Novel fluorogenic substrates for imaging beta-lactamase gene expression.

A new class of small nonfluorescent fluorogenic substrates becomes brightly fluorescent after beta-lactamase hydrolysis with up to 153-fold enhancement in the fluorescence intensity. Less than 500 fM of beta-lactamase in cell lysates can be readily detected, and beta-lactamase expression in living cells can be imaged with a red fluorescence derivative. These new fluorogenic substrates should find uses in clinical diagnostics and facilitate the applications of beta-lactamase as a biosensor.