Nanostructure-assisted optical tweezers for microspectroscopic polymer analysis

Abstract

Raman/fluorescence microspectroscopic analysis of individual polymer chains and nanobeads dissolved in solution will become a powerful analytical method to study their molecular structure and characteristics. With this motivation, we focused on the use of Raman microspectroscopy for optically trapped soft matter. A tightly focused near-infrared laser beam formed a microassembly of thermoresponsive polymer chains such as poly(N-isopropylacrylamide) due to a local photothermal effect and optical force. By using this method, we developed a technique for determining the polymer concentration in a polymer microassembly. Furthermore, we demonstrated a molecular condensation and detection technique based on microassembly on plasmonic nanostructures. For this molecular condensation and detection process, localized surface plasmons play an essential role in the optical force enhancement and local temperature increase around the plasmonic nanostructures. Finally, aiming toward novel manipulation methods of smaller soft nanomaterials, nanostructured semiconductor-assisted (NASSCA) optical tweezers are introduced. In this paper, we reviewed the optical manipulation methods of polymer chains and nanobeads and their applications in analytical chemistry. We reviewed our recent studies on optical manipulation techniques for microspectroscopic analysis of optically trapped polymers. A focused laser beam exerts an optical force on polymer chains, leading to the microassembly formation of them. We applied the conventional optical tweezers for the concentration determination techniques of phase-separated thermoresponsive polymer chains by combining with microspectroscopies. To overcome the limitations of the conventional optical tweezers, localized surface plasmon has attracted much attention. Finally, we introduced our original manipulation technique based on nanostructured semiconductor-assisted optical tweezers; NASSCA optical tweezers.