Ultrasensitive, dynamic, and online monitoring photonic sensors for protein conformation

Abstract

The monitoring of molecular dynamic transition and protein conformation changes is important for some neurodegenerative diseases (NDs) and has attracted much attention due to its ability to reveal the pathological mechanism of several NDs. Here, a label-free optical detection method with an ultrahigh refractive index sensitivity (S) and dynamical S tuning range was developed to provide a novel technology roadmap for the online monitoring of protein conformation. The real-time conformation variation process was transduced into a visualization optical signal, allowing it to be monitored. The biosensor prototype was constructed by the cross-overlapping of two rows of square capillaries on a gold mirror to form two microcavities with different free spectral ranges (denoted as the sensing and reference cavities). The coupling of the resonance mode between the two microcavities induced the generation of the Vernier effect and the magnifying of S, presented in the form of a modulated envelope in the spectrum. S values ranged from −17,256 nm/RIU to 93,937 nm/RIU, indicating that the biosensor could not only realize large dynamic tuning ranges but also an ultrahigh S. The conformation changes of silk proteins from the random coil to the β–sheet were sensitively monitored by the output spectrum after it was stimulated with ethanol solution. This ultrasensitive biosensor (which is both label-free and optical) provides a novel and supplementary technique to monitor the structural and conformation changes process of proteins. The results reveal its significant potential for clinical diagnosis, healthcare, pharmaceutical screening, and food security.