An Enzymatic Reaction Modulated Fluorescence-on Omethoate Biosensor Based on Fe3O4@GO and Copper Nanoparticles

The employing of organophosphorus pesticides (OPs), especially, the abusing of OPs, leads to residue accumulation, which causes immense effect to human health and environment. So, it is an urgent task to develop highly sensitive OPs’ detection platforms. A novel enzyme modulated fluorescence-on sensor for sensitive detection of omethoate was successfully constructed, using AT-rich double-stranded DNA (dsDNA) templated copper nanoparticles (CuNPs) as the fluorescent signal and covalently combined magnetic Fe3O4 and graphene oxide (GO) as the single-stranded DNA (ssDNA) adsorbent. The assay just associates acetylcholinesterase (AChE), one strand of dsDNA, acetylcholinein (ATCh), Fe3O4@GO and ascorbic acid (AA)/Cu2+. T6-1 and T6-2 are two strands single-stranded DNA (ssDNA) with the AT-rich sequence and continuous T bases at their two ends, respectively. In the aid of Hg2+, they can hybridize into a blunt-ended dsDNA with one AT-rich end and one T-Hg2+-T base pairs end. Once omethoate exists, it can inhibit AChE from transducing acetylcholinein (ATCh) into thiocholine (TCh). So, no TCh can snatch Hg2+ from T-Hg2+-T base pairs in blunt-ended T6-1/T6-2. T6-1/T6-2 still keeps its integrity in blunt-ended dsDNA configuration, and hence the subsequently added Fe3O4@GO cannot absorb it. The remained blunt-ended T6-1/T6-2 in supernatant can act as the template of CuNPs to produce strong luminescence. The developed detection offers a signal-on omethoate detection, which can sensitively detect omethoate in the linear range of 5–200 nmol/L with a detection limit of 2.48 nmol/L. More importantly, it can detect omethoate in food and environmental samples, demonstrating high potential in real sample detection.