A plasmonic colorimetric strategy for biosensing through enzyme guided growth of silver nanoparticles on gold nanostars.

A plasmonic colorimetric strategy was designed for sensitive detection of biomolecules through enzyme guided silver nanoparticles (AgNPs) growth on gold nanostars (AuNS). The growth of AgNPs on AuNS led to a substantial blue shift of the localized surface plasmon resonance (LSPR) peak and the color change of AuNS from blue to dark blue, purple and ultimately orange. Both the LSPR blueshift wavelength and the color of detection solution containing AuNS, Ag(+) and ascorbic acid 2-phosphate (AAP) depend on the amount of enzyme that catalyzed the dephosphorylation of AAP to reduce Ag(+) on AuNS surface. Thus this strategy could be used for LSPR and naked-eye detections of both the enzyme such as alkaline phosphatase (ALP) and other biomolecules involved in biorecognition events using ALP as a tag. The LSPR detection method for ALP showed a linear range from 1.0 pM to 25 nM with a detection limit of 0.5 pM. Using DNA as a mode target molecule, this technique showed a detection range from 10 fM to 50 pM DNA with a detection limit of 2.6 fM through the convenient combination with hybridization chain reaction amplification. The proposed plasmonic colorimetric strategy could be extended as a general analytical platform for design of immunosensors and aptasensors with ALP as a label.