Novel layer-by-layer silica nanoparticles as an adorbent bed for micro-fabricated preconcentrators

This paper reports the application of SiO₂ nanoparticles (NPs) as an adsorbent bed for capturing volatile organic compounds (VOCs) in a micropreconcentrator (μPC) chip for the first time. The adsorbent coating is deposited inside and on the sidewalls of the microfabricated 3D square structures using layer-by-layer (LbL) self-assembly technique. The device consists of 12mm×9mm×0.5mm chip with square pillars having 50μm side length, embedded inside an 8mm×8mm×0.24mm cavity. The LbL technique provides excellent control over the adsorbent thickness with low cost and batch fabrication ability. The deposited SiO₂ NPs offer high porosity and surface area, essential for trapping VOCs. Moreover, the high temperature sustainability (800°C) proves to be vital for excellent silicon-glass anodic bonding process. In our test, μPC chip with SiO₂ NPs adsorbent bed totally adsorbs xylene compound and generate a sharp desorption peak during thermal desorption process. In addition, it also shows the ability to adsorb a mixture of three compounds, which have been successfully separated and detected after desorption.