Glutathione-Functionalized Organosilicon Oxide Nanoparticles for Bioimaging and Forensics

Herein, we report an electron beam mediated one-pot, rapid approach for the synthesis of blue light emitting organosilicon oxide nanoparticles (OSiNPs) in aqueous solution with a potential for scale-up production. Mechanistic studies based on pulse radiolysis revealed that unlike the generally believed solvated electron (esol–) driven process, the present synthesis proceeds through the reaction of hydroxyl radical (·OH) with the precursor molecules resulting in the formation of silane-derived radicals. Subsequently, these radicals react with each other to form OSiNPs. Compositional studies by XPS, FTIR, and Raman indicate the presence of siloxane/silicone and silica (SiO2) like units as the major constituents in the NPs. XRD pattern signifies the amorphous nature of the NPs, while imaging studies revealed self-assembling of NPs (3–5 nm) into a porous structure. Notably, the NPs exhibited excitation-wavelength-dependent photoluminescence (PL) spectra, pointing to the presence of multiple emission centers with varying energy levels. The nature of these emission centers and their heterogeneous distribution was analyzed in detail through pH and absorbed dose dependent PL studies, HF treatment, fluorescence excitation spectrum, temperature dependent steady state, and time-resolved PL studies. Moreover, OSiNPs were functionalized with a biocompatible ligand, i.e., l-glutathione (l-Glu), which significantly enhanced the quantum efficiency (up to ∼25%) of emission as well as colloidal stability. These functionalized NPs (l-Glu@OSiNPs) were found to exhibit less toxicity up to a concentration of ∼0.5 mg/mL. Interestingly, the l-Glu@OSiNPs exhibited tumor selectivity (in A549 human lung cancer cells) at lower pH along with cell labeling capabilities with propensity to localize at the nucleus. Furthermore, in addition to their usage in anticounterfeiting measures, application of l-Glu@OSiNPs in fingerprinting was also demonstrated by testing on a variety of surfaces. Meanwhile, linear and reproducible PL intensity variations of OSiNPs signify highly sensitive and robust thermosensing properties of OSiNPs.