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

Abstract

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 (R² = 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.