Abstract
A photographic process includes a sensitive chemical amplification step catalyzed by silver metal (Ag°) nuclei which are responsible for the formation of silver images. Although the Ag nuclei are normally produced by exposure to light, we observed that they are formed by treatment of an unexposed negative film with a certain kind of compound (a nucleating reagent) without exposure. Moreover, a linear relationship clearly existed between the optical density of the film developed and the logarithm of concentration of the compound over the range from 2.0 × 10-8 M to 8.0 × 10-8 M. On the basis of the findings, a highly sensitive photographic assay procedure of α-amylase by using the photographic development process was proposed. In line with the concept, an a-amylase substrate incorporating the nucleating reagent newly observed, as a labeling component, was synthesized regioselectively. The analysis of enzymatic degradation proved that the substrate synthesized can release efficiently the nucleating reagent without loss of photographic activity. This provides the first successful approach for application of a photographic system into a quantitative determination of trace organic molecules.
