modeling the optimized ratio of fluorophores: a step towards enhancing the sensitivity of ratiometric probes

Abstract: in recent decades, ratiometric fluorescent probes have attracted considerable interest due to their potential for visual qualitative/quantitative detection in a range of applications [1]. in ratiometric strategy, mixing two or more fluorophore provides an intermediate emission color. in some designs, some fluorophores are introduced as internal standards, while in others they are analyte-sensitive. following the interaction of the target with one or even several fluorophores in the probe, the fluorescence emission of the probes changes due to the quenching or enhancing phenomena, altering the emission color of the probe. in order to provide maximum variation in emission color of the probe in the presence of the target, the ratio of the fluorophores is required to be optimized. a number of experiments are required though [2]. despite a lot of efforts in optimization of fluorophores, it is still remains an elusive task to estimate an accurate and low-cost method to obtain a real optimized condition of mixing fluorophores. the visual monitoring of the targets in ratiometric probes relies on acquiring photos using smartphones, cameras and scanners. the emission intensity and tonality of the probe is concentration-dependent. thus monitoring the color space of the systems is an appropriate signal enabling quantitative detection of the targets. it seems that modeling the response profile of two-component or multi-component ratiometric probes is a way toward achieving the real-optimal ratio of fluorophores. herein, in a two-component ratiometric nanoprobe, emission color of the nanoprobe is recorded in the presence of methyl parathion (mp), an organophosphate pesticide, using yellow emissive tga-capped cdte qds (yqds) and blue emissive carbon dots (cds). in this regard, the emission profile of the internal standard, herein cds, in the absence of mp, also the emission color of the dynamic fluorophore, yqds, in the absence/presence of mp were primarily recorded and modeled using mathematical polynomial equations. based on the additive color theory, the entire range of emission colors in the color gamut can be predicted by control of mixing ratios of the fluorescent probes [3]. hence, using fitted equations and additive color theory, the color of binary mixtures of cds and yqds in the absence and presence of mp were calculated. finally, the distance between the color of the fluorophores in the absence and presence of the analyte in the cie xyy color space was calculated using euclidean distance method. the maximum distance can be find the real-optimal concentration of the fluorophores.