Freestanding Porous Silicon Membranes for Sensing Enabled by Flow-Through Decoration of Gold Nanoparticles

Tuning and optimizing the optical, physical, and chemical properties of porous silicon (PSi) by decoration with plasmonic nanoparticles (NPs) are a trending yet challenging topic. The current NPs deposition methods tend to cluster them on top of the pores instead of maximizing the plasmonic effect by homogeneous distribution inside the pores. Here, a novel flow-through strategy is introduced to homogeneously decorate PSi freestanding membranes (FSM) with a colloidal NPs suspension. FSM offers high ease of fabrication, but the main current challenges are low repeatability and difficult microfluidic integration. We used a numerical simulation to determine the main fabrication parameters, unlocking the reliable release of FSM with very large pores up to 67 nm. To enable the flow-through, the FSM was subsequently integrated into a microfluidic cell using a flexible Kapton holder. Solving these challenges allowed us to fully decorate the pores with presynthesized Au NPs and obtain a homogeneous decoration of the whole FSM thickness. As a representative application, reflective interferometric Fourier transform spectroscopy (RIFTS) measurements demonstrated enhanced sensing performance with both increased sensitivity and reduced standard deviation. These results highlight the potential of decorated FSM as versatile substrates for plasmonic, catalytic, sensing, and other nanophotonic applications.