( Invited ) Engineering Porous Silicon Optical Biosensors: When Nanostructure, Mass Transport, and Surface Chemistry Converge

Abstract

Anodized porous silicon films have been widely studied for biosensing applications, enabling label-free optical detection of numerous targets. Their appeal stems from the unique combination of tunable micro- and nanostructure with strong photonic properties, allowing precise control over pore size, layer thickness, and optical interference modes. Together with the large internal surface area, these attributes position PSi as a highly versatile optical transducer platform. However, our work has shown that this same nanostructure also introduces a fundamental bottleneck: analyte delivery to reactive sites inside the porous matrix is strongly limited by mass transport. In PSi biosensors, target molecules must diffuse from the bulk solution to the sensor surface and then infiltrate the porous network, where transport is hindered by nanoscale confinement and coupled to surface binding kinetics. This leads to analyte depletion at pore entrances and along pore walls, effectively decoupling photonic sensitivity and surface area from molecular recognition, and imposing severe limits on detection performance at low analyte concentrations. This talk will focus on integrated strategies to overcome these limitations by simultaneously engineering mass transport and surface chemistry in PSi optical biosensors for biomedical applications. We will present approaches developed by our group to enhance sensitivity using electrokinetic focusing for on-chip analyte pre-concentration, as well as microfluidic designs that promote convective transport and reduce diffusion boundary layers. In addition, we will discuss surface passivation strategies to minimize non-specific binding and the rational tailoring of capture probe conjugation to preserve accessibility and binding efficiency within the porous network. Together, these examples illustrate how aligning photonic design, mass transport, and surface chemistry enables porous silicon biosensors to move beyond diffusion-limited operation toward highly sensitive, application-relevant detection.