Printable hetero-structured bioelectronic interfaces with enhanced

Research Article www.acsami.org

Printable Heterostructured Bioelectronic Interfaces with Enhanced Electrode Reaction Kinetics by Intermicroparticle Network Rodtichoti Wannapob,†,‡ Mikhail Yu Vagin,†,⊥ Yu Liu,†,¶ Panote Thavarungkul,§ Proespichaya Kanatharana,‡ Anthony P. F. Turner,† and Wing Cheung Mak*,† †

Biosensors and Bioelectronics Centre, Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden ‡ Department of Chemistry, Faculty of Science and §Department of Physics, Faculty of Science, Prince of Songkla University, Hat Yai, Songkla 90112, Thailand ⊥ Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, 602 21 Norrköping, Sweden ¶ College of Life and Science, Sichuan Agricultural University, Yaan 625014, People’s Republic of China S Supporting Information *

ABSTRACT: Printable organic bioelectronics provide a fast and cost-effective approach for the fabrication of novel biodevices, while the general challenge is to achieve optimized reaction kinetics at multiphase boundaries between biomolecules and electrodes. Here, we present an entirely new concept based on a modular approach for the construction of heterostructured bioelectronic interfaces by using tailored functional “biological microparticles” combined with “transducer microparticles” as modular building blocks. This approach offers high versatility for the design and fabrication of bioelectrodes with a variety of forms of interparticle spatial organization, from layered-structures to more advance bulk heterostructured architectures. The heterostructured biocatalytic electrodes delivered twice the reaction rate and a six-fold increase in the effective diffusion kinetics in response to a catalytic model using glucose as the substrate, together with the advantage of shortened diffusion paths for reactants between multiple interparticle junctions and large active particle surface. The consequent benefits of this improved performance combined with the simple means of mass production are of major significance for the emerging printed electronics industry. KEYWORDS: microparticles, enzymes, conducting polymers, spatial organization, bioelectronics

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INTRODUCTION Considerable attention has been focused on the development of low cost, stable, and high performance electrode materials for printed electronic and bioelectronic devices.1−3 The general challenge in bioelectronic devices is how to integrate biomolecules with transducer materials and to achieve optimized electrode reaction kinetics at multiphase boundaries between biomolecules and the electrode materials. The organization and structural morphology of the multiphase boundaries is critical to enhance the mass-transfer process (diffusion of reactants) and charge transport (redox-process) for improved device performance.4 In particular for biosensors, the synchronized contributions of biocatalytic activity, controllable mass transfer (diffusion of analyte/substrate), and charge transport (redox-process) under appropriate operating conditions must be combined at multiphase boundaries to optimize performance.5 Conventionally, the construction of biosensors is based on coupling the biomolecules onto a planar transducer surface with immobilization techniques such as covalent bonding with cross-linking reagents, adsorption, entrapment, affinity interaction, and combinations of these.6 However, the effective surface area for communication between the © 2017 American Chemical Society

biomolecules and the transducer is limited by the layer structure at a planar bioelectronic interface. This limiting feature could be overcome by the introduction of nano/ microdimensional structures and three-dimensional (3D) organization of materials at the interfaces.7 In particular, enhanced performance with nano/microstructured and porous electrode materials is observed not only because of the higher surface-to-volume ratios, but also because of real size effects and the interfacial microenvironment reflecting changes in the material properties.8,9 The development of multilayered nano/ microstructures or 3D architectures built from blocks of nano/ microstructured materials could be a way to develop high performance electronic interfaces.10−12 Individual building blocks having a relatively large active surface area could significantly increase the multiphase boundary interactions.13,14 Conducting polymers have been widely used for printed organic electronic devices and exhibit a variety of exceptional properties such as electrical conductivity over the whole Received: August 21, 2017 Accepted: August 28, 2017 Published: August 28, 2017 33368

DOI: 10.1021/acsami.7b12559 ACS Appl. Mater. Interfaces 2017, 9, 33368−33376

Research Article

ACS Applied Materials & Interfaces

continuously stirred at 600g for 30 s to produce CaCO3 microparticles as a sacrificial template. The CaCO3 microparticles were washed twice with Milli-Q water, followed by washing with ethanol and 2-propanol using centrifugation (800g, 1 min) and redispersion cycles, consecutively. The purified pyrrole monomer doped with POM (5 mM) was mixed with the CaCO3 microparticles followed by incubation for 30 min at room temperature, which allowed the loading of the monomer and POM. The pyrrole/POM-loaded CaCO3 microparticles were washed by centrifugation (800g, 1 min), and the supernatant was discarded to remove excess monomers and POM. A chemical polymerization of PPy was carried out by mixing the resulting pyrrole/POM-loaded CaCO3 microparticles with a 1 mL of copper(II) perchlorate solution (1.0 M) and incubating for 6 h. The microparticles were then washed twice with a sequence of 2-propanol, ethanol, and Milli-Q water interspersed with centrifugation (800g, 1 min) and redispersion cycles. Subsequently, the CaCO3 template was removed by the addition of 1 mL of EDTA solution (0.2 M) followed by incubation for 1 h at room temperature. Finally, the resulting POM−PPyMPs were washed twice with Milli-Q water using centrifugation (800g, 1 min) and redispersion. Preparation of Modified Electrodes. The layer-structured modified electrodes were prepared by deposition of 3.5 μL of POM−PPyMPs (∼2.5 mg mL−1) as the first layer onto a glassy carbon electrode (GCE) and cured at 60 °C for 30 min, followed by deposition of 1.5 μL of BSA-GOxMP (∼2.5 mg mL−1) as the second layer over the preceding POM−PPyMPS layer and then cured at 60 °C for 30 min. The heterostructured modified electrodes were prepared by deposition of a blended mixture of 3.5 μL of POM− PPyMPs and 1.5 μL of BSA-GOxMPs onto a GCE, followed by curing at 60 °C for 30 min. Optical and Scanning Electron Microscopy. Optical microscopy images were recorded using a Nikon ECLIPSE Ti (Nikon, Japan). Images were captured by using a NIS-Elements AR (Version 4.1, Nikon, Japan). Scanning electron microscopy (SEM) images of the microparticles were recorded with PHENOM PRO (FEI, Netherlands), and high resolution SEM images were recorded with LEO 1550 Gemini (Zeiss, Germany). Microparticle samples suspended in Milli-Q water were applied onto a flat silicon surface, air-dried at ambient temperature, and coated with platinum. Particle Size Analysis. The particle size of the microparticles was measured using a Zetasizer Nano ZS90 (Malvern Instruments Ltd., Worcestershire, UK). The measurement was based on dynamic light scattering, measuring the Brownian motion of the particles, and converting the data into a size distribution graph using the Stokes− Einstein relationship. The measurements were performed at 25 °C, and the average diameter was calculated by taking an average of three repeated measurements. Electrochemical Analysis. All electrochemical experiments and simulations were performed with a PGSTAT30 potentiostat (Autolab, Netherlands) under NOVA or GPES software control employing a conventional three-electrode electrochemical cell. A glassy carbon electrode (GCE, 3 mm diameter, surface area 0.0707 cm2) and platinum electrode (3 mm diameter, surface area 0.0707 cm2) were used as the working electrode, a platinum wire as the auxiliary electrode, and a silver/silver chloride as the reference electrode (3 M KCl) in aqueous media in all experiments, unless otherwise stated. Prior to use, the working electrode was successively polished with 1.0, 0.3, and 0.05 μm alumina powders and sonicated in water for 10 min after each polishing step. Finally, the electrode was washed with ethanol and then dried with a high purity argon stream. Modified working electrodes were prepared by drop casting different microparticle suspensions onto the electrode surface followed by curing at 60 °C for 30 min.

insulator-semiconductor-metal range, reversible doping/dedoping processes, ionic conductivity, mechanical flexibility, and cost advantages.15,16 However, interfacing conducing polymers with biomolecules remains a challenge. Covalent attachment of biomolecules interrupts the conjugation of polymer, which leads to a conductivity decrease,17 while direct blending will partly inactivate the biomolecules due to unfavorable biomolecule/conducing polymer interactions.18 We have recently demonstrated the fabrication of water processable conducting polymer microparticles and explored their electrochemical properties for controlled drug release and construction of electrochemical interfaces.13,19 These polypyrrole microparticles with a favorable high surface morphology could be interesting processable materials for the construction of biosensors. To address these challenges, we developed an entirely new concept based on a modular approach for the construction of advanced, spatially organized, electrochemical biosensor interfaces. This approach is based on the development of tailored functional “biological modules” and “transducer modules” as microparticle building blocks for the construction of biosensor and biocatalytic interfaces. The controllable compartmentalization of the conducting polymer and biomolecules into water-processable microparticle modules provides a common interface for the integration of biomolecules into the bulk of the bioelectronics composite. Biological modules composed of albumin-glucose oxidase microparticles (BSA-GOxMPs) and transducer modules, composed of polyoxometalate-conducting polymer microparticles (POM−PPyMPs) with defined morphology and electrochemical catalytic function, were fabricated as modular building blocks for the construction of various spatially organized bioelectronic interfaces, and their analytical performance were studied.

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EXPERIMENTAL SECTION

Materials. The potassium salt of parent Dawson-type polyoxometalate [P2W18O62]6− (POM) was synthesized as described previously.20 Calcium chloride, copper(II) perchlorate, pyrrole, sodium carbonate, ethylenediaminetetracetic acid (EDTA), lithium perchlorate, glucose oxidase (GOx), bovine serum albumin (BSA), ethanol, and 2-propanol were purchased from Sigma-Aldrich (St. Louis, MO, USA) and were used as received. Pyrrole (99%) was received from Sigma-Aldrich and purified before use by passing through a neutral column of alumina (0.05 μm) to obtain a colorless liquid. Water was purified using Milli-Q water purification system. Microparticle Fabrication. The BSA-GOxMP was prepared by a template-assisted protein cross-linking method.21,22 In brief, a solution containing 450 μL of BSA solution (20 mg mL−1), 50 μL of GOx (10 mg mL−1), and 500 μL of calcium chloride (0.5 M) was rapidly mixed with 1 mL of sodium carbonate solution (0.5 M) with stirring at 600g for 30 s to produce BSA-GOx-loaded calcium carbonate (CaCO3) microparticle. The BSA-GOx-loaded calcium carbonate (CaCO3) microparticles were washed three times with PBS (10 mM, pH 7.2) by centrifugation (800g, 2 min) followed by redispersion. The resulting BSA-GOx-loaded CaCO3 microparticles were incubated in 1 mL (2.0% v/v) of glutaraldehyde for 30 min at room temperature. Subsequently, the microparticles were washed five times with PBS by repeated centrifugation at 800g for 2 min to remove unreacted glutaraldehyde. Finally, the CaCO3 template was removed by adding 0.2 M EDTA and incubating for 30 min. The resulting BSA-GOxMPs were washed twice with PBS by centrifugation (800g, 1 min) and finally redispersed in PBS. The polypyrrole microparticles (PPyMPs) doped with POM were prepared by template assisted polymerization.13,14 In brief, 1 mL of sodium bicarbonate (Na2CO3, 0.5 M) was rapidly added to 1 mL of calcium chloride (CaCl2, 0.5 M) and

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RESULTS AND DISCUSSION

The biological module (BSA-GOxMP) and transducer module (POM−PPyMP) were prepared using a generic CaCO3 template-assisted technique. The porous structure and inorganic nature of the CaCO3 allows the effective loading of 33369


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Figure 1. (A, B) Optical microscopy images of the BSA-GOxMPs and POM−PPyMPs, respectively; (C, D) SEM images of the BSA-GOxMPs and POM−PPyMPs, respectively; (E, F) corresponding high magnification SEM images showing the surface morphology of the BSA-GOxMPs and POM−PPyMPs, respectively.

various small organic, inorganic, and biological molecules such as monomer (i.e., pyrrole), electrocatalyst−Dawson-type polyoxometalate (POM),20 or enzyme (e.g., glucose oxidase GOx), thus providing a universal method for fabrication of microparticles with different chemical natures.21−24 The macroscopic morphologies of the BSA-GOxMPs and POM− PPyMPs were characterized by optical microscopy. Optical images showed that the BSA-GOxMPs and POM−PPyMPs exhibited a fairly uniform spherical shape and a homogeneous narrow size distribution (Figure 1A,B) with an average diameter of 2.3 ± 0.3 μm and 2.6 ± 0.4 μm, respectively (Figure S1). The narrow particle size distribution results from the advantage of having a fairly uniform CaCO3 template that regulates the size of the resulting BSA-GOxMPs and POM−PPyMPs. The surface morphology of BSA-GOxMPs and POM−PPyMPs appeared rough with an assembled nanoscaled granular structure (Figure 1C,D). The granule size of POM−PPyMPs was larger and rougher than that of BSA-GOxMPs (Figure 1E,F). This is likely due to the different chemical processes involved in the formation of POM−PPyMPs and BSAGOxMPs. The POM−PPyMPs were fabricated via templateassisted polymerization, which resulted in extensive growth of the PPy from the polymerization process yielding a larger grain size. In contrast, the BSA-GOxMPs were fabricated by a template-assisted protein cross-linking reaction between adjacent protein molecules, without an extensive growth process, and this resulted in a relatively smaller grain size. Moreover, EDX spectrum of the POM−PPyMPs showed a

characteristic nitrogen peak of PPy with molecular formula of (C4H3N)n and a chloride peak as the anionic dopant. Meanwhile, a characteristic tungsten peak was observed indicates the presence of the POM with molecular formula of [P2W18O62]6−) in the POM−PPyMPs (Figure S2). To demonstrate the electrocatalytic performance of both BSA-GOxMPs and POM−PPyMPs, voltammetry on modified electrodes was used to assay hydrogen peroxide via both oxidation and reduction. Hydrogen peroxide generated by the BSA-GOxMPs in the presence of glucose was quantified via oxidation on a platinum electrode modified with BSAGOxMPs. In the presence of glucose anodic current began to flow at +0.20 V versus Ag/AgCl and almost constant at beyond +0.35 V (Figure 2A). This current response observed resulted from the electrochemical oxidation of H2O2,25 which was generated by the GOx in biological microparticles (BSAGOxMPs) that were not observed in the control BSA-MPs (Figure 2A, insert). This illustrates the retention of the biocatalytic function of BSA-GOxMPs due to the relatively mild microparticle fabrication conditions at neutral pH, room temperature, and in an aqueous environment. The steady-state character of the observed voltammetric responses on additions of glucose illustrates the fast enzymatic turnover arising from the porous hierarchical microparticle film structure, yielding the appearance of diffusional independence due to the appearance of enzymatically generated hydrogen peroxide in close proximity to the electrode surface. Moreover, immobilization of enzymes by cross-linking with BSA in the microparticles 33370


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Figure 2. (A) Cyclic voltammograms of BSA-GOxMPs modified electrode before and after addition of glucose (0.5−2.0 mM); 10 mM PBS, pH 7.2, 50 mV s−1 (inset shows the control BSA-MPs modified electrode and reaction of H2O2 on the surface electrode). (B) Cyclic voltammograms of POM−PPyMPs modified electrode before and after addition of hydrogen peroxide (1.0−4.0 mM); 10 mM PBS, pH 7.2, 50 mV s−1 (inset shows the control PPyMPs modified electrode and reaction of H2O2 on the surface electrode).

(1.0 mM) (Figure S3), and a particle ratio of 70:30 w/w was chosen for further experiments. Figure 3Aii and Bii show the microscopic images of the layer-structured film and heterostructured film (70:30), respectively. The BSA-GOxMPs were labeled with fluorescein. For the layer-structured film, the POM−PPyMPs and BSA-GOxMPs were organized in a spatially separated layered fashion. In contrast, for the bulk heterostructured film, the POM−PPyMPs and BSA-GOxMPs were organized in a relatively homogeneous fashion. In addition, the microparticles are highly dispersible in aqueous solution forming a microparticle ink. This microparticle ink can be easily processed and deposited onto a substrate by drop casting or printing through a mask to form various shapes (Figure S4A). The deposited microparticles were cured at 60 °C for 30 min to promote intermicroparticle assembly and to create the hierarchical film structure. It has been reported the thermal stability of the immobilized GOx or GOx−polymer complex was enhanced up to 65−70 °C compared with the free GOx molecules (50 °C).30,31 The enhanced thermal stability of the GOx−polymer complex was explained by the interaction between the GOx and the polymer matrix to prevent subunit dissociation. SEM images showed the bulk morphology of the microparticle film with a hierarchically porous structure, composed of intermicroparticle channels built during the assembly process (Figure S4B). It is well-known that hierarchically porous structures, with their advantages of high active surface areas and open porous structure, facilitate the diffusion of substances (e.g., analytes, electrolytes, etc.) to the active site of immobilized enzymes and electron mediators.32−35 The bioelectrode reaction rates of the layer-structured and heterostructured films were compared using amperometric

allowed a higher loading of enzyme together with a large active surface, and maintenance of the stability of the enzymes due to the features of the BSA such as hydrophilicity, biocompatibility, and highly cross-linked networks.26,27 POM has been shown to have a good electrocatalytic properties toward the reduction of hydrogen peroxide and undergo multiple electron transfer.28,29 The voltammetry measurements on POM−PPyMP-modified electrodes showed the appearance of a cathodic wave accompanied by a decrease in anodic counterpart currents (Figure 2B) upon the addition of hydrogen peroxide. In contrast, pure PPyMPs showed insignificant electrocatalytic activities (Figure 2B, insert). Therefore, the observed voltammetric response corresponds to the electrocatalytic reduction of hydrogen peroxide on the POM−PPyMP composite. By exploiting colloidal assembly, the microparticle modules offer high flexibility for the design and fabrication of bioelectronic interfaces with various intermicroparticle spatial organization, progressing from a conventional layered architecture, toward a new advanced 3D bulk heterostructured architecture (Figure 3Ai,Bi). The layer-structured bioelectrodes were constructed by deposition of a layer of POM−PPyMPs (transducer module) onto the supporting GCE and drying, followed by deposition of a second layer of BSA-GOxMPs (biological module), while the heterostructured bioelectrodes were constructed by deposition of a blended mixture of POM− PPyMPs and BSA-GOxMPs onto the GCE. The optimized conditions for the electrode preparation were initially studied by blending POM−PPyMPs and BSA-GOxMPs in different ratios of 90:10, 80:20, 70:30, 60:40, and 50:50 w/w, respectively. The results showed that a microparticle ratio of 70:30 w/w provided the highest current response for glucose 33371


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Figure 3. (A, B) Schematic shows the design of bioelectrode with various intermicroparticle spatial organizations of (Ai) layer-structured and (Bi) bulk heterostructured architecture, and (ii) corresponding microscopic images of the microparticle films with BSA-GOxMPs labeled with fluorescein. (C) Calibration curves of the layer-structured (circle) and the heterostructured (square) bioelectrodes for amperometric glucose detection. (D) Electrode reaction kinetics assessed by impedance spectroscopy. The impedance spectra were measured on a GCE with a layer-structured film (circle) the heterostructured film (square) in absence (solid) and in the presence (open) of glucose (2 mM); −0.6 V (vs Ag/AgCl), 5 mV amplitude, 0.1 M KCl, 0.01 M PBS pH 7.4, solid lines = spectra simulated by distributed model.

film, the heterostructured film showed larger values of total impedance by reflecting the blend of conducting material with the insulating BSA-GOxMPs. Quantitative analysis of the impedance spectra obtained from all developed microparticle-modified electrodes was carried out using both the conventional equivalent circuit proposed for supercapacitors (Figure S5)14,36,37 and a circuit based on a transmission line model (Figure S6) developed by Bisquert for porous electrodes.38 Since the boundary between the layers is not ideally smooth, the conventional circuit has been converted to a more complicated, distributed model featuring constant phase elements (CPE) rather than a pure double layer capacitor. The capacitance values were calculated as39

measurement of glucose under an operating potential of −0.50 V versus saturated Ag/AgCl reference. Figure 3C shows the corresponding calibration curves of the layer-structured and heterostructured glucose biosensors. The sensitivity of the heterostructured biosensors was 363.9 nA mg−1 mM−1, while that of the layer-structured biosensors was 173.2 nA mg−1 mM−1; thus, the heterostructured biosensors resulted in an approximately 2.1-fold increases in electrode reaction rate in response to glucose. This increase could be explained by the shorter diffusion distance for shutting the reactants between the biocatalyst microparticles BSA-GOxMPs and the transducer microparticles POM−PPyMPs and thus enhancing the overall electrode kinetics within the heterostructure film (Figure 3Ai,Bi). Moreover, the synthesized BSA-GOxMPs and POM−PPyMPs have been stored for 4−6 weeks as raw materials for making the biosensors, and they showed no significant difference in sensitivity between experiments. A comparative evaluation of the effect of membrane architecture on the electrode function was performed by impedance spectroscopy (Figure 3D). The difference in spectra obtained in pure electrolyte solution illustrates the significantly diverse film conductivities. In contrast to the layer-structured

C = (P(R S)(1 − ϕ))(1 − ϕ)

(1)

where RS is the solution resistance, P is a fitting parameter of the CPE, and ϕ is the fitted exponent factor, which varies from 0 to 1. When ϕ is equal to 0, the CPE behaves as a pure resistor, and when ϕ = 1, the CPE represents a pure capacitor. The distributed conventional circuit also consists of the solution resistance RS; RCT, charge transfer resistance as a measure of electrode reaction kinetics; WS, generalized finite 33372


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Figure 4. (A) Illustration showing the fabrication of fully printed microparticle-based heterostructured bioelectrodes: deposition of (i) conductive track onto PET, (ii) deposition of an insulation layer, and (iii) deposition of microparticles. (B) Configuration of the heterostructured bioelectrode. (C) Amperometric responses and (D) calibration curve of the heterostructured bioelectrodes for glucose detection.

Warburg element corresponding to the diffusion contribution; and CF, capacitance raised due to the pseudocapacitive process. Good matches between the fitted and experimental impedance spectra were obtained for all modified electrodes in the absence and in the presence of 2 mM glucose in PBS pH 7.2 (Figure 3D). In response to glucose, the heterostructured film showed a 25.9% change in RCT value compared with the layer-structured film, which showed only a 2.3% change in RCT value. Hence, the changes in RCT were 10-times higher for the heterostructured film illustrating the faster electrode reaction kinetics (Table S1). Consistent with the distributed model, the impedance data analysis based on the transmission line model illustrated that the heterostructured film showed a 36.9% change in RCT value compared with the layer-structured film, which showed only a 21.2% change in RCT value in response to glucose. Hence, the heterostructured film resulted in 1.9-times faster electrode reaction kinetics (Table S2). Results from the impedance analysis are in agreement with the amperometric measurements. Furthermore, the addition of glucose led to larger changes in the diffusion properties of the heterostructured film in comparison with the layer-structured film, illustrating that the reactant diffusion kinetics were more efficient on the heterostructured film with an average shorter intermicroparticle distance between the BSA-GOxMPs and POM−PPyMPs. Being inversely proportional to the square root of the diffusion coefficient, the Warburg coefficient W1 showed up to a 30% decrease in the presence of glucose for the heterostructured film, while the layer-structured film revealed only a 12% decrease (Table S1). The changes in effective diffusion thickness (L) estimated for the heterostructured film and layered-structured film in response to glucose were 85% and 516%, respectively; hence, the heterostructured film

showed a six-fold increase in the effective diffusion kinetics in response to glucose (Table S1). These results demonstrated that the bulk heterostructure film led to more efficient shuttling of the reactants with a shorter diffusion length between the BSA-GOxMPs and POM−PPyMPs and thus enhanced the enzymatic and POM catalytic reaction kinetics facilitated by diffusion in comparison with the spatially separated layerstructured film. We further demonstrated the use of this microparticle modular approach for the direct fabrication of bioelectrodes (Figure 4A,B). In the first step, carbon conductive tracks (1 mm × 20 mm) were printed onto a polyethylene terephthalate (PET) substrate (Figure 4Ai), followed by deposition of an insulation layer on top of the conductive track, which left 4 mm at the top and 2 mm at the end uncovered (Figure 4Aii). Finally, microparticle-based heterostructured bioelectrodes with a diameter of 3 mm were constructed by deposition of a blended mixture of POM−PPyMPs and BSA-GOxMPs (70:30) onto the 2 mm end of the conductive track (Figure 4Aiii). The configuration of the resulting bioelectrode is shown in Figure 4B. The performance of the bioelectrodes was evaluated by amperometric measurement for the successive addition of glucose (Figure 4C). The catalytic current displayed a rapid and sensitive response to the addition glucose with a steady state current being obtained within 5 s. The fast response may be attributed to the porous microparticle film that combines high active surface areas with intermicroparticle channels that facilitate efficient diffusion. A calibration curve of the electrocatalytic currents generated as a function of different glucose concentrations is shown in Figure 4D. The bioelectrodes delivered a linear response to glucose concentration in the range of 0.5−8.0 mM. The sensitivity and limits 33373


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ACS Applied Materials & Interfaces of detection (LoD) of the electrodes were 589.1 nA mg−1 mM−1 and 0.28 mM (LoD was calculated as 3 × SD/sensitivity, where SD is the standard deviation of the blank signal),40 respectively. The performance of the biosensors fabricated with our microparticle modular approach has a higher sensitivity compared with most of the conventional PPy-based glucose biosensors and has a comparable linear range and response time with other conventional systems (Table 1). It is important to

boundaries between biomolecules and the conducting polymer materials within a heterostructured architecture glucose biosensor. This microparticle modular approach provides a new method for integration and interfacing biomolecules and conducing polymer and could be formulated as functional inks for the construction of a variety of new printable bioelectronic devices for medical diagnostic and energy applications.

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biosensors BSA-GOxMPs/ PPyMPs microparticle modules Chi-Py/Au/GOx film PPy-flim/GOx GOD/flat PPy/Pt PPy-polyanion− GOD PPy/polyanion/ PEG/GOD PPy−GOx-Gel|Pt composite PPy-GOx−Pt PyCO2H/Au Au-AAO/GOx/ PPy

sensitivity (nA cm−2 mM−1)

linear range (mM)

response time (s)

references

589.1

0.5−8.0

5

this work

580.0

1.0−20

4

41

81.1 330 203.7

0.001−20 0−17

270

1.0−22

281

1−15

637 420 80

1−10 1.0−18.0 0.5−5.0

9 20 30

ASSOCIATED CONTENT

S Supporting Information *

Table 1. Comparison of Analytical Performances of PPyBased Glucose Biosensors

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b12559. Microparticle film with different shapes; distributed equivalent circuit; transmission line equivalent circuit; table of fitted parameters of distributed equivalent circuit (PDF)

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AUTHOR INFORMATION

Corresponding Author

42 43 44

*E-mail: [email protected]. ORCID

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Mikhail Yu Vagin: 0000-0001-8478-4663 Wing Cheung Mak: 0000-0003-3274-6029

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46

Notes

18 2 15

46 47 48

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The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors would like to acknowledge the Swedish Research Council (VR-2015-04434) for financial support to carry out this research. This work was also supported by the Scholarship for an overseas thesis research study by Graduate School Prince of Songkla University; Higher Education Research Promotion and National Research University Project of Thailand (NRU); Office of higher Education Commission; Center of Excellence for Innovation in Chemistry (PERCH−CIC); and Ministry of Education, Thailand.

note that most of the reported PPy-based biosensors are doped with favorable metal nanoparticles catalyst (such as AuNPs and PtNPs), which is difficult to make a direct comparison. Nevertheless, the high sensitivity of our microparticle modular based biosensor (in the absence of a metal nanoparticle catalyst) likely resulted from the relatively high active surface of the microparticle modules and favorable heterostructured bioelectronic interfaces. To improve the selectively of our system, we employed 0.05 wt % Nafion as a binder for packaging of the microparticlebased electrodes. The selectively of the heterostructured glucose biosensors was studied by the addition of common interfering substances present in biological samples, that is, 0.5 mM uric acid and 0.5 mM ascorbic acid (Figure S7). The concentrations of the tested interferences were chosen based on their respective concentrations in human serum.49 There was no noticeable interference upon addition of uric acid and ascorbic acid during the amperometric measurment of glucose, likely due to the anti-interference properties of the Nafion matrix.50

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REFERENCES

(1) Baeumner, A. J. Biosensors for Environmental Pollutants and Food Contaminants. Anal. Bioanal. Chem. 2003, 377, 434−445. (2) Kamyshny, A.; Magdassi, S. Conductive Nanomaterials for Printed Electronics. Small 2014, 10, 3515−3535. (3) Turner, A. P. F. Biosensors: Sense and Sensibility. Chem. Soc. Rev. 2013, 42, 3184−3196. (4) Proietti, E.; Jaouen, F.; Lefèvre, M.; Larouche, N.; Tian, J.; Herranz, J.; Dodelet, J.-P. Iron-Based Cathode Catalyst with Enhanced Power Density in Polymer Electrolyte Membrane Fuel Cells. Nat. Commun. 2011, 2, 416−9. (5) Jaouen, F.; Proietti, E.; Lefevre, M.; Chenitz, R.; Dodelet, J.-P.; Wu, G.; Chung, H. T.; Johnston, C. M.; Zelenay, P. Recent Advances in Non-Precious Metal Catalysis for Oxygen-Reduction Reaction in Polymer Electrolyte Fuel Cells. Energy Environ. Sci. 2011, 4, 114−130. (6) Talbert, J. N.; Goddard, J. M. Enzymes on Material Surfaces. Colloids Surf., B 2012, 93, 8−19. (7) Perelaer, J.; Smith, P. J.; Mager, D.; Soltman, D.; Volkman, S. K.; Subramanian, V.; Korvink, J. G.; Schubert, U. S. Printed Electronics: The Challenges Involved in Printing Devices, Interconnects, and Contacts Based on Inorganic Materials. J. Mater. Chem. 2010, 20, 8446−8453. (8) Arico, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J.-M.; van Schalkwijk, W. Nanostructured Materials for Advanced Energy Conversion and Storage Devices. Nat. Mater. 2005, 4, 366−377. (9) Maier, J. Nanoionics: Ion Transport and Electrochemical Storage in Confined Systems. Nat. Mater. 2005, 4, 805−815.

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CONCLUSION In conclusion, we demonstrated a new modular approach using various functional microparticles as modular building blocks for the construction of spatially organized bioelectronic interfaces. The microparticle modules offer high flexibility for the design and fabrication of bioelectronic interfaces with various intermicroparticle spatial organizations, thus moving from a conventional layer-structured configuration toward an advanced bulk heterostructured architecture. We demonstrated the concept of spatial organization and intermicroparticle communications to enhance electrode reactions at the multiphase 33374


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Printable hetero-structured bioelectronic interfaces with enhanced

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