Signal amplification techniques are broadly used to improve the detection sensitivity of various analytes for diagnostic purposes. We have developed a novel, non-PCR-based modular technique for exponential amplification of diagnostic signals that is conveniently performed in an aqueous environment. The technique is based on a distinctive dendritic chain reaction (DCR); the diagnostic signal is generated upon disassembly of a self-immolative dendrimer that releases chromogenic molecules. Under ideal conditions, a single analyte molecule initiates a DCR that generates a strong diagnostic signal. When coupled with a protease diagnostic probe, the DCR technique detected the activity of penicillin-G-amidase with high sensitivity. This is the first example of exponential signal amplification performed under aqueous conditions that is not based on PCR.