π-Conjugated poly(3-hexylthiophene-2,5-diyl) thin film as a SERS substrate for molecule detection application

Surface-enhanced Raman scattering (SERS) has drawn attention to broad applications. Here, we investigate the SERS property of the π-conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) for molecule detection. The crystal structure of π-conjugated P3HT thin films is of the great significance to its SERS property. Our results show that the optimized crystal structure can significantly improve its SERS property. The SERS substrate has an excellent signal reproducibility (RSD < 10%). In addition, the SERS substrate still remains a good Raman enhancement after one year and shows excellent long-term stability compared with those of other types of SERS substrate. The result of our theory calculation shows that significant π-stacking of the probe molecules with the thiophene π-cores molecules plays an important role in the large SERS enhancement by the charge transfer mechanism. The increase in the crystallinity of the P3HT film can improve the charge transfer of the substrate molecules and the methylene blue (MB) molecules via more effective chemisorption of the probe molecules with the substrate molecules. The study contributed to the rational design of the organic semiconductor polymer SERS substrate with high sensitivity, selectivity, and long-term stability. Graphical abstract