Due to the fast diffusion, small molecules such as hydronium ions (H₃O⁺) are expected to be homogeneously distributed, even close to the site-of-origin. Given the importance of H₃O⁺ in numerous processes, it is surprising that H₃O⁺ concentration ([H₃O⁺]) has yet to be profiled near its generation site with nanometer resolution. Here, we innovated a single-molecule method to probe [H₃O⁺] in nanometer proximity of individual alkaline phosphatases. We designed a mechanophore with cytosine (C)–C mismatch pairs in a DNA hairpin. Binding of H₃O⁺ to these C–C pairs changes mechanical properties, such as stability and transition distance, of the mechanophore. These changes are recorded in optical tweezers and analyzed in a multivariate fashion to reduce the stochastic noise of individual mechanophores. With this method, we found [H₃O⁺] increases in the nanometer vicinity of an active alkaline phosphatase, which supports that the proximity effect is the cause for increased rates in cascade enzymatic reactions.

中文翻译：

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单分子机械化学pH值检测揭示了碱性磷酸酶产生的Hydro的邻近效应

由于快速扩散，预计诸如水合氢离子（H ₃ O ⁺）的小分子将均匀分布，甚至接近起源位置。考虑到H ₃ O ⁺在许多过程中的重要性，令人惊讶的是，H ₃ O ^+的浓度（[H ₃ O ⁺ ]）尚未在其生成位置附近以纳米级解析。在这里，我们创新了一种单分子方法，可以在单个碱性磷酸酶的纳米附近探测[H ₃ O ⁺ ]。我们设计了在DNA发夹中具有胞嘧啶（C）–C错配对的机制。H ₃ O ^+的结合这些C–C对的变化会改变机械基团的机械性能，例如稳定性和过渡距离。这些变化记录在光镊中，并以多变量方式进行分析，以减少各个机械体的随机噪声。通过这种方法，我们发现[H ₃ O ⁺ ]在活性碱性磷酸酶的纳米附近增加，这表明邻近效应是级联酶促反应速率增加的原因。