The development of NAD+-dependent dehydrogenase screen-printed biosensor based on enzyme and nanoporous gold co-catalytic strategy

Non-invasive alcohol biosensor based on gold nanoparticles and carbon nanotubes network for dynamic monitoring of sweat alcohol

Intemperance can lead to health issues or other potential harms to society. Consequently, accurate detection of alcohol concentration in human fluid is an essential and challenging task. In this paper, we reported an efficient and reliable method for highly sensitive and selective monitoring of alcohol in sweat. This stretchable alcohol biosensor has been fabricated by transferring multi-walled carbon nanotubes (MWCNTs) film on polydimethylsiloxane (PDMS) substrate followed by immobilization of Au nanoparticles (AuNPs) and alcohol oxidase enzyme (AOx). The biosensor possesses satisfactory mechanical stability, including excellent resistance to stretching, bending and twisting. Sandwich structure formed on the electrode surface by MWCNTs and AuNPs provides excellent electrical conductivity and electrochemical performance for biosensors. The biosensor exhibited a wide linear range from 1.5 μM to 30 mM toward alcohol and the detection limit was 0.5 μM. Furthermore, owing to the specificity of the AOx, the biosensor displayed splendid selectivity. The real sample tests show that the constructed biosensor has the ability to monitor sweat alcohol, and the results were consistent with those obtained by gas chromatography. This research offers a versatile method for the development of flexible electrochemical biosensors, which has promising applications in noninvasive and accurate detection of alcohol in human sweat.

Advanced nanomaterials for electrochemical sensors: application in wearable tear glucose sensing technology

In the last few decades, tear-based biosensors for continuous glucose monitoring (CGM) have provided new avenues for the diagnosis of diabetes. The tear CGMs constructed from nanomaterials have been extensively demonstrated by various research activities in this field and are gradually witnessing their most prosperous period. A timely and comprehensive review of the development of tear CGMs in a compartmentalized manner from a nanomaterials perspective would greatly broaden this area of research. However, to our knowledge, there is a lack of specialized reviews and comprehensive cohesive reports in this area. First, this paper describes the principles and development of electrochemical glucose sensors. Then, a comprehensive summary of various advanced nanomaterials recently reported for potential applications and construction strategies in tear CGMs is presented in a compartmentalized manner, focusing on sensing properties. Finally, the challenges, strategies, and perspectives used to design tear CGM materials are emphasized, providing valuable insights and guidance for the construction of tear CGMs from nanomaterials in the future.

Combining plasmonic and electrochemical biosensing methods

The idea of combining electrochemical (EC) and plasmonic biosensor methods was introduced almost thirty years ago and the potential of electrochemical-plasmonic (EC-P) biosensors has been highlighted ever since. Despite that, the use of EC-P biosensors in analytics has been rather limited so far and the search for unique applications of the EC-P method continues. In this paper, we review the advances in the field of EC-P biosensors and discuss the features and benefits they can provide. In addition, we identify the main challenges for the development of EC-P biosensors and the limitations that prevent EC-P biosensors from more widespread use. Finally, we review applications of EC-P biosensors for the investigation and quantification of biomolecules, and for the study of biomolecular and cellular processes.

Insight into the binding characteristics of epigallocatechin-3-O-gallate and alcohol dehydrogenase: Based on the spectroscopic and molecular docking analysis

Alcohol dehydrogenase (ADH) is one of the pivotal enzymes for alcohol metabolism, which plays an important role in many physiological processes. In this study, the activation effects of epigallocatechin-3-O-gallate (EGCG) on ADH and the characteristics of the interaction were investigated via biochemical method, spectroscopy methods, and molecular docking. The results demonstrated that EGCG significantly increased the catalytic activity of ADH with a 33.33% activation rate and that EGCG blending slightly altered the microenvironment surrounding ADH aromatic amino acids, with an increase in the quantity of β-sheet and a decrease in the α-helix. Through the thermal stability analysis, it is further shown that the interaction of the two affects the intra-molecular hydrogen bond formation of the protein, and the conformation is partially extended. Besides, a total of 8 residues in ADH participated in the docking with EGCG, among which Asp-227, Lys-231, Glu-234, Gly-365 and Glu-366 participated in the formation of hydrogen bonds. At the same time, EGCG and amino group of Lys-231 form a noncovalent bond through cation-π interaction. In particular, hydrogen bonding was beneficial to keep the stability of EGCG-ADH, which was the primary driver of ADH activity activation. The results supply a new way for EGCG to activate ADH and a theoretical basis for the development of anti-alcoholism products.

Fully integrated wearable microneedle biosensing platform for wide-range and real-time continuous glucose monitoring

Wearable microneedle sensors for continuous glucose monitoring (CGM) have great potential for clinical impact by allowing access to large data sets to provide individualized treatment plans. To date, their development has been challenged by the accurate wide linear range tracking of interstitial fluid (ISF) glucose (Glu) levels. Here, we present a CGM platform consisting of a three-electrode microneedle electrochemical biosensor and a fully integrated radio-chemical analysis system. The long-term performance of the robust CGM on diabetic rats was achieved by electrodepositing Prussian blue (PB), and crosslinking glucose oxidase (GOx) and chitosan to form a 3D network using glutaraldehyde (GA). After redox by GOx, PB rapidly decomposes hydrogen peroxide and mediates charge transfer, while the 3D network and graphite powder provide enrichment and release sites for Glu and catalytic products, enabling a sensing range of 0.25-35 mM. Microneedle CGM has high sensitivity, good stability, and anti-interference ability. In diabetic rats, CGM can accurately monitor Glu levels in the ISF in real-time, which are highly consistent with levels measured by commercial Glu meters. These results indicate the feasibility and application prospects of the PB-based CGM for the clinical management of diabetes. STATEMENT OF SIGNIFICANCE: This study addresses the challenge of continuous glucose monitoring system design where the narrow linear range of sensing due to the miniaturization of sensors fails to meet the monitoring needs of clinical diabetic patients. This was achieved by utilizing a three-dimensional network of glutaraldehyde cross-linked glucose oxidase and chitosan. The unique topology of the 3D network provides a large number of sites for glucose enrichment and anchors the enzyme to the sensing medium and the conductive substrate through covalent bonding, successfully blocking the escape of the enzyme and the sensing medium and shortening the electron transfer and transmission path.

Integration of Glutamate Dehydrogenase and Nanoporous Gold for Electrochemical Detection of Glutamate

Glutamate, a non-essential amino acid produced by fermentation, plays a significant role in disease diagnosis and food safety. It is important to enable the real-time monitoring of glutamate concentration for human health and nutrition. Due to the challenges in directly performing electrochemical oxidation-reduction reactions of glutamate, this study leverages the synergistic effect of glutamate dehydrogenase (GLDH) and nanoporous gold (NPG) to achieve the indirect and accurate detection of glutamate within the range of 50 to 700 μM by measuring the generated quantity of NADH during the enzymatic reaction. The proposed biosensor demonstrates remarkable performance characteristics, including a detection sensitivity of 1.95 μA mM-1 and a limit of detection (LOD) of 6.82 μM. The anti-interference tests indicate an average recognition error ranging from -3.85% to +2.60%, spiked sample recovery rates between 95% and 105%, and a relative standard deviation (RSD) of less than 4.97% for three replicate experiments. Therefore, the GLDH-NPG/GCE biosensor presented in this work exhibits excellent accuracy and repeatability, providing a novel alternative for rapid glutamate detection. This research contributes significantly to enhancing the precise monitoring of glutamate concentration, thereby offering more effective guidance and control for human health and nutrition.

A New Highly Sensitive Electrochemical Biosensor for Ethanol Detection Based on Gold Nanoparticles/Reduced Graphene Oxide/Polyallylamine Hydrochloride Nanocomposite

A highly sensitive electrochemical biosensor for ethanol based on a screen-printed electrode modified with gold nanoparticles-electrochemically reduced graphene oxide-poly (allylamine hydrochloride) nanocomposite (AuNPs-ERGO-PAH) is reported in this work. Ethanol was oxidized in the presence of the oxidized form of the nicotinamide adenine dinucleotide (NAD+) in a reaction catalyzed by alcohol dehydrogenase (ADH) immobilized in sol-gel. The AuNPs-ERGO-PAH nanocomposite was used as a transducer for the electrocatalytic oxidation of the reduced form the nicotinamide adenine dinucleotide (NADH) produced in the enzyme reaction. Under the optimal conditions, the ethanol biosensor exhibits a wide dynamic range from 0.05 to 5 mM with a low detection limit of 10 µM (S/N = 3) and a high sensitivity of 44.6 ± 0.07 µA/mM·cm2 for the linear range between 0.05 and 0.2 mM. The biosensor response was stable for up to 6 weeks. Furthermore, the developed biosensor has been used to detect ethanol in alcoholic beverages with good results, suggesting its potential application in various fields, including fermentation processes and food quality control.

Focus Review on Nanomaterial-Based Electrochemical Sensing of Glucose for Health Applications

Diabetes management can be considered the first paradigm of modern personalized medicine. An overview of the most relevant advancements in glucose sensing achieved in the last 5 years is presented. In particular, devices exploiting both consolidated and innovative electrochemical sensing strategies, based on nanomaterials, have been described, taking into account their performances, advantages and limitations, when applied for the glucose analysis in blood and serum samples, urine, as well as in less conventional biological fluids. The routine measurement is still largely based on the finger-pricking method, which is usually considered unpleasant. In alternative, glucose continuous monitoring relies on electrochemical sensing in the interstitial fluid, using implanted electrodes. Due to the invasive nature of such devices, further investigations have been carried out in order to develop less invasive sensors that can operate in sweat, tears or wound exudates. Thanks to their unique features, nanomaterials have been successfully applied for the development of both enzymatic and non-enzymatic glucose sensors, which are compliant with the specific needs of the most advanced applications, such as flexible and deformable systems capable of conforming to skin or eyes, in order to produce reliable medical devices operating at the point of care.

Direct Electrochemistry of Glucose Dehydrogenase-Functionalized Polymers on a Modified Glassy Carbon Electrode and Its Molecular Recognition of Glucose

A glucose biosensor was layer-by-layer assembled on a modified glassy carbon electrode (GCE) from a nanocomposite of NAD(P)⁺-dependent glucose dehydrogenase, aminated polyethylene glycol (mPEG), carboxylic acid-functionalized multi-wall carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymers. The electrochemical electrode was denoted as NF/IL/GDH/mPEG-fMWCNTs/GCE. The composite polymer membranes were characterized by cyclic voltammetry, ultraviolet-visible spectrophotometry, electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. The cyclic voltammogram of the modified electrode had a pair of well-defined quasi-reversible redox peaks with a formal potential of -61 mV (vs. Ag/AgCl) at a scan rate of 0.05 V s^-1. The heterogeneous electron transfer constant (k_s) of GDH on the composite functional polymer-modified GCE was 6.5 s^-1. The biosensor could sensitively recognize and detect glucose linearly from 0.8 to 100 µM with a detection limit down to 0.46 μM (S/N = 3) and a sensitivity of 29.1 nA μM^-1. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 0.21 mM. The constructed electrochemical sensor was compared with the high-performance liquid chromatography method for the determination of glucose in commercially available glucose injections. The results demonstrated that the sensor was highly accurate and could be used for the rapid and quantitative determination of glucose concentration.

Electrochemical Nanosensors for Sensitization of Sweat Metabolites: From Concept Mapping to Personalized Health Monitoring

Sweat contains a broad range of important biomarkers, which may be beneficial for acquiring non-invasive biochemical information on human health status. Therefore, highly selective and sensitive electrochemical nanosensors for the non-invasive detection of sweat metabolites have turned into a flourishing contender in the frontier of disease diagnosis. A large surface area, excellent electrocatalytic behavior and conductive properties make nanomaterials promising sensor materials for target-specific detection. Carbon-based nanomaterials (e.g., CNT, carbon quantum dots, and graphene), noble metals (e.g., Au and Pt), and metal oxide nanomaterials (e.g., ZnO, MnO2, and NiO) are widely used for modifying the working electrodes of electrochemical sensors, which may then be further functionalized with requisite enzymes for targeted detection. In the present review, recent developments (2018-2022) of electrochemical nanosensors by both enzymatic as well as non-enzymatic sensors for the effectual detection of sweat metabolites (e.g., glucose, ascorbic acid, lactate, urea/uric acid, ethanol and drug metabolites) have been comprehensively reviewed. Along with this, electrochemical sensing principles, including potentiometry, amperometry, CV, DPV, SWV and EIS have been briefly presented in the present review for a conceptual understanding of the sensing mechanisms. The detection thresholds (in the range of mM-nM), sensitivities, linear dynamic ranges and sensing modalities have also been properly addressed for a systematic understanding of the judicious design of more effective sensors. One step ahead, in the present review, current trends of flexible wearable electrochemical sensors in the form of eyeglasses, tattoos, gloves, patches, headbands, wrist bands, etc., have also been briefly summarized, which are beneficial for on-body in situ measurement of the targeted sweat metabolites. On-body monitoring of sweat metabolites via wireless data transmission has also been addressed. Finally, the gaps in the ongoing research endeavors, unmet challenges, outlooks and future prospects have also been discussed for the development of advanced non-invasive self-health-care-monitoring devices in the near future.

Disposable electrocatalytic sensor for whole blood NADH monitoring

Monitoring nicotinamide adenine dinucleotide (NADH) is important because NADH is involved in cellular redox reactions and cellular energy production. Currently, few biosensors quantify NADH in whole blood. However, they still have limitations due to several defects, including poor repeatability, long analysis time, and their requirement of extra sample pretreatment. In this study, we developed electrocatalytic sensors using screen-printed electrodes with a redox-active monolayer 4′-mercapto-N-phenylquinone diamine formed by a self-assembled monolayer of a 4-aminothiophenol (4-ATP). We exhibited their behavior as electrocatalysts toward the oxidation of NADH in whole blood. Finally, the electrocatalytic sensors maintained stability and exhibited 3.5 µM limit of detection, with 0.0076 ± 0.0006 µM/µA sensitivity in a mouse’s whole blood. As proof of concept, a polyhexamethylene guanidine phosphate–treated mouse model was used to induce inflammatory and fibrotic responses, and NADH level was measured for 45 days. This work demonstrates the potential of electrocatalytic sensors to analyze NADH in whole blood and to be developed for extensive applications.