Hot injection versus room temperature synthesis of CdSe quantum dots: A differential spectroscopic and bioanalyte sensing efficacy evaluation

In this work, we have performed an exhaustive comparative study of structural, optical, and sensing properties of CdSe quantum dots (QDs) synthesized by hot-injection (HI), and room temperature (RT) protocols. CdSe QDs were synthesized in aqueous solution at room temperature by reacting cadmium chloride pentahydrate (CdCl2·5H2O) with sodium hydrogen selenide (NaHSe) in presence of capping agent 3-mercaptopropionic acid (MPA). In hot-injection (HI) method elemental Se was reacted with CdO at 225 °C. These were characterized by XRD, TEM, EDX, UV–vis, and fluorescence spectroscopy. The EDX measurements indicated that these quantum dots were highly pure, and had their composition as ≈Cd:Se = (1:1) (atomic% by weight) for both types of QD samples. These exhibited relatively narrow fluorescence band and high fluorescence intensity in the yellow spectral range. The HI-QDs exhibited high photochemical stability, and offered sufficient promise for application in design of optoelectronic devices. Steady state and time resolved fluorescence spectra revealed differential quantum yield (higher for HI-QDs), and life-times as function of synthesis protocol. However, the optical response profile revealed higher binding efficacy of RT-QDs in respect for oxalic, ascorbic acid, citric acid, and hydrogen peroxide analytes. Therefore, it is concluded that HI-QDs had rich spectroscopic signature, but poor sensing attributes (against ascorbic acid, citric acid, oxalic acid, and hydrogen peroxide) compared to RT-QDs. Further, HI-QDs could be synthesized in the size range of 2.5–6.3 nm whereas by RT method only fixed size (≈3.3 nm) nanoparticles could be prepared.