Macroporous silicon microcavities for detection of large biological molecules have been fabricated from highly doped n‐type silicon. Well‐defined controllable pore sizes up to 120 nm have been obtained by systematically optimizing the etching parameters. The dependence of the sensor sensitivity on pore size is discussed. Excellent infiltration inside these macroporous silicon microcavities is demonstrated using 60 nm diameter latex spheres and rabbit IgG (150 kDa; 1Da = 1 g mol–1). The sensing performance of the device is tested using a biotin/streptavidin couple, and protein concentration down to 1–2 μM (equivalent to 0.3 ng mm–2) could be detected. Simulations show that the sensitivity of the technique is currently approximately 1–2 % of a protein monolayer.

The optical response of porous silicon affinity biosensors depends strongly on their nanomorphology because the sensing species does not completely fill the pores but is instead attached to the pore walls. The performance and sensitivity of porous silicon microcavity biosensors are calculated as a function of pore size using a simplified effective medium approximation. Excellent agreement is obtained between the model predictions and the experimental results after binding of aminopropyltriethoxysilane and glutaraldehyde in mesoporous and macroporous silicon microcavities. Detection of layers thinner than 0.01nm should be possible.

No abstract

Electrical and thermal modulation of porous silicon microcavities is demonstrated based on a change in the refractive index of liquid crystals infiltrated in the porous silicon matrix. Positive and negative anisotropy liquid crystals are investigated, leading to controllable tuning to both longer and shorter wavelengths. Extinction ratios greater than 10 dB have been demonstrated. Larger attenuation can be achieved by increasing the Q-factor of the microcavities.

Photonic bandgap (PBG) structures have remarkable optical properties that can be exploited for biosensing applications. We describe the fabrication of 1-D PBG biosensors using porous silicon. The optical properties of porous silicon PBGs are sensitive to small changes of refractive index in the porous layers, which makes them a good sensing platform capable of detecting binding of the target molecules to the bioreceptors. The material nanostructure and device configuration that lead to optimum performance of the devices are investigated in detail by modeling the optical response. It is shown that porous silicon based PBG sensors are useful for detecting biological matter, from small molecules to larger proteins.