A selective electroanalysis and photocatalytic removal strategy for pesticide residues using urchin-like LaPO4@Ag

Bimetallic Fe/Co-MOF dispersed in a PVA/chitosan multi-matrix hydrogel as a flexible sensor for the detection of lactic acid in sweat samples

A novel bimetallic Fe/Co-metal-organic framework (MOF) hydrogel-based wearable sweat sensor was developed. Morphological and structural analysis of the hydrogel shows uniformly sized spines and spindle-shaped particles of the Fe/Co-MOF, and it has a high surface area (132.306 m2 g-1) and porosity (0.059 cm3 g-1) as confirmed by Brunauer-Emmett-Teller (BET) studies. The integration of the bimetallic MOF into a polyvinyl alcohol/chitosan (PVA/CS)-mixed matrix resulted in a multiple network hydrogel. The optimisation study investigated  the effects of different pH of the PBS electrolyte, scan rates, and accumulation time in voltammetry. The electrochemical methods such as cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) provided information on the redox behaviour, electrochemical stability, and catalytic activity of the hydrogel. The sensor demonstrates a wide linear detection range from 0.05 µM to 100 mM, a superior sensitivity of 0.02 mA mM-1 cm-2, and a lower limit of detection of 0.01 µM . Active sites distributed over the hydrogel surface, specifically Fe2+ and Co2+ within the MOF structure, catalyse the oxidation of L-lactic acid, resulting in electron transfer and the formation of pyruvic acid. Notably, the fabricated sensor exhibits high selectivity, effectively discriminating against interfering species such as uric acid, ascorbic acid, glucose, urea, dopamine, NaCl, and CaCl2. Real-time analysis conducted in a simulated sweat sample via the standard addition method resulted in good recovery percentages of a minimum of 98%. The work presented here is a versatile and simple platform for point-of-care testing, especially for athletes and military personnel.

Near-infrared light-driven lab-on-paper cathodic photoelectrochemical aptasensing for di(2-ethylhexyl)phthalate based on AgInS2/Cu2O/FeOOH photocathode

Di(2-ethylhexyl)phthalate (DEHP) is commonly released from plastics in aqueous environment, which can disrupt endocrine system and cause adverse effects on public health. There is a pressing need to highly sensitive detect DEHP. Herein, a near-infrared (NIR) light-driven lab-on-paper cathodic photoelectrochemical aptasensing platform integrated with AgInS2/Cu2O/FeOOH photocathode and "Y"-like ternary conjugated DNA nanostructure-mediated "ON-OFF" catalytic switching of hemin monomer-to-dimer was established for ultrasensitive DEHP detection. Profiting from the collaborative roles of the effective photosensitization of NIR-response AgInS2 and the fast hole extraction of FeOOH, the NIR light-activated AgInS2/Cu2O/FeOOH photocathode generated a markedly enhanced photocathodic signal. The dual hemin-labelled "Y"-like ternary conjugated DNA nanostructures made the hemin monomers separated in space and they maintained highly active to catalyze in situ generation of electron acceptors (O2). The hemin monomers were relocated in close proximity with the help of target-induced allosteric change of DNA nanostructures, which could spontaneously dimerize into catalytically inactive hemin dimers and fail to mediate electron acceptors generation, resulting in a decreased photocathodic signal. Therefore, the ultrasensitive DEHP detection was realized with a linear response range of 1 pM-500 nM and a detection limit of 0.39 pM. This work rendered a promising prototype to construct powerful paper-based photocathodic aptasensing system for sensitive and accurate screening of DEHP in aqueous environment.

Integration of Ultrathin Bubble Walls and Electrochemistry: Innovation in Microsensing for Forensic Nitrite Detection and Microscale Metallic Film Deposition

We present a strategy for electrochemical measurements using a durable minute bubble wall with a thickness of 27 μm (D = 1.8 cm) as an innovative electrochemical medium. The composition, thickness, and volume of the tiny bubble film were investigated and estimated using the spectroscopic method and the Beer-Lambert law. A carbon microelectrode (D = 10 μm) was then employed as the working electrode, inserted through the bubble wall to function as the solution interface. First, the potential of this method for microelectrodeposition of metallic Ag and Pd films in a tiny bubble was investigated. Interestingly, microscopic images of the deposited film clearly demonstrated that the bubble thickness determines and confines the electrochemical deposition zone. In other words, innovative template-free microelectrodeposition was achieved. In the second phase of our work, microelectroanalysis of trace levels of nitrite ions was performed within the bubble wall and on a foam-covered hand, between the fingers directly, with a low limit of detection of 28 μM. This technique holds significance in criminal investigations, as the presence of NO2- ions on the hand indicates the potential presence of gunshot residue and aids in identifying suspects. In comparison to current methods, this approach is rapid, simple, cost-effective, and amenable to on-site applications, eliminating the need for sample treatment. Ultimately, the utilization of a bubble wall as a novel electrochemical microreactor can open new ways in microelectrochemical analysis, presenting novel opportunities and applications in the field of electrochemical sensors.

Malathion detection based on polydopamine enhanced oxidase-mimetic activity of palladium nanocubes

Nowadays, fabricating simple and efficient pesticide detection methods become a research focus due to the great threat pesticide residues posed to human health and environment. Herein, we constructed a high-efficiency and sensitive colorimetric detection platform for malathion detection based on polydopamine-dressed Pd nanocubes (PDA-Pd/NCs). The Pd/NCs coated with PDA exhibited excellent oxidase-like activity, which was attributed to the substrates accumulation and accelerated electron transfer induced by PDA. What's more, we successfully achieved sensitive detection of acid phosphatase (ACP) using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, relying on the satisfactory oxidase activity from PDA-Pd/NCs. However, the addition of malathion could inhibit the activity of ACP and limit the production of medium AA. Therefore, we constructed a colorimetric assay for malathion based on PDA-Pd/NCs + TMB + ACP system. The wide linear range (0-8 μM) and low detection limit (0.023 μM) indicate excellent analytical performance, which is superior to most malathion analysis methods previously reported. This work not only provides a new idea for dopamine coated nano-enzyme to improve its catalytic activity, but also creates a new tactics for the detection of pesticides such as malathion.