This work proposed two new colorimetric methods; gold nanoparticles (AuNPs) method and paper-based Jaffe reaction, for the determination of creatinine in human urine samples. For the AuNPs method, sample extraction by sulfonic acid-functionalized silica gel was introduced to separate creatinine from urine matrix before the detection with citrate-capped AuNPs. The assembly of AuNPs was induced by attachment of positively charged amino groups on creatinine, resulting in a change of the color of AuNPs solution from red to purple or blue, which could be observed by naked eyes. The surface plasmon absorption band was shifted towards longer wavelengths when the concentration of creatinine increased which could be measured with a UV-Visible spectrophotometer. This method had a linear range of 15-40 mg/L and limit of detection (S/N = 3) of 13.7 mg/L. The recovery of creatinine in sample observed by the proposed method was 94.0-104.0% and the relative standard deviation was less than 9.4%. For the paper-based colorimetric method, 3-propylsulfonic acid trimethoxysilane was coated on the filter paper before application for creatinine extraction. The absorbed creatinine on the filter paper was detected with the standard Jaffé method. The color change on filter paper could be observed visually and the color intensity was determined by Image J software. The linearity range was observed in the range of 0-60 mg/L. The recovery of creatinine in sample observed by the proposed method was 91.9-113.8% and the relative standard deviation was 8.6 %. These methods were applied to determine creatinine in urine samples with acceptable accuracy and precision.

Thesis (Ph.D.)--Chulalongkorn University, 2014