|Georgia Tech researchers Ken Sandhage, left, and Ali Adibi examine a porous-silicon optical sensing device and a silicon wafer. (Credit: Gary Meek)
Researchers at Georgia Institute of Technology (Georgia Tech; Atlanta, GA), have developed a novel method for improving silicon-based optical sensors used to detect biochemicals and other molecules in liquids. The simplified approach produces microscale optical-detection devices that cost less to make than other designs, and provide a sixfold increase in sensitivity to target molecules.1
The new technique uses a thin film of porous silicon material to coat a layer of light-conducting dense silicon. The porous silicon thin film contains many connected pores and internal surfaces that greatly increase the effective area onto which a chemical component of interest (the "analyte") can bind. The increased surface area allows the porous silicon to capture larger numbers of analyte molecules, which increases overall detection sensitivity, boosting detection of analytes occurring in low concentrations.
Standard SOI substrates
Unlike earlier methods for generating porous silicon, the Georgia Tech thin-film process is more easily adapted for use with standard silicon-on-insulator (SOI) substrates, and also allows for highly precise control of the thickness of the porous silicon layer. The sensor, which uses a racetrack optical resonator, has a high Q factor of around 22,000, and can sense quantities of analyte down to about 0.8 pm (pg mm-2)-1.
The work was part of the Centers in Integrated Photonics Engineering Research (CIPhER) program, a $4.3 million, two-year effort funded by the Defense Advanced Research Projects Agency (DARPA) to develop advanced lab-on-a-chip sensing technology capable of detecting multiple biological and chemical threats on a compact integrated platform. Other center participants included Emory University (Atlanta, GA), Massachusetts Institute of Technology (MIT: Cambridge, MA), University of California-Santa Cruz, and Yale University (New Haven, CT).
1. Zhixuan Xia et al., Advanced Optical Materials (2014); doi: 10.1002/adom.201300465