Biosensing Using Porous Silicon Double-Layer Interferometers:  Reflective Interferometric Fourier Transform Spectroscopy

Abstract

A simple, chip-based implementation of a double-beam interferometer that can separate biomolecules based on size and that can compensate for changes in matrix composition is introduced. The interferometric biosensor uses a double-layer of porous Si comprised of a top layer with large pores and a bottom layer with smaller pores. The structure is shown to provide an on-chip reference channel analogous to a double-beam spectrometer, but where the reference and sample compartments are stacked one on top of the other. The reflectivity spectrum of this structure displays a complicated interference spectrum whose individual components can be resolved by fitting of the reflectivity data to a simple interference model or by fast Fourier transform (FFT). Shifts of the FFT peaks indicate biomolecule penetration into the different layers. The small molecule sucrose penetrates into both porous Si layers, whereas the large protein bovine serum albumin (BSA) only enters the large pores. BSA can be detected even in a large (100-fold by mass) excess of sucrose from the FFT spectrum. Detection can be accomplished either by computing the weighted difference in the frequencies of two peaks or by computing the ratio of the intensities of two peaks in the FFT spectrum.

Synthesis and characterization of a nanostructured porous silicon/carbon dot-hybrid for orthogonal molecular detection

“…13 Application of fast Fourier transform to the reflectivity data yielded a peak with characteristic EOT and intensity (Figure 1d, right), which are distinctive features of the detected analytes. 30,31 Figure 1e depicts a representative fluorescence emission spectrum generated by the C-dots embedded within the PSiO 2 pores. Modulation of the fluorescence of Nanostructured PSi/C-dot-hybrid for orthogonal molecular detection N Massad-Ivanir et al the C-dots, that is, both the wavelength and intensity, is induced upon adsorption of molecules in close proximity to the embedded carbon nanoparticles.…”

Vapor-phase silanization of oxidized porous silicon for stabilizing composition and photoluminescence

“…14 A significant benefit of biosensing with PSi photonic crystals is the labelfree transduction by optical interference ͑change in refractive index n within the film͒. 15,16 Unfortunately, the instability of the underlying surface to aqueous environments has hindered the wide-scale employment of PSi for biological applications. 17,18 Recent interest in PSi was focused on its use as a delivery vehicle for therapeutic agents such as ibuprofen 19 and insulin.…”

Use of TOF-SIMS to study adsorption and loading behavior of methylene blue and papain in a nano-porous silicon layer

“…Negative fragments (SiOSH 3 Ϫ and SiO 2 SCH -) also suggested chemisorption via O bridging of the substrate Si and methylene blue S. The larger Papain molecule (23,406 Da) distributed itself in a similar manner to methylene blue demonstrating larger molecules can be effectively incorporated into such pore structures. (J Am Soc Mass Spectrom 2010, 21, 254 -260) © 2010 American Society for Mass Spectrometry P orous silicon (pSi) is a nanostructured material with 2-50 nm pores and has been investigated for use in a range of applications, including; optical [1,2], biosensing [3], radiotherapy (brachytherapy) [4], and the delivery of active pharmaceutical ingredients [5,6]. The ongoing interest in pSi for use as a therapeutic delivery system is due to the large internal surface area available, the readily modified surface chemistry [7] and, in particular, the excellent in vivo biodegradation and biocompatibility (low toxicity) of the silicon substrate, hydrolysing to form orthosilicic acid, which is readily excreted [8].…”