Efficient transportation and delivery of analytes to the surface of optical sensors are crucial for overcoming limitations in diffusion-limited transport and analyte sensing. In this study, researchers from Vanderbilt University propose a novel approach that combines metasurface optics with optofluidics-enabled active transport of extracellular vesicles (EVs). By leveraging this combination, the researchers show that they can rapidly capture EVs and detect their adsorption through a color change generated by a specially designed optical metasurface that produces structural colors. These results demonstrate that the integration of optofluidics and metasurface optics enables spectrometer-less and label-free colorimetric read-out for EV concentrations as low as 107 EVs/ml, achieved within a short incubation time of two minutes.
(a) Experimental setup for fast incubation and color metasurface imaging. BS: beam-splitter. DM: short-pass dichroic mirror with 650 nm cutoff wavelength. (b) Schematic illustration of the metasurface’s color change triggered by EVs (extracellular vesicles) binding to the surface. Using optofluidic flows to rapidly concentrate particles and bring them down to the nanostructured substrate, the local color would change due to the refractive index contrast induced by the EV capture. Schematic of the color metasurface illuminated with white light (c) before EV concentration on the sensing surface, and (d) after EV concentration on the sensing surface. The color changes over the region with the captured EVs. The optimized metasurface enables a highly perceivable color change imaged by the CCD camera.