Flow-through self-standing porous silicon sensor

Porous silicon (PS) is a good host for fabricating high sensitivity sensors due to the high aspect ratio between surface and volume that can be achieved. The anodization in hydrofluoric acid solutions forms nano-size pores with a few microns of thickness that can be functionalized for the detection of analytes. However, closed-ended porous silicon films have some drawbacks, like air entrapment and bad flow diffusion that can lower the sensitivity.

Porous silicon membranes appeared as a solution to those effects by flowing the substances through open-ended films. This reduces the time of detection, optimises the sensitivity and avoid mixture of different substances [1].

Lift-off of a porous silicon film is the easiest method for obtaining self-standing porous silicon membranes. The layer is detached from the substrate in a single step by electrochemically etching with a current close to electropolishing.

In this work, we present the experimental results of sensing with a PS sensor based on the lift-off method. We have measured the reflectance spectrum each 30 seconds and followed the shift while flowing through the pores. Experimental sensitivity values are in good agreement with the theoretical simulations performed.

[1] Y. Zhao, G. Gaur, R.L. Mernaugh, P.E. Laibinis, S.M, Weiss, Comparative kinetics analysis of closed-ended and open-ended porous silicon, Nanoscale Research Letters, 11:395, 2016.