Precisely Tuning LSPR Property via "Peptide-Encoded" Morphological Evolution of Gold Nanorods for Quantitative Visualization of Enzyme Activity.

Longitudinal surface plasmon resonance (LSPR)-based optical signals possess unique advantages in biomolecular sensing and detection which can be attributed to their ultrahigh sensitivity and signal-to-noise ratio. However, the lack of effective strategies for morphological control of gold nanorods (GNRs) complicates the precise tuning of their LSPR property. Herein, a "peptide-encoded" strategy was first developed to precisely control the morphologies of GNRs via overgrowth of GNR seeds in the presence of thiol-containing peptides. Significantly, the "peptide-encoded" GNRs exhibit a tunable LSPR peak ranging from 685 to 877 nm by altering the amount of peptide. A few obvious colorimetric changes were accompanied from pink to purple and even to blue. Other parameters, e.g., pH, temperature, and Ag+ concentration, could also be utilized to regulate the morphologies of the "peptide-encoded" GNRs. The ultrasensitive detection of tumor-related protease activities based on LSPR peak shifts was further successfully performed without the need for labeling or instrumental aid, achieving a limit of detection of 60 fM. It is much lower than traditional absorption-based analysis (1 nM) and enzyme-linked immunosorbent assay (ELISA) method (1 pM), indicating the great potential of this peptide-encoded strategy in the application of ultrasensitive biomarker assay and clinical diagnosis.