Electrochemical Diagnosis of Urinary Tract Infection Using Boron-Doped Diamond Electrodes

Brain-Computer Interface and Electrochemical Sensor Based on Boron-Nitrogen Co-Doped Graphene-Diamond Microelectrode for EEG and Dopamine Detection

The simultaneous detection of electroencephalography (EEG) signals and neurotransmitter levels plays an important role as biomarkers for the assessment and monitoring of emotions and cognition. This paper describes the development of boron and nitrogen codoped graphene-diamond (BNGrD) microelectrodes with a diameter of only 200 μm for sensing EEG signals and dopamine (DA) levels, which have been developed for the first time. The optimized BNGrD microelectrode responded sensitively to both EEG and DA signals, with a signal-to-noise ratio of 9 dB for spontaneous EEG signals and a limit of detection as low as 124 nM for DA. Furthermore, the BNGrD microelectrodes demonstrate excellent repeatability, reproducibility, and stability for the detection of EEG and dopamine. These results indicate that the BNGrD microelectrode creates suitable conditions for establishing a correlation between the EEG signals and neurotransmitters. A flexible printed circuit board with BNGrD microelectrodes for an eight-channel EEG headband, portable EEG collector, and light stimulation glasses are designed. The self-designed EEG collector adopts a split design strategy of digital and analog signal modules and uses miniaturized impedance-matched BNGrD microelectrodes, which effectively reduce the noise of the electrophysiological signals. The BNGrD microelectrode-based portable EEG/electrochemical analysis system detects EEG signals and DA levels in a noninvasive and minimally invasive manner and has application prospects in remote online diagnosis and treatment of patients with emotional and cognition-related diseases.

Portable Mini-Electrochemical Cell: Integrating Microsampling and Micro-Electroanalysis for Multipurpose On-Site Nitrite Sensing

In modern analytical chemistry, one of the primary goals is to develop miniaturized, easy-to-use sensing tools, particularly those with multitasking capabilities. In this work, we designed a mini-voltammetric cell that integrates a modified Au microelectrode (Au/Au NPs as the working electrode) and an Ag/AgCl reference electrode installed within a micropipette tip. This combined tool not only enables portable and on-site microvolume sampling─requiring only a microvolume (around 20-40 μL) or a single droplet─but also facilitates direct micro-electroanalysis in a short time. To evaluate its capabilities, the mini-voltammetric cell was optimized for trace analysis of nitrite ions and demonstrated linear responses in the ranges of 20-150 and 150-1200 μM, with an acceptable limit of detection (LOD) of 18.40 μM, meeting both WHO and EPA standards for nitrite levels. Furthermore, it exhibited high selectivity, stability (up to 36 continuous measurements with only a 3.24% signal drop), and acceptable repeatability (RSD of 2.98%, n = 15). The analytical performance of this miniaturized tool was further assessed through the sampling and detection of nitrite ions in various real samples with different matrixes: (1) urine samples, for the fast diagnosis of urinary tract infections (UTIs), where nitrite ions are detected as biomarkers of UTIs; (2) river water polluted with agricultural waste, where nitrite ions serve as pollutants from nitrogen fertilizers; and (3) on the hands and in forensic investigations, where nitrite ions are detected as indicators of gunshot residue, crucial in crime scene examinations. All real samples were analyzed using the standard addition method and recovery tests, yielding acceptable results. Additionally, the proposed mini-analytical tool was evaluated for its sustainability and applicability using two recognized metrics: The Green Analytical Procedure Index (GAPI) and the Blue Applicability Grade Index (BAGI). The results confirmed that this method can be classified as both a green analytical method and highly applicable. Finally, the practical results demonstrated that the proposed miniaturized electroanalytical tool exhibits reliable performance, high sensitivity and selectivity, and fast response in the on-site microanalysis of nitrite, without the need for any reagents or complex sampling steps, across different real samples (such as clinical, forensic, and environmental samples). We believe the proposed mini-voltammetric cell could be used as an alternative to current detection methods, and with suitable modifications, it could be adapted for the microanalysis of other applications and (bio)targets with small volumes in the near future.

Constructing a Hydrophilic Microsensor for High-Antifouling Neurotransmitter Dopamine Sensing

Real-time sensing of dopamine is essential for understanding its physiological function and clarifying the pathophysiological mechanism of diseases caused by impaired dopamine systems. However, severe fouling from nonspecific protein adsorption, for a long time, limited conventional neural recording electrodes concerning recording stability. This study reported a high-antifouling nanocrystalline boron-doped diamond microsensor grown on a carbon fiber substrate. The antifouling properties of this diamond sensor were strongly related to the grain size (i.e., nanocrystalline and microcrystalline) and surface terminations (i.e., oxygen and hydrogen terminals). Experimental observations and molecular dynamics calculations demonstrated that the oxygen-terminated nanocrystalline boron-doped diamond microsensor exhibited enhanced antifouling characteristics against protein adsorption, which was attributed to the formation of a strong hydration layer as a physical and energetic barrier that prevents protein adsorption on the surface. This finally allowed for in vivo monitoring of dopamine in rat brains upon potassium chloride stimulation, thus presenting a potential solution for the design of next-generation antifouling neural recording sensors. Experimental observations and molecular dynamics calculations demonstrated that the oxygen-terminated nanocrystalline boron-doped diamond (O-NCBDD) microsensor exhibited ultrahydrophilic properties with a contact angle of 4.9°, which was prone to forming a strong hydration layer as a physical and energetic barrier to withstand the adsorption of proteins. The proposed O-NCBDD microsensor exhibited a high detection sensitivity of 5.14 μA μM-1 cm-2 and a low detection limit of 25.7 nM. This finally allowed for in vivo monitoring of dopamine with an average concentration of 1.3 μM in rat brains upon 2 μL of potassium chloride stimulation, thus presenting a potential solution for the design of next-generation antifouling neural recording sensors.