Smartphone-based low-cost and rapid quantitative detection of urinary creatinine with the Tyndall effect

Selective and naked eye colorimetric detection of creatinine through aptamer-based target-induced passivation of gold nanoparticles

We report a simple naked eye colorimetric detection assay developed for the small molecule creatinine using the surface passivation of gold nanoparticles (AuNPs) which is conjugated with a creatinine binding aptamer. The selective binding of creatinine to aptamer sequences causes a decrease in the catalytic activity of AuNPs, and the color change time of the 4-nitrophenol reduction was used for the quantitative colorimetric detection of creatinine. Herein, the surfaces of AuNPs acted as the catalyst for the reduction of 4-nitrophenol (yellow) to 4-aminophenol (colorless), and the passivation with creatinine bound aptamer sequences delayed the reduction. The developed assay was able to detect creatinine in a linear range of 2-20 mM with a limit of detection of 0.87 mM. The developed colorimetric assay was very selective and repeatable and could detect creatinine in the presence of interfering biomolecules. Moreover, the assay showed excellent results for the analysis of creatinine in artificial urine samples. The developed assay can be used as a point of care (POC) device for the naked eye detection of creatinine within few minutes without any instrument support.