Functional Group-Assisted Fluorescence Sensing Platform for Nanomolar-Level Detection of an Antineoplastic Drug and a Neurotransmitter from Environmental Water and Human Biofluids

A fast, sensitive, selective, and biocompatible dual sensor of an antineoplastic medication (methotrexate) and a neurotransmitter (adrenaline) is still being searched by present-day scientists. To overcome this issue, we have designed a functionalized, robust, bio-friendly luminescent MOF for the sensitive, selective, and rapid monitoring of methotrexate and adrenaline. This probe is the first ever reported MOF-based fluorescence sensor of methotrexate and second only for adrenaline. This fluorescence probe has a very low limit of detection (LOD) of 0.34 and 11.2 nM for adrenaline and methotrexate, respectively. The sensor can detect both the targeted analytes rapidly within 5 s. It can also detect adrenaline and methotrexate from human blood serum and urine accurately and precisely. This reusable sensor is equally efficient in detecting methotrexate from environmental water specimens. Biocompatible, user-friendly, and inexpensive chitosan@MOF@cotton composites were fabricated for the detection of adrenaline and methotrexate from the nanomolar to the micromolar range by the naked eye under a fluorescence lamp. This probe displayed high reproducibility, precision, and accuracy in sensing methotrexate and adrenaline. Fluorescence resonance energy transfer (FRET) and the inner filter effect (IFE) are the possible mechanisms for adrenaline and methotrexate sensing, respectively. The possible mechanism was supported by using required instrumental techniques and theoretical simulations.

Development and Characterization of Nano-Ink from Silicon Carbide/Multi-Walled Carbon Nanotubes/Synthesized Silver Nanoparticles for Non-Enzymatic Paraoxon Residuals Detection

The ongoing advancement in the synthesis of new nanomaterials has accelerated the rapid development of non-enzymatic pesticide sensors based on electrochemical platforms. This study aims to develop and characterize Nano-ink for applying organophosphorus pesticides using paraoxon residue detection. Multi-walled carbon nanotubes, silicon carbide, and silver nanoparticles were used to create Nano-ink using a green synthesis process in 1:1:0, 1:1:0.5, and 1:1:1 ratios, respectively. These composites were combined with chitosan of varying molecular weights, which served as a stabilizing glue to keep the Nano-ink employed in a functioning electrode stable. By using X-ray powder diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy, and a field emission scanning electron microscope, researchers were able to examine the crystallinity, element composition, and surface morphology of Nano-ink. The performance of the proposed imprinted working electrode Nano-ink was investigated using cyclic voltammetry and differential pulse voltammetry techniques. The Cyclic voltammogram of Ag NPs/chitosan (medium, 50 mg) illustrated high current responses and favorable conditions of the Nano-ink modified electrode. Under the optimized conditions, the reduction currents of paraoxon using the DPV techniques demonstrated a linear reaction ranging between 0.001 and 1.0 µg/mL (R2 = 0.9959) with a limit of detection of 0.0038 µg/mL and a limit of quantitation of 0.011 µg/mL. It was concluded that the fabricated Nano-ink showed good electrochemical activity for non-enzymatic paraoxon sensing.

MOF-Fabric Composites Based on a Multi-Functional MOF as Luminescent Sensors for a Neurotransmitter and an Anti-Cancer Drug

A biocompatible, reliable, fast, and nanomolar-level dual-functional sensor for a neurotransmitter (e.g., adrenaline) and an anti-cancer drug (e.g., 6-mercaptopurine (6-MP)) is still far away from the hand of modern-day researchers. To address this issue, we synthesized an aqua-stable, bio-friendly, thiourea-functionalized Zr(IV) metal-organic framework (MOF) for selective, rapid sensing of adrenaline and 6-MP with ultra-low limit of detection (LOD for adrenaline = 1.9 nM and LOD for 6-MP = 28 pM). This is the first MOF-based fluorescent sensor of both the targeted analytes. The sensor not only can detect adrenaline in HEPES buffer medium but also in different bio-fluids (e.g., human urine and blood serum) and pH media. It also exhibited 6-MP sensing ability in aqueous medium and in various wastewater specimens and pH solutions. For the quick and on-site detection of this neuro-messenger (adrenaline) and the drug (6-MP), cost-effective sensor-coated cotton fabric composites were fabricated. The MOF@cotton fabric composite is capable of detecting both the analytes up to the nanomolar level by the naked eye under UV light. The sensor can be recycled up to five times without significantly losing its efficiency. The Förster resonance energy transfer in the presence of adrenaline and inner-filter effect in the presence of 6-MP are the most likely reasons behind the quenching of the MOF's fluorescence intensity, which were proved with the help of appropriate instrumental techniques.

Biosensing Dopamine and L-Epinephrine with Laccase (Trametes pubescens) Immobilized on a Gold Modified Electrode

Engineering electrode surfaces through the electrodeposition of gold may provide a range of advantages in the context of biosensor development, such as greatly enhanced surface area, improved conductivity and versatile functionalization. In this work we report on the development of an electrochemical biosensor for the laccase-catalyzed assay of two catecholamines—dopamine and L-epinephrine. Variety of electrochemical techniques—cyclic voltammetry, differential pulse voltammetry, electrochemical impedance spectroscopy and constant potential amperometry have been used in its characterization. It has been demonstrated that the laccase electrode is capable of sensing dopamine using two distinct techniques—differential pulse voltammetry and constant potential amperometry, the latter being suitable for the assay of L-epinephrine as well. The biosensor response to both catecholamines, examined by constant potential chronoamperometry over the potential range from 0.2 to −0.1 V (vs. Ag|AgCl, sat KCl) showed the highest electrode sensitivity at 0 and −0.1 V. The dependencies of the current density on either catecholamine’s concentration was found to follow the Michaelis—Menten kinetics with apparent constants K_M^app = 0.116 ± 0.015 mM for dopamine and K_M^app = 0.245 ± 0.031 mM for L-epinephrine and linear dynamic ranges spanning up to 0.10 mM and 0.20 mM, respectively. Calculated limits of detection for both analytes were found to be within the sub-micromolar concentration range. The biosensor applicability to the assay of dopamine concentration in a pharmaceutical product was demonstrated (with recovery rates between 99% and 106%, n = 3).

Advances in chemiluminescence and electrogenerated chemiluminescence based on silicon nanomaterials

Since 1950, when chemiluminescence (CL) of siloxane upon treatment with strong oxidants was discovered by Kurtz, many silicon-based nanomaterials with different elements, specific molecules, shapes and sizes have been developed as light emitters, energy acceptors, and catalyzers to provide valuable CL and electrogenerated CL (ECL) detection platforms in analytical chemistry fields. This review mainly focuses on the recent development of their mechanisms and sensing methodologies for small molecules, free radicals, ion, enzyme, protein, DNA, cancer cells, and metabolites based on specific reactions such as aptamer sensing and enzymatic reaction. Additionally, the future trend is discussed.

A novel fluorescent biosensor for adrenaline detection and tyrosinase inhibitor screening

In this work, a novel simple fluorescent biosensor for the highly sensitive and selective detection of adrenaline was established. Firstly, water-soluble CuInS₂ quantum dots (QDs) capped by L-Cys were synthesized via a hydrothermal synthesis method. Then, the positively charged adrenaline was assembled on the surface of CuInS₂ QDs due to the electrostatic interactions and hydrogen bonding, which led to the formation of adrenaline-CuInS₂ QD (Adr-CuInS₂ QD) electrostatic complexes. Tyrosinase (TYR) can catalyze adrenaline to generate H₂O₂, and additionally oxidize the adrenaline to adrenaline quinone. Both the H₂O₂ and the adrenaline quinone can quench the fluorescence of the CuInS₂ QDs through the electron transfer (ET) process. Thus, the determination of adrenaline could be facilely achieved by taking advantage of the fluorescence "turn off" feature of CuInS₂ QDs. Under the optimum conditions, the fluorescence quenching ratio I_f/I_f0 (I_f and I_f0 were the fluorescence intensity of Adr-CuInS₂ QDs in the presence and absence of TYR, respectively) was proportional to the logarithm of adrenaline concentration in the range of 1 × 10^-8-1 × 10^-4 mol L^-1 with the detection limit of 3.6 nmol L^-1. The feasibility of the proposed biosensor in real sample assay was also studied and satisfactory results were obtained. Significantly, the proposed fluorescent biosensor can also be utilized to screen TYR inhibitors. Graphical abstract Schematic illustration of the fluorescent biosensor for adrenaline detection (A) and tyrosinase inhibitor screening (B).

Review of Electrochemically Triggered Macromolecular Film Buildup Processes and Their Biomedical Applications

Macromolecular coatings play an important role in many technological areas, ranging from the car industry to biosensors. Among the different coating technologies, electrochemically triggered processes are extremely powerful because they allow in particular spatial confinement of the film buildup up to the micrometer scale on microelectrodes. Here, we review the latest advances in the field of electrochemically triggered macromolecular film buildup processes performed in aqueous solutions. All these processes will be discussed and related to their several applications such as corrosion prevention, biosensors, antimicrobial coatings, drug-release, barrier properties and cell encapsulation. Special emphasis will be put on applications in the rapidly growing field of biosensors. Using polymers or proteins, the electrochemical buildup of the films can result from a local change of macromolecules solubility, self-assembly of polyelectrolytes through electrostatic/ionic interactions or covalent cross-linking between different macromolecules. The assembly process can be in one step or performed step-by-step based on an electrical trigger affecting directly the interacting macromolecules or generating ionic species.

Ferrocyanide-Ferricyanide Redox Couple Induced Electrochemiluminescence Amplification of Carbon Dots for Ultrasensitive Sensing of Glutathione

Here we report a novel solid-state ECL sensor for ultrasensitive sensing of glutathione (GSH) based on ferrocyanide-ferricyanide redox couple (Fe(CN)6(3-/4-)) induced electrochemiluminescence (ECL) amplification of carbon dots (C-dots). The electropolymerization of C-dots and (11-pyrrolyl-1-yl-undecyl) triethylammonium tetrafluoroborate (A2) enabled immobilization of the hydrophilic C-dots on the surface of glassy carbon electrode (GCE) perfectly, while the excellent conductivity of polypyrrole was exploited to accelerate electron transfer between them. The Fe(CN)6(3-/4-) can expeditiously convert the C-dots and S2O8(2-) to C-dot(•-) and SO4(•-), respectively. High yields of the excited state C-dots (C-dots*) were obtained, and a ∼10-fold ECL amplification was realized. The C-dots* obtained through the recombination of electron-injected and hole-injected processes may be impeded due to the interference of GSH to K2S2O8. Therefore, the constructed sensor for GSH showed a detection limit down to 54.3 nM (S/N = 3) and a wide linear range from 0.1-1.0 μM with a correlation coefficient of 0.997.

A novel biosensor array with a wheel-like pattern for glucose, lactate and choline based on electrochemiluminescence imaging

An ECL imaging biosensor was fabricated for detecting glucose, lactate and choline, as well as for simultaneous multicomponent assay.

Human stress monitoring through an organic cotton-fiber biosensor

Selective detection of bioanalytes in physiological fluids, such as blood, sweat or saliva, by means of low-cost and non-invasive devices, is of crucial importance to improve diagnosis and prevention in healthcare.