Combing force manipulation and Raman spectroscopy characterization to study protein structures

Single-molecule force spectroscopy delineates the individual behavior of molecules from the molecular extensions associated with conformational changes versus force manipulations. Vibrational spectroscopy depicts the molecular structures from the endogenous oscillations of all chemical bonds inside the molecules upon irradiation. Leveraging both tools, we are able to precisely control a single molecule, directly monitor the force-associated structural changes, and efficiently characterize the designated intermediates in dynamic processes. Recently, we have combined optical tweezers and surface-enhanced Raman spectroscopy (SERS) to create a hotspot to characterize the protein secondary structures in a label-free manner. This optical tweezers-controlled hotspot can provide tunable and reproducible SERS enhancements with up to single-molecule level sensitivity, which helps to identify the transient species of alpha-synuclein (an intrinsically disordered protein closely linked to Parkinson's disease) to further reveal the mechanism of amyloid protein aggregation. Besides, it also has the potential to integrate with other surface-sensitive techniques to make single-molecule detections easier.