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.

中文翻译：

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便携式微型电化学池：集成微量采样和微量电分析，用于多用途现场亚硝酸盐传感


在现代分析化学中，主要目标之一是开发小型化、易于使用的传感工具，尤其是那些具有多任务处理能力的工具。在这项工作中，我们设计了一个微型伏安电池，它集成了改性的 Au 微电极（Au/Au NPs 作为工作电极）和安装在微量移液器吸头内的 Ag/AgCl 参比电极。这种组合工具不仅可以实现便携式和现场微量采样（仅需微量（约 20–40 μL）或单个液滴），还有助于在短时间内进行直接微量电分析。为了评估其功能，对微型伏安池进行了优化，用于亚硝酸盐离子的痕量分析，并在 20–150 μM 和 150–1200 μM 范围内表现出线性响应，可接受的检测限 （LOD） 为 18.40 μM，符合 WHO 和 EPA 亚硝酸盐水平标准。此外，它还表现出高选择性、稳定性（多达 36 次连续测量，仅 3.24% 的信号下降）和可接受的重复性（RSD 为 2.98%，n = 15）。通过对具有不同基质的各种真实样品中的亚硝酸盐离子进行采样和检测，进一步评估了这种小型化工具的分析性能：（1） 尿液样本，用于快速诊断尿路感染 （UTI），其中亚硝酸盐离子被检测为 UTI 的生物标志物;（2） 被农业废弃物污染的河水，其中亚硝酸盐离子是氮肥的污染物;（3） 在手上和法医调查中，亚硝酸盐离子被检测到作为枪击残留物的指标，这在犯罪现场检查中至关重要。使用标准加入法和回收率测试对所有真实样品进行分析，得到可接受的结果。 此外，使用两个公认的指标评估了拟议的小型分析工具的可持续性和适用性：绿色分析程序指数 （GAPI） 和蓝色适用性等级指数 （BAGI）。结果证实，该方法既可以归类为绿色分析方法，又具有高度适用性。最后，实际结果表明，所提出的小型化电分析工具在亚硝酸盐的现场微量分析中表现出可靠的性能、高灵敏度和选择性以及快速响应，无需任何试剂或复杂的采样步骤，跨越不同的真实样品（如临床、法医和环境样品）。我们相信所提出的微型伏安池可以用作当前检测方法的替代品，并且通过适当的修改，它可以在不久的将来适用于其他应用和小体积（生物）靶标的微量分析。