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Dynamic Biosensing

Ever since the development of the Gram stains (more than 100 years ago), the identification of bacterial species, using staining techniques, has been based solely on the final appearance of the stained cells. Hence, each test yields a Boolean outcome (i.e., in principle, the reagents either stain or do not stain the analyzed bacteria). As a result, each analysis affords a classification of species into only two groups on the basis of the staining pattern. Although morphology analysis, for example, can permit narrowing of the identification, further tests with higher specificity are required. Similarly, Boolean assays with high specificity (such as PCR and immunofluorescence staining) provide information solely about the presence of species that are sought. Thus pathogens, which are present in the sample but not targeted by the particular stain, remain undetected. 

For the first time, we observed that the staining dynamics depends particularly on the microorganisms and on the staining agents, rather than on their concentration. These characteristics of staining dynamics provide a means for unprecedented discernibility between bacterial species, and hence for results that exceed considerably beyond the Boolean outcomes of the current assays.