Prereduction-promoted enhanced growth of silver nanoparticles for ultrasensitive colorimetric detection of alkaline phosphatase and carbohydrate antigen 125

A highly sensitive colorimetric method for detection of alkaline phosphatase (ALP) and carbohydrate antigen (CA125) was developed, which was achieved by ascorbic acid (AA) - mediated enhanced growth of silver nanoparticles (AgNPs) promoted with NaBH4 as pre-reducing agent. With prereduction by NaBH4, the AA controlled growth of AgNPs was promoted and the localized surface plasmon resonance absorbance was much higher compared with that without prereduction. ALP could hydrolyze L-ascorbic acid 2-phosphate trisodium salt (AAP) to form AA, which could then reduce Ag+ to AgNPs resulting in the enhancement of localized surface plasmon resonance peak of AgNPs and accompanying the color change from colorless to bright yellow. Benefiting from the highly sensitive response of Ag+ to AA, the detection limit for ALP could be lowered to 0.003 U L-1, and the proposed plasmonic ELISA could achieve a low detection limit of 1.75 U mL(-1) for CA125. Moreover, this method was validated for the analysis of ALP and CA125 in human serum samples, giving results matched well with conventional method, demonstrating the potential application of the developed method in clinical diagnosis.