Dopamine (DA) is a vital neurotransmitter, and accurate detection of its concentration is critical for both clinical diagnostics and neuroscience research. Due to its electrochemical activity, DA is commonly detected using electrochemical methods, which are favored for their simplicity, fast response time, and suitability for in vivo analysis. In this work, a highly sensitive DA electrochemical sensor was developed using an Au@MoS₂ composite, created by modifying molybdenum disulfide (MoS₂) nanosheets with gold nanoparticles through HAuCl₄ reduction, and it was aimed at enhancing DA adsorption and improving detection performance. Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), Energy Dispersive Spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray Diffraction (XRD) confirmed the successful synthesis of Au@MoS₂ and the uniform distribution of gold nanoparticles across the MoS₂ nanosheets. Then, the electrochemical characterization demonstrated that the Au@MoS₂/GCE exhibited distinct oxidation peaks in a 10 μmol·L^-1 DA solution, with significantly enhanced electrochemical activity compared to both unmodified GCE and pristine MoS₂. Furthermore, differential pulse voltammetry (DPV) further revealed a strong linear relationship between DA concentration and the current response in the range of 800 nmol·L^-1 to 10 μmol·L^-1, with a low detection limit (LOD) of 78.9 nmol·L^-1 (S/N=3). Additionally, the sensor showed excellent selectivity against other interfering substances. Moreover, the laser-induced Au@MoS₂ (LIAu@MoS₂), with its abundance of negatively charged surface defects, enabled the ultra-sensitive detection of the ultra-low concentrations of DA. In conclusion, the successfully fabricated Au@MoS₂ based sensor offers advantages such as low cost, ease of operation, and scalability, making it a promising candidate for biosensing applications due to its enhanced DA detection capabilities.

Detection of target analytes at low concentrations is significant in various fields, including pharmaceuticals, healthcare, and environmental protection. Theophylline (TP), a natural alkaloid used as a bronchodilator to treat respiratory disorders such as asthma, bronchitis, and emphysema, has a narrow therapeutic window with a safe plasma concentration ranging from 55.5-111.0 µmol·L^-1 in adults. Accurate monitoring of TP levels is essential because too low or too high can cause serious side effects. In this regard, non-enzymatic electrochemical sensors offer a practical solution with rapidity, portability, and high sensitivity. This article aims to provide a comprehensive review of the recent developments of non-enzymatic electrochemical sensors for TP detection, highlighting the basic principles, electro-oxidation mechanisms, catalytic effects, and the role of modifying materials on electrode performance. Carbon-based electrodes such as glassy carbon electrodes (GCEs), carbon paste electrodes (CPEs), and carbon screen-printed electrodes (SPCEs) have become the primary choices for non-enzymatic sensors due to their chemical stability, low cost, and flexibility in modification. This article identifies the significant contribution of various modifying materials, including nanomaterials such as carbon nanotubes (CNTs), graphene, metal oxides, and multi-element nanocomposites. These modifications enhance sensors' electron transfer, sensitivity, and selectivity in detecting TP at low concentrations in complex media such as blood plasma and pharmaceutical samples. The electro-oxidation mechanism of TP is also discussed in depth, emphasizing the hydroxyl and carbonyl reaction pathways strongly influenced by pH and electrode materials. These mechanisms guide the selection of the appropriate electrode material for a particular application. The main contribution of this article is to identify superior modifying materials that can improve the performance of non-enzymatic electrochemical sensors. In a recent study, the combination of multi-element nanocomposites based on titanium dioxide(TiO₂), CNTs, and gold nanoparticles(AuNPs) resulted in the lowest detection limit of 3 × 10^-5 µmol·L^-1, reflecting the great potential of these materials for developing high-performance electrochemical sensors. The main conclusion of this article is the importance of a multidisciplinary approach in electrode material design to support the sensitivity and selectivity of TP detection. In addition, there is still a research gap in understanding TP's more detailed oxidation mechanism, especially under pH variations and complex environments. Therefore, further research on electrode modification and analysis of the TP oxidation mechanism are urgently needed to improve the accuracy and stability of the sensor while expanding its applications in pharmaceutical monitoring and medical diagnostics. By integrating various innovative materials and technical approaches, this review is expected to be an essential reference for developing efficient and affordable non-enzymatic electrochemical sensors.

Metal-organic framework (MOF) nanostructures have emerged as a prominent class of materials in the advancement of electrochemical sensors. The rational design of bimetallic MOF-functionalized microelectrode is of importance for improving the electrochemical performance but still in great challenge. In this work, the bimetallic FeCo-MOF nanostructures were assembled onto a gold disk ultramicroelectrode (Au UME, 5.2 µm in diameter) via an in-situ electrodeposition method, which enhanced the sensitive detection of epinephrine (EP). The in-situ electrodeposited FeCo-MOF exhibited a characteristic nanoflower-like morphology and was uniformly dispersed on the Au UME. The FeCo-MOF/Au UME demonstrated excellent electrochemical performance on the detection of EP with a high sensitivity of 36.93 μA·μmol^-1·L·cm^-2 and a low detection limit of 1.28 μmol·L^-1. It can be attributed to the nonlinear diffusion of EP onto the ultra-micro working substrate, coupled with synergistical catalytic activity of the bimetallic Fe, Co within MOF structure. Furthermore, the FeCo-MOF/Au UME has been successful applied to the analysis of EP in human serum samples, yielding high recovery rates. These results not only contribute to the expansion of the research area of electrochemical sensors, but also provide novel insights and directions into the development of high-performance MOF-based electrochemical sensors.