Tuning fluorescence of dapoxetine by blocking of photoinduced electron transfer (PET): Application in real human plasma

Photoinduced electron transfer (PET) is the most common mechanism proposed to account for quenching of fluorophores. Herein, the intrinsic fluorescence of dapoxetine (DPX) hydrochloride is in the “OFF” state, owing to the deactivation effect of PET. When the amine moiety is protonated, the fluorescence is restored. Protonation of the nitrogen atom of the tertiary amine moiety in DPX leads to “ON” state of fluorescence due to hindrance of the deactivating effect of PET by protonation of the amine moiety. This permits specific and sensitive determination of DPX in human plasma lower limit of quantification (LLOQ) = 30.0  $\mathrm{ng}{\mathrm{mL}}^{?1}$]. The suggested method adopts protonation of DPX using 0.25 M hydrochloric acid in anionic micelles 6.94 mM sodium dodecyl sulfate (SDS)] leads to a marked enhancement of DPX-fluorescence, after excitation at 290 nm.