| Criteria | Gold Nanoparticles (AuNPs) | Silver Nanoparticles (AgNPs) | Remarks |
| Definition | Nanoscale particles composed of elemental gold, typically ranging from 1–100 nm in diameter. | Nanoscale particles composed of elemental silver, usually 1–100 nm in diameter. | Both are noble metal nanoparticles with unique physicochemical and biological properties. |
| Color and Optical Properties | Exhibit ruby-red to purple color due to surface plasmon resonance (SPR) around ~520 nm. | Exhibit yellowish-brown to grey color due to SPR around ~400 nm. | SPR wavelength difference is key for their optical applications. |
| Chemical Stability | Highly stable; resistant to oxidation and chemical degradation. | Less stable; prone to oxidation and tarnishing over time. | Gold’s inertness gives it superior biocompatibility. |
| Antimicrobial Activity | Weak or negligible antimicrobial properties. | Strong antimicrobial and antifungal activity. | Silver nanoparticles are widely used as antimicrobial agents. |
| Biocompatibility | Highly biocompatible and non-toxic at moderate concentrations. | Can exhibit cytotoxicity at higher concentrations due to silver ion release. | Gold nanoparticles are preferred for in vivo biomedical use. |
| Applications | Used in drug delivery, biosensing, imaging, photothermal therapy, and diagnostics. | Used in antimicrobial coatings, wound dressings, textiles, and sensors. | Application focus differs based on stability and bioactivity. |
| Surface Functionalization | Easily functionalized with biomolecules (DNA, peptides, antibodies). | Can also be functionalized, but surface oxidation may interfere with stability. | Gold offers better surface chemistry for conjugation. |
| Synthesis Methods | Chemical reduction (e.g., citrate method), green synthesis, or seed-mediated growth. | Chemical, electrochemical, and biological synthesis methods. | Both can be synthesized via eco-friendly or chemical routes. |
