Tunable photoluminescence properties of selenium nanoparticles: biogenic versus chemogenic synthesis

Various technological and biomedical applications rely on the ability of materials to emit light (photoluminescence [PL]), and, among them, metal nanoparticles (NPs) and semi-conductor Quantum Dots (QDs) represent ideal candidates as sensing probes and imaging tools, portraying better PL features than conventional organic dyes. However,theknowledgeofPLbehaviorofsemiconductorNPs – i.e., selenium; SeNPs – is still in its infancy, especially for those synthesized by microorganisms. Considering the essential role played by biogenic SeNPs as antimicrobial, anticancer, and antioxidant agents, or food supplements, their PL properties must be explored to take full advantage of them as eco-friendly and versatile tools. Here, PL features of SeNPs produced by the Se-tolerant Stenotrophomonasmaltophilia SeITE02 strain, compared with chemogenic ones, are investigated, highlighting the PL dependency on the NP size. Indeed, PL emission shifted from indigo-blue (emission wavelength λem 400–450 nm) to green-yellow (λem 480– 570 nm) and orange-red (λem 580–700 nm) for small (ca. 50 nm) and big (ca. 100 nm) SeNPs respectively, revealing the versatility of an environmental bacterial isolate to synthesize diverse PL probes. Besides, biogenic SeNPs show PL lifetime comparable to those of the most used fluorophores, supporting their potential application as markers for (bio)imaging.