Wavelength and shape dependent SERS study to develop ultrasensitive nanotags for imaging of cancer cells

The Raman signal enhancement depends mainly on four critical factors. These factors are localized surface plasmon resonance (LSPR) of gold substrates along with shape and electronic absorbance of Raman reporters along with laser sources. Hence, the effects of all these four parameters were systematically studied by changing either the different geometries/shapes of the gold substrates having a wide range of SPR or electronic absorbance of Raman reporters under a fixed laser excitation of 633 nm or 785 nm. Enhancement factor (EF) values were evaluated for each individual substrate with respect to five different Raman reporters which cover the maximum absorbance from 530 nm to 800 nm. The EF values suggest that the signal intensity has been increased by at least ten times compared to previous reports. Among the five different shapes of the gold nanoparticles, the substrate of gold nanostars (GNSt) was found to be the most suitable substrate for the highest signal enhancement under both excitation laser sources. The substrate of gold nanosphere (GNSp) is the second best at 633 nm laser excitation; however it is the modest substrate for SERS enhancement at 785 nm laser excitation. After finding the key tools for the development of ultrasensitive SERS nanoprobes, we selected the best Raman reporter (Cy7LA) for the development of biocompatible SERS nanotags in three different SERS substrates for the effective detection of cancer cells under 785 nm laser source.