Zinc metal-organic frameworks- graphene quantum dots nanocomposite mediated highly sensitive and selective fluorescence "On-Off-On" probe for sensing of quercetin.

Presently, there is a necessity to design novel methods because of quercetin's significant biological relevance. Therefore, we developed the rose petal-derived graphene quantum dots embedded zinc metal organic frameworks (RP-GQDs@Zn-MOFs) based fluorescence "On-Off-On" nanoprobe for quercetin sensing. Initially, RP-GQDs were synthesized using rose petal waste and then subjected to embedding into Zn-MOFs. Herein, the addition of copper ions (Cu2+) results in fluorescence "Switch Off" whereas quercetin inclusion resulted in the formation of the quercetin-Cu2+ complex. It regains the RP-GQDs@Zn-MOFs quenched fluorescence termed as "Switch On" because of the static quenching mechanism. It demonstrated a wide concentration range and low detection limit of 100 ng/mL to 1400 ng/mL (R2=0.99) and 37.84 ng/mL, respectively. The selectivity study shows the high specificity for quercetin in presence of interfering compounds because of Cu2+ coordination between the carbonyl oxygen atom and the 3-OH group of quercetin. Moreover, the designed probe shows good stability, repeatability, and real-time analysis possibility.