Fabrication of nano-porous n-type freestanding optical sensor for the detection of organic solvents

In this study, ethanol/HF- and water/HF-based electrolyte solutions were utilized to optimize the fabrication of high-quality (Q = 70) n-type freestanding porous silicon microcavity (MC) and monolayer structures. The fabricated structures exhibit tunable pore sizes ranging from ∼40–120 nm, making them promising candidates for biosensing applications. Two types of electrochemical solution methods were adopted; first, a water-based solution was used to modulate current density to form a mesoporous multilayer MC structure or a single layer, and then another solution, which enables detachment of the sensing membrane. MC photonic structure has been achieved on an n-type silicon substrate with a sensitivity of 644 nm RIU −1 and a maximum quality factor of 70. The sensitivities of MCs having quality factors of 30, 50, and 70 are recognized with methanol-ethanol solutions and changes of ∼2.44 × 10 −5 , 1.91 × 10 −5 and 1.08 × 10 −5 can be detected. Additionally, a polarimetric sensing approach with a limit of detection (LOD) of 3.59 × 10 −4 RIU was demonstrated using a porous silicon (PSi) monolayer as a proof-of-concept platform, highlighting its potential for future point-of-care diagnostic devices.