Synthesis and use of QCy7-derived modular probes for the detection and imaging of biologically relevant analytes

This protocol describes the synthesis of modular turn-ON QCy7-based probes for the detection of biologically relevant analytes, such as hydrogen peroxide, ubiquitous sulfhydryl and β-galactosidase. The probes presented herein are prepared through a simple procedure that involves the preliminary alkylation of 4-hydroxy-isophthalaldehyde with a relevant analyte-responsive protecting group, followed by condensation of the resulting product with 2 equivalents of sulfo-indolium moieties. Evaluation of the turn-ON near-IR fluorescence response to their relevant analytes for the three different QCy7 probes is also reported. The preparation of a QCy7 diagnostic probe requires 1-2 d. Probes for other analytes can be prepared according to this modular procedure by incorporating a specific analyte-responsive group as a triggering substrate.