An aptamer based aggregation assay for the neonicotinoid insecticide acetamiprid using fluorescent upconversion nanoparticles and DNA functionalized gold nanoparticles.

Abstract

An acetamiprid-binding aptamer (ABA), gold nanoparticles (AuNPs) and upconversion nanoparticles (UCNPs) are used in a colorimetric and fluorometric method for the ultrasensitive and selective detection of the pesticide acetamiprid. The ABA is first configured into a duplex with a complementary DNA covalently attached to AuNPs. The resulting dsDNA-functionalized AuNP probe is not stable in 0.15M NaCl solution and aggregates. This causing the color to change from red to purple. In the presence of acetamiprid, the ABA undergoes a structural switch from a DNA duplex to an aptamer-acetamiprid complex and consequently dissociates from the AuNPs. The partially unhybridized AuNPs are stable against salt-induced aggregation and show red color. The ratio of absorbances at 524nm (red) and 650nm (purple blue) varies with the concentration of acetamiprid in the 0.025-10μM concentration range. The colorimetric signal can be further amplified by introducing DNA-modified carboxylated UCNPs (silica-coated NaYF4:Yb,Er) which display red and green fluorescence under 980nm excitation. An inner filter effect occurs between DNA-modified UCNPs and dsDNA-modified AuNPs. The fluorometric assay is based on the measurement of the ratio of red (654nm) and green (540nm) fluorescence and works in the 0.025 to 1μM acetamiprid concentration range and has a 0.36nM detection limit (at a signal-to-noise ratio of 3). Because of the specificity of the aptamer, the assay is high selective. It was successfully used to quantify acetamiprid in contaminated real samples. Graphical abstract Schematic presentation of an upconversion fluorescent assay for acetamiprid. It involves the principle of analyte-triggered structural switch of aptamers, salt-induced AuNP aggregation, and signal amplification from UCNP.