RESUMO
Urinary creatinine concentration is a critical physiological parameter that enables reliable assessment of patient renal function and diagnosis of a broad spectrum of diseases. In this study, a simple and inexpensive sensor comprising monodisperse, citrate-capped silver nanoparticles (cc-AgNPs) was developed, which enabled rapid, sensitive and selective quantitation of creatinine directly in unprocessed urine. The mechanism of this sensor entails the creatinine-mediated aggregation of the cc-AgNPs (within 1â¯min) under alkaline conditions (pH 12). This is attributed to the tautomerization of creatinine to its amino anionic species at alkaline pH, which cross-link the cc-AgNPs via hydrogen bond networks with the negatively charged citrate caps. Creatinine elicited visibly-discernable color changes of the cc-AgNPs colloids in a concentration-dependent manner up to 10⯵M. UV-visible spectroscopic analyses of the cc-AgNPs revealed that creatinine elicited a concentration-dependent decrease in intensity of the localized surface plasmon resonance (LSPR) band centered around 403â¯nm, with a concomitant increase in intensity of the red-shifted LSPR band at 670â¯nm. This observation denotes a creatinine-mediated increase in cc-AgNP particle size via aggregation, as confirmed by transmission electron microscopy analysis. The cc-AgNP sensor exhibited a linear correlation between the A670/A403 extinction ratio and creatinine concentration range of 0-4.2⯵M in aqueous solutions (R2â¯=â¯0.996), and a low detection limit of 53.4â¯nM. Hence, the simplicity, short assay time, and high sensitivity and selectivity of our cc-AgNP sensor affirms its utility as a creatinine monitoring assay for low-resource, point-of-care settings.