In Situ pH Measurements of Individual Levitated Microdroplets Using Aerosol Optical Tweezers
In Situ pH Measurements of Individual Levitated Microdroplets Using Aerosol Optical Tweezers
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DOI：
10.1021/acs.analchem.9b04152
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发表时间：
2020-01-07
影响因子：
7.4
通讯作者：
Sullivan, Ryan C.
中科院分区：
文献类型：
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作者：
Boyer, Hallie C.;Gorkowski, Kyle;Sullivan, Ryan C.
微尺度反应环境的pH值控制着许多物理化学过程，需要实时pH微探针。我们提出了高度准确的实时pH值测量的微液滴使用气溶胶光镊（AOT）和分析的回音壁模式（WGM）中包含的腔增强拉曼光谱。通过对3.3 min内以0.5 Hz采集的拉曼帧求平均值，可获得皮升液滴pH值在+/- 0.03至0.06范围内的非线性。通过结合AOT方法独特提供的两个独立测量值，可实现pH值测定的高精度：来自自发拉曼光谱的阴离子浓度比，和总溶质浓度从折射率检索从受激腔增强拉曼光谱的WGM分析。使用硫酸氢钠水溶液体系，可在-0.36至0.76的范围内测定pH值。该技术能够直接测量单个微粒所经历的pH依赖性化学和物理变化，并探索pH在受限微环境的化学行为中的作用。
The pH of microscale reaction environments controls numerous physicochemical processes, requiring a real-time pH microprobe. We present highly accurate real-time pH measurements of microdroplets using aerosol optical tweezers (AOT) and analysis of the whispering gallery modes (WGMs) contained in the cavity-enhanced Raman spectra. Uncertainties ranging from +/- 0.03 to 0.06 in pH for picoliter droplets are obtained through averaging Raman frames acquired at 0.5 Hz over 3.3 min. The high accuracy in pH determination is achieved by combining two independent measurements uniquely provided by the AOT approach: the anion concentration ratio from the spontaneous Raman spectra, and the total solute concentration from the refractive index retrieved from WGM analysis of the stimulated cavity-enhanced Raman spectra. pH can be determined over a range of -0.36 to 0.76 using the aqueous sodium bisulfate system. This technique enables direct measurements of pH-dependent chemical and physical changes experienced by individual microparticles and exploration of the role of pH in the chemical behavior of confined microenvironments.