A photoacoustic-fluorescent imaging probe for proteolytic gingipains expressed by Porphyromonas gingivalis

Porphyromonas gingivalis is a keystone pathogen in periodontal disease. We herein report a dual-modal fluorescent and photoacoustic imaging probe for the detection of gingipain proteases secreted by P. gingivalis. This probe harnesses the intramolecular dimerization of peptide-linked cyanine dyes to induce fluorescence and photoacoustic off-states. Upon proteolytic cleavage by Arg-specific gingipain (RgpB), five-fold photoacoustic enhancement and >100-fold fluorescence activation was measured with detection limits of 1.1 nM RgpB and 5.0E4 CFU/mL bacteria in vitro. RgpB activity was imaged in the subgingival pocket of porcine jaws with 25 nM sensitivity. The diagnostic efficacy of the probe was evaluated in gingival crevicular fluid (GCF) samples from subjects with (n = 14) and without (n = 6) periodontal disease, wherein activation was correlated to qPCR-based detection of P. gingivalis (Pearson’s r = 0.71). The highest activity was seen in subjects with the most severe disease. Finally, photoacoustic imaging of RgpB-cleaved probe was achieved in murine brains ex vivo, demonstrating relevance and potential utility for animal models of general infection by P. gingivalis, motivated by the recent biological link between gingipain and Alzheimer’s disease.