Sensitive optical biosensors for unlabeled targets: a review.

Organometallic chemistry on silicon and germanium surfaces.

Novel organic−inorganic hybrid mesoporous materials have been synthesized, in which organic and inorganic oxide moieties are distributed homogeneously at the molecular level in the framework, forming a covalently bonded network. They are highly ordered at the mesoscale, with two- and three-dimensional hexagonal symmetries and well-defined external morphologies. Nitrogen adsorption measurements show a uniform pore-size distribution with pore diameters of 31 and 27 A, and high surface areas of 750 and 1170 m2/g. The synthetic procedure to polymerize the organosilane monomer containing two trialkoxysilyl groups in the presence of surfactant can be applied to the synthesis of a variety of highly ordered organic−inorganic hybrid mesoporous materials.

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/J%20Ame%20Che%20Soc121,%209611.pdf

Novel Mesoporous Materials with a Uniform Distribution of Organic Groups and Inorganic Oxide in Their Frameworks

http://nathan.instras.com/documentDB/paper-69.pdf

Porous silicon: a quantum sponge structure for silicon based optoelectronics

A simple and effective method is presented for producing light-emitting porous silicon (PSi) A thin (d<10 nm) layer of Au, Pt, or Au/Pd is deposited on the (100) Si surface prior to immersion in a solution of HF and H2O2 Depending on the type of metal deposited and Si doping type and doping level, PSi with different morphologies and light-emitting properties is produced PSi production occurs on the time scale of seconds, without electrical current, in the dark, on both p- and n-type Si Thin metal coatings facilitate the etching in HF and H2O2, and of the metals investigated, Pt yields the fastest etch rates and produces PSi with the most intense luminescence A reaction scheme involving local coupling of redox reactions with the metal is proposed to explain the metal-assisted etching process The observation that some metal remains on the PSi surface after etching raises the possibility of fabricating in situ PSi contacts

Metal-assisted chemical etching in HF/H2O2 produces porous silicon

A biosensor has been developed based on induced wavelength shifts in the Fabry-Perot fringes in the visible-light reflection spectrum of appropriately derivatized thin films of porous silicon semiconductors. Binding of molecules induced changes in the refractive index of the porous silicon. The validity and sensitivity of the system are demonstrated for small organic molecules (biotin and digoxigenin), 16-nucleotide DNA oligomers, and proteins (streptavidin and antibodies) at pico- and femtomolar analyte concentrations. The sensor is also highly effective for detecting single and multilayered molecular assemblies.

https://science.sciencemag.org/content/sci/278/5339/840.full.pdf

A Porous Silicon-Based Optical Interferometric Biosensor

The reversibility, specificity, stability, and scaling of signal response to analyte mass were quantified for a porous silicon-based optical interferometric biosensor. The sensor system studied consisted of a thin layer (5μm) of porous silicon modified with Protein A. The system was probed with various fragments of an aqueous Human IgG analyte. The sensor operates by measurement of the Fabry−Perot fringes in the white light reflection spectrum from the porous silicon layer. Molecular binding is detected as a shift in wavelength of these fringes. IgG was added to and removed from the protein A-modified surface by changing solution pH in a flow cell, and the system was found to be reversible through several on−off cycles. The molecule used to link protein A to the porous Si surface incorporated bovine serum albumin (BSA). This approach was found to completely eliminate signal due to nonspecific binding, tested by exposure of the sensor to the F(ab‘)2 fragment of IgG (which does not bind to protein A). The l...

A Porous Silicon Optical Biosensor: Detection of Reversible Binding of IgG to a Protein A-Modified Surface

We present in this paper that porous silicon can be used as a large surface area matrix as well as the transducer of biomolecular interactions. We report the fabrication of heavily doped p-type porous silicon with pore diameters that can be tuned, depending on the etching condition, from approximately 5 to 1200 nm. The structure and porosity of the matrixes were characterized by scanning force microscopy (SFM) and scanning electron microscopy (SEM), Brunnauer−Emmett−Teller nitrogen adsorption isotherms, and reflectance interference spectroscopy. The thin porous silicon layers are transparent to the visible region of the reflectance spectra due to their high porosity (80−90%) and are smooth enough to produce Fabry−Perot fringe patterns upon white light illumination. Porous silicon matrixes were modified by ozone oxidation, functionalized in the presence of (2-pyridyldithiopropionamidobutyl)dimethylmethoxysilane, reduced to unmask the sulfhydryl functionalities, and coupled to biotin through a disulfide-bon...

Macroporous p-Type Silicon Fabry−Perot Layers. Fabrication, Characterization, and Applications in Biosensing

Porous silicon films displaying a distribution of pore dimensions can be generated by electrochemically etching silicon in aqueous ethanolic HF using an asymmetric electrode configuration. The median pore size and breadth of the size-distribution in the film can be set by adjusting the HF concentration, current density, and position of the counter electrode relative to the silicon electrode. Films with pore sizes in the range of a few nanometers are used as size-exclusion matrices to perform an on-chip determination of macromolecule dimensions. The test molecule used in this study is bovine serum albumin (BSA). Optical reflectivity spectra of the thin porous Si films display distinctive shifts in the Fabry–Perot fringes in regions of the film where the pore dimensions are larger than a critical size, interpreted to be the characteristic dimensions of the protein. Gating of the protein in and out of the porous films is demonstrated by adjustment of the solution pH below and above the pI (isoelectric point) value, respectively.

Determining Protein Size Using an Electrochemically Machined Pore Gradient in Silicon

The measurement of the wavelength shifts in the reflectometric interference spectra of a porous semiconductor substrate such as silicon, make possible the highly sensitive detection, identification and quantification of small analyte molecules. The sensor of the subject invention is effective in detecting multiple layers of biomolecular interactions, termed “cascade sensing”, including sensitive detection of small molecule recognition events that take place relatively far from the semiconductor surface.

Keiki-Pua S. Dancil

Papers

A Porous Silicon-Based Optical Interferometric Biosensor

A Porous Silicon Optical Biosensor: Detection of Reversible Binding of IgG to a Protein A-Modified Surface

Macroporous p-Type Silicon Fabry−Perot Layers. Fabrication, Characterization, and Applications in Biosensing

Determining Protein Size Using an Electrochemically Machined Pore Gradient in Silicon

Porous semiconductor-based optical interferometric sensor