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1. Employing Conductive Metal-Organic Frameworks for Voltammetric Detection of Neurochemicals

   https://doi.org/10.1021/jacs.9b13402  

   Ko, Michael; Mendecki, Lukasz; Eagleton, Aileen M.; Durbin, Claudia G.; Stolz, Robert M.; Meng, Zheng; Mirica, Katherine A (March 2020, Journal of the American Chemical Society)

   This paper describes the first implementation of an array of two-dimensional (2D) layered conductive metal–organic frameworks (MOFs) as drop-casted film electrodes that facilitate voltammetric detection of redox active neurochemicals in a multi-analyte solution. The device configuration comprises a glassy carbon electrode modified with a film of conductive MOF (M3HXTP2; M = Ni, Cu; and X = NH, 2,3,6,7,10,11-hexaiminotriphenylene (HITP) or O, 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP)). The utility of 2D MOFs in voltammetric sensing is measured by the detection of ascorbic acid (AA), dopamine (DA), uric acid (UA), and serotonin (5-HT) in 0.1 M PBS (pH=7.4). In particular, Ni3HHTP2 MOF demonstrated nanomolar detection limits of 63 ± 11 nM for DA and 40 ± 17 nM for 5-HT through a wide concentration range (40 nM – 200 µM). The applicability in biologically-relevant detection was further demonstrated in simulated urine using Ni3HHTP2 MOFs for the detection of 5-HT with nanomolar detection limit of 63 ± 11 nM for 5-HT through a wide concentration range (63 nM – 200 µM) in the presence of constant background of DA. The implementation of conductive MOFs in voltammetric detection holds promise for further development of highly modular, sensitive, selective, and stable electroanalytical devices. 

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2. Two-Dimensional Tellurium Nanosheets for the Efficient Nonenzymatic Electrochemical Detection of H2O2

   https://doi.org/10.3390/chemosensors12020017  

   Shringi, Amit Kumar; Kumar, Rajeev; Dennis, Netanya F.; Yan, Fei (February 2024, Chemosensors)

   This study reports, for the first time, the utilization of two-dimensional (2D) tellurium (Te) nanosheets for the efficient nonenzymatic detection of hydrogen peroxide (H2O2). H2O2 acts as a pivotal biomarker with widespread applications across environmental, biological, industrial, and food processing domains. However, an excessive accumulation of H2O2 in the body poses a severe threat to human life. Consequently, the imperative need for a selective, sensitive, and cost-effective sensing platform for H2O2 detection has gained paramount significance. Employing a low-cost and straightforward hydrothermal method, Te nanosheets were synthesized to address the escalating demand for a reliable detection platform. The as-synthesized Te nanosheets are characterized through Raman spectroscopy and atomic force microscopy techniques. The electrochemical performance of the Te nanosheets integrated onto a glassy carbon (Te-GC) electrode was thoroughly investigated using cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. The experiments were designed to evaluate the response of the Te-GC electrode in the presence and absence of H2O2, alongside its performance in the detection of other pertinent interfering analytes. The sensor shows a limit of detection of 0.47 µM and a sensitivity of 27.2 µA µM−1 cm−2 towards H2O2. The outcomes of this study demonstrate the efficacy of Te nanosheets as a promising material for nonenzymatic H2O2 detection in urine samples. The simplicity and cost-effectiveness of the hydrothermal synthesis process, coupled with the notable electrochemical performance of the Te/GC electrode, highlight the potential of Te nanosheets in the development of a robust sensing platform. This research contributes to the ongoing efforts to enhance our capabilities in monitoring and detecting H2O2, fostering advancements in environmental, biomedical, and industrial applications. 

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3. Continuous Real-Time Detection of Serotonin Using an Aptamer-Based Electrochemical Biosensor

   https://doi.org/10.3390/bios13110983  

   Ahmad, Habib_M N; Andrade, Arturo; Song, Edward (November 2023, Biosensors)

   Serotonin (5-HT) is a critical neurotransmitter involved in many neuronal functions, and 5-HT depletion has been linked to several mental diseases. The fast release and clearance of serotonin in the extracellular space, low analyte concentrations, and a multitude of interfering species make the detection of serotonin challenging. This work presents an electrochemical aptamer-based biosensing platform that can monitor 5-HT continuously with high sensitivity and selectivity. Our electrochemical sensor showed a response time of approximately 1 min to a step change in the serotonin concentration in continuous monitoring using a single-frequency EIS (electrochemical impedance spectroscopy) technique. The developed sensing platform was able to detect 5-HT in the range of 25–150 nM in the continuous sample fluid flow with a detection limit (LOD) of 5.6 nM. The electrochemical sensor showed promising selectivity against other species with similar chemical structures and redox potentials, including dopamine (DA), norepinephrine (NE), L-tryptophan (L-TP), 5-hydroxyindoleacetic acid (5-HIAA), and 5-hydroxytryptophan (5-HTP). The proposed sensing platform is able to achieve high selectivity in the nanomolar range continuously in real-time, demonstrating the potential for monitoring serotonin from neurons in organ-on-a-chip or brain-on-a-chip-based platforms. 

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4. Adsorption Kinetic Model Predicts and Improves Reliability of Electrochemical Serotonin Detection

   https://doi.org/10.3390/mps6010006  

   Chapin, Ashley Augustiny; Han, Jinjing; Ghodssi, Reza (February 2023, Methods and Protocols)

   Serotonin (5-HT) is a neurotransmitter involved in many biophysiological processes in the brain and in the gastrointestinal tract. Electrochemical methods are commonly used to quantify 5-HT, but their reliability may suffer due to the time-dependent nature of adsorption-limited 5-HT detection, as well as electrode fouling over repeated measurements. Mathematical characterization and modeling of adsorption-based electrochemical signal generation would improve reliability of 5-HT measurement. Here, a model was developed to track 5-HT electrode adsorption and resulting current output by combining Langmuir adsorption kinetic equations and adsorption-limited electrochemical equations. 5-HT adsorption binding parameters were experimentally determined at a carbon-nanotube coated Au electrode: KD = 7 × 10−7 M, kon = 130 M−1 s−1, koff = 9.1 × 10−5 s−1. A computational model of 5-HT adsorption was then constructed, which could effectively predict 5-HT fouling over 50 measurements (R2 = 0.9947), as well as predict electrode responses over varying concentrations and measurement times. The model aided in optimizing the measurement of 5-HT secreted from a model enterochromaffin cell line—RIN14B—minimizing measurement time. The presented model simplified and improved the characterization of 5-HT detection at the selected electrode. This could be applied to many other adsorption-limited electrochemical analytes and electrode types, contributing to the improvement of application-specific modeling and optimization processes. 

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5. A Fluidics-Based Biosensor to Detect and Characterize Inhibition Patterns of Organophosphate to Acetylcholinesterase in Food Materials

   https://doi.org/10.3390/mi12040397  

   Pham, Dang Song; Nguyen, Xuan Anh; Marsh, Paul; Chu, Sung Sik; Lau, Michael P.; Nguyen, Anh H.; Cao, Hung (April 2021, Micromachines)

   A chip-based electrochemical biosensor is developed herein for the detection of organophosphate (OP) in food materials. The principle of the sensing platform is based on the inhibition of dimethoate (DMT), a typical OP that specifically inhibits acetylcholinesterase (AChE) activity. Carbon nanotube-modified gold electrodes functionalized with polydiallyldimethylammonium chloride (PDDA) and oxidized nanocellulose (NC) were investigated for the sensing of OP, yielding high sensitivity. Compared with noncovalent adsorption and deposition in bovine serum albumin, bioconjugation with lysine side chain activation allowed the enzyme to be stable over three weeks at room temperature. The total amount of AChE was quantified, whose activity inhibition was highly linear with respect to DMT concentration. Increased incubation times and/or DMT concentration decreased current flow. The composite electrode showed a sensitivity 4.8-times higher than that of the bare gold electrode. The biosensor was challenged with organophosphate-spiked food samples and showed a limit of detection (LOD) of DMT at 4.1 nM, with a limit of quantification (LOQ) at 12.6 nM, in the linear range of 10 nM to 1000 nM. Such performance infers significant potential for the use of this system in the detection of organophosphates in real samples. 

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