Cooperative application of SiO₂ nanospheres and carbon-coated core-shell structures in latent fingerprint visualization

Monodisperse SiO 2 nanospheres (∼50–200 nm) were synthesized via a modified Stöber method involving hydrolysis and condensation reactions to generate SiO 2 templates. The SiO 2 surface bears negative charges through silanol (Si OH) groups, while positively charged ammonium ions (NH 4 + ) from the carbon precursor electrostatically self-assemble onto the SiO 2 surface, forming organic-coated SiO 2 nanospheres. Subsequent high temperature sintering under an argon atmosphere yields SiO 2 @C composite nanospheres. TEM and XPS confirm the spherical morphology, narrow size distribution, and the presence of a graphitized carbon layer. When applied as fingerprint developing powders on typical forensic substrates knife blades, rusted iron pieces and unpolished silicon wafer, the powders rapidly adsorb fingerprint residues and emit weak fluorescence under multi-band illumination, markedly enhancing the contrast of ridge details. The inherent chemical inertness and low cost of SiO 2 , combined with the optical scattering and fluorescence properties of the carbon coating, endow these nanocomposite powders with superior latent fingerprint visualization performance across diverse substrates, offering a highly efficient and environmentally friendly material for forensic evidence collection.