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 (Pb²⁺), 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 Pb²⁺ monitoring. The sensing platform leverages the strong volumetric effect of AuNPs to magnify subtle DNA conformational changes induced by Pb²⁺-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 50 nM‒a notable improvement over AuNP-free systems. The sensor demonstrated excellent selectivity against interfering species and successfully quantified Pb²⁺ 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.