Block-copolymer-tailored plasmonic nanoparticles for metal-enhanced fluorescence

Abstract

Metal-enhanced fluorescence (MEF) is an emerging spectroscopy technique based on localized surface plasmon resonance (LSPR) that has attracted great interest in sensing, optoelectronic and biomedicine in the recent years. However, to achieve efficient and uniform signal enhancement at single particle level and practical applications in clinically relevant models remain major challenges. In this thesis, we have successfully developed a series of fluorescent amphiphilic block copolymer to construct concentric core-shell AuNP@BCP for achieving considerable MEF with wavelength range from visible to NIR region. The MEF from these core-shell nanoplatforms have been well studied in theory and experiment, which may provide a universal strategy to design efficient multiplexing nano-emitters for meeting various requirements of applications. In the first project, we successfully synthesized amphiphilic dye-grafted block copolymer (BCP) via the combination of atom transfer radical polymerization (ATRP) and “click” chemistry and constructed concentric core-shell AuNP@BCP-dyes by a typical self-assembly strategy. The structural parameters of the polymer and nanoparticle are tunable in a broad range. We then theoretically and experimentally studied the MEF from visible to NIR-I and NIR-II spectral region. This work provides theoretical and experimental methods to reliably predict and realize consistent MEF from metal-emitter system with defined spacing. In the second project, we reported the synthesis of amphiphilic semiconducting block copolymers (SBCP) in which the semiconducting polymer (SP) served as a middle fluorescent building block. We have successfully prepared concentric AuNS@SBCP1 and AuNS@SBCP2 and achieved considerable MEF in visible and NIR-I wavelength region from these two nanoplatforms, respectively. To understand the MEF in such core-shell nanostructures, simulation with several approximations of the SBCP layer was carried out, which showed excellent agreement with the experimental results. These results enable simple prediction of average fluorescence enhancement from a core-shell metal-SBCP nanoplatform, which may direct the experimental design to achieve desirable MEF for SBCP. Moreover, the NIR fluorescent AuNR@SBCP2 with low cytotoxicity was successfully applied for in vivo fluorescence and photoacoustic (PA) imaging of tumor. Our studies provide a novel strategy based on BCP synthesis, self-assembly, LSPR, and computational simulation to achieve metal-enhanced optical properties for the rigid SP emitters, which thus profits the multiplexing bioimaging by employing this unique nanoplatform.