Rational design and one-step formation of multifunctional gel transducer for simple fabrication of integrated electrochemical biosensors

NAD(P)-dependent glucose dehydrogenase: Applications for biosensors, bioelectrodes, and biofuel cells

This review discusses the physical and chemical properties of nicotinamide redox cofactor dependent glucose dehydrogenase (NAD(P) dependent GDH) and its extensive application in biosensors and bio-fuel cells. GDHs from different organisms show diverse biochemical properties (e.g., activity and stability) and preferences towards cofactors, such as nicotinamide adenine dinucleotide (NAD⁺) and nicotinamide adenine dinucleotide phosphate (NADP⁺). The (NAD(P)⁺) play important roles in biological electron transfer, however, there are some difficulties related to their application in devices that originate from their chemical properties and labile binding to the GDH enzyme. This review discusses the electrode modifications aimed at immobilising NAD⁺ or NADP⁺ cofactors and GDH at electrodes. Binding of the enzyme was achieved by appropriate protein engineering techniques, including polymerisation, hydrophobisation or hydrophilisation processes. Various enzyme-modified electrodes applied in biosensors, enzymatic fuel cells, and biobatteries are compared. Importantly, GDH can operate alone or as part of an enzymatic cascade, which often improves the functional parameters of the biofuel cell or simply allows use of cheaper fuels. Overall, this review explores how NAD(P)-dependent GDH has recently demonstrated high potential for use in various systems to generate electricity from biological sources for applications in implantable biomedical devices, wireless sensors, and portable electronic devices.

High-power biofuel cells based on three-dimensional reduced graphene oxide/carbon nanotube micro-arrays

Miniaturized enzymatic biofuel cells (EBFCs) with high cell performance are promising candidates for powering next-generation implantable medical devices. Here, we report a closed-loop theoretical and experimental study on a micro EBFC system based on three-dimensional (3D) carbon micropillar arrays coated with reduced graphene oxide (rGO), carbon nanotubes (CNTs), and a biocatalyst composite. The fabrication process of this system combines the top-down carbon microelectromechanical systems (C-MEMS) technique to fabricate the 3D micropillar array platform and bottom-up electrophoretic deposition (EPD) to deposit the reduced rGO/CNTs/enzyme onto the electrode surface. The Michaelis-Menten constant KM of 2.1 mM for glucose oxidase (GOx) on the rGO/CNTs/GOx bioanode was obtained, which is close to the KM for free GOx. Theoretical modelling of the rGO/CNT-based EBFC system via finite element analysis was conducted to predict the cell performance and efficiency. The experimental results from the developed rGO/CNT-based EBFC showed a maximum power density of 196.04 µW cm-2 at 0.61 V, which is approximately twice the maximum power density obtained from the rGO-based EBFC. The experimental power density is noted to be 71.1% of the theoretical value.

Tuning interionic interaction for highly selective in vivo analysis

The development of highly selective methodologies to enable in vivo recording of chemical signals is of great importance for studying brain functions and brain activity mapping. However, the complexity of cerebral systems presents a great challenge in the development of chem/(bio)sensors that are capable of directly and selectively recording bioactive molecules involved in brain functions. As one of the most important and popular interactions in nature, interionic interaction constitutes the chemical essence of high specificity in natural systems, which inspires us to develop highly selective chem/(bio)sensors for in vivo analysis by precisely engineering interionic interaction in the in vivo sensing system. In this tutorial review, we focus on the recent progress in the tuning of interionic interaction to improve the selectivity of biosensors for in vivo analysis. The type and property of the interionic interaction is first introduced and several strategies to improve the selectivity of the biosensors, including enzyme-based electrochemical biosensors, aptamer-based electrochemical biosensors, and the strategies to recruit recognition molecules are reviewed. We also present an overview of the potential applications of the biosensors for in vivo analysis and thereby for physiological investigations. Finally, we present the major challenges and opportunities regarding the high selectivity of in vivo analysis based on tuning interionic interaction. We believe that this tutorial review provides critical insights for highly selective in vivo analysis and offers new concepts and strategies to understand brain chemistry.

Rational Design of Bioelectrochemically Multifunctional Film with Oxidase, Ferrocene, and Graphene Oxide for Development of in Vivo Electrochemical Biosensors

This study demonstrates a new strategy to develop in vivo electrochemical biosensors through rational design and simple formation of bioelectrochemically multifunctional film (BMF). The BMF is rationally designed by first efficiently incorporating oxidase, ferrocene mediator, and graphene oxide into polymaleimidostyrene/polystyrene (PMS/PS) matrix to form a homogeneous mixture and then simply formed by drop-coating the mixture onto solid conducting substrate. By using the as-formed BMF, electrochemical biosensors could be constructed with a technical simplicity and high reproducibility. To illustrate the BMF-based biosensors for in vivo applications, we directly couple the biosensors to in vivo microdialysis to establish an online electrochemical system (OECS) for in vivo monitoring of glucose in rat auditory cortex during salicylate-induced tinnitus model. The OECS with the BMF-based biosensor as the detector shows a linear response toward glucose within a concentration range from 50 to 500 μM with a detection limit of 10 μM (S/N = 3). Additionally, the OECS is stable and does not suffer from the interference from the electroactive species endogenously coexisting in the brain microdialysate. With the BMF-based OECS, the basal level of glucose in the microdialysate continuously sampled from rat auditory cortex is determined to be 120 ± 10 μM (n = 5). After the rats were administrated with salicylate to induce transient tinnitus, the microdialysate glucose concentration in the rat auditory cortex remarkably increased to 433 ± 190 μM (n = 5) at the time point of 1.5 h. This study essentially offers a new, technically simple and reproducible approach to development of in vivo electrochemical biosensors, which is envisaged to be relatively useful for understanding of the molecular basis of brain functions.

Quantification of ethanol in plasma by electrochemical detection with an unmodified screen printed carbon electrode

Simple, rapid and accurate detection of ethanol concentration in blood is very crucial in the diagnosis and management of potential acute ethanol intoxication patients. A novel electrochemical detection method was developed for the quantification of ethanol in human plasma with disposable unmodified screen-printed carbon electrode (SPCE) without sample preparation procedure. Ethanol was detected indirectly by the reaction product of ethanol dehydrogenase (ADH) and cofactor nicotinamide adenine dinucleotide (NAD⁺). Method validation indicated good quantitation precisions with intra-day and inter-day relative standard deviations of ≤9.4% and 8.0%, respectively. Ethanol concentration in plasma is linear ranging from 0.10 to 3.20 mg/mL, and the detection limit is 40.0 μg/mL (S/N > 3). The method shows satisfactory correlation with the reference method of headspace gas chromatography in twenty human plasma samples (correlation coefficient 0.9311). The proposed method could be applied to diagnose acute ethanol toxicity or ethanol-related death.

A durable non-enzymatic electrochemical sensor for monitoring H2O2 in rat brain microdialysates based on one-step fabrication of hydrogels

A non-enzymatic electrochemical H₂O₂ sensor was developed by in situ fabrication of biocompatible chitosan hydrogels, in which a specific recognition molecule for H₂O₂ – thionine – was stably immobilized via one-step electrodeposition.

Redox-functionalized graphene oxide architecture for the development of amperometric biosensing platform

We describe the redox functionalization of graphene oxide (GO) and the development of versatile amperometric biosensing platforms for clinically important analytes such as cholesterol ester, uric acid and glucose. Ferrocene (Fc) redox units were covalently tethered onto the GO backbone using diamine sigma spacers of different chain lengths (C3-, C6-, and C9-diamines). The functionalized GO (Fc-GO) displays a pair of redox peak corresponding to Fc/Fc(+) redox couple at ~0.225 V. The surface coverage and heterogeneous electron transfer rate constant of Fc-GO depends on the length of sigma spacer. Amperometric biosensors for cholesterol (total), uric acid and glucose have been developed by integrating Fc-GO and the respective redox enzymes with screen printed electrode. Fc-GO efficiently mediates the bioelectrocatalytic oxidation of the substrates in the presence of the redox enzymes. The spacer length of Fc-GO controls the bioelectrocatalytic response of the biosensing platforms. The sensitivity of the biosensors based on C9 sigma spacer is significantly higher than the others. The detection limit (S/N = 3) of the biosensors for cholesterol and uric acid was 0.1 μM and for glucose it was 1 μM. Excellent stability, reproducibility, selectivity and fast response time were achieved. Biosensing of cholesterol, uric acid and glucose in human serum sample is successfully demonstrated with the biosensors, and the results are validated with the clinical laboratory measurement.

One-step fabrication of integrated disposable biosensor based on ADH/NAD+/meldola's blue/graphitized mesoporous carbons/chitosan nanobiocomposite for ethanol detection

A novel strategy to simplify the dehydrogenase-based electrochemical biosensor fabrication through one-step drop-coating nanobiocomposite on a screen printed electrode (SPE) was developed. The nanobiocomposite was prepared by successively adding graphitized mesoporous carbons (GMCs), meldola's blue (MDB), alcohol dehydrogenase (ADH) and cofactor nicotinamide adenine dinucleotide (NAD(+)) in chitosan (CS) solution. MDB/GMCs/CS film was prepared. Cyclic voltammetry measurements demonstrated that MDB was strongly adsorbed on GMCs. After optimizing the concentration of MDB and the working potential, the MDB/GMCs/CS film presented a fast amperometric response (5s), excellent sensitivity (10.36 nA μM(-1)), wide linear range (10-410 μM) toward NADH and without any other interference signals (such as AA, UA, DA, H2O2 and metal ions). Furthermore, concentrations of ADH and NAD(+) in nanobiocomposite and the detection conditions (temperature and pH) were also optimized. The constructed disposable ethanol biosensor showed an excellent linear response ranged from 0.5 to 15 mM with high sensitivity (67.28 nA mM(-1)) and a low limit of detection (80 μM) and a remarkable long-term stability (40 days). The intra-batch and inter-batch variation coefficients were both less than 5% (n=5). The ethanol recovery test demonstrated that the proposed biosensor offered a remarkable and accurate method for ethanol detection in the real blood samples.