Optical Nanotweezers for Monitoring Conformational Dynamics of Single, Unmodified Proteins

Dr Cuifeng Ying is a Senior Lecturer in Electrical Engineering at the Department of Engineering in the School of Science and Technology at Nottingham Trent University. She is a member of the Advanced Optics and Photonics Group (www.aoplab.com).

Abstract: 

Conformational dynamics of proteins are critical for their biological functions but are challenging to study at the single-molecule level. Here, we present our ongoing research in using aperture-based plasmonic nanotweezers to investigate the conformational dynamics of single unmodified proteins in aqueous solutions (Figure 1). We utilise gold double-nanohole (DNH) structures to induce a localised surface plasmon resonance, creating a highly confined optical field capable of trapping individual proteins for extended periods (Fig. 1b). The transmitted optical signal through the DNH correlates to the local refractive index within the hotspot, which is related to the polarizability of the trapped protein [1-2]. In this work, we trap individual proteins in the DNH for hours and monitor their conformational dynamics of proteins in response to sequential environmental changes, such as pHs and substrate concentrations [3]. We demonstrate that plasmonic nanotweezers can resolve conformational states of single proteins and monitor transitions between these conformations (Fig. 1c). This presentation will showcase the capabilities of optical nanotweezers in various applications at single-molecule level, including protein disassembly pathway [4], protein-small molecule binding kinetics [3], and energy landscape of intrinsically disordered proteins [5]. The approach presented here can be widely adopted by other biophysical studies on conformational dynamics of single proteins without the requirement of site-specific modifications. 

References
[1] Y. Pang & R. Gordon, Nano Lett 12, 402–406 (2012).
[2] R. Gordon, M. Peters, C. Ying, Quarterly Reviews of Biophysics, 57, e12 (2024)
[3] A. Yousefi, C. Ying, CDJ Parmenter, M. Assadipapari, G. Sanderson, Z. Zheng, L. Xu, S. Zargarbashi, G. J. Hickman, R. B. Cousins, C. J. Mellor, M. Mayer, and M. Rahmani Nano Lett. 23, 3251–3258 (2023).
[4] A. Yousefi, Z. Zheng, S. Zargarbashi, M. Assadipapari, G. J. Hickman, C. D. Parmenter, G. Sanderson, D. Craske, L. Xu, M. Rahmani, and C. Ying, ACS Nano, 18, 15617- 15626 (2024)
[5] M. Peters, T. Zhao, S. George, V.G. Truong, S. N. Chormaic, C. Ying, R. Nome, R. Gordon npj Biosensing 1, 14 (2024)