Digital Biology.

Number of a molecule is discrete by its nature. Therefore, when detection sensitivity of analytical methods approaches the single molecule level, one faces the intrinsic discreteness of the measured concentration and number of analytes. An emerging analytical method that employs this intrinsic discreteness is digital counting. When an analyte solution is partitioned into many small reaction compartments, such that each molecule is individually encapsulated into a compartment, the analyte quantification is inevitably digitized; each compartment contains none or one molecule of analyte. When a solution of enzyme or enzyme-conjugated molecule is partitioned into such small reactors with fluorogenic substrate, one can count the number of the molecule as that of fluorescent reactors under an optical microscope. We refer to this strategy as “digital counting”. One of the most successful examples of digital counting is digital ELISA, in which target molecules are individually encapsulated in a water-in-oil droplet after bound to enzyme-conjugated antibody. Although the chemistry of digital ELISA; antibody and enzyme is common to conventional ELISA, the detection sensitivity of digital ELISA is higher than that of conventional ELISA by 4 to 6 orders of magnitude. In this review, we introduce recent achievements in digital ELISA and relevant methods. [ABSTRACT FROM AUTHOR]