Droplet evaporation has previously been used as a concentration enrichment strategy; however, the measurement technique of choice requires quantification in rather large volumes. Electrochemistry has recently emerged as a method to robustly probe volumes even down to the attoliter (10^–18 L) level. We present a concentration enrichment strategy based on the dissolution of a microdroplet placed on the surface of a Au ultramicroelectrode (radius ∼ 6.25 μm). By precisely positioning a 1,2-dichloroethane microdroplet onto the ultramicroelectrode with a microinjector, we are able to track the droplet’s behavior optically and electrochemically. Because the droplet spontaneously dissolves over time, given the relative solubility of 1,2-dichloroethane in the water continuous phase, the change in volume with time enriches the concentration of the redox probe (Cp₂*(Fe)^II) in the droplet. We demonstrate robust electrochemical detection down to sub-nM (800 pM) concentrations of Cp₂*(Fe)^II. For this droplet, 800 pM constitutes only about 10⁶ molecules. We extend the strategy in a single-blind study to determine unknown concentrations, emphasizing the promise of the new methodology. These results take voltammetric quantification easily to the sub-μM regime.

中文翻译：

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溶解微滴的浓度富集：实现亚纳摩尔电分析

液滴蒸发以前被用作浓缩浓缩策略；然而，所选择的测量技术需要相当大的体积进行量化。电化学最近成为一种可以稳健地探测体积甚至低至阿托升 (10 ^–18 L) 水平的方法。我们提出了一种基于金超微电极（半径约 6.25 μm）表面上微滴溶解的浓度富集策略。通过使用显微注射器将 1,2-二氯乙烷微滴精确定位到超微电极上，我们能够以光学和电化学方式跟踪液滴的行为。由于液滴随着时间的推移自发溶解，考虑到 1,2-二氯乙烷在水连续相中的相对溶解度，体积随时间的变化丰富了液滴中氧化还原探针 (Cp ₂ *(Fe) ^{II ) 的浓度。我们展示了对 Cp} ₂ *(Fe) ^II浓度低至亚 nM (800 pM) 浓度的稳健电化学检测。对于该液滴，800 pM 仅构成约 10 ^{6 个}分子。我们在单盲研究中扩展了该策略以确定未知浓度，强调了新方法的前景。这些结果使伏安定量可以轻松达到亚μM范围。