Leakage-free polypyrrole–Au nanostructures for combined Raman detection and photothermal cancer therapy

A bifunctional gold-coated polypyrrole (PPy-Au) nanostructure with Raman and photothermal activity was developed, in which polypyrrole spheres (PPy NSs) were used as the core and coated with small Au NPs to form polypyrrole-Au (PPy-Au) nanostructures. As a result of the contribution from the coated Au nanoparticles (Au NPs), coupling occurred between the Au NPs and the PPy NSs, leading to an enhanced pyrrole Raman signal. PPy-Au nanostructures were thus used as Raman tags without requiring additional Raman dyes labeling and leaking the cargo dyes even in the absence of a complicated encapsulation process. When conjugated with aptamer S2.2, the nanostructures could specifically bind with the membrane protein MUC1, a kind of tumor-related biomarker that is overexpressed on the surface of human breast cancer cells (MCF-7). The specific detection of MCF-7 cells was thus achieved based on the pyrrole Raman signal. Moreover, the capacity of the PPy-Au nanostructures for transforming NIR light into heat was also greatly enhanced because of the coupling between the Au NPs and the PPy NSs, as indicated by the efficiency of the photothermal conversion up to 70.0% compared to 44.7% for the pure PPy NSs. Photothermal experiments proved that MCF-7 cells incubated with the nanostructures nearly died under 808 nm irradiation (0.5 W cm-2) for 20 min, and the tumors bearing on the mice were also effectively inhibited after the PTT.