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An innovative modular approach for facile design and construction of flexible microfluidic biosensor platforms based on a dry manufacturing "craft-and-stick" approach is developed. The design and fabrication of the flexible graphene paper electrode (GPE) unit and polyethylene tetraphthalate sheet (PET)6/adhesive fluidic unit are completed by an economic and generic xurographic craft approach. The GPE widths and the microfluidic channels can be constructed down to 300 mu m and 200 mu m, respectively. Both units were assembled by simple double-sided adhesive tapes into a microfluidic integrated GPE (MF-iGPE) that are flexible, thin (<0.5 mm), and lightweight (0.4 g). We further functionalized the iGPE with Prussian blue and glucose oxidase for the fabrication of MF-iGPE glucose biosensors. With a closed-channel PET fluidic pattern, the MF-iGPE glucose biosensors were packaged and sealed to protect the integrated device from moisture for storage and could easily open with scissors for sample loading. Our glucose biosensors showed 2 linear dynamic regions of 0.05-1.0 and 1.0-5.5 mmol L-1 glucose. The MF-iGPE showed good reproducibility for glucose detection (RSD < 6.1%, n = 6) and required only 10 mu L of the analyte. This modular craft-and-stick manufacturing approach could potentially further develop along the concept of paper-crafted model assembly kits suitable for low-resource laboratories or classroom settings., Funding Agencies|Royal Golden Jubilee Ph.D. Scholarship from the Thailand Research Fund under the Office of the Prime Ministry, the Royal Thai Government [PHD/0213/2560]

Flexible electronics have gained more attention for emerging electronic devices such as sensors, biosensors, and batteries with advantageous properties including being thin, lightweight, flexible, and low-cost. The development of various forms of allotropic carbon papers provided a new dry-manufacturing route for the fabrication of flexible and wearable electronics, while the electrochemical performance and the bending stability are largely influenced by the bulk morphology and the micro-/nanostructured domains of the carbon papers. Here, we evaluate systematically the intrinsic physicoelectrochemical properties of allotropic carbon-based conducting papers as flexible electrodes including carbon-nanotubes-paper (CNTs-paper), graphene-paper (GR-paper), and carbon-fiber-paper (CF-paper), followed by functionalization of the allotropic carbon papers for the fabrication of flexible electrodes. The morphology, chemical structure, and defects originating from the allotropic nanostructured carbon materials were characterized by scanning electron microscopy (SEM) and Raman spectroscopy, followed by evaluating the electrochemical performance of the corresponding flexible electrodes by cyclic voltammetry and electrochemical impedance spectroscopy. The electron-transfer rate constants of the CNTs-paper and GR-paper electrodes were similar to 14 times higher compared with the CF-paper electrode. The CNTs-paper and GR-paper electrodes composed of nanostructured carbon showed significantly higher bending stabilities of 5.61 and 4.96 times compared with the CF-paper. The carbon-paper flexible electrodes were further functionalized with an inorganic catalyst, Prussian blue (PB), forming the PB-carbon-paper catalytic electrode and an organic conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), forming the PEDOT-carbon-paper capacitive electrode. The intrinsic attribute of different allotropic carbon electrodes affects the deposition of PB and PEDOT, leading to different ele, Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR-2015-04434]; Royal Golden Jubilee Ph.D. program (RGJ) from the Thailand Research Fund [PHD/0212/2560]

Flexible skin patch biosensors are promising for the noninvasive determination of physiological parameters in perspiration for fitness and health monitoring. However, various prerequisites need to be met for the development of such biosensors, including the creation of a flexible conductive platform, bending/contact stability, fast electrochemical kinetics, and immobilization of biomolecules. Here, we describe a conducting polymer-reinforced laser-irradiated graphene (LIG) network as a heterostructured three-dimensional (3D) transducer for flexible skin patch biosensors. LIG with a hierarchically interconnected graphene structure is geometrically patterned on polyimide via localized laser irradiation as a flexible conductive platform, which is then reinforced by poly(3,4-ethylenedioxythiophene) (PEDOT) as a conductive binder (PEDOT/LIG) with improved structural/contact stability and electrochemical kinetics. The interconnected pores of the reinforced PEDOT/LIG function as a 3D host matrix for high loading of "artificial" (Prussian blue, PB) and natural enzymes (lactate oxidase, LOx), forming a compact and heterostructured 3D transducer (LOx/PB-PEDOT/LIG) for lactate biosensing with excellent sensitivity (11.83 mu A mM-1). We demonstrated the fabrication of flexible skin patch biosensors comprising a custom-built integrated three-electrode system achieve amperometric detection of lactate in artificial sweat over a wide physiological linear range of 0-18 mM. The advantage of this facile and versatile transducer is further illustrated by the development of a folded 3D wristband lactate biosensor and a dual channel biosensors for simultaneous monitoring of lactate and glucose. This innovative design concept of a heterostructured transducer for flexible biosensors combined with a versatile fabrication approach could potentially drive the development of new wearable and skin-mountable biosensors for monitoring various physiological parameters in biofluids for noninvasive, Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR-2015-04434]

The rapidly emerging field of organic bioelectronics has witnessed the wide use of conducting polymers (CPs) to fabricate advanced chemically modified electrodes (CMEs) for biosensors and biomedical devices. The electrochemical performance of the CPs in such devices is closely related to the quality and physiochemical nature of the dopants. A bi-functional graphene oxide derivative with high reduction degree and negatively-charged sulphonate functionality, i.e. sulphonate-coupled reduced graphene oxide (S-RGO), was developed and used as an efficient dopant for a CP with enhanced electrochemical performance. The S-RGO was synthesised via a facile one-pot hydrothermal reaction using 4-hydrazinobenzosulphonic acid (4-HBS) as reductant and sulphonate precursor simultaneously. The resulting S-RGO possesses high aqueous dispersion stability (more than 6 months), high electrical conductivity (1493.0 S m−1) and sulphonate functionality. Due to these specific properties, S-RGO demonstrated improved electropolymerisation efficiency for poly(3,4-ethylenedioxythiophene) (PEDOT) proving an effective dopant for the preparation of a PEDOT:S-RGO film (5 mC) with faster polymerisation time (37 s) compared to the conventional 2D dopants GO (PEDOT:GO, 129 s) and RGO (PEDOT:RGO, 66 s). The resulting PEDOT:S-RGO appeared as a homogenous film with uniformly distributed S-RGO dopant, low equivalent series resistance and low charge transfer resistance. Moreover, the electrochemical transduction performance of the PEDOT:S-RGO interface was evaluated with 4 different analytes, including ferric/ferrocyanide redox probe, dopamine, nicotinamide adenine dinucleotide and hydrogen peroxide. As a result of the synergistic effect of S-RGO and PEDOT, the PEDOT:S-RGO demonstrated enhanced electrochemical performance with respect to faster electrode kinetics (smaller ΔEp), ∼2 and ∼4 times increased current responses, and lower peak potentials compared to PEDOT:GO and PEDOT:RGO. This bi-functional S-RGO, Funding agencies: Swedish Research CouncilSwedish Research Council [VR-2015-04434]; China Scholarship CouncilChina Scholarship Council [201606910036]

Recent advances in biosensors and point-of-care (PoC) devices are poised to change and expand the delivery of diagnostics from conventional lateral-flow assays and test strips that dominate the market currently, to newly emerging wearable and implantable devices that can provide continuous monitoring. Soft and flexible materials are playing a key role in propelling these trends towards real-time and remote health monitoring. Affinity biosensors have the capability to provide for diagnosis and monitoring of cancerous, cardiovascular, infectious and genetic diseases by the detection of biomarkers using affinity interactions. This review tracks the evolution of affinity sensors from conventional lateral-flow test strips to wearable/implantable devices enabled by soft and flexible materials. Initially, we highlight conventional affinity sensors exploiting membrane and paper materials which have been so successfully applied in point-of-care tests, such as lateral-flow immunoassay strips and emerging microfluidic paper-based devices. We then turn our attention to the multifarious polymer designs that provide both the base materials for sensor designs, such as PDMS, and more advanced functionalised materials that are capable of both recognition and transduction, such as conducting and molecularly imprinted polymers. The subsequent content discusses wearable soft and flexible material-based affinity sensors, classified as flexible and skin-mountable, textile materials-based and contact lens-based affinity sensors. In the final sections, we explore the possibilities for implantable/injectable soft and flexible material-based affinity sensors, including hydrogels, microencapsulated sensors and optical fibers. This area is truly a work in progress and we trust that this review will help pull together the many technological streams that are contributing to the field.

Modulation of chemical functional groups on conducting polymers (CPs) provides an effective way to tailor the physicochemical properties and electrochemical performance of CPs, as well as serves as a functional interface for stable integration of CPs with biomolecules for organic bioelectronics (OBEs). Herein, we introduced a facile approach to modulate the carboxylate functional groups on the PEDOT interface through a systematic evaluation on the effect of a series of carboxylate-containing molecules as counterion dopant integrated into the PEDOT backbone, including acetate as monocarboxylate (mono-COO-), malate as dicarboxylate (di-COO-), citrate as tricarboxylate (tri-COO-), and poly(acrylamide-co-acrylate) as polycarboxylate (poly-COO-) bearing different amounts of molecular carboxylate moieties to create tunable PEDOT:COO- interfaces with improved polymerization efficiency. We demonstrated the modulation of PEDOT:COO- interfaces with various granulated morphologies from 0.33 to 0.11 mu m, tunable surface carboxylate densities from 0.56 to 3.6 mu M cm(-2), and with improved electrochemical kinetics and cycling stability. We further demonstrated the effective and stable coupling of an enzyme model lactate dehydrogenase (LDH) with the optimized PEDOT:poly-COO- interface via simple covalent chemistry to develop biofunctionalized PEDOT (Bio-PEDOT) as a lactate biosensor. The biosensing mechanism is driven by a sequential bioelectrochemical signal transduction between the bio-organic LDH and organic PEDOT toward the concept of all-polymer-based OBEs with a high sensitivity of 8.38 mu A mM(-1) cm(-2) and good reproducibility. Moreover, we utilized the LDH-PEDOT biosensor for the detection of lactate in spiked serum samples with a high recovery value of 91-96% and relatively small RSD in the range of 2.1-3.1%. Our findings provide a new insight into the design and optimization of functional CPs, leading to the development of new OBEs for sensing, biosensing, bioenginee, Funding Agencies|Swedish Research CouncilSwedish Research Council [VR-2015-04434]; Thailand Science Research and Innovation (TSRI) [IRN62W0002]; Royal Golden Jubilee Ph.D program (RGJ) from the Thailand Research Fund [PHD/0212/2559]; Development and Promotion of Science and Technology Talents projects (DPST) from the Royal Thai Government

The rapidly developing field of conducting polymers in organic electronics has many implications for bioelectronics. For biosensing applications, tailoring the functionalities of the conducting polymers surface is an efficient approach to improve both sensitivity and selectivity. Here, we demonstrated a facile and economic approach for the fabrication of a high-density, negatively charged carboxylic-acid-group-functionalized PEDOT (PEDOT:COOH) using an inexpensive ternary carboxylic acid, citrate, as a dopant. The polymerization efficiency was significantly improved by the addition of LiClO4 as a supporting electrolyte yielding a dense PEDOT:COOH sensing interface. The resulting PEDOT:COOH interface had a high surface density of carboxylic acid groups of 0.129 mu mol/cm(2) as quantified by the toluidine blue O (TBO) staining technique. The dopamine response measured with the PEDOT:COOH sensing interface was characterized by cyclic voltammetry with a significantly reduced Delta E-p of 90 mV and a 3-fold increase in the I-pa value compared with those of the nonfunctionalized PEDOT sensing interface. Moreover, the cyclic voltammetry and electrochemical impedance spectroscopy results demonstrated the increased electrode kinetics and highly selective discrimination of dopamine (DA) in the presence of the interferents ascorbic acid (AA) and uric acid (UA), which resulted from the introduction of negatively charged carboxylic acid groups. The negatively charged carboxylic acid groups could favor the transfer, preconcentration, and permeation of positively charged DA to deliver improved sensing performance while repelling the negatively charged AA and UA interferents. The PEDOT:COOH interface facilitated measurement of dopamine over the range of 1-85 mu M, with a sensitivity of 0.228 mu A mu M-1, which is 4.1 times higher than that of a nonfunctionalized PEDOT electrode (0.055 mu A mu M-1). Our results demonstrate the feasibility of a simple and economic fabrication of a hi, Funding Agencies|Swedish Research CouncilSwedish Research Council [VR-2015-04434]; China Scholarship CouncilChina Scholarship Council [201606910036]

Conducting polymers, with unique ion/electron transfer capability, reversible doping/dedoping and controllable chemical and electrochemical properties, have received many attention as advanced interfaces in electronic and bioelectronic devices. Recent advancement is focus on fine-tailoring the conducting polymer interfaces with addition functionality and controlled morphology with enhanced performance beyond its intrinsic properties. Here, we demonstrate the tailoring of physico-chemical properties of poly (3,4-ethylenedioxythiophene) (PEDOT) with high density carboxyl functionality and tailored nano-structure, and its application in dopamine sensing and lactate biosensing with enhanced selectivity and sensitivity. For dopamine sensing, we developed a high-density negatively-charged carboxyl functionalized PEDOT interface using a low-cost organic acid citrate as dopant. Citrate contains a high content of carboxyl functionality and small size allowing well distribution of the citrate dopant within the PEDOT with a high surface carboxyl density upto 26 µM/cm2. The carboxyl confined PEDOT interface with nano-globular structure showed increased electrode kinetics and increased discriminationof dopamine from interferences (ascorbic acid and uric acid). For lactate biosensing, we further developed a nano-fibrillar carboxyl PEDOT interface that can detect dihydronicotinamide adenine dinucleotide (NADH) at low potential at ~0.43 V. Based on the post-immobilisation of NAD-dependent lactate dehydrogenase via carboxyl coupling, lactate biosensor was developed with good analytical performance and low operation potential to reduce interferences. These results demonstrated tailoring of physico-chemical properties of PEDOT interface with improved sensing performance, thus could potentially applied for next generation bioelectronic devices such as wearable and flexible sensors and biosensors.

Conducting polymers have attracted considerable attention as potential electrode materials in electrochemical sensors and biosensors. While conducting polymers possess unique electrical and physicochemical properties, they suffer from the drawback of poor processability because of interchain interactions. Here, we introduce the concept of aqueous processable poly(ethylenedioxythiophene) microparticles (PEDOT-MPs) in colloidal dispersion synthesized by CaCO3 template-assisted method. The processable PEDOT-MPs was utilised as building blocks for the fabrication of electrodes with hierarchically-structured interfaces. Compared to commercial PEDOT:PSS electrodes, which have a dense film, the electrodes prepared with the colloidal PEDOT-MPs possess a hierarchically-structured film, which provides a larger accessible active surface and inter-particle space facilitates molecular diffusion. Taking NADH as a model analyte, such novel PEDOT-MPs electrodes detect NADH at a lower operation potential and with enhanced electrocatalytic activity (oxidation peak 1.7 times higher) compared to the commercial PEDOT:PSS electrode. The calculated diffusion coefficient of the hierarchically-structured PEDOT-MPs electrode was 1.61 x 10-6 cm2 s-1, which is ~4 times higher than that of the dense PEDOT:PSS electrode (3.98 x10-7 cm2 s-1). The PEDOT-MPs electrodes detected NADH over the range from 20 to 240 uM, with a sensitivity of 15.61 uA/mM and a limit of detection of 5.3 uM. Moreover, the hierarchically-structured PEDOT-MPs electrode exhibited improved stability (1.3 times higher over 10 measuring cycles) compared to the commercial PEDOT:PSS due to reduced fouling by the oxidised products (NAD+ and dimer), which can be ascribed to the positive surface charges (21.3 ± 4.27 mV) of the PEDOT-MPs. This colloidal PEDOT-MPs show good processability for facile preparation of electrodes, and micro-structured morphology to enhance the analytical performance for NADH biosensing, as well as reduced