Size Tuning, Phase Stabilization, and Anticancer Efficacy of Amorphous Selenium Nanoparticles: Effect of Ion-Pair Interaction, −OH Functionalization, and Reuse of RTILs as Host Matrix
Apurav Guleria, Chinnu M. Baby, Aniet Tomy, Dharmendra Kumar Maurya, Suman Neogy, Anil K. Debnath, Soumyakanti Adhikari
Abstract
Se nanoparticles (NPs) of predominantly amorphous phase (α-Se) have been prepared in room-temperature ionic liquids (RTILs). The effects of ion-pair combination and −OH functionalization of RTILs on the size and phase stability of Se NPs were investigated. The RTILs used were 1-ethyl-3-methyl imidazolium boron tetrafluoride ([EMIM][BF4]), 1-(2-hydroxyethyl)-3-methyl imidazolium boron tetrafluoride ([EOHMIM][BF4]), and 1-ethyl-3-methyl imidazolium methane sulfonate ([EMIM][MS]). The size of Se NPs@[EOHMIM][BF4] was found to be the smallest (∼32 nm), followed by Se NPs@[EMIM][BF4] (∼57 nm) and Se NPs@[EMIM][MS] (∼60 nm), respectively. Interestingly, the stability studies revealed minimal size variations for Se NPs@[EMIM][MS], followed by Se NPs@[EOHMIM][BF4] and Se NPs@[EMIM][BF4], respectively. The observed trends could be correlated with the strength of interionic interactions in the respective RTILs, as well as their packing order (density). Importantly, the RTILs played the role of a solvent, a stabilizer, and an in situ source of reducing species. Pulse radiolysis study revealed imidazolium-originated radical species-driven formation of Se NPs. Further, anticancer efficacy studies demonstrated the role of NP size, wherein Se NPs@[EOHMIM][BF4] exhibited the highest cancer cell killing, followed by Se NPs@[EMIM][BF4] and Se NPs@[EMIM][MS]. Another significant highlight of this work is the reuse of the spent RTILs for the synthesis of the next batch of Se NPs.