A novel method utilizing a portable digital image-based colorimeter detector and a glutathione-functionalized gold nanoparticles (GSH-AuNPs) sensor for the highly selective and sensitive detection of creatinine in urine sample

Various methods can be employed to detect creatinine in urine, but the colorimetric method stands out for its speed, simplicity, and cost-effectiveness. In this study, glutathione-functionalized gold nanoparticles (GSH-AuNPs) were synthesized and used as a sensor to detect creatinine, utilizing a portable digital image-based colorimeter developed in our laboratory. The synthesized GSH-AuNPs exhibit a distinctive wine-red colour and have a uniform spherical shape with an average size of 56.7 nm, showing a maximum absorbance peak at a wavelength of 522 nm. The optimum conditions for detecting creatinine were a pH of 6 and a reaction time of 20 min. FTIR data confirm that the detection mechanism involves hydrogen bond between the -NH₂ group of creatinine and the -COO^- group on the surface of the GSH-AuNPs. This is evidenced by a shift in the stretching vibration of the -COO^-, leading to the aggregation of the GSH-AuNPs, resulting in an average size of 191.5 nm. The developed portable colorimeter, used as a detector for the GSH-AuNPs sensor in creatinine detection, achieved a limit of detection (LoD) of 0.016 mM. In comparison, the UV–Vis spectrophotometer as the detector has a LoD of 0.029 mM, and the Jaffe method has a LoD of 0.038 mM, making the proposed colorimetric method the most sensitive. The proposed colorimetric method demonstrates good selectivity for creatinine and has been successfully applied to detect creatinine in artificial urine with a recovery value of 99–103 %.