Integration of optical tweezers and surface enhanced Raman spectroscopy for biomolecular characterizations at single molecule level

Abstract

By removing ensemble averaging to probe the properties and behaviors of individual molecules, single molecule techniques revolutionize the applications in physical, chemical and biological sciences. Among various techniques implemented for single molecule detection, Surface Enhanced Raman spectroscopy (SERS) has been considered as one of the most promising approaches for the characterizations of biological systems in aqueous conditions, owing to its chemical specificity, water compatibility and non-invasive nature. Benefited from the enhanced electromagnetic field upon the excitation of localized surface plasmonic resonance (LSPR), SERS amplifies the vibrational signals of molecules within the plasmonic hotspots and enables single molecule sensitivity. However, conventional SERS approaches may suffer from low efficiency and poor reproducibility for liquid-phase single molecule detections, due to the difficulty to locate the target molecules in hotspot originated from the inherent Brownian motion and diffusion as well as optical diffraction limit. Optical tweezers leverage the gradient forces generated by highly focused laser beams to trap and manipulate individual objects in liquid medium with high precision, making it an ideal tool to integrate with SERS system to provide additional versatility and improvement on SERS measurements. The purpose of this proposal is to develop a multifunctional optical tweezers-integrated SERS platform to accommodate various biomolecules studies in aqueous environments with single molecule sensitivity. Our work is mainly composed of three sections: In the first section, we utilize far-field optical tweezers to manipulate two silver nanoparticle-coated silica microbeads and generate a dynamic SERS detection window with good controllability and reproducibility. We demonstrate the ability to resolve the structural details of globular proteins and intrinsic disordered protein in aqueous solution without perturbation to their native states, which offers an accessible and promising strategy for single molecule SERS measurement in biological systems. In the second section, we develop a near-field optical plasmonic tweezer to construct a dynamic SERS-active nanocavity, which overcomes the diffraction-limited detection volume to empower high-throughput single molecule characterizations in heterogeneous aqueous milieu. We investigate the heterogeneous conformational population of human Islet Amyloid Polypeptide (amylin, hIAPP) and spectroscopically differentiate the low-populated transient species among the natively predominant species at the early aggregation stage, providing mechanistic interpretations and insights to the structural behavior of hIAPP in pH-dependent amyloid formation. In the third section, we exploit the precise force manipulation of dual-trap optical tweezers to investigate DNA-drug interaction and perform site-specified real-time SERS scanning by translocating the DNA tether throughout the hotspot in a programmable manner. By correlating the force and position control of single-molecule with site-specified SERS characterizations, we showcase an effective configuration for credible and selective SERS measurements of biomacromolecules using optical manipulation. Our method opens up new avenues for the applications of molecular interactions, encryption, and sequencing.

Date of Award	2023
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jinqing HUANG (Supervisor)