Liu et al. prepare silver nanoparticles (AgNPs) using gallic acid as both reducing and stabilizing agent, then exploit the aggregation of AgNPs induced by hydrogen bonding between melamine and gallic acid as a colorimetric signal. The color shifts from yellow to brown in proportion to melamine concentration. The sensor was validated in spiked raw milk.
Key numbers
- LOD for melamine: 0.099 µM (0.012 ppm) in raw milk (abstract).
- Safety limit reference: 1.0 ppm (China), 2.0 ppm (EU) for melamine in food; the LOD is approximately 83 to 167 times below the applicable safety limit (abstract).
- Color change: yellow to brown as melamine concentration increases; visible to the naked eye.
- Gallic acid concentration optimization: 4 to 8 µM range; R2 = 0.992 (body text, Figure data).
Methods (brief)
AgNPs were synthesized by mixing gallic acid with AgNO3; aggregation behavior in the presence of melamine was monitored by UV-Vis absorption at 400 to 500 nm. Selectivity was tested against other food adulterants, sugars, proteins, and anions. Raw milk samples were spiked with melamine and analyzed directly after sample preparation.
Evidence fitness
Supports documentation of silver nanoparticles as colorimetric reagents for detecting melamine adulteration in milk, the principal food safety target after the 2008 Chinese infant formula adulteration incident. Silver is the analytical platform; melamine is the target analyte. No dietary silver exposure is involved.
Limitations
Validated in spiked (not incurred) raw milk. Performance in processed milk, infant formula, or ultra-high temperature milk may differ due to protein denaturation and matrix interference. Recovery rates in spiked milk are not explicitly reported in the sections reviewed.
Related evidence
- Silver
- ingredients/milk
Update history
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