Gold nanoparticles (GNPs) and carbon quantum dots (CQDs) are widely used in immunosensing due to their tunable optical/electronic properties and flexible surface chemistry. However, inconsistent synthesis, complex and poorly controlled nano-bio interactions, and non-standardized bioconjugation hinder reproducibility and clinical translation. This critical review synthesizes recent advances (2015–2025) in surface functionalization and conjugation strategies for GNP- and CQD-based immunosensors, with emphasis on practical, reproducible workflows that support translational diagnostics. While this review primarily focuses on covalent bioconjugation strate-gies to improve stability and reproducibility, non-covalent interactions also play a critical, complementary role in nano-bio systems. Reversible interactions, such as antibody–antigen and ligand–receptor binding, provide dynamic, tunable interfaces that can be exploited for controlled binding, competitive displacement, and enhanced assay versatility. We conducted a focused, structured literature review across major databases to identify high-impact, translationally relevant studies. Emphasis was placed on mechanistic insights, quality control metrics, and conjugation methods that preserve biomolecule function in complex biological matrices. Optimized chemical and physical syntheses (including microfluidic and plasma routes) improve batch consistency; CQD bottom-up methods yield high quantum yields for fluorescence assays; and site-specific conjugation approaches (site-directed thiol–gold chemistry, click chemistry, and Fc-oriented immobilization) substantially enhance antibody orientation and assay reproducibility. Antifouling strategies (PEGylation, zwitterionic coatings) and hybrid GNP-CQD designs enable dual-mode sensing and improved stability. We distill best-practice recommendations (GMP-aware synthesis, rigorous QC: size/PDI/ligand density, validated conjugation protocols) and outline key translational barriers-protein corona effects, steric hindrance, scale-up, and regulatory constraints. The practical workflows and QC checklists provided here aim to accelerate the clinical readiness of nanomaterial immunosensors. With standardized synthesis, validated site-specific bioconjugation, and comprehensive in vivo evaluation, GNPs and CQDs hold strong potential for precision diagnostics and point-of-care theranostics.
Sanavandi et al. (Mon,) studied this question.