Rapid and green synthesis of highly luminescent MoS2 quantum dots via microwave exfoliation of MoS2 powder and its application as a fluorescence probe for cortisol detection in human saliva
2022
Mohammad-Andashti, Parastou | Ramezani, Zahra | Zare-Shahabadi, Vahid | Torabi, Parviz
We have introduced a simple, straightforward, green, and fast microwave exfoliation of MoS₂ powder to prepare highly luminescent MoS₂ quantum dots (QDs). The microwave irradiation of MoS₂ powder was evaluated in the different solvents, including EtOH 30%, MeOH 30%, NaOH 1 M, and NH₄OH 1 M in both open and closed microwave system setups. The results indicated that the highest luminescent MoS₂ QDs is obtained when MoS₂ powder was dispersed in 1 M ammonium solution and exposed to 850 W microwave radiation in a closed microwave system at 30 bars for 30 min. Different microscopic and spectroscopic techniques were used to characterize as-prepared MoS₂ QDs. The MoS₂ QDs have shown the maximum emission at 413 nm with excitation at 310 nm. The Quantum yield of as-prepared QDs was 1.98%. Cu²⁺, Pb²⁺, Cd²⁺, Ag⁺, Fe³⁺, and Al³⁺ quenched the luminescence intensity of MoS₂ QDs. The luminescence of MoS₂ QDs-Ag⁺ and Cu²⁺ mixtures were recovered on addition of cortisol with the higher emission recovery for Cu²⁺ ion. Therefore, proof-of-concept for cortisol sensing in human saliva was evaluated and discussed using off-on protocol. A linear cortisol calibration curve was obtained in the range of 100 ng mL⁻¹ to 500 ng mL⁻¹, with a detection limit of 16 ng mL⁻¹ (S / N = 3). The method was successful in determining the cortisol content of saliva.
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