8-hydroxyquinolinyl azo dyes: a class of surface-enhanced resonance Raman scattering-based probes for ultrasensitive monitoring of enzymatic activity.

A series of surface-enhanced resonance Raman scattering (SERRS) based probes for the detection of lipase activity are reported. A number of novel SERRS-active 8-hydroxylquinolinyl azo dyes have been prepared and via synthetic esterification or subsequent enzymatic hydrolysis at the 8-hydroxyl position the SERRS signal can be "switched" on or off. In the first instance, the technique has been demonstrated for the successful detection of lipase from Pseudomonas cepacia, and these new compounds offer a limit of detection of 0.2 ng mL-1 enzyme, up to a 100-fold lower limit than observed for benzotriazolyl dyes used in previous studies. The chemical synthesis is straightforward and allows for facile introduction of a wide range of different masking groups, using commonly known synthetic methodologies. The potential for multiplexing analysis of enzyme activity using this technology is presented within.