Traditional approaches to cellular analysis, such as ELISA assays, are based on population-averaged measurements and thus mask the heterogeneity of cellular secretions. In reality, even within phenotypically similar groups, secretion variability exists and strongly influences biological functions and responses to molecular signals. Understanding when, where, and how cells secrete cytokines remains a major challenge, as these biochemical signals are produced transiently, locally, in very small quantities, and heterogeneously from one cell to another—making single-cell analysis essential. This thesis contributes to addressing this challenge by aiming to develop a microanalytical platform designed to locally capture and analyze secretions from individual cells. To achieve this, a microfluidic biosensor was developed based on a silicon substrate, combining the use of conducting polymers for surface functionalization with electrochemiluminescence (ECL) for detection. 

Silicon, the reference material in microfabrication, was selected as the substrate due to its compatibility with lithographic processes. However, its semiconducting properties and tendency to become passivated in aqueous environments necessitated the addition of a functional conductive layer. Therefore, polythiophene films and functionalized copolymers were prepared via electropolymerization on silicon substrates to serve as active electrochemical interfaces. Initially, electropolymerization conditions were optimized to produce stable, electroactive films on silicon. Their ability to immobilize biological probes (biotin, DNA) was then demonstrated using fluorescence microscopy. The feasibility of detecting biomolecular interactions via electrochemiluminescence (ECL) on these surfaces was subsequently evaluated. 

While polymer-functionalized surfaces allow for specific ECL detection, they present significant limitations in terms of signal stability and the number of possible readouts. To address this, a complementary strategy was explored in which biological interactions were relocated onto functionalized magnetic beads. In parallel, a microfluidic platform was numerically simulated and then designed to capture and isolate cell-sized objects (approximately 10 µm). Simulations helped optimize geometries and flow conditions to ensure stable single-particle trapping. The device was then fabricated and experimentally validated. 

Although significant work remains, this study helped refine the technological choices necessary for developing microfluidic devices that integrate single-cell capture functions for the purpose of studying their individual secretory activity.