A Noninvasive Sweat Glucose Biosensor Based on Glucose Oxidase/Multiwalled Carbon Nanotubes/Ferrocene-Polyaniline Film/Cu Electrodes

Diabetes remains a great threat to human beings' health and its world prevalence is projected to reach 9.9% by 2045. At present, the detection methods used are often invasive, cumbersome and time-consuming, thus increasing the burden on patients. In this paper, we propose a novel noninvasive and low-cost biosensor capable of detecting glucose in human sweat using enzyme-based electrodes for point-of-care uses. Specifically, an electrochemical method is applied for detection and the electrodes are covered with multilayered films including ferrocene-polyaniline (F-P), multi-walled carbon nanotubes (MWCNTs) and glucose oxidase (GOx) on Cu substrates (GOx/MWCNTs/F-P/Cu). The coated layers enhance the immobilization of GOx, increase the conductivity of the anode and improve the electrochemical properties of the electrode. Compared with the Cu electrode and the F-P/Cu electrode, a maximum peak current is obtained when the MWCNTs/F-P/Cu electrode is applied. We also study its current response by cyclic voltammetry (CV) at different concentrations (0-2.0 mM) of glucose solution. The best current response is obtained at 0.25 V using chronoamperometry. The effective working lifetime of an electrode is up to 8 days. Finally, to demonstrate the capability of the electrode, a portable, miniaturized and integrated detection device based on the GOx/MWCNTs/F-P/Cu electrode is developed. The results exhibit a short response time of 5 s and a correlation coefficient R² of 0.9847 between the response current of sweat with blood glucose concentration. The LOD is of 0.081 mM and the reproducibility achieved in terms of RSD is 3.55%. The sweat glucose sensor is noninvasive and point-of-care, which shows great development potential in the health examination and monitoring field.

Development of a highly sensitive glucose nanocomposite biosensor based on recombinant enzyme from corn

BACKGROUND

Enzymes are biocatalysts that play a vital role in the production of biomolecules. Plants can be a valuable and cost-effective source for producing well-structured recombinant enzymes. Glucose is one of the most important biological molecules, providing energy to most living systems. An electrochemical method for immobilization of enzyme is promising because it is economic, generates less component waste, improves the signal-to-noise ratio, leads to a lower limit of detection, and stabilizes and protects the enzyme structure.

RESULTS

A glucose biosensor was constructed using polyaniline (PANI) and a recombinant enzyme from corn, plant-produced manganese peroxidase (PPMP), with polymerization of aniline as a monomer in the presence of gold nanoparticles (AuNPs)-glucose oxidase (GOx), and bovine serum albumin. Using linear sweep voltammetry and cyclic voltammetry techniques, PANI-AuNPs-GOx-PPMP/Au electrode exhibited a superior sensing property with a wider linear range of 0.005-16.0 mm, and a lower detection limit of 0.001 mm compared to PANI-GOx-PPMP/Au electrode and PANI-GOx-PPMP/AuNPs/Au electrode. The biosensor selectivity was assessed by determining glucose concentrations in the presence of ascorbic acid, dopamine, aspartame, and caffeine.

CONCLUSION

We conclude that a plant-produced Mn peroxidase enzyme combined with conductive polymers and AuNPs results in a promising nanocomposite biosensor for detecting glucose. The use of such devices for quality control in the food industry can have a significant economic impact. © 2022 Society of Chemical Industry.

Applications of Pristine and Functionalized Carbon Nanotubes, Graphene, and Graphene Nanoribbons in Biomedicine

This review is dedicated to a comprehensive description of the latest achievements in the chemical functionalization routes and applications of carbon nanomaterials (CNMs), such as carbon nanotubes, graphene, and graphene nanoribbons. The review starts from the description of noncovalent and covalent exohedral modification approaches, as well as an endohedral functionalization method. After that, the methods to improve the functionalities of CNMs are highlighted. These methods include the functionalization for improving the hydrophilicity, biocompatibility, blood circulation time and tumor accumulation, and the cellular uptake and selectivity. The main part of this review includes the description of the applications of functionalized CNMs in bioimaging, drug delivery, and biosensors. Then, the toxicity studies of CNMs are highlighted. Finally, the further directions of the development of the field are presented.

A novel electrochemical glucose biosensor based on a poly (L-aspartic acid)-modified carbon-paste electrode

A new amperometric biosensor was fabricated by means of electropolymerization of L-aspartic acid on a carbon-paste electrode (CPE) for the bioelectrochemical determination of glucose. The electropolymerization process was conducted via cyclic voltammetry (CV). The modified CPE with poly (L-aspartic acid) (PAA) provided free carboxyl groups so as to immobilize the glucose oxidase (GOx), and further, enhanced the electrocatalytic activity of the hydrogen peroxide (H₂O₂). The biosensor displayed both good stability and good bioactivity. The sensitivity of the prepared biosensor was 5.3 µA cm^-2mM^-1. Its linear range extended from 0.05 mM to 1.0 mM, with the low limit of detection (LOD) being 69.2 µM. The Michaelis-Menten constant was found to be 1.17 mM. Furthermore, the biosensor showed good anti-interference ability in relation to dopamine, uric acid, and ascorbic acid. Taken together, these results demonstrate that PAA/CPE is a promising material for the fabrication of glucose biosensor.

Formation and Electrochemical Evaluation of Polyaniline and Polypyrrole Nanocomposites Based on Glucose Oxidase and Gold Nanostructures

Nanocomposites based on two conducting polymers, polyaniline (PANI) and polypyrrole (Ppy), with embedded glucose oxidase (GOx) and 6 nm size gold nanoparticles (AuNPs_(6nm)) or gold-nanoclusters formed from chloroaurate ions (AuCl₄⁻), were synthesized by enzyme-assisted polymerization. Charge (electron) transfer in systems based on PANI/AuNPs_(6nm)-GOx, PANI/AuNPs_(AuCl4⁻₎-GOx, Ppy/AuNPs_(6nm)-GOx and Ppy/AuNPs_(AuCl4⁻₎-GOx nanocomposites was investigated. Cyclic voltammetry (CV)-based investigations showed that the reported polymer nanocomposites are able to facilitate electron transfer from enzyme to the graphite rod (GR) electrode. Significantly higher anodic current and well-defined red-ox peaks were observed at a scan rate of 0.10 V s⁻¹. Logarithmic function of anodic current (log I_pa), which was determined by CV-based experiments performed with glucose, was proportional to the logarithmic function of a scan rate (log v) in the range of 0.699–2.48 mV s⁻¹, and it indicates that diffusion-controlled electrochemical processes were limiting the kinetics of the analytical signal. The most efficient nanocomposite structure for the design of the reported glucose biosensor was based on two-day formed Ppy/AuNPs_(AuCl4⁻₎-GOx nanocomposites. GR/Ppy/AuNPs_(AuCl4⁻₎-GOx was characterized by the linear dependence of the analytical signal on glucose concentration in the range from 0.1 to 0.70 mmol L⁻¹, the sensitivity of 4.31 mA mM cm⁻², the limit of detection of 0.10 mmol L⁻¹ and the half-life period of 19 days.

A Critical Review of Electrochemical Glucose Sensing: Evolution of Biosensor Platforms Based on Advanced Nanosystems

The research field of glucose biosensing has shown remarkable growth and development since the first reported enzyme electrode in 1962. Extensive research on various immobilization methods and the improvement of electron transfer efficiency between the enzyme and the electrode have led to the development of various sensing platforms that have been constantly evolving with the invention of advanced nanostructures and their nano-composites. Examples of such nanomaterials or composites include gold nanoparticles, carbon nanotubes, carbon/graphene quantum dots and chitosan hydrogel composites, all of which have been exploited due to their contributions as components of a biosensor either for improving the immobilization process or for their electrocatalytic activity towards glucose. This review aims to summarize the evolution of the biosensing aspect of these glucose sensors in terms of the various generations and recent trends based on the use of applied nanostructures for glucose detection in the presence and absence of the enzyme. We describe the history of these biosensors based on commercialized systems, improvements in the understanding of the surface science for enhanced electron transfer, the various sensing platforms developed in the presence of the nanomaterials and their performances.

Glucose Oxidase Immobilized on a Functional Polymer Modified Glassy Carbon Electrode and Its Molecule Recognition of Glucose

In the present study, a glucose oxidase (GluOx) direct electron transfer was realized on an aminated polyethylene glycol (mPEG), carboxylic acid functionalized multi-walled carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymer modified glassy carbon electrode (GCE). The amino groups in PEG, carboxyl groups in multi-walled carbon nanotubes, and IL may have a better synergistic effect, thus more effectively adjust the hydrophobicity, stability, conductivity, and biocompatibility of the composite functional polymer film. The composite polymer membranes were characterized by cyclic voltammetry (CV), ultraviolet-visible (UV-Vis) spectrophotometer, fluorescence spectroscopy, electrochemical impedance spectroscopy (EIS), and transmission electron microscopy (TEM), respectively. In 50 mM, pH 7.0 phosphate buffer solution, the formal potential and heterogeneous electron transfer constant (ks) of GluOx on the composite functional polymer modified GCE were -0.27 V and 6.5 s-1, respectively. The modified electrode could recognize and detect glucose linearly in the range of 20 to 950 μM with a detection limit of 0.2 μM. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 143 μM. The IL/mPEG-fMWCNTs functional polymer could preserve the conformational structure and catalytic activity of GluOx and lead to high sensitivity, stability, and selectivity of the biosensors for glucose recognition and detection.

Enzyme immobilisation on poly-l-lysine-containing calcium phosphate particles for highly sensitive glucose detection

High catalytic activities of enzymes are necessary for enzyme immobilising technology for the development of glucose sensors. The aim of this study is to synthesise two types of poly(l-lysine)-containing calcium phosphate particles (pLys-HAp) and to achieve the immobilisation of glucose oxidase (GOX) on them. The oxidation activity of GOX immobilised on these particles was more than 80% compared to that of native GOX (considered to be 100%). Additionally, the relative activity of GOX immobilised on poly-ε-lysine-containing HAp (ε-pLys-HAp) remained approximately 70% after ten cycles. Moreover, glucose detection was able to be performed in the linear range of 4–400 μM using GOX immobilised on pLys-HAp composites. In the direct electrochemistry measurement using the cyclic voltammetry (CV) method, a glassy carbon electrode (GCE) modified by ε-pLys-HAp was a good enzyme electrode and can be used for glucose detection with high sensitivity. From these results, poly(l-lysine)-containing HAp composites can be expected to be enzyme immobilisation agents with high stability and biosensors with high sensitivity.

The as-synthesised poly-l-lysine-containing HAp with high enzyme stability could be a candidate for a glucose sensor with high sensitivity.

Layered double hydroxide nanoparticles embedded in a biopolymer: a novel platform for electroanalytical determination of diazepam

A Co–Al layered double hydroxide/poly(tyrosine) modified glassy carbon electrode was prepared and used for electrocatalytic determination of diazepam in real samples.

Capillary electrophoresis analysis of affinity to assess carboxylation of multi-walled carbon nanotubes

Surface oxidation improves the dispersion of carbon nanotubes in aqueous solutions and plays a key role in the development of biosensors, electrochemical detectors and polymer composites. Accurate characterization of the carbon nanotube surface is important because the development of these nano-based applications depends on the degree of functionalization, in particular the amount of carboxylation. Affinity capillary electrophoresis is used to characterize the oxidation of multi-walled carbon nanotubes. A polytryptophan peptide that contains a single arginine residue (WRWWWW) serves as a receptor in affinity capillary electrophoresis to assess the degree of carboxylation. The formation of peptide-nanotube receptor-ligand complex was detected with a UV absorbance detector. Apparent dissociation constants (K_D) are obtained by observing the migration shift of the WRWWWW peptide through background electrolyte at increasing concentrations of multi-walled carbon nanotubes. A 20% relative standard deviation in method reproducibility and repeatability is determined with triplicate analysis within a single sample preparation and across multiple sample preparations for a commercially available carbon nanotube. Affinity capillary electrophoresis is applied to assess differences in degree of carboxylation across two manufacturers and to analyze acid treated carbon nanotubes. The results of these studies are compared to X-ray photoelectron spectroscopy and zeta potential. Affinity capillary electrophoresis comparisons of carbon nanotube samples prepared by varying acid treatment time from 30 min to 3 h yielded significant differences in degree of carboxylation. X-ray photoelectron spectroscopy analysis was inconclusive due to potential acid contamination, while zeta potential showed no change based on surface charge. This work is significant to research involving carbon nanotube-based applications because it provides a new metric to rapidly characterize carbon nanotubes obtained from different vendors, or synthesized in laboratories using different procedures.

Recent advances in carbon nanotube based electrochemical biosensors

There is an increasing need for rapid, low cost, reusable, reliable and sensitive detection systems for diagnosing infectious diseases, metabolic disorders, rapidly advancing cancers and detecting the presence of environmental pollutants. Most traditional methods are invasive, slow, expensive and laborious, requiring highly specialized instruments. Introduction of biosensors with nanomaterials as transducers of signals have helped in removing the disadvantages associated with traditional detectors. The properties of high mechanical strength, better electrical conductivity and ability to serve as efficient signal transducers make carbon nanotubes (CNTs) ideal material for biosensor applications among the gamut of nanomaterials. Further, CNTs with their high surface areas, easily functionalizable surfaces for receptor immobilization are gaining importance in the construction of biosensors. The expanding field of CNTs bridges the physical sciences with biology, as chemical methods are employed to develop novel tools and platforms for understanding biological systems, in disease diagnosis and treatment. This review presents recent advances in surface functionalization of CNTs necessary for immobilization of enzymes and antibodies for biosensor applications and the methodologies used for the detection of a number of chemical and biological species. The review ends with a speculation on future prospects for CNTs in biology and medicine.

Electrochemical investigation and determination of procaterol hydrochloride on poly(glutamic acid)/carboxyl functionalized multiwalled carbon nanotubes/polyvinyl alcohol modified glassy carbon electrode

Poly(glutamic acid) (P-GLU)/carboxyl functionalized multiwalled carbon nanotubes (MWCNTs-COOH)/polyvinyl alcohol (PVA) modified glassy carbon electrode (GCE) has been successfully prepared and the electrochemical behavior of procaterol hydrochloride (ProH) was studied. The results show that the as-prepared modified electrode exhibits a good electrocatalytic property towards the oxidation of ProH in 0.2M phosphate buffer solution (PBS) (pH 6.0) due to the enhanced oxidation peak current at ~+0.59V. Under optimal reaction conditions, the oxidation peak current of ProH is proportional to its concentration in the linear dynamic ranges of 0.060 - 8.0μM (R = 0.9974), with a detection limit of 8.0 × 10^-9M. Finally, this method was efficiently used for the determination of ProH in tablets and human urine with recoveries of 88.5~98.7% and 89.2 ~ 108.0%, respectively.

Effects of the surface chemistry and structure of carbon nanotubes on the coating of glucose oxidase and electrochemical biosensors performance

Glucose oxidase has been immobilized on multiwall and herringbone carbon nanotubes for glucose biosensing.

Electrochemical behavior of tectoridin and its sensitive determination based on L-arginine modified electrode

A simple, inexpensive and highly sensitive voltammetric method for the determination of tectoridin was developed using a poly(L-Arginine) modified electrode. The redox character of tectoridin at proposed electrode was studied systematically and some dynamic parameters were calculated for the first time. A reasonable reaction mechanism of tectoridin on the poly(L-Arginine)/GCE was also dicussed and proposed, which could be a reference for the pharmacological action of tectoridin in clinical study. And the electroanalytical method for determination of tectoridin was established by differential pulse voltammograms (DPV). Under optimum conditions, the response peak currents were linear relationship with tectoridin concentrations in the range of 5.0×10(-8)-2.0×10(-6) mol L(-1) with a detection limit of 4.0×10(-8) mol L(-1). Therefore, the high sensitivity for tectoridin sensing at the proposed electrode was achieved, and the proposed method could also be used to detect tectoridin in the Chinese medicinal herb Blackberrylily with satisfactory results.

Fabrication of a non-enzymatic Ni(ii) loaded ZSM-5 nanozeolite and multi-walled carbon nanotubes paste electrode as a glucose electrochemical sensor

A template-free ZSM-5 nanozeolite was synthesized and then carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite, multi-walled carbon nanotubes and Ni²⁺ and was used as catalyst for the electrooxidation of glucose (EC′ mechanism).