An aptamer based method is described for the determination of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using resonance light scattering (RLS). Magnetic nanoparticles (MNPs) were employed as RLS probes. The probe DNA was placed on the surface of MNPs, which produces a rather low RLS signal. If, however, probe DNA hybridizes with the aptamer against 8-OHdG, a sandwich structure will be formed. This results in a significant enhancement of RLS intensity. The aptamer was used as the recognition element to capture 8-OHdG. 8-OHdG has a stronger affinity for the aptamer than probe DNA, and the conformation of the aptamer therefore switches from a double-stranded to a G-quadruplex structure. As a result, MNPs labeled with probe DNA are released, and RLS intensity decreases. The method allows 8-OHdG to be detected with a linear response in the 32 pM - 12.0 nM concentration range and an 11 pM limit of detection (at 3.29SB/m, according to the recent recommendation of IUPAC). The MNPs can be reused 5 times by applying an external magnetic field for collection. The method was successfully applied to analyze human urine samples for its content of 8-OHdG. It was also found that the levels of 8-OHdG noticeably increased with the increase of the Air Quality Index. Conceivably, the method is a viable tool to investigate the relationship between 8-OHdG levels and the effect of air pollution. Graphical abstract A reusable sensing strategy was constructed to detect urinary 8-OHdG based on "turn-off" resonance light scattering. The LOD was as low as 11 pM. This study showed some preliminary data for the association between oxidative stress and air pollution.
Keywords: 8-OHdG; Air quality index; Aptamer; Biomarker; Conformational change; G-quadruplex; Magnetic biosensor; Oxidation of DNA; Reusability; Urine samples.