Multiwalled carbon nanotubes coated with cobalt(II) sulfide nanoparticles for electrochemical sensing of glucose via direct electron transfer to glucose oxidase

All-printed wearable biosensor based on MWCNT-iron oxide nanocomposite ink for physiological level detection of glucose in human sweat

Wearable sensors for sweat glucose monitoring are gaining massive interest as a patient-friendly and non-invasive way to manage diabetes. The present work offers an alternative on-body method employing an all-printed flexible electrochemical sensor to quantify the amount of glucose in human sweat. The working electrode of the glucose sensor was printed using a custom-formulated ink containing multi-walled carbon nanotube (MWCNT), poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOPT: PSS), and iron (II, III) oxide (Fe3O4) nanoparticles. This novel ink composition has good conductivity, enhanced catalytic activity, and excellent selectivity. The working electrode was modified using Prussian blue (PB) nanoparticles and glucose oxidase enzyme (GOx). The sensor displayed a linear chronoamperometric response to glucose from 1 μM to 400 μM, with a precise detection limit of ∼0.38 μM and an impressive sensitivity of ∼4.495 μAμM-1cm-2. The sensor stored at 4 °C exhibited excellent stability over 60 days, high selectivity, and greater reproducibility. The glucose detection via the standard addition method in human sweat samples acquired a high recovery rate of 96.0-98.6%. Examining human sweat during physical activity also attested to the biosensor's real-time viability. The results also show an impressive correlation between glucose levels obtained from a commercial blood glucose meter and sweat glucose concentrations. Remarkably, the present results outperform previously published printed glucose sensors in terms of detection range, low cost, ease of manufacturing, stability, selectivity, and wearability.

Reversed Electron Transfer in Dual Single Atom Catalyst for Boosted Photoreduction of CO2

Photogenerated charge localization on material surfaces significantly affects photocatalytic performance, especially for multi-electron CO2 reduction. Dual single atom (DSA) catalysts with flexibly designed reactive sites have received significant research attention for CO2 photoreduction. However, the charge transfer mechanism in DSA catalysts remains poorly understood. Here, for the first time, a reversed electron transfer mechanism on Au and Co DSA catalysts is reported. In situ characterizations confirm that for CdS nanoparticles (NPs) loaded with Co or Au single atoms, photogenerated electrons are localized around the single atom of Co or Au. In DSA catalysts, however, electrons are delocalized from Au and accumulate around Co atoms. Importantly, combined advanced spectroscopic findings and theoretical computation evidence that this reversed electron transfer in Au/Co DSA boosts charge redistribution and activation of CO2 molecules, leading to highly significantly increased photocatalytic CO2 reduction, for example, Au/Co DSA loaded CdS exhibits, respectively, ≈2800% and 700% greater yields for CO and CH4 compared with that for CdS alone. Reversed electron transfer in DSA can be used for practical design for charge redistribution and to boost photoreduction of CO2 . Findings will be of benefit to researchers and manufacturers in DSA-loaded catalysts for the generation of solar fuels.

Heterointerface promoted trifunctional electrocatalysts for all temperature high-performance rechargeable Zn-air batteries

The rational design of wide-temperature operating Zn-air batteries is crucial for their practical applications. However, the fundamental challenges remain; the limitation of the sluggish oxygen redox kinetics, insufficient active sites, and poor efficiency/cycle lifespan. Here we present heterointerface-promoted sulfur-deficient cobalt-tin-sulfur (CoS_1-δ/SnS_2-δ) trifunctional electrocatalysts by a facile solvothermal solution-phase approach. The CoS_1-δ/SnS_2-δ displays superb trifunctional activities, precisely a record-level oxygen bifunctional activity of 0.57 V (E_1/2 = 0.90 V and E_j=10 = 1.47 V) and a hydrogen evolution overpotential (41 mV), outperforming those of Pt/C and RuO₂. Theoretical calculations reveal the modulation of the electronic structures and d-band centers that endorse fast electron/proton transport for the hetero-interface and avoid the strong adsorption of intermediate species. The alkaline Zn-air batteries with CoS_1-δ/SnS_2-δ manifest record-high power density of 249 mW cm^-2 and long-cycle life for >1000 cycles under harsh operations of 20 mA cm^-2, surpassing those of Pt/C + RuO₂ and previous state-of-the-art catalysts. Furthermore, the solid-state flexible Zn-air battery also displays remarkable performance with an energy density of 1077 Wh kg^-1, >690 cycles for 50 mA cm^-2, and a wide operating temperature from +80 to -40 °C with 85% capacity retention, which provides insights for practical Zn-air batteries.

Recent Developments in the Design and Fabrication of Electrochemical Biosensors Using Functional Materials and Molecules

Electrochemical biosensors are superior technologies that are used to detect or sense biologically and environmentally significant analytes in a laboratory environment, or even in the form of portable handheld or wearable electronics. Recently, imprinted and implantable biosensors are emerging as point-of-care devices, which monitor the target analytes in a continuous environment and alert the intended users to anomalies. The stability and performance of the developed biosensor depend on the nature and properties of the electrode material or the platform on which the biosensor is constructed. Therefore, the biosensor platform plays an integral role in the effectiveness of the developed biosensor. Enormous effort has been dedicated to the rational design of the electrode material and to fabrication strategies for improving the performance of developed biosensors. Every year, in the search for multifarious electrode materials, thousands of new biosensor platforms are reported. Moreover, in order to construct an effectual biosensor, the researcher should familiarize themself with the sensible strategies behind electrode fabrication. Thus, we intend to shed light on various strategies and methodologies utilized in the design and fabrication of electrochemical biosensors that facilitate sensitive and selective detection of significant analytes. Furthermore, this review highlights the advantages of various electrode materials and the correlation between immobilized biomolecules and modified surfaces.

Glucose Biosensor Based on Glucose Oxidase Immobilized on BSA Cross-Linked Nanocomposite Modified Glassy Carbon Electrode

Glucose sensors based blood glucose detection are of great significance for the diagnosis and treatment of diabetes because diabetes has aroused wide concern in the world. In this study, bovine serum albumin (BSA) was used to cross-link glucose oxidase (GOD) on a glassy carbon electrode (GCE) modified by a composite of hydroxy fullerene (HFs) and multi-walled carbon nanotubes (MWCNTs) and protected with a glutaraldehyde (GLA)/Nafion (NF) composite membrane to prepare a novel glucose biosensor. The modified materials were analyzed by UV-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), and cyclic voltammetry (CV). The prepared MWCNTs-HFs composite has excellent conductivity, the addition of BSA regulates MWCNTs-HFs hydrophobicity and biocompatibility, and better immobilizes GOD on MWCNTs-HFs. MWCNTs-BSA-HFs plays a synergistic role in the electrochemical response to glucose. The biosensor shows high sensitivity (167 μA·mM^-1·cm^-2), wide calibration range (0.01-3.5 mM), and low detection limit (17 μM). The apparent Michaelis-Menten constant Kmapp is 119 μM. Additionally, the proposed biosensor has good selectivity and excellent storage stability (120 days). The practicability of the biosensor was evaluated in real plasma samples, and the recovery rate was satisfactory.

Immobilization of Glucose Oxidase on Glutathione Capped CdTe Quantum Dots for Bioenergy Generation

An efficient immobilization of Glucose oxidase (GOx) on an appropriate substrate is one of the main challenges of developing fuel cells that allow energy to be obtained from renewable substrates such as carbohydrates in physiological environments. The research importance of biofuel cells relies on their experimental robustness and high compatibility with biological organisms such as tissues or the bloodstream with the aim of obtaining electrical energy even from living systems. In this work, we report the use of 5,10,15,20 tetrakis (1-methyl-4-pyridinium) porphyrin and glutathione capped CdTe Quantum dots (GSH-CdTeQD) as a support matrix for the immobilization of GOx on carbon surfaces. Fluorescent GSH-CdTeQD particles were synthesized and their characterization by UV-Vis spectrophotometry showed a particle size between 5–7 nm, which was confirmed by DLS and TEM measurements. Graphite and Toray paper electrodes were modified by a drop coating of porphyrin, GSH-CdTeQD and GOx, and their electrochemical activity toward glucose oxidation was evaluated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Additionally, GOx modified electrode activity was explored by scanning electrochemical microscopy, finding that near to 70% of the surface was covered with active enzyme. The modified electrodes showed a glucose sensitivity of 0.58 ± 0.01 μA/mM and an apparent Michaelis constant of 7.8 mM. The addition of BSA blocking protein maintained the current response of common interferent molecules such as ascorbic acid (AA) with less than a 5% of interference percentage. Finally, the complex electrodes were employed as anodes in a microfluidic biofuel cell (μBFC) in order to evaluate the performance in energy production. The enzymatic anodes used in the μBFC allowed us to obtain a current density of 7.53 mAcm−2 at the maximum power density of 2.30 mWcm−2; an open circuit potential of 0.57 V was observed in the biofuel cell. The results obtained suggest that the support matrix porphyrin and GSH-CdTeQD is appropriate to immobilize GOx while preserving the enzyme’s catalytic activity. The reported electrode arrangement is a viable option for bioenergy production and/or glucose quantification.

Carbon Nanotube and Its Derived Nanomaterials Based High Performance Biosensing Platform

After the COVID-19 pandemic, the development of an accurate diagnosis and monitoring of diseases became a more important issue. In order to fabricate high-performance and sensitive biosensors, many researchers and scientists have used many kinds of nanomaterials such as metal nanoparticles (NPs), metal oxide NPs, quantum dots (QDs), and carbon nanomaterials including graphene and carbon nanotubes (CNTs). Among them, CNTs have been considered important biosensing channel candidates due to their excellent physical properties such as high electrical conductivity, strong mechanical properties, plasmonic properties, and so on. Thus, in this review, CNT-based biosensing systems are introduced and various sensing approaches such as electrochemical, optical, and electrical methods are reported. Moreover, such biosensing platforms showed excellent sensitivity and high selectivity against not only viruses but also virus DNA structures. So, based on the amazing potential of CNTs-based biosensing systems, healthcare and public health can be significantly improved.

Construction of liquid metal-based soft microfluidic sensors via soft lithography

Background

Liquid metal (LM) can be integrated into microfluidic channel, bringing new functionalities of microfluidics and opening a new window for soft microfluidic electronics, due to the superior advantages of the conductivity and deformability of LMs. However, patterning the LMs into microfluidic channels requires either selective surface wetting or complex fabrication process.

Results

In this work, we develop a method to pattern the LMs onto the soft elastomer via soft lithographic process for fabrication of soft microfluidic sensors without the surface modification, bulky facilities, and complicated processes. The combination of the interfacial hydrogen bond and surface tension enables the LM patterns transfer to the soft elastomer. The transferred LM patterns with an ellipse-like cross-section further improve the stability under the mechanical deformation. Three proof-of-concept experiments were conducted to demonstrate the utilization of this method for development of thermochromic sensors, self-powered capacity sensors and flexible biosensor for glucose detection.

Conclusions

In summary, the proposed method offers a new patterning method to obtain soft microfluidic sensors and brings new possibilities for microfluidics-related wearable devices.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01471-0.

A highly sensitive electrochemical biosensor for the detection of hydroquinone based on magnetic covalent organic frameworks and enzyme for signal amplification

Possessing prominent customization in structural design as well as unique physicochemical properties, covalent organic frameworks (COFs) show great potential in biosensing field. In this paper, we prepared a novel COF...

Urchin-like PtNPs@Bi2S3: synthesis and application in electrochemical biosensor

Novel urchin-like Pt nanoparticles@Bi2S3 composite materials were prepared by a simple route. The composite nanomaterial was used to modify an electrode for the immobilization of enzyme molecules to construct a sensitive electrochemical biosensor.

Dual-strategy biosensing of glucose based on multifunctional CuWO4 nanoparticles

The multifunctional CuWO4 NPs were prepared and exhibit large specific surface area, good conductivity and excellent peroxidase-like activity, which was exploited for electrochemical and colorimetric dual-strategy biosensing of glucose.

Superior Non-Invasive Glucose Sensor Using Bimetallic CuNi Nanospecies Coated Mesoporous Carbon

The assessment of blood glucose levels is necessary for the diagnosis and management of diabetes. The accurate quantification of serum or plasma glucose relies on enzymatic and nonenzymatic methods utilizing electrochemical biosensors. Current research efforts are focused on enhancing the non-invasive detection of glucose in sweat with accuracy, high sensitivity, and stability. In this work, nanostructured mesoporous carbon coupled with glucose oxidase (GO_x) increased the direct electron transfer to the electrode surface. A mixed alloy of CuNi nanoparticle-coated mesoporous carbon (CuNi-MC) was synthesized using a hydrothermal process followed by annealing at 700 °C under the flow of argon gas. The prepared catalyst's crystal structure and morphology were explored using X-ray diffraction and high-resolution transmission electron microscopy. The electrocatalytic activity of the as-prepared catalyst was investigated using cyclic voltammetry (CV) and amperometry. The findings show an excellent response time of 4 s and linear range detection from 0.005 to 0.45 mM with a high electrode sensitivity of 11.7 ± 0.061 mA mM cm^-2 in a selective medium.

Enhanced Performance of Bioelectrodes Made with Amination-Modified Glucose Oxidase Immobilized on Carboxyl-Functionalized Ordered Mesoporous Carbon

This research reveals the improved performance of bioelectrodes made with amination-modified glucose oxidase (GOx-NH2) and carboxyl-functionalized mesoporous carbon (OMC-COOH). Results showed that when applied with 10 mM EDC amination, the functional groups of NH2 were successfully added to GOx, according to the analysis of 1H-NMR, elemental composition, and FTIR spectra. Moreover, after the aminated modification, increased enzyme immobilization (124.01 ± 1.49 mg GOx-NH2/g OMC-COOH; 2.77-fold increase) and enzyme activity (1.17-fold increase) were achieved, compared with those of non-modified GOx. Electrochemical analysis showed that aminated modification enhanced the peak current intensity of Nafion/GOx-NH2/OMC-COOH (1.32-fold increase), with increases in the charge transfer coefficient α (0.54), the apparent electron transfer rate constant ks (2.54 s-1), and the surface coverage Γ (2.91 × 10-9 mol·cm-2). Results showed that GOx-NH2/OMC-COOH exhibited impressive electro-activity and a favorable anodic reaction.

In Situ Synthesis of CoCeSx Bimetallic Sulfide Nanoparticles on a Bi-Pyrene Terminated Molecular Wire Modified Graphene Surface for Supercapacitors

The excellent electrical conductivity of graphene is due to its highly-conjugated structures. Manipulation of the electronic and mechanical properties of graphene can be achieved by controlling the destruction of its in-sheet conjugation system. Herein, we report the preparation of CoCeS_x -SA@BPMW@RGO through π-π stacking interactions at the molecular level. In this study, sodium alginate was reacted with Co²⁺ and Ce³⁺ , and the composite was loaded onto a graphene surface. The graphene sheets were prepared using a bi-pyrene terminated molecular wire (BPMW) to avoid re-stacking of the grapheme sheets, thereby forming nanoscale spaces between sheets. The angle between the BPMW coplanar pyrene group and the phenyl group was 33.2°, and the graphene layer is supported in an oblique direction. Finally, a three-dimensional porous composite was obtained after annealing and vulcanization. The obtained CoCeS_x -SA@BPMW@RGO exhibited excellent electrical conductivity and remarkable cycle stability. When the current density was 1 A g^-1 , its specific capacitance was as high as 1004 F g^-1 . BPMW modifies graphene through the synergistic effect of π-π stacking interaction and special structure to obtain excellent electrochemical performance. Moreover, a solid-state asymmetric supercapacitor device was fabricated based on the synthesized CoCeS_x -SA@BPMW@RGO hybrid, which exhibited a power density of 979 W kg^-1 at an energy density of 23.96 Wh kg^-1 .

Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

The detection of glucose is crucial in the management of diabetes and other medical conditions but also crucial in a wide range of industries such as food and beverages. The development of glucose sensors in the past century has allowed diabetic patients to effectively manage their disease and has saved lives. First-generation glucose sensors have considerable limitations in sensitivity and selectivity which has spurred the development of more advanced approaches for both the medical and industrial sectors. The wide range of application areas has resulted in a range of materials and fabrication techniques to produce novel glucose sensors that have higher sensitivity and selectivity, lower cost, and are simpler to use. A major focus has been on the development of enzymatic electrochemical sensors, typically using glucose oxidase. However, non-enzymatic approaches using direct electrochemistry of glucose on noble metals are now a viable approach in glucose biosensor design. This review discusses the mechanisms of electrochemical glucose sensing with a focus on the different generations of enzymatic-based sensors, their recent advances, and provides an overview of the next generation of non-enzymatic sensors. Advancements in manufacturing techniques and materials are key in propelling the field of glucose sensing, however, significant limitations remain which are highlighted in this review and requires addressing to obtain a more stable, sensitive, selective, cost efficient, and real-time glucose sensor.

Facile synthesis of a nanorod-like MoS2 nanostructure for sensitive electrochemical biosensing application

A novel nanorod-like MoS2 semiconductor nanostructure was synthesized through a simple two-step method. The nanorod-like MoS2 nanostructure was exploited as an electrode material to immobilize enzymes and for electrochemical sensing application. Characterization of the nanorod-like MoS2 nanostructure and the resultant biosensor was performed by scanning electron microscopy, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Enzyme molecules loaded at the MoS2 nanostructure retained their native structure and bioactivity. The direct electron transfer of glucose oxidase at the MoS2 nanostructure coated glassy carbon electrode was enhanced greatly. At an optimal potential of -0.45 V, the electrochemical glucose sensor had wide linear ranges of 1.5 × 10-5-3.25 × 10-4 M and 3.25 × 10-4-1.43 × 10-3 M, and a low detection limit of 0.005 mM (S/N = 3) with a high sensitivity of 25.06 ± 0.5 mA M-1 cm-2. At the same time, the present biosensor showed excellent selectivity, reproducibility and stability for glucose. What's more, the biosensor was successfully applied to the determination of practical samples.

An Overview on Recent Progress of Metal Oxide/Graphene/CNTs-Based Nanobiosensors

Nanobiosensors are convenient, practical, and sensitive analyzers that detect chemical and biological agents and convert the results into meaningful data between a biologically active molecule and a recognition element immobilized on the surface of the signal transducer by a physicochemical detector. Due to their fast, accurate and reliable operating characteristics, nanobiosensors are widely used in clinical and nonclinical applications, bedside testing, medical textile industry, environmental monitoring, food safety, etc. They play an important role in such critical applications. Therefore, the design of the biosensing interface is essential in determining the performance of the nanobiosensor. The unique chemical and physical properties of nanomaterials have paved the way for new and improved sensing devices in biosensors. The growing demand for devices with improved sensing and selectivity capability, short response time, lower limit of detection, and low cost causes novel investigations on nanobiomaterials to be used as biosensor scaffolds. Among all other nanomaterials, studies on developing nanobiosensors based on metal oxide nanostructures, graphene and its derivatives, carbon nanotubes, and the widespread use of these nanomaterials as a hybrid structure have recently attracted attention. Nanohybrid structures created by combining these nanostructures will directly meet the future biosensors' needs with their high electrocatalytic activities. This review addressed the recent developments on these nanomaterials and their derivatives, and their use as biosensor scaffolds. We reviewed these popular nanomaterials by evaluating them with comparative studies, tables, and charts.

Limitation-induced fluorescence enhancement of carbon nanoparticles and their application for glucose detection

Rational design of detection strategy is the key to high-performance fluorescence analysis. In this article, we found that the glucose-induced limitations can greatly enhance the fluorescence of functionalized carbon nanoparticles (CNPs), which are synthesized through one-step thermal pyrolysis method using phenylboronic acid derivative as the precursors. The glucose can assembly onto the surface of the CNPs to form a "shell", limiting the surfaces' intramolecular rotation and reducing non-radiative decay, which hence resulted in enhanced fluorescence of the CNPs. Under optimal conditions, the fluorescence intensity of the CNPs is nearly 70-fold enhanced, and the method has low detection limit (10 μM) and linear response in the concentration range from 50 μM to 2000 μM. Based on this interesting "target-triggered limitation-induced fluorescence enhancement" phenomenon, a simple and effective non-enzymatic fluorescence enhancement method was developed and successfully applied to the determination of glucose in spiked serum samples. This work provides new insight into the design of fluorescence-enhanced detection strategies based on the limitation-induced property.

Synthesis of a novel hedgehog-shaped Bi2S3 nanostructure for a sensitive electrochemical glucose biosensor

A novel hedgehog-shaped Bi2S3 nanostructure was synthesized using a simple hydrothermal route with a composite soft template and further used to construct a sensitive glucose biosensor.

Oxidases, carbon nanotubes, and direct electron transfer: A cautionary tale

The case study of four FAD-dependent oxidase enzymes is presented in the context of the often-claimed direct electron transfer (DET) to glucose oxidase at carbon nanotubes (CNT). The selected enzymes included d-amino acid (AAOx), alcohol (AOx), pyranose (PyOx), and choline oxidase (ChOx). Each enzyme (E) was mixed with chitosan and CNT (either multi- or single-walled) to form a CNT/E film on the surface of glassy carbon electrode. All eight CNT/E films displayed redox activity depicted by voltammetric current peaks near -0.4 V. However, no DET was observed for any of the films as indicated by the absence of expected substrate- and oxygen-induced asymmetry in the anodic-to-cathodic charge ratio. The peaks are suggested to be due to the redox of either a dissociated FAD cofactor, in the case of AAOx and AOx, or denatured enzyme in the case of PyOx and ChOx. The amperometric assays of the films revealed the lowering of enzymatic activity of all four oxidases by CNT. The results are consistent with the hypothesis of oxidase molecules displaying a spectrum of enzymatic activity in CNT/E films ranging from voltammetrically untraceable (for molecules adsorbed on CNT) to amperometrically measurable (for molecules remote from CNT). The kinetic studies showed that enzyme molecules with no net charge leached at the slowest rate from CNT/E films. This work adds to a growing number of reports challenging the fallacy of DET to FAD-dependent native oxidases.