Nanoporous silicon for diagnostics

Click to Enlargeby Neha Choksi, contributing editor

June 30, 2010 – Proteomics is an important field for the pursuit of drug discovery, vaccine development, and drug manufacturing. However, prevalent methods require fluorescent labeling and 2D evaluation through electrophoresis or mass spectrometry. Hus Tigli, CEO of Silicon Kinetics, shared an alternative approach that leverages nanotechnology, at the San Francisco Bay Area IEEE Nanotechnology Sixth Annual Symposium: "Nanotechnology: State of the art and applications" (May 18-19 in Santa Clara, CA).

The company’s SKi biosensor consists of nanoporous silicon chips embedded in probes or flow cells, technology developed over approximately three years. By starting with n-type silicon and employing wet etch techniques, the resulting sensor area can achieve 70%-90% porosity with an average pore diameter of 80nm. This design was chosen to allow molecules to enter and exit as needed. Thickness, diameter, and etch uniformity are carefully controlled through statistical process control methods. The nanopores are important because they provide a large surface area for binding the first molecule of interest to create the desired surface chemistry. This functionalized sensor can then be used to detect the biomolecule of interest present in the solution that is being analyzed.

These biosensors are used in the company’s SKi Pro nanoporous optical interferometry (NPOI) platform. Depending on what molecule attaches to the first molecule of interest, the effective refractive index changes in the nanopore, leading to an optical path difference. Utilizing the platform’s interferogram, software is utilized to study the resultant pattern changes which form through constructive and destructive interference. The rate of change over time can be studied to extract information regarding the amount of molecule of interest that has bound to the biosensor.

Click to Enlarge

Because the nanopores are at a depth of 1.5-2nm into the wafer, the light used in the system passes through multiple layers of biomaterial, yielding a high throughput 3D approach. This "label free" method does not require sample preparation and does not interfere with the structure of the molecule of interest. The sensor is reusable 10-50×, and the company’s platform has automated cleaning using a solvent solution.

The company has taken the need for flexibility into account with the design of their system. "In addition to being highly sensitive, the NanoPore Optical Interferometry (NPOI) platform uniquely allows dual format experiments on the same instrument, either high-throughput ranking of interactions as well as detailed kinetic analysis," according to Tigli. Either way, the company aims to have an impact in the fields of drug discovery and disease research.

Neha K. Choksi is an independent consultant based in Mountain View, CA. She has worked for a variety of MEMS companies including as director of product engineering at Silicon Microstructures and as a consultant focusing on commercialization and high-volume production of MEMS devices. E-mail: Choksi [at] gmail.

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