A HOLOGRAM BIOSENSOR FOR PROTEASES

The concept of using a hologram as the interactive element in a one-sh ot biosensor is presented. The theoretical basis for a directly observ ed optical response to biological molecules is introduced. The most im mediate application of such a device, restricted to the detection of p roteases, is described in this paper. Using spectrographic measurement s, a reflection hologram in gelatin in particular has been applied to the detection of 20 mu g ml(-1) trypsin and 23 mu g ml(-1) chymotrypsi n, showing a greater sensitivity to trypsin. Enhanced specificity to t rypsin has been shown following treatment of the hologram with bovine pancreatic trypsin inhibitor (BPTI), although measurements of pancreat in have yielded only a non-calibrated response. Sensitivity to trypsin down to 0.04 mu g ml(-1) has been shown. The sensitivities described are relevant to normal trypsin levels in duodenal fluid and faeces, su ggesting that a holographic biosensor of this type will be useful as a low-cost quantitative screening test for pancreatic disorders manifes t by low levels of enzyme. Improve ment in specificity and extension o f the concept to other types of analytes is likely to require modified gelatin or hologram-bearing materials other than gelatin.