Design Aspects for Portable LED-Based Colorimetric Characterisation Systems Targeting Liquid Analytes

Abstract

Colorimetric characterisation systems based on LEDs and RBG sensors are straightforward to implement, are highly integrable allowing for portable measurement systems and can be constructed using widespread and affordable components. They have already proved to be a satisfactory solution in several applications related to chemical analysis. In this paper, we present an RGB sensor-based prototype for colorimetric characterisation, which can accommodate cuvettes with optical paths of 10 mm and 40 mm. We assessed the impact of experimental condition parameters such as the variability of the analyte volume in the cuvette, as well as the presence of floating particles or deposits at the bottom of the cuvette. While these would not impact the result given by a spectrophotometer that generally has a directional light source, they must be considered in LED/RGB sensor analysers in which the light path is not tightly controlled. We demonstrated that there is a minimal sensor height above the bottom of the cuvette and a minimal analyte level (both depending on the prototype optical path length) above which the analyte volume and the presence of floating particles and deposits have no impact on the prototype output signal. Finally, based on these results, we proposed a test method for a quick dye-displacement assay, in which the reagent is a dye-loaded molecularly imprinted polymer that is poured directly into a cuvette.