Peroxidase mimicking DNA-gold nanoparticles for fluorescence detection of the lead ions in blood

Oligonucleotide (T30695) modified gold nanoparticles (T30695-Au NPs) have been prepared and employed for quantification of lead ions (Pb2+) in blood. The detection of Pb2+ ions is through the formation of Au-Pb alloys and oligonucleotide-Pb2+ complexes that catalyze the H2O2-mediated oxidation of non-fluorescent Amplex UltraRed (AUR) to form a highly fluorescent oxidized AUR product. Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) and inductively coupled plasma mass spectrometry (ICP-MS) revealed the formation of Au-Pb alloys on the surfaces of the 40T30695-Au NPs (i.e., the system featuring 40 molecules of T30695 per Au NP) in the presence of Pb2+ ions, leading to increased catalytic activity for the H2O2-mediated oxidation of AUR. The fluorescence intensity (excitation/emission maxima: ca. 540/584 nm) of the oxidized AUR product is proportional to the concentration of Pb2+ ions over the range 0.1-100 nM, with a linear correlation (R-2 = 0.99). The 40T30695-Au NP/AUR probe is highly selective toward Pb2+ ions (by at least 200-fold over other tested metal ions). The 40T30695-Au NPs/AUR probe provided limits of detection (LOD, at a signal-to-noise ratio 3) for Pb2+ ions of 0.05 and 0.1 nM, in Tris-acetate solution (5 mM, pH 8.0) without and with salt (150 mM NaCl, 5 mM KCl, 1 mM MgCl2, and 1 mM CaCl2), respectively. Without conducting tedious sample pretreatment, the approach allows detection of Pb2+ ions in blood samples, showing the potential of the 40T30695-Au NPs/AUR assay for on-site and real-time detection of Pb2+ ions in biological samples.