Independent spectral characteristics of functionalized silver nanoparticles for colorimetric assay of arginine and spermine in biofluids
A colorimetric assay was developed for highly selective and sensitive detection of arginine and spermine in biofluids using 6-aza-2-thiothymine-functionalized silver nanoparticles (6-ATT-AgNPs) as a probe via independent spectral characteristics and color changes. This colorimetric sensor was fabricated by functionalizing 6-ATT molecules on the surfaces of AgNPs. The as-synthesized 6-ATT-AgNPs had an average size of 20 ± 4.4 nm and were dispersed in water. The NPs exhibited highly selective interactions with arginine and spermine, showing a drastic decrease in the intensity of 6-ATT-AgNPs at 400 nm for arginine and a remarkable red shift in the surface plasmon resonance (SPR) band (from 400 nm to 522 nm) for spermine, respectively. Furthermore, those showed noticeable independent color changes from yellow to greenish for arginine and to orange-red for spermine. The sensing is based on the aggregation of 6-ATT-AgNPs induced by both analytes (arginine and spermine) via noncovalent interactions. This sensor exhibited linear calibration curves of the SPR intensity at 400 nm in the concentration range of 5.0 - 60 µM for arginine and the absorption ratio at A522/A400 in the concentration range of 2.5 - 20 µM for spermine, respectively. Common chemical species (anions, biomolecules, and metal ions) had no significant effects on the colorimetric assay of arginine and spermine. The sensor was successfully applied to quantify arginine and spermine in biofluids. With its advantages of simplicity, rapidity, and low cost, this sensor is a promising miniaturized platform for assaying arginine and spermine in biofluids.