Tunable electronic and optical properties of functionalized silicon nanoclusters: A DFT study for nanomedical applications

Silicon-based nanostructures are emerging as promising platforms for biomedical imaging and phototherapy due to their biocompatibility and tunable optoelectronic properties. In this work, we propose a rationally designed nano-bait based on glucose-functionalized sila-dodecahedrane for the selective optical detection of cancer cells. Density functional theory (DFT) and time-dependent DFT calculations were employed to investigate the structural stability, electronic characteristics, optical response, and interfacial interactions of pristine and glucose-modified silicon nanocages. The results reveal that glucose functionalization induces controlled bandgap narrowing and a pronounced red-shift in absorption and emission spectra, enabling visible-light activation without compromising structural integrity. Noncovalent interaction (NCI) analysis demonstrates that van der Waals forces and weak hydrogen bonding dominate glucose–cage stabilization, ensuring strong adsorption while preserving electronic confinement within the silicon core. This noncovalent decoupling allows the glucose branches to retain an electronic signature comparable to free glucose, facilitating biological recognition while maintaining electronic inertness and low toxicity. The combined structure–properties–relationships analysis establishes surface functionalization density as an effective design parameter for tuning optical response independently of nanoparticle size. These findings provide fundamental insights into the design of silicon-based nano-baits for targeted bioimaging and optically activated therapeutic applications.