Guoguang Rong

Nanoscale porous silicon waveguide for label-free DNA sensing

Porous silicon (PSi) is an excellent material for biosensing due to its large surface area and its capability for molecular size selectivity. In this work, we report the experimental demonstration of a label-free nanoscale PSi resonant waveguide biosensor. The PSi waveguide consists of pores with an average diameter of 20nm. DNA is attached inside the pores using standard amino-silane and glutaraldehyde chemistry. Molecular binding in the PSi is detected optically based on a shift of the waveguide resonance angle. The magnitude of the resonance shift is directly related to the quantity of biomolecules attached to the pore walls. The PSi waveguide sensor can selectively discriminate between complementary and non-complementary DNA. The advantages of the PSi waveguide biosensor include strong field confinement and a sharp resonance feature, which allow for high sensitivity measurements with a low detection limit. Simulations indicate that the sensor has a detection limit of 50nM DNA concentration or equivalently, 5pg/mm2.

Label-free porous silicon membrane waveguide for DNA sensing

We report a label-free porous silicon membrane waveguide biosensor based on a 1μm thick freestanding porous silicon film with 100nm diameter pores. The sensor operates in the Kretschmann configuration. A formvar polymer film provides robust adhesion of the porous silicon membrane to a rutile prism and enables confinement of guided modes in the porous silicon membrane. Attenuated total reflectance measurements are performed, along with theoretical calculations, to fully characterize the waveguide. The sensitivity of the sensor is investigated through DNA hybridization in the porous silicon membrane. A detection limit of 42nM was demonstrated for 24-base pair DNA oligonucleotides.

Grating couplers on porous silicon planar waveguides for sensing applications

We study the use of polymer gratings as light couplers into porous silicon planar waveguides for sensing applications. Experimental evidence of a guided mode in a grating-coupled porous silicon structure is presented, along with a study of its detuning due to waveguide infiltration with a chemical linker. All the measurements are in good agreement with simulations obtained by means of a Fourier modal method, where the porous silicon birefringence is considered. These results demonstrate that this system is potentially useful for chemical and biological sensing applications.

High Sensitivity Sensor Based on Porous Silicon Waveguide

Porous silicon (PSi) waveguides are fabricated as a new platform for high sensitivity biosensors. Biomolecules infiltrated into the PSi waveguide increase the effective refractive index of the waveguide and change the angle at which incident light couples into a waveguide mode. Due to the high surface area to volume ratio of PSi and the confinement of optical energy in the region where the biomolecules reside, the waveguide resonance is very sensitive to small concentrations of infiltrated molecular species. A resonance width below 0.1˚ has been obtained, which is sufficient to detect one monolayer of DNA covering the pore walls. In this work, a prism is used for the waveguide coupling in an arrangement that is similar to traditional surface plasmon resonance (SPR) sensing. Theoretical analysis suggests that an optimized PSi waveguide resonant sensor will show a 60-fold improvement in sensitivity when compared to a conventional SPR sensor due to the enhanced interaction between the electromagnetic field and biological material.

Influence of biomolecule size on performance of nanostructured sensing devices

Porous silicon is an excellent material for biosensing because of its large surface area and ability to filter out large contaminant species. In order to characterize the sensitivity of porous silicon based biosensors for biomolecules of different sizes, a mesoporous silicon waveguide with average pore diameter of 20 nm is used to detect single strand DNA oligos with different numbers of base pairs at different concentrations. Experimental results indicate that 16-mer DNA is detected most sensitively with the mesoporous silicon waveguide.

Gratings on porous silicon structures for sensing applications

We investigate the use of gratings on porous silicon structures for sensing applications. Examples of two classes of systems are studied: grating-coupled waveguide biosensors, and diffraction-based biosensors.

Porous Silicon Waveguides for DNA Detection

A porous silicon resonant waveguide sensor has been demonstrated for high sensitivity detection of biomolecules. Simulations predict a 60-fold enhancement over conventional SPR technology and initial experimental results using DNA oligos have been performed

Porous waveguide in the Kretschmann configuration for small molecule detection

In this work, we theoretically and experimentally demonstrate a highly sensitive porous silicon membrane waveguide biosensor in the Kretschmann configuration, and show how the cladding material directly impacts the waveguide sensor detection sensitivity and resonance width. Dielectric and metal-clad porous waveguides in the Kretchmann configuration have the potential to achieve significantly enhanced performance for small molecule detection compared to planar waveguide and surface plasmon resonance sensors due to increased surface area and strong field confinement in the porous waveguide layer. First order perturbation theory calculations predict that the quality factors of polymer-cladded porous silicon waveguides with porous silicon losses less than ~500 dB/cm are at least two times larger than the quality factors of gold-cladded porous silicon waveguides and traditional surface plasmon resonance sensors.

Nanoscale porous silicon waveguides for biosensing applications

Nanoscale porous silicon waveguides, both on silicon substrates and free-standing membranes, are explored for biosensing applications. Measured detection limits in the nanomolar range are reported for DNA sensing.

Porous Silicon Waveguides for Biosensing Applications

Porous silicon waveguides are designed and fabricated to achieve well-defined resonances suitable for high sensitivity biosensing. Two coupling schemes are investigated based on fabrication, measurement complexity, coupling losses, resonance quality, and DNA detection sensitivity.