Sensitivity Comparison of a Self-Standing Porous Silicon Membrane Under Flow-Through and Flow-Over Conditions

Abstract

An optical sensor based on a self-standing porous silicon (PS) membrane is presented. The sensor was created by electrochemically etching a heavily doped p-type silicon wafer with an organic electrolyte that contained dimethylformamide (DMF). After fabrication, a high current density close to electropolishing was applied in order to allow the detachment from the substrate using a lift-off method. The PS membrane was integrated in a microfluidic cell for sensing purposes and reflectance spectra were continuously obtained while the target substance was flowed. A comparison of the bulk sensitivity achieved when flowing through and over the pores is reported. During the experiments, a maximum sensitivity of 770 nm/RIU measured at 1700 nm was achieved. Experimental sensitivity values are in good agreement with the theoretical calculations performed when flowing through the PS membrane, meaning that the highest possible sensitivity of that sensor was achieved. In contrast, a drop in the sensitivity of around 25% was observed when flowing over the PS membrane.

Simultaneous Refractive Index Sensing Using an Array of Suspended Porous Silicon Membranes

“…A good solution would be implementing an active flow where the substances were forced to flow through the pores. As we proved in another work [46], it is possible to reach the theoretical sensitivity experimentally by doing this. Unfortunately, we were not able to implement the active flow in this study due to some limitations such as the complexity of the fluidic cell, the attenuation of the optical signal and the flow resistance of the porous layer, some of which could be overcome increasing the pore size, reducing more the thickness of the substrate and fabricating structures with higher Q-factor.…”

Diatom Frustule Array for Flow-Through Enhancement of Fluorescent Signal in a Microfluidic Chip

“…Flow-over and flow-through mode are two frequently used techniques in lab-on-chip sensing [ 36 , 37 , 38 ]. In flow-over assays, molecular binding mainly depends on the transportation of bulk analyte through diffusion and convection [ 39 ].…”

Porous Silicon Biosensor for the Detection of Bacteria through Their Lysate

“…Porous silicon membranes are promising biosensors: with their flow-through operation, they overcome the lack of sensitivity of flow-over PSi-based biosensors and are characterized by short response times [18][19][20][21][22]. Moreover, they do not require any stratagems to transport and concentrate the analyte on the transducer.…”

“…Instead of a close-ended PSi layer over which the analyte must flow, an open-ended PSi membrane allows the analyte to flow through the porous matrix. PSi membranes have been fabricated as early as the 1990s [17] but the interest in PSiMs for sensing applications only arose recently [18][19][20][21][22]. PSiMs can be self-supported, meaning still partly attached to the silicon substrate, or freestanding.…”

“…Recently, lateral PSiMs have also been fabricated [23][24][25]. For biosensing applications, PSiMs have been found to increase both the response time and amplitude of the sensors [18][19][20][21][22].…”