Research Notes

A silicon chip biosensor the size of a grain of sand and developed at the University of Rochester can distinguish Gram-negative from Gram-positive bacteria. According to Benjamin Miller, assistant professor of chemistry, and Philippe Fauchet, professor and chair of electrical and computer engineering, this "smart bandage" offers promising applications in diagnostics, forensics, and food safety (S. Chan et al., "Identification of Gram negative bacteria using nanoscale silicon microcavities," The Journal of the American Chemical Association, 123[47]:11797-8, 2001). The classic Gram stain dates to 1884, and distinguishes bacterial cell wall differences--Gram-positive turns purplish blue, whereas the Gram-negative lipopolysaccharide (LPS) outer layer becomes pink. "The Gram stain has been an important tool in analyzing bacteria for more than a century, but it's amazing to me that we're still using a procedure that's effectively out of the Stone Age," says Miller. The biosensor's nanoscale silicon layers has a microcavity that embraces an organic probe molecule which has an affinity for a target; in this case, the highly conserved lipid A portion of the LPS layer. When the sensor binds its target, the patterns of light refraction shift, causing a wavelength shift on a spectrophotometer. Household versions on the horizon will have a color change visible to the unaided eye, Miller says. In an initial experiment, the biosensor distinguished Gram-negative Escherichia coli from Gram-positive Bacillus subtilis. The research team is applying the technology to many bacteria, including antibiotic resistant strains, and envisions a smart bandage with many such sensors embedded.