Nashville, TN--A type of porous silicon that acts like a sponge to help optically identify toxins has been created by researchers at Vanderbilt University. The toxin, or other small molecules to be detected, fills the spaces in the silicon, changing its optical properties. For example, capturing a particular sequence of DNA can be done by seeding the sensor with a single strand of DNA, so that only the complementary strand can attach to it and everything else gets rinsed away.
Often, conventional sensors are so large that small molecules don't perturb the sensor's properties enough for detection. But, as Vanderbilt University's Xing Wei, a graduate student, and Sharon Weiss, an associate professor of electrical engineering and physics, report in Optics Express, it's possible to eliminate this challenge by making sensors with features that are comparative in size to the molecules being detected, greatly increasing the sensitivity of current sensing technology. 1
The value of porous versus nonporous silicon is described by Weiss in an example: take two cubes, one of which is 3 cm on a side, with a flat surface that DNA can be attached to--providing 54 cm2 of available surface area. The other is an identical-sized cube, made into a porous silicon sponge and with the ability to access the volume of the cube with all of the internal surface area, providing a surface area that is nearly 10,000 times greater than the first cube.
In the device, an optical grating on the sensor's surface channels light into the sensor; the grating's angle of diffraction changes upon sensing a DNA molecule. "By knowing how much the angle changes, for example, we can quantify how many molecules are present," says Weiss. "So not only can we identify our DNA sequence or toxin, but we can also know how much is present as well. For diagnostics, it's very helpful to know how much is present."
1. Xing Wei and Sharon M. Weiss, Optics Express, Volume 19, Issue 12, pp. 11330-11339 (2011).
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