Ratiometric fluorescence sensors for heparin and heparinase based on enhanced excimer emission of perylene probe induced by cationic silver nanoparticles

Herein, cationic MUTAB-Ag NPs of different sizes were synthesized and their interactions with a negatively charged perylene probe, N,N′-bis(6-caproic acid)-3,4:9,10-perylenediimide (PDI-COOH), were investigated. MUTAB-Ag NPs could result in significant monomer quenching and excimer formation by inducing probe aggregation due to the strong electrostatic attractive interactions between them. Moreover, significant excimer emission could be observed at extremely low probe concentration when induced by larger MUTAB-Ag NPs. A possible mechanism of metal-enhanced fluorescence was proposed, which is evidenced by the strong dependence between surface plasmon resonance absorption spectra of MUTAB-Ag NPs and the excimer emission spectra of PDI-COOH, together with the sharp decrease in fluorescence lifetime of excimer compared with that induced by poly(allylamine). Consequently, ratiometric fluorescence sensors for heparin and heparinase were developed based on the Ag NP-induced excimer emission of PDI-COOH. The adsorption of heparin on the surface of MUTAB-Ag NPs led to the release of monomer, while the degradation of heparin by heparinase facilitated the formation of PDI-COOH excimer. The monomer-excimer transition signal was harnessed for heparin and heparinase sensing, which exhibited good sensitivity and excellent selectivity. Finally, application of the present system for detection of heparin and heparinase in human serum sample was successfully demonstrated.