From colloids to dendrites: Silica nanoparticles as advanced solid-phase extraction sorbents for sample preparation in the analysis of trace metals: Fundamental review

The reliable determination of trace metals in environmental, food, industrial, and biological matrices depends on effective sample-preparation strategies that enable analyte preconcentration, minimize matrix-induced interferences, and preserve species stability prior to atomic spectrometric measurement. Solid-phase extraction (SPE) remains a widely adopted approach due to its operational versatility, low solvent consumption, and compatibility with offline, online, dispersive, and magnetic formats. Within this context, silica nanoparticles have emerged as a highly adaptable class of sorbents, not merely because of their high surface area, but due to the chemical precision with which their solid-liquid interface can be engineered to regulate selectivity, binding strength, and compatibility with diverse extraction configurations. This review provides a critical, application-oriented assessment of silica nanoparticle-based SPE systems, tracing their structural evolution from dense Stöber-derived particles to mesoporous silica nanoparticles (MSNs), magnetic core-shell architectures, hollow and bimodal structures, dendritic fibrous (e.g., KCC-1) materials, and hybrid composites. Unlike conventional classifications based primarily on material type, this work organizes the discussion around the analytical limitations that each structural design was intended to address, including diffusion constraints, limited accessibility of active sites, sorbent recovery challenges, and matrix-related suppression effects. Several persistent sources of terminological ambiguity are systematically clarified. In particular, Stöber-derived silica is shown to be chemically equivalent to base or acid catalysed sol-gel silica rather than a distinct class. Likewise, micron-scale ordered mesoporous silicas such as MCM-41 and SBA-15 are distinguished from their mesoporous nanoscale counterparts, which are commonly referred to as MSNs. The progression from dense to hierarchical and hybrid architectures is therefore interpreted as a sequence of design responses to analytical constraints rather than a simple optimization of surface area. The review further highlights developments in the synthesis of SNPs from sustainable silicate precursors and emphasizes the need for standardized reporting practices to ensure methodological reproducibility and cross-study comparability. The key remaining challenges, particularly nanoparticle aggregation, batch-to-batch variability, ligand leaching, and inconsistent analytical validation, are critically evaluated. Finally, key research priorities are outlined, focusing on greener synthesis routes, improved structural control, and harmonized performance metrics for rigorous evaluation. Hence, this work provides a consolidated framework for the rational design and application of SNPs-based SPE sorbents in the analysis of trace metals in complex matrices.