Speaker
Description
Chemical concentration gradients at the microscale are omnipresent, shaping fundamental processes in a wide range of systems from cell signaling to transport phenomena. Despite their ubiquity, visualizing chemical gradients typically requires the addition of labels, such as fluorescent dyes, for optical readout. Because dyes bleach, or may interfere with the processes of interest, i.e. up to inducing toxicity for biological systems, alternative, label-free approaches are sought after. For systems that lack optical contrast, interferometric methods are a label-free solution that relate refractive index (RI) to a compound's identity or concentration in situ. I will present here a tool that expands on the principles of Fabry-Pérot interferometry to two dimensions to obtain RI mapping within a microfluidic chip. By tracking fringes of equal chromatic order our tool achieves a RI resolution of 1e-5 refractive index units per image pixel, for instance sensitive to 1 mM changes in concentration of NaCl. The tool, which we named RIO for refractive index observer, mounts onto any microscope and I will report its resolution and RI precision, as well as demonstrate its potential by quantifying dynamically evolving concentration gradients of dissolved NaCl in a microfluidic channel and concentration gradients resulting from catalytic reactions. We envisage that RIO will give unprecedented access to a broad range of microscale phenomena, from polymerization and enzymatic reactions to cell signaling and electrochemical processes.