Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, United States.
School of Chemical Engineering and Technology, Key Laboratory of Advanced Materials of Tropical Island Resources of Ministry of Education, Hainan University, Haikou, Hainan 570228, China.
Anal Chem. 2021 Oct 12;93(40):13694-13702. doi: 10.1021/acs.analchem.1c03394. Epub 2021 Sep 30.
Fluorescence-based sensing in droplet microfluidics requires small sample volumes, allows for high-throughput assays, and does not suffer from photobleaching as each flowing sensor is only scanned one time. In this paper, we report a selective and sensitive fluorescence-based ion-sensing methodology in droplet microfluidics using a T-junction PDMS chip. The oil stream is doped with sensor ingredients including an ionophore, a cation exchanger, and a permanently cationic fluorophore as the optical reporter. Electrolyte cations from the aqueous sample are extracted into oil segments and displace the cationic dyes into aqueous droplets. Laser-induced fluorescence of the two immiscible phases is collected alternately, which is in clear contrast to most other ion-selective optode configurations such as nanoparticle suspensions that rely on mixed optical signals of two phases. The cation exchanger, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, is found to dramatically enhance the dye emission in the nonpolar sensing oil by preventing ion-pairing interactions and aggregations of the dye molecules, providing new insights into the mechanism of cationic dye-based ion sensors. The high dye brightness allows us to use low concentrations of sensing chemicals (e.g., 10 μM) in the oil and attain high sensitivity for detection of ions in an equal volume of sample. Using valinomycin as the ionophore and methylene blue as the dye, K is detected with a response time of ∼11 s, a logarithmic linear range of 10 to 10 M, a 20-fold total fluorescence response, >1000-fold selectivity against other electrolyte cations, and negligible cross-sensitivity toward the sample pH. The K concentration in untreated and undiluted whole blood and sweat samples is successfully determined by this microfluidic sensing method without optical interference from the droplet sample to the sensing oil. Detection of other ionic analytes can be achieved using the corresponding ionophores.
在液滴微流控中基于荧光的传感需要小的样品体积，允许高通量测定，并且不会遭受由于每个流动传感器仅被扫描一次而导致的光漂白。在本文中，我们报告了在使用 T 型 PDMS 芯片的液滴微流控中基于荧光的选择性和灵敏的离子传感方法。油相被掺杂有传感器成分，包括离子载体、阳离子交换剂和作为光学报告器的永久性阳离子荧光染料。来自水性样品的电解质阳离子被萃取到油段中，并将阳离子染料置换到水性液滴中。交替地收集两个不混溶相的激光诱导荧光，这与大多数其他离子选择性光导纤维配置形成鲜明对比，后者依赖于两相的混合光学信号，例如纳米颗粒悬浮液。发现四[3,5-双（三氟甲基）苯基]硼酸盐阳离子交换剂通过防止染料分子的离子对相互作用和聚集，极大地增强了非极性传感油中的染料发射，为阳离子染料基离子传感器的机制提供了新的见解。高染料亮度使我们能够在油中使用低浓度的传感化学品（例如 10 μM），并在相同体积的样品中实现对离子的高灵敏度检测。使用缬氨霉素作为离子载体和亚甲蓝作为染料，K 的检测响应时间约为 11 s，对数线性范围为 10 到 10 M，总荧光响应增加 20 倍，对其他电解质阳离子的选择性超过 1000 倍，并且对样品 pH 的交叉敏感性可忽略不计。未经过处理和未稀释的全血和汗液样品中的 K 浓度可以通过这种微流控传感方法成功确定，而不会对感测油产生液滴样品的光学干扰。可以使用相应的离子载体来检测其他离子分析物。
