A new type of biosensor that combines the inexpensiveness and mass-produceability of reflection holograms with the selectivity and specificity of enzymes is described. pH-sensitive holographic sensors were fabricated from ionizable monomers incorporated into thin, polymeric, hydrogel films which were transformed into volume holograms using a diffusion method coupled with holographic recording, using a frequency-doubled Nd:YAG laser (532 nm). These holograms were used as transducer systems to monitor the pH changes associated with specific enzymatic reactions to construct prototype urea- and penicillin-sensitive biosensors. The diffraction wavelength (color) of the holographic biosensors was used to characterize their shrinkage and swelling behavior as a function of analyte concentration. The potential of these sensors for the measurement of the clinically and industrially important metabolites urea and penicillin G is demonstrated.
