Portable Mini-Electrochemical\nCell: Integrating Microsampling\nand Micro-Electroanalysis for Multipurpose On-Site Nitrite Sensing

In modern analytical chemistry, one of the primary goals\nis to\ndevelop miniaturized, easy-to-use sensing tools, particularly those\nwith multitasking capabilities. In this work, we designed a mini-voltammetric\ncell that integrates a modified Au microelectrode (Au/Au NPs as the\nworking electrode) and an Ag/AgCl reference electrode installed within\na micropipette tip. This combined tool not only enables portable and\non-site microvolume samplingrequiring only a microvolume (around\n20–40 μL) or a single dropletbut also facilitates\ndirect micro-electroanalysis in a short time. To evaluate its capabilities,\nthe mini-voltammetric cell was optimized for trace analysis of nitrite\nions and demonstrated linear responses in the ranges of 20–150\n and 150–1200 μM, with an acceptable limit of detection\n(LOD) of 18.40 μM, meeting both WHO and EPA standards for nitrite\nlevels. Furthermore, it exhibited high selectivity, stability (up\nto 36 continuous measurements with only a 3.24% signal drop), and\nacceptable repeatability (RSD of 2.98%, <i>n</i> = 15).\nThe analytical performance of this miniaturized tool was further assessed\nthrough the sampling and detection of nitrite ions in various real\nsamples with different matrixes: (1) urine samples, for the fast diagnosis\nof urinary tract infections (UTIs), where nitrite ions are detected\nas biomarkers of UTIs; (2) river water polluted with agricultural\nwaste, where nitrite ions serve as pollutants from nitrogen fertilizers;\nand (3) on the hands and in forensic investigations, where nitrite\nions are detected as indicators of gunshot residue, crucial in crime\nscene examinations. All real samples were analyzed using the standard\naddition method and recovery tests, yielding acceptable results. Additionally,\nthe proposed mini-analytical tool was evaluated for its sustainability\nand applicability using two recognized metrics: The Green Analytical\nProcedure Index (GAPI) and the Blue Applicability Grade Index (BAGI).\nThe results confirmed that this method can be classified as both a\ngreen analytical method and highly applicable. Finally, the practical\nresults demonstrated that the proposed miniaturized electroanalytical\ntool exhibits reliable performance, high sensitivity and selectivity,\nand fast response in the on-site microanalysis of nitrite, without\nthe need for any reagents or complex sampling steps, across different\nreal samples (such as clinical, forensic, and environmental samples).\nWe believe the proposed mini-voltammetric cell could be used as an\nalternative to current detection methods, and with suitable modifications,\nit could be adapted for the microanalysis of other applications and\n(bio)targets with small volumes in the near future.