Sustainable Geothermal Silica Quantum Dots Synthesized via Acid–Base Hydrothermal Method for Selective Melanoma Theranostics and Bioimaging

This study reports the synthesis and characterization of silica quantum dots (silica QDs) derived from geothermal-waste silica sourced from the Dieng Geothermal Field, Central Java Province, Indonesia. It supports green chemistry by converting abundant waste into valuable nanomaterials, contributing to sustainable energy and material recovery. Characterization using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and dynamic light scattering (DLS) confirms the formation of spherical silica QDs with a uniform size distribution between 2-5 nm, averaging 3 nm. A zeta potential of -28 mV indicates strong colloidal stability in both suspension and biological media. Silica QDs exhibit excitation-dependent photoluminescence with a 20% quantum yield, making them suitable for applications such as bioimaging and photoresponsive drug delivery. In vitro results show selective cytotoxicity against B16F0 melanoma cells while sparing NIH3T3 normal fibroblasts, indicating biocompatibility and potential for targeted therapy. These findings reveal the dual role of silica QDs as diagnostic and therapeutic tools. This work reinforces the link between sustainable nanomaterial synthesis and biomedical innovation, illustrating how waste-to-resource strategies can drive advances in nanomedicine.