Multifunctional nanocomplex for surface-enhanced Raman scattering imaging and near-infrared photodynamic antimicrobial therapy of vancomycin-resistant bacteria

Abstract

Since vancomycin (Van)-resistant enterococci (VRE) strains first emerged as a serious threat to public health, extensive studies focused on optical imaging and antimicrobial therapy have been performed for monitoring and microbiological control. In this study, we developed silicon 2,3-naphthalocyanine dihydroxide (Nc) and Van functionalized silica-encapsulated, silver-coated gold nanoparticles (Au@AgNP@SiO2@Nc-Van) as a novel theranostic system for surface-enhanced Raman scattering (SERS) detection and antimicrobial photodynamic therapy (aPDT) of VRE strains. The silver-coated gold nanoparticle, as the SERS-active core, exhibited excellent Raman enhancement efficacy. Results of in vitro bacterial SERS imaging revealed Van-enhanced specific binding affinity toward VRE. Meanwhile, Si(IV) naphthalocyanine, serving as a near-infrared (NIR) photosensitizer, was axially linked to the nanoparticle surface, yielding nanostructured hybrid materials that could photoinactivate VRE. Almost 4–5 logs of bacterial reduction were obtained upon in vitro photodynamic therapy of VRE treated with a nanomolar concentration of the nanocomplex. Mouse infection assays were applied for an in vivo evaluation of VRE lethality. Upon near-infrared light irradiation, this hybrid nanomaterial caused obvious infection regression and even complete eradication compared to the findings in the non-treated groups. Therefore, this novel nanosystem integrating SERS imaging and noninvasive aPDT has huge potential for applications in theranostics with regard to VRE management.