Evanescent scattering imaging of single protein binding kinetics and DNA conformation changes

Evanescent illumination has been widely used to detect single biological macromolecules because it can notably enhance light-analyte interaction. However, the current evanescent single-molecule detection system usually requires specially designed microspheres or nanomaterials. Here we show that single protein detection and imaging can be realized on a plain glass surface by imaging the interference between the evanescent lights scattered by the single proteins and by the natural roughness of the cover glass. This allows us to quantify the sizes of single proteins, characterize the protein-antibody interactions at the single-molecule level, and analyze the heterogeneity of single protein binding behaviors. In addition, owing to the exponential distribution of evanescent field intensity, the evanescent imaging system can track the analyte axial movement with high resolution, which can be used to analyze the DNA conformation changes, providing one solution for detecting small molecules, such as microRNA. This work demonstrates a label-free single protein imaging method with ordinary consumables and may pave a road for detecting small biological molecules. Single molecule detection based on evanescent illumination usually require specially designed nanomaterials. Here, the authors show that single molecule detection can be realised on a plain glass surface via interference between the evanescent lights scattered by molecules and the natural roughness of the glass.

Automated summary

This study demonstrates a method for detecting and imaging single proteins on a plain glass surface through the interference between evanescent lights and the natural roughness of the glass, providing a label-free solution for single molecule detection without the need for specially designed nanomaterials. It also paves the way for detecting small biological molecules.