The concept of using a hologram as the interactive element in a one-shot biosensor is presented. The theoretical basis for a directly observed optical response to biological molecules is introduced. The most immediate application of such a device, restricted to the detection of proteases, is described in this paper. Using spectrographic measurements, a reflection hologram in gelatin in particular has been applied to the detection of 20 μg ml-1 trypsin and 23 μg ml-1 chymotrypsin, showing a greater sensitivity to trypsin. Enhanced specificity to trypsin has been shown following treatment of the hologram with bovine pancreatic trypsin inhibitor (BPTI), although measurements of pancreatin have yielded only a non-calibrated response. Sensitivity to trypsin down to 0.04 μg ml-1 has been shown. The sensitivities described are relevant to normal trypsin levels in duodenal fluid and faeces, suggesting that a holographic biosensor of this type will be useful as a low-cost quantitative screening test for pancreatic disorders manifest by low levels of enzyme. Improvement in specificity and extension of the concept to other types of analytes is likely to require modified gelatin or hologram-bearing materials other than gelatin.
