Phone. ACS nano 2013, 7, 9147. (22) Symes, M. D.; Kitson, P. J.; Yan, J.; Richmond, C. J.; Cooper, G. J.; Bowman, R. W.; Vilbrandt, T.; Cronin, L. Integrated 3D-printed Reactionware for Chemical Synthesis and Analysis. Nat. Chem. 2012, 4, 349-354. (23) Ge, L.; Yan, J.; Song, X.; Yan, M.; Ge, S.; Yu, J. Three-dimensional Paper-based Electrochemiluminescence Immunodevice for Multiplexed Measurement of Biomarkers and Point-of-care Testing. Biomaterials 2012, 33, 1024-1031. (24) Whitesides, G. M. The Origins and the Future of Microfluidics. Nature 2006, 442, 368-373. (25) Morozan, A.; Jaouen, F. Metal Organic Frameworks for Electrochemical Applications. Energy Environ. Sci. 2012, 5, 9269. (26) Gai, P.; Zhang, H.; Zhang, Y.; Liu,

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Chara Corallina: Model Calculations and Measurements with the Pressure Probe Suggest Transport of H2O2 Across Water Channels. J. Exp. Bot. 2000, 51, 2053. (36) Sun,

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Figure 1. (a) Velocity profiles in microfluidic cell with different injection angles. Sample was injected from left inlet to right outlet along (A) 90º, (B) 45º and (C) 0º. The initial velocity is 0.037 m/s, the height of the channel is 0.8 mm. (b) Stripping voltammetry curves obtained by detecting a sample solution containing Pb2+ in corresponding modes (A), (B) and (C) shown in Figure 1(a).

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Figure 2. (a) The relationship between channel height and thickness of diffusion layer resulting from FEM simulation. Velocity: 0.037 m/s. Diffusion coefficient: 1000 μm2/s. (b) The relationship between velocity and thickness of diffusion layer. The height of channel: 1.5 mm.

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Figure 3. (a, b) Optical images of the devices without and with the screen-printed electrode (SPE). (c) The photograph depicting SPE which is flexible and can be bended easily. (d) The computational domain of microfluidic cell with the work electrode. (e) The velocity profile of microfluidic cell from the side view.

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Figure 4. Schematic illustration of the detecting system for heavy metal ions.

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Figure 5. (a) XRD patterns of Mn-MOF and Mn2O3. (b) XPS spectra of Mn2O3. (c, d) High resolution XPS spectra of O 1s and Mn 2p.

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Figure 6. (a) SEM images of SPE without modification. (b) SEM image of Mn2O3 modified SPE. (c) HRTEM image of Mn2O3. (d) Crystal structure of Mn2O3. (e) Nitrogen adsorption-desorption isotherm of Mn2O3. (f) Pore size distribution of Mn2O3.

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Figure 7. (a) DPASV curves of C/Mn2O3/Nafion, C/Nafion and C electrodes in the presence of 40 μg L-1 of Cd(II). (b) DPASV curves of C/Mn2O3/Nafion at different concentrations of Cd(II). (c) Calibration curves of C/Mn2O3/Nafion electrode towards Cd(II). (d) DPASV curves of Cd(II) and Pb(II) at C/Mn2O3/Nafion after the addition of 60 μg L−1 Cd(II) and Pb(II) in the solution. (e, f) DPASV curves of Cd(II) for optimized ASV and traditional ASV system.

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Table 1. The initial and boundary conditions (BCs) for numerical solutions of Eq.1 and Eq.2 in the computation domain sketched in Figure 3e. surface

Eq.1(BCs)

Eq.2 (BCs)

AB

µx=0.037 m/s

constant concentration c=c0

CD

No slip

c=0

EF

p=0

convective flux

No slip

insulation/symmetry

BC, DE, AF

Initial conditions c0=0.29 mmol/m3

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TOC


3D Printed Microfluidic Device with Microporous ... - ACS Publications

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