Printable Heterostructured Bioelectronic Interfaces with Enhanced

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Printable hetero-structured bioelectronic interfaces with enhanced electrode reaction kinetics via inter-microparticle network Rodtichoti Wannapob, Mikhail Yu. Vagin, Yu Liu, Panote Thavarungkul, Proespichaya Kanatharana, Anthony P. F. Turner, and Wing Cheung Mak ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b12559 • Publication Date (Web): 28 Aug 2017 Downloaded from http://pubs.acs.org on August 29, 2017

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ACS Applied Materials & Interfaces

Printable hetero-structured bioelectronic interfaces with enhanced electrode reaction kinetics by inter-microparticle network Rodtichoti Wannapob,[a,b] Mikhail Yu. Vagin,[a,d] Yu Liu,[a,e] Panote Thavarungkul,[c] Proespichaya Kanatharana,[b] Anthony P.F. Turner,[a] Wing Cheung Mak*[a] a

Department of Physics, Chemistry and Biology, Linköping University, SE-581 83, Linköping,

Sweden b

Department of Chemistry, Faculty of Science, Prince of Songkla University, Hat Yai, Songkla,

90112, Thailand c

Department of Physics, Faculty of Science, Prince of Songkla University, Hat Yai, Songkla,

90112, Thailand d

Laboratory of Organic Electronics, Department of Science and Technology, Linköping

University, Norrköping, Sweden e

College of Life and Science, Sichuan Agricultural University, Yaan 625014, People’s Republic

of China. Corresponding Author: [email protected]

Keywords: microparticles, enzymes, conducting polymers, spatial organization, bioelectronics

1 ACS Paragon Plus Environment


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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 kinetic at multiphase boundaries between biomolecules and electrodes. Here, we present an entirely new concept based on a modular approach for the construction of hetero-structured 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 inter-particle spatial organization, from layered-structures to more advance bulk hetero-structured 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.


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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 masstransfer process (diffusion of reactants) and charge transport (redox-process) for improved device performance.4 In particular for biosensors, the synchronized contributions of bio-catalytic activity, controllable mass transfer (diffusion of analyte/substrate) and charge transport (redox-process) under appropriate operating conditions, must be combined at multiphase boundaries in order 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 crosslinking reagents, adsorption, entrapment, affinity interaction and combinations of these.6 However, the effective surface area for communication between the 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/micro-dimensional structures and three-dimensional (3D) organization of materials at the interfaces.7 In particular, enhanced performance with nano/micro-structured 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 micro-environment 3 ACS Paragon Plus Environment


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reflecting changes in the material properties.8,

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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 insulatorsemiconductor-metal range, reversible doping/de-doping 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 explore their electrochemical properties for controlled drug relased and construction of electrochemical interfaces.13, 19 While these polypyrrole microparticles with a favorable high surface morphology could be an 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


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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 polyoxometalateconducting 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.

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 crosslinking method.21,

22

In

brief, a solution containing 450 µL BSA solution (20 mg mL-1), 50 µL GOx (10 mg mL-1) and 500 µL calcium chloride (0.5 M) was rapidly mixed with 1 mL sodium carbonate solution (0.5 M) with stirring at 600 g for 30 seconds to produce BSA-GOx-loaded calcium carbonate (CaCO3) microparticle. The BSA-GOx-loaded calcium carbonate (CaCO3) microparticles were



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washed three times with PBS (10 mM, pH 7.2) by centrifugation (800 g., 2 minutes) followed by re-dispersion. The resulting BSA-GOx-loaded CaCO3 microparticles were incubated in 1 mL (2.0% v/v) of glutaraldehyde for 30 minutes at room temperature. Subsequently, the microparticles were washed five times with PBS by repeated centrifugation at 800 g for 2 minutes to remove unreacted glutaraldehyde. Finally, the CaCO3 template was removed by adding 0.2 M EDTA and incubating for 30 minutes. The resulting BSA-GOxMPs were washed twice with PBS by centrifugation (800 g, 1 min) and finally re-dispersed 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 continuously stirred at 600 g for 30 seconds 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 (800 g, 1 min) and re-dispersion cycles, consecutively. The purified pyrrole monomer doped with POM (5 mM) was mixed with the CaCO3 microparticles followed by incubation for 30 minutes at room temperature, allowing the loading of the monomer and POM. The pyrrole/POMloaded CaCO3 microparticles were washed by centrifugation (800 g, 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 copper (II) perchlorate solution (1.0 M) and incubating for 6 hours. The microparticles were then washed twice with a sequence of 2-propanol, ethanol and Milli-Q water interspersed with centrifugation (800 g, 1 min) and re-dispersion cycles. Subsequently, the CaCO3 template was removed by the addition of 1 mL EDTA solution (0.2 M) followed by incubation for 1 hour at


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room temperature. Finally, the resulting POM-PPyMPs were washed twice with Milli-Q water using centrifugation (800 g, 1 min) and re-dispersion. Preparation of modified electrodes The layer-structured modified electrodes were prepared by deposition of 3.5 µL of POMPPyMPs (~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 3 repeated measurements.



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Electrochemical analysis All electrochemical experiments and simulations were performed with a PGSTAT30 potentiostat (Autolab, Netherlands) under NOVA or GPES software control employing a conventional threeelectrode 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 (3M 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.

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 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 the BSA-GOxMPs and POM-PPyMPs exhibited a fairly uniform spherical shape and a homogeneous narrow size 8 ACS Paragon Plus Environment

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distribution (Figure. 1 A-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 BSAGOxMPs and POM-PPyMPs. The surface morphology of BSA-GOxMPs and POMPPyMPs appeared rough with an assembled nanoscaled granular structure (Figure. 1CD). The granule size of POM-PPyMPs was larger and rougher than that of BSA-GOxMPs (Figure. 1 E-F). This is likely due to the different chemical processes involved in the formation of POM-PPyMPs and BSA-GOxMPs. The POM-PPyMPs were fabricated via template-assisted polymerization, which results 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 crosslinking 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 prescence of the POM with molecular formula of [P2W18O62]6-) in the POM-PPyMPs (Figure S2). In order to demonstrate the electrocatalytic performance of both BSA-GOxMPs and POMPPyMPs, 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 BSA-GOxMPs. 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 is resulted from the



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electrochemical oxidation of H2O2,25 that was generated by the GOx in biological microparticles (BSA-GOxMPs) which 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 crosslinking with BSA in the microparticles 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 crosslinked networks.26, 27 POM has been shown to have a good electrocatalytic properties towards the reduction of hydrogen peroxide, undergoing 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 its 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 POMPPyMP composite. By exploiting colloidal assembly, the microparticle modules offer high flexibility for the design and fabrication of bioelectronic interfaces with various inter-microparticle spatial organization, progressing from a conventional layered architecture, towards a new


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advanced 3D bulk hetero-structured architecture (Figure. 3Ai and Bi). The layerstructured 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 hetero-structured 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 was 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 (1.0 mM) (Figure S3) and a particle ratio of 70:30 w/w was chosen for futher experiments. Figure. 3Aii and 3Bii show the microscopic images of the layer-structured film and hetero-structured 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 homogenous 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 minutes 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 upto 65-70 °C compared with the free GOx molecules (50 ºC).30, 31 The enhanced thermal



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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 inter-microparticle 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 rate of the layer-structured and hetero-structured films were compared using amperometric measurement of glucose under an operating potential of -0.50 V vs. saturated Ag/AgCl reference. Figure. 3C shows the corresponding calibration curves of the layer-structured and hetero-structured glucose biosensors. The sensitivity of the hetero-structured biosensors was 363.9 nA mg-1 mM-1, while that of the layerstructured biosensors was 173.2 nA mg-1 mM-1, thus the hetero-structured 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 hetero-structure film (Figure. 3Ai and Bi). Moreover, the synthesized BSA-GOxMPs and POM-PPyMPs have been stored for 4-6 weeks as raw materials for making the biosensors, and it showed no significant different 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


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conductivities. In contrast to the layer-structured film, the hetero-structured film showed larger values of total impedance, reflecting the blend of conducting material with the insulating BSA-GOxMPs. Quantitative analysis of the impedance spectra obtained from all developed microparticle-modified electrodes were 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: C= (P (RS )(1-ϕ))1/ϕ

(1)

where RS is the solution resistance, P is a fitting parameter of the CPE and Ø is the fitted exponent factor, which varies from 0 to 1. When Ø is equal to 0 the CPE behaves as a pure resistor and when Ø = 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 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 hetero-structured 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



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for the hetero-structured 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 hetero-structured 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 hetero-structured 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 hetero-structured film in comparison with the layer-structured film, illustrating that the reactant diffusion kinetics were more efficient on the hetero-structured 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 hetero-structured film, while the layer-structured film revealed only a 12% decrease (Table S1). The changes in effective diffusion thickness (L) estimated for the hetero-structured film and layeredstructured film in response to glucose were 85% and 516%, respectively, hence the hetero-structured film showed a 6 fold increase in the effective diffusion kinetics in response to glucose (Table S1). These results demonstrated that the bulk hetero-structure 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 spatiallyseparated layer-structured film.


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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 x 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, leaving 4 mm at the top and 2 mm at the end uncovered (Figure. 4Aii). Finally, microparticle-based hetero-structured 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 seconds. The fast response may be attributed to the porous microparticle film that combines high active surface areas with inter-microparticle channels that facilitates 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 0.5 to 8.0 mM. The sensitivity and limits of detection (LoD) of the electrodes were 589.1 nA mg1

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 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



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microparticle modular based biosensor (in the absence of a metal nanoparticle catalyst) is likely resulted from the relatively high active surface of the microparticle modules and favorable hetero-structured bioelectronic interfaces.

To improve the selectively of our system, we employed 0.05 wt% Nafion as a binder for packaging of the microparticle-based electrodes. The selectively of the hetero-structured glucose biosensors was studied by the addition of common interfering substances present in biological samples, i.e. 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

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 inter-microparticle spatial organizations, thus moving from a conventional layer-structured configuration, towards an advanced bulk hetero-structured architecture. We demonstrated the concept of spatial organization and inter-microparticle communications, to enhance electrode reactions at the multiphase boundaries between biomolecules and the conducting polymer materials within a hetero-structured architecture glucose biosensor. This microparticle modular approach provides a new method for integration 16 ACS Paragon Plus Environment

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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.

ASSOCIATED CONTENT Supporting Information Microparticle film with different shapes, the distributed equivalent circuit, transmission line equivalent circuit, table of fitted parameters of distributed equivalent circuit. This material

is

available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *[email protected] ACKNOWLEDGEMENTS The authors would like to acknowledge the Swedish Research Council (VR-2015-04434) for financial support to carry out this research. This work 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.

REFERENCES



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(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., IronBased Cathode Catalyst with Enhanced Power Density in Polymer Electrolyte Membrane Fuel Cells. Nat. Commun. 2011, 2- 416, 1-9. (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, 819. (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. (10) Rolison, D. R.; Long, J. W.; Lytle, J. C.; Fischer, A. E.; Rhodes, C. P.; McEvoy, T. M.; Bourg, M. E.; Lubers, A. M., Multifunctional 3d Nanoarchitectures for Energy Storage and Conversion. Chem. Soc. Rev. 2009, 38, 226-252. (11) Smay, J. E.; Gratson, G. M.; Shepherd, R. F.; Cesarano, J.; Lewis, J. A., Directed Colloidal Assembly of 3d Periodic Structures. Adv. Mater. 2002, 14, 1279-1283. (12) Long, J. W.; Rolison, D. R., Architectural Design, Interior Decoration, and ThreeDimensional Plumbing En Route to Multifunctional Nanoarchitectures. Acc. Chem. Res. 2007, 40, 854-862. (13) Vagin, M. Y.; Jeerapan, I.; Wannapob, R.; Thavarungkul, P.; Kanatharana, P.; Anwar, N.; McCormac, T.; Eriksson, M.; Turner, A. P. F.; Jager, E. W. H.; Mak, W. C., WaterProcessable Polypyrrole Microparticle Modules for Direct Fabrication of Hierarchical Structured Electrochemical Interfaces. Electrochim. Acta 2016, 190, 495-503.


Page 18 of 27

Page 19 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(14) Wannapob, R.; Vagin, M. Y.; Jeerapan, I.; Mak, W. C., Pure Nanoscale Morphology Effect Enhancing the Energy Storage Characteristics of Processable Hierarchical Polypyrrole. Langmuir 2015, 31, 11904-11913. (15) Heeger, A. J., Semiconducting and Metallic Polymers: The Fourth Generation of Polymeric Materials (Nobel Lecture). Angew. Chem. Int. Ed. 2001, 40, 2591-2611. (16) Skotheim, T. A.; Elsenbaumer, R. L.; Reynolds, J. R., Handbook of Conducting Polymers. 2nd ed.; Marcel Dekker: New York, 1998. (17) Ravichandran, R.; Sundarrajan, S.; Venugopal, J. R.; Mukherjee, S.; Ramakrishna, S., Applications of Conducting Polymers and Their Issues in Biomedical Engineering. J. R. Soc., Interface 2010, 7, S559-S579. (18) Huang, Z.-B.; Yin, G.-F.; Liao, X.-M.; Gu, J.-W., Conducting Polypyrrole in Tissue Engineering Applications. Front. Mater. Sci. 2014, 8, 39-45. (19) Sankoh, S.; Vagin, M. Y.; Sekretaryova, A. N.; Thavarungkul, P.; Kanatharana, P.; Mak, W. C., Colloid Electrochemistry of Conducting Polymer: Towards Potential-Induced inSitu Drug Release. Electrochim. Acta 2017, 228, 407-412. (20) Mbomekalle, I. M.; Cao, R.; Hardcastle, K. I.; Hill, C. L.; Ammam, M.; Keita, B.; Nadjo, L.; Anderson, T. M., Synthesis, Structural Characterization, and Electrocatalytic Studies of Αββα-(Zniioh2)2(Feiii)2(X2w15o56)214– (X = P or as). C. R. Chim. 2005, 8, 1077-1086. (21) Lai, K. K.; Renneberg, R.; Mak, W. C., Multifunctional Protein Particles with Dual Analytical Channels for Colorimetric Enzymatic Bioassays and Fluorescent Immunoassays. Biosens. Bioelectron. 2012, 32, 169-176. (22) Mak, W. C.; Georgieva, R.; Renneberg, R.; Bäumler, H., Protein Particles Formed by Protein Activation and Spontaneous Self-Assembly. Adv. Funct. Mater. 2010, 20, 41394144. (23) Lai, K. K.; Renneberg, R.; Mak, W. C., Bioinspired Protein Microparticles Fabrication by Peptide Mediated Disulfide Interchange. RSC Adv. 2014, 4, 11802-11810. (24) Lai, K. K.; Renneberg, R.; Mak, W. C., High Efficiency Single-Step Biomaterial-Based Microparticle Fabrication Via Template-Directed Supramolecular Coordination Chemistry. Green Chem. 2016, 18, 1715-1723. (25) Kondo, T.; Horitani, M.; Yuasa, M., Sensitive Electrochemical Detection of Glucose at Glucose Oxidase-Cobalt Phthalocyanine-Modified Boron-Doped Diamond Electrode. Int. J. Electrochem. 2012, 2012, 1-6. (26) Ben-Knaz, R.; Avnir, D., Bioactive Enzyme–Metal Composites: The Entrapment of Acid Phosphatase within Gold and Silver. Biomaterials 2009, 30, 1263-1267.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(27) Tang, B.; Cao, L.; Xu, K.; Zhuo, L.; Ge, J.; Li, Q.; Yu, L., A New Nanobiosensor for Glucose with High Sensitivity and Selectivity in Serum Based on Fluorescence Resonance Energy Transfer (Fret) between Cdte Quantum Dots and Au Nanoparticles. Chem. Eur. J. 2008, 14, 3637-3644. (28) Keita, B.; Nadjo, L., Polyoxometalate-Based Homogeneous Catalysis of Electrode Reactions: Recent Achievements. J. Mol. Catal. A: Chem. 2007, 262, 190-215. (29) Naseer, R.; Mal, S. S.; Ibrahim, M.; Kortz, U.; Armstrong, G.; Laffir, F.; Dickinson, C.; Vagin, M.; McCormac, T., Redox, Surface and Electrocatalytic Properties of Layer-byLayer Films Based Upon Fe(Iii)-Substituted Crown Polyoxometalate [P8w48o184fe16(Oh)28(H2o)4]20. Electrochim. Acta 2014, 134, 450-458. (30) ICHIJO, H.; UEDAIRA, H.; SUEHIRO, T.; NAGASAWA, J. i.; YAMAUCHI, A.; AISAKA, N., Thermal Stability of Free and Immobilized Glucose Oxidase Studied by Activity Assay and Calorimetry. Agric. Biol. Chem. 1989, 53, 833-834. (31) Padilla-Martínez, S. G.; Martínez-Jothar, L.; Sampedro, J. G.; Tristan, F.; Pérez, E., Enhanced Thermal Stability and Ph Behavior of Glucose Oxidase on Electrostatic Interaction with Polyethylenimine. Int. J. Biol. Macromol. 2015, 75, 453-459. (32) Jia, L.; Lawrence, G.; Balasubramanian, V. V.; Choi, G.; Choy, J.-H.; Abdullah, A. M.; Elzatahry, A.; Ariga, K.; Vinu, A., Highly Ordered Nanoporous Carbon Films with Tunable Pore Diameters and Their Excellent Sensing Properties. Chem. Eur. J. 2015, 21, 697-703. (33) Ndamanisha, J. C.; Guo, L.-p., Ordered Mesoporous Carbon for Electrochemical Sensing: A Review. Anal. Chim. Acta 2012, 747, 19-28. (34) Wu, S.; Ju, H. X.; Liu, Y., Conductive Mesocellular Silica–Carbon Nanocomposite Foams for Immobilization, Direct Electrochemistry, and Biosensing of Proteins. Adv. Funct. Mater. 2007, 17, 585-592. (35) Zhang, R.; Olin, H., Porous Gold Films—a Short Review on Recent Progress. Materials 2014, 7, 3834-3854. (36) Choi, B. G.; Hong, J.; Hong, W. H.; Hammond, P. T.; Park, H., Facilitated Ion Transport in All-Solid-State Flexible Supercapacitors. ACS nano 2011, 5, 7205-7213. (37) Giri, S.; Ghosh, D.; Das, C. K., Growth of Vertically Aligned Tunable Polyaniline on Graphene/Zro2 Nanocomposites for Supercapacitor Energy-Storage Application. Adv. Funct. Mater. 2014, 24, 1312-1324. (38) Bisquert, J., Influence of the Boundaries in the Impedance of Porous Film Electrodes. Phys. Chem. Chem. Phys. 2000, 2, 4185-4192.


Page 20 of 27

Page 21 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(39) Jović, V. D.; Jović, B. M., Eis and Differential Capacitance Measurements onto Single Crystal Faces in Different Solutions: Part I: Ag(111) in 0.01 M Nacl. J. Electroanal. Chem. 2003, 541, 1-11. (40) Long, G. L.; Winefordner, J. D., Limit of Detection a Closer Look at the Iupac Definition. Anal. Chem. 1983, 55, 712A-724A. (41) Şenel, M., Simple Method for Preparing Glucose Biosensor Based on in-Situ Polypyrrole Cross-Linked Chitosan/Glucose Oxidase/Gold Bionanocomposite Film. Mater. Sci. Eng., C 2015, 48, 287-293. (42) Ren, X.; Jiang, Y.; Liang, X.; Liu, J.; Zhang, P. In Preparation of Ppy Film and Its Application to Glucose Biosensor, 2008 2nd International Conference on Bioinformatics and Biomedical Engineering, 16-18 May 2008; 2008; pp 1617-1620. (43) Ma, M.; Qu, L.; Shi, G., Glucose Oxidase Electrodes Based on Microstructured Polypyrrole Films. J. Appl. Polym. Sci. 2005, 98, 2550-2554. (44) Sung, W. J.; Bae, Y. H., A Glucose Oxidase Electrode Based on Electropolymerized Conducting Polymer with Polyanion−Enzyme Conjugated Dopant. Anal. Chem. 2000, 72, 2177-2181. (45) Sung, W. J.; Bae, Y. H., A Glucose Oxidase Electrode Based on Polypyrrole with Polyanion/Peg/Enzyme Conjugate Dopant. Biosens. Bioelectron. 2003, 18, 1231-1239. (46) Kotanen, C. N.; Tlili, C.; Guiseppi-Elie, A., Amperometric Glucose Biosensor Based on Electroconductive Hydrogels. Talanta 2013, 103, 228-235. (47) Şenel, M.; Nergiz, C., Novel Amperometric Glucose Biosensor Based on Covalent Immobilization of Glucose Oxidase on Poly(Pyrrole Propylic Acid)/Au Nanocomposite. Curr. Appl. Phys. 2012, 12, 1118-1124. (48) Liu, L.; Jia, N.-q.; Zhou, Q.; Yan, M.-m.; Jiang, Z.-y., Electrochemically Fabricated Nanoelectrode Ensembles for Glucose Biosensors. Mater. Sci. Eng., C 2007, 27, 57-60. (49) Safavi, A.; Maleki, N.; Moradlou, O.; Tajabadi, F., Simultaneous Determination of Dopamine, Ascorbic Acid, and Uric Acid Using Carbon Ionic Liquid Electrode. Anal. Biochem. 2006, 359, 224-229. (50) Manesh, K. M.; Kim, H. T.; Santhosh, P.; Gopalan, A. I.; Lee, K.-P., A Novel Glucose Biosensor Based on Immobilization of Glucose Oxidase into Multiwall Carbon Nanotubes–Polyelectrolyte-Loaded Electrospun Nanofibrous Membrane. Biosens. Bioelectron. 2008, 23, 771-779.



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Table Table 1. Comparison of analytical performances of PPy-based glucose biosensors. Biosensors

BSA-GOxMPs/PPyMPs

Linear range (mM)

Sensitivity (nA cm-2 mM-1)

Response time (s)

References

589.1

0.5-8.0

5

This work

Chi-Py/Au/GOx film

580.0

1.0-20

4

41

PPy-flim/GOx

81.1

0.001-20

9

42

GOD/flat PPy/Pt

330

0-17

20

43

PPy-polyanion−GOD

203.7

-

30

44

PPy/polyanion/PEG/GOD

270

1.0-22

-

45

PPy–GOx-Gel|Pt composite

281

1-15

50

46

PPy-GOx–Pt

637

1-10

18

46

PyCO2H/Au

420

1.0-18.0

2

47

Au-AAO/GOx/PPy

80

0.5.0

15

48

microparticle modules


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Figures

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) The corresponding high magnification SEM images showing the surface morphology of the BSA-GOxMPs and POM-PPyMPs, respectively.



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Figure 2. (A) The 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) The 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).


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Figure 3. (A-B) A schematic shows the design of bioelectrode with various inter-microparticle spatial organizations of (Ai) layer-structured and (Bi) bulk hetero-structured architecture, and (ii) the corresponding microscopic images of the microparticle films with BSA-GOxMPs labelled with fluorescein. (C) Calibration curves of the layer-structured (circle) and the hetero-structured (square) bioelectrodes for amperometric glucose detection. (D) The electrode reaction kinetics assessed by impedance spectroscopy. The impedance spectra were measured on a GCE with a layer-structured film (circle) the hetero-structured 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.



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Figure 4. (A) An 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) The configuration of the heterostructured bioelectrode. (C) Amperometric responses and (D) calibration curve of the heterostructured bioelectrodes for glucose detection.


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The table of contents


Printable Heterostructured Bioelectronic Interfaces with Enhanced

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