Microfluidic-assisted green synthesis of Calotropis procera-derived ZnO quantum dots and evaluation of their antibacterial and antifungal properties against plant pathogens

This study compared ultrasonic- and microfluidic-assisted green synthesis of zinc oxide quantum dots (ZnO QDs) using Calotropis procera leaf extract as a bio-reducing and stabilizing agent. Both routes generated phase-pure wurtzite ZnO confirmed by XRD; the microfluidic route yielded sharper reflections and narrower size distribution, indicating higher crystallinity and monodispersity. TEM showed aggregated ultrasonic QDs (5–15 nm) versus uniform spherical ones under continuous flow. Optical analyses displayed size-dependent absorption near 398 nm (ultrasonic) and 392 nm (microfluidic) with luminescence peaks at 552–557 nm. EDX verified Zn–O bonding and minimal impurities. Antimicrobial tests revealed stronger activity for QDs than the plant extract, with MIC = 0.10 mg/mL for Ralstonia solanacearum and 0.40–0.80 mg/mL for Pseudomonas syringae . Incorporation into a PDMS-glass microfluidic bio-platform enhanced efficacy via improved nanoparticle–cell contact and mixing, causing 1.4-fold higher nucleic-acid leakage and 25 % greater K + efflux in 15 min. The QDs also inhibited Botrytis cinerea and Fusarium spp. and showed biosafety (LC 50 = 850 ± 21 μg/mL). Overall, the microfluidic method produced structurally uniform, pure, and bio-efficient ZnO QDs, establishing C. procera -derived QDs as sustainable, high-performance antimicrobial nanomaterials. • Microfluidic ZnO QDs showed higher crystallinity, uniformity, and monodispersity. • Calotropis procera extract enabled eco-engineered synthesis of phase-pure ZnO QDs. • ZnO QDs exhibited fold higher leakage and stronger antibacterial performance. • Continuous-flow system enhanced purity and biosafe antimicrobial nanomaterial yield.