Department of Inorganic and Analytical Chemistry , University of Geneva , Quai Ernest-Ansermet 30 , CH-1211 Geneva , Switzerland.
ACS Sens. 2019 Dec 27;4(12):3093-3101. doi: 10.1021/acssensors.9b01802. Epub 2019 Dec 5.
Colorimetric measurements by image analysis, giving RGB or HSV data, have become commonplace with optical indicator-based assays and as a readout for paper-based analytical devices (PADs). Yet, most works on PADs tend to ignore the quantitative relationship between color data and concentration, which may hamper their establishment as analytical devices and make it difficult to properly understand chemical or biological reactions on the paper substrate. This Perspective Article discusses how image color data are computed into colorimetric absorbance values that correlate linearly to dye concentration and compare well to traditional spectrophotometry. Thioflavin T (ThT), Neutral Red (NR), and Orange IV are used here as model systems. Absorbance measurements in solution correlate well to image data (and Beer's law) from the color channel of relevance if the gamma correction normally used to render the picture more natural to the human eye is removed. This approach also allows one to correct for color cast and variable background color, which may otherwise limit quantitation in field measurements. Reflectance measurements on paper color spots are equally found to correlate quantitatively between spectroscopy and imaging devices. In this way, deviations from Beer's law are identified that are explained with dye interactions on the paper substrate.
基于光学指示剂的分析物检测和纸基分析器件（PAD）作为读出器，比色测量通过图像分析得到 RGB 或 HSV 数据，已经变得很常见。然而，大多数关于 PAD 的研究往往忽略了颜色数据与浓度之间的定量关系，这可能会妨碍它们作为分析器件的建立，并使得难以正确理解纸质基底上的化学或生物反应。本文从讨论如何将图像颜色数据计算为与染料浓度呈线性相关的比色吸光度值开始，这与传统分光光度法进行了比较。本文使用了硫黄素 T（ThT）、中性红（NR）和橙色 IV 作为模型系统。如果去除通常用于使图像更自然地呈现给人眼的伽马校正，则溶液中的吸光度测量与相关颜色通道的图像数据（和比尔定律）非常吻合。这种方法还可以校正颜色偏差和可变背景颜色，否则可能会限制现场测量的定量。还发现，纸基色点的反射率测量在光谱仪和成像设备之间同样具有定量相关性。通过这种方式，可以识别出偏离比尔定律的情况，并解释在纸质基底上的染料相互作用。
