AuNP-enhanced DNA microcavity for the highly sensitive detection of lead ions in Chinese herbal medicines

The safety of Chinese herbal medicines (CHMs) is compromised by heavy metal contamination, particularly lead (<i>P</i><i>b</i>²⁺), which requires ultrasensitive detection methods to mitigate health risks. Herein, we report a gold nanoparticle (AuNP)-amplified whispering gallery mode (WGM) biosensor for highly sensitive and specific <i>P</i><i>b</i>²⁺ monitoring. The sensing platform leverages the strong volumetric effect of AuNPs to magnify subtle DNA conformational changes induced by <i>P</i><i>b</i>²⁺-dependent DNAzyme cleavage. When the DNAzyme cleaves its substrate strand, AuNP-tagged oligonucleotides are released, causing a pronounced shift in the WGM resonance wavelength. The incorporation of AuNPs significantly enhanced detection sensitivity, achieving a limit of detection of 14.15 nM-a notable improvement over AuNP-free systems. The sensor demonstrated excellent selectivity against interfering species and successfully quantified <i>P</i><i>b</i>²⁺ in complex CHM samples such as goji berry and astragalus, showing high consistency with standard ICP-MS measurements. This AuNP-enhanced WGM strategy offers a powerful tool for quality assurance in medicinal products and environmental safety monitoring.