Porphyrin‐conjugated silver‐coated gold nanostars for ultrasensitive detection and multiplexing

Abstract

Here, we propose the use of silver-coated gold nanostars as the basis for a multiplex sensing system based on surface-enhanced Raman scattering (SERS)/surface-enhanced resonance Raman scattering (SERRS) ultrasensitive detection of porphyrins using a 532 nm laser excitation. By modifying the synthetic parameters, we were able to shift the plasmon peak to an optimized position for SERS enhancement of 540 nm for silver-coated gold nanostars, estimating a SERS enhancement factor around 4.6 × 105. Furthermore, we show high-resolution transmission electron microscopy (HR-TEM) images and electron energy-loss (EEL) spectra of silver-coated gold nanostars, which provide solid experimental proof on the proposed silver coating mechanism. Finally, we compare the multiplex performance of common reporters such as cyanines and malachite green with the performance of covalently bound porphyrins and show the superiority of the latter. We studied the multiplex detection capabilities of the system with three different porphyrins. By deconvoluting a mixture spectrum into individual porphyrin spectra, we were able to determine the relative concentration of porphyrins with an average error of 3.1%.