Facile fabrication of electrochemically reduced graphene oxide/polythionine-methylene blue and its use as a platform for detection of nicotinamide adenine dinucleotide in the artificial urine sample

Polymer nanocomposite-based biomolecular sensor for healthcare monitoring

Polymer-derived nanocomposites have gained significant attention in biosensing due to their ability to integrate the mechanical flexibility of polymers with the high electrical conductivity, large surface area and porosity, enhanced catalytic activity, and excellent biocompatibility of nanoscale materials. When combined with biomolecules, these nanocomposites form advanced polymer-bio interfaces that enhance electrochemical signal transduction, molecular recognition, and surface stability critical factors for achieving high sensitivity and selectivity in diagnostic applications. This review provides a comprehensive overview of recent progress in the development and application of polymer-derived nanocomposites, such as conducting polymers, carbon nanotubes (CNTs), graphene, dendrimers, and molecularly imprinted polymers (MIPs), in the field of electrochemical biosensing. We delve into the fundamental interfacial mechanisms, including adsorption phenomena, electron transfer behavior, and catalytic activity that govern biosensor performance. The review also discusses the synthesis and functionalization of nanocomposites, sensor fabrication strategies, and mechanistic insights into their sensing/biosensing capabilities across various clinical and biomedical targets. Lastly, we evaluate key performance metrics ("figures of merit" refer to key sensing parameters such as materials, analytes, sensitivity, linear range, limit of detection (LOD), and real samples testing), address current challenges in optimizing polymer-bio interfaces, and highlight emerging opportunities for advancing next-generation diagnostic technologies.

Highly sensitive electrochemical immunosensor based on methylene blue-reduced graphene oxide nanocomposites as signal probes for IL-6 detection in gingival crevicular fluid samples

As an important inflammatory cytokine, interleukin-6 (IL-6) can mediate the entire pathological process of periodontitis and is closely associated with the degree of inflammation. Therefore, it is critical to develop convenient quantitative methods for monitoring IL-6 quantity in gingival crevicular fluid. In this study, methylene blue (MB)-decorated reduced graphene oxide (rGO) is employed as signal probe to further support the antibody-enabling specific recognition of IL-6. Due to π-π stacking and electrostatic interactions, rGO-MB nanocomposites can be stably obtained. rGO with good conductivity and large surface area characteristics promotes the redox signals of MB on the glassy carbon electrode (GCE). In addition, through the simple in situ self-polymerization of dopamine, the polydopamine (PDA) obtained can be not only directly used as a biological crosslinking agent for covalent immobilization of anti-IL-6 antibody but can also be regarded as a protective layer to enhance the stability of rGO-MB on the GCE surface. Such a designed PDA/rGO-MB/GCE-based immunosensor enables specific binding with IL-6 and produces a decreased electrochemical signal for MB, realizing the selective and sensitive quantitative measurement of IL-6. Consequently, our fabricated PDA/rGO-MB/GCE-based electrochemical immunosensor has an excellent linear relationship with IL-6 ranging from 1 pg/mL to 100 ng/mL, with a limit of detection as low as 0.48 pg/mL. Moreover, our as-prepared sensing strategy shows accurate monitoring of the IL-6 quantity in gingival crevicular fluid samples.

Synergistic Applications of Graphene-Based Materials and Deep Eutectic Solvents in Sustainable Sensing: A Comprehensive Review

The recently explored synergistic combination of graphene-based materials and deep eutectic solvents (DESs) is opening novel and effective avenues for developing sensing devices with optimized features. In more detail, remarkable potential in terms of simplicity, sustainability, and cost-effectiveness of this combination have been demonstrated for sensors, resulting in the creation of hybrid devices with enhanced signal-to-noise ratios, linearities, and selectivity. Therefore, this review aims to provide a comprehensive overview of the currently available scientific literature discussing investigations and applications of sensors that integrate graphene-based materials and deep eutectic solvents, with an outlook for the most promising developments of this approach.

Molecularly imprinted sensor based on poly-o-phenylenediamine-hydroquinone polymer for β-amyloid-42 detection

A sensitive and selective molecularly imprinted polymer (MIP) sensor was developed for the determination of amyloid-β (1-42) (Aβ₄₂). The glassy carbon electrode (GCE) was successively modified with electrochemical reduction graphene oxide (ERG) and poly(thionine-methylene blue) (PTH-MB). The MIPs were synthesized by electropolymerization with Aβ₄₂ as a template and o-phenylenediamine (o-PD) and hydroquinone (HQ) as functional monomers. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CC), and differential pulse voltammetry (DPV) were used to study the preparation process of the MIP sensor. The preparation conditions of the sensor were investigated in detail. In optimal experimental conditions, the response current of the sensor was linear in the range of 0.12-10 μg mL^-1 with a detection limit of 0.018 ng mL^-1. The MIP-based sensor successfully detected Aβ₄₂ in commercial fetal bovine serum (cFBS) and artificial cerebrospinal fluid (aCSF).

Self-Testing of Ketone Bodies, along with Glucose, Using Touch-Based Sweat Analysis

β-Hydroxybutyrate (HB) is one of the main physiological ketone bodies that play key roles in human health and wellness. Besides their important role in diabetes ketoacidosis, ketone bodies are currently receiving tremendous attention for personal nutrition in connection to the growing popularity of oral ketone supplements. Accordingly, there are urgent needs for developing a rapid, simple, and low-cost device for frequent onsite measurements of β-hydroxybutyrate (HB), one of the main physiological ketone bodies. However, real-time profiling of dynamically changing HB concentrations is challenging and still limited to laboratory settings or to painful and invasive measurements (e.g., a commercial blood ketone meter). Herein, we address the critical need for pain-free frequent HB measurements in decentralized settings and report on a reliable noninvasive, simple, and rapid touch-based sweat HB testing and on its ability to track dynamic HB changes in secreted fingertip sweat, following the intake of commercial ketone supplements. The new touch-based HB detection method relies on an instantaneous collection of the fingertip sweat at rest on a porous poly(vinyl alcohol) (PVA) hydrogel that transports the sweat to a biocatalytic layer, composed of the β-hydroxybutyrate dehydrogenase (HBD) enzyme and its nicotinamide adenine dinucleotide (NAD⁺) cofactor, covering the modified screen-printed carbon working electrode. As a result, the sweat HB can be measured rapidly by the mediated oxidation reaction of the nicotinamide adenine dinucleotide (NADH) product. A personalized HB dose-response relationship is demonstrated within a group of healthy human subjects taking commercial ketone supplements, along with a correlation between the sweat and capillary blood HB levels. Furthermore, a dual disposable biosensing device, consisting of neighboring ketone and glucose enzyme electrodes on a single-strip substrate, has been developed toward the simultaneous touch-based detection of dynamically changing sweat HB and glucose levels, following the intake of ketone and glucose drinks.

Flow-Through Acetylcholinesterase Sensor with Replaceable Enzyme Reactor

Fast and reliable determination of enzyme inhibitors are of great importance in environmental monitoring and biomedicine because of the high biological activity and toxicity of such species and the necessity of their reliable assessment in many media. In this work, a flow-through biosensor has been developed and produced by 3D printing from poly(lactic acid). Acetylcholinesterase from an electric eel was immobilized on the inner walls of the reactor cell. The concentration of thiocholine formed in enzymatic hydrolysis of the substrate was monitored amperometrically with a screen-printed carbon electrode modified with carbon black particles, pillar[5]arene, electropolymerized Methylene blue and thionine. In the presence of thiocholine, the cathodic current at −0.25 V decreased because of an alternative chemical reaction of the macrocycle. The conditions of enzyme immobilization and signal measurements were optimized and the performance of the biosensor was assessed in the determination of reversible (donepezil, berberine) and irreversible (carbofuran) inhibitors. In the optimal conditions, the flow-through biosensor made it possible to determine 1.0 nM–1.0 μM donepezil, 1.0 μM–1.0 mM berberine and 10 nM to 0.1 μM carbofuran. The AChE biosensor was tested on spiked samples of artificial urine for drugs and peanuts for carbofuran. Possible interference of the sample components was eliminated by dilution of the samples with phosphate buffer. Easy mounting, low cost of replaceable parts of the cell and satisfactory analytical and metrological characteristics made the biosensor a promising future application as a point-of-care or point-of-demand device outside of a chemical laboratory.