Nano-Science Center and Department of Chemistry , University of Copenhagen , Universitetsparken 5 , 2100 Copenhagen Ø , Denmark.
FRS-systems ApS , Hovedgaden 20 , 4621 Gadstrup , Denmark.
ACS Sens. 2019 Mar 22;4(3):764-773. doi: 10.1021/acssensors.9b00148. Epub 2019 Feb 28.
Since Sørensen and Bjerrum defined the pH scale, we have relied on two methods for determining pH, the colorimetric or the electrochemical. For pH electrodes, calibration is easy as a linear response is observed in the interesting pH range from 1 to ∼12. For colorimetric sensors, the response follows the sigmoidal Bjerrum diagram of an acid-base equilibrium. Thus, calibration of colorimetric sensors is more complex. Here, seven pH responsive fluorescent dyes based on the same diazaoxatriangulenium (DAOTA) fluorophore linked to varying receptor groups were prepared. Photoinduced electron transfer (PeT) quenching from appended aniline or phenol receptors generated the pH response of the DAOTA dyes, and the position of the p K value of the dye was tuned using the Hammett relationship as a guideline. The fluorescence intensity of the dyes in a sol-gel matrix environment was measured as a function of pH in universal buffer, and it was found that the dyes behave as perfect pH responsive probes under these conditions. The response of optical pH sensors is nonlinear and was found to be limited to 2-3 pH units for a precision of 0.01 pH unit. As sensors with a broader sensitivity range can be achieved by mixing multiple dyes with different p K values, mixtures of dyes in solution were investigated, and a broad range pH sensor with a precision of 0.006 pH units over a range of 3.6 pH units was demonstrated. Further, approximating the sensor response as linear was considered, and a limiting precision for this approach was determined. As the responses of the pH responsive DAOTA dyes were found to be ideally sigmoidal and as the six dyes were shown to have p K values scattered over a range from ∼2 to ∼9, this allows for design of a broad range optical pH sensor in the pH range from 1 to 10. This hypothesis was tested using quaternary mixtures of the different DAOTA dyes, and these were found to behave as a direct sum of the individual components. Thus, while linear calibration is limited to a precision of 0.02 in a range of 2-3 pH units, calibration using ideal sigmoidal functions is possible in the range of 1-10 with a precision better than 0.01, and as good as 0.002 pH units.
自 Sørensen 和 Bjerrum 定义了 pH 标度以来，我们一直依赖两种方法来确定 pH 值，即比色法或电化学法。对于 pH 电极，由于在 1 到 ∼12 的有趣 pH 范围内观察到线性响应，因此校准很容易。对于比色传感器，响应遵循酸碱平衡的 Bjerum 图。因此，比色传感器的校准更为复杂。在这里，我们制备了七种基于相同的二氮杂氧杂环戊烯 (DAOTA) 荧光团并连接到不同受体基团的 pH 响应荧光染料。通过附加苯胺或苯酚受体的光诱导电子转移 (PeT) 猝灭产生了 DAOTA 染料的 pH 响应，并且使用 Hammett 关系作为指导来调整染料的 pK 值的位置。在溶胶-凝胶基质环境中测量染料的荧光强度作为 pH 的函数，在通用缓冲液中发现这些染料在这些条件下表现为完美的 pH 响应探针。光学 pH 传感器的响应是非线性的，并且发现对于 0.01 pH 单位的精度，其限制在 2-3 pH 单位内。由于通过混合具有不同 pK 值的多种染料可以实现具有更宽灵敏度范围的传感器，因此研究了溶液中染料的混合物，并证明了在 3.6 pH 单位的范围内具有 0.006 pH 单位精度的宽范围 pH 传感器。此外，还考虑了将传感器响应近似为线性，并确定了这种方法的限制精度。由于发现 pH 响应的 DAOTA 染料的响应理想地呈 sigmoidal 形状，并且由于六种染料的 pK 值分布在 ∼2 到 ∼9 的范围内，因此可以设计在 1 到 10 pH 范围内的宽范围光学 pH 传感器。通过使用不同的 DAOTA 染料的四元混合物对该假设进行了测试，发现这些混合物的行为类似于各个成分的直接和。因此，虽然线性校准在 2-3 pH 单位的范围内精度限于 0.02，但使用理想的 sigmoidal 函数可以在 1-10 的范围内进行校准，精度优于 0.01，精度优于 0.002 pH 单位。
