A novel acetylcholinesterase regulated upconversion-FITC fluorescence aptasensor for supersensitive detection of sulfadiazine in aquatic products

In this study, a novel fluorescence aptasensor was designed for the detection of sulfadiazine (SDZ) based on the pH-sensitive strategy to improve the fluorescence resonance energy transfer (FRET) efficiency. Acetylcholinesterase (AChE) was employed to regulated microenvironment responsiveness of the FRET between upconversion nanoparticles (UCNPs) as donors and pH-sensitive fluorescein isothiocyanate (FITC) dye as the effective acceptor. An energy transfer effect resulted in FITC strongly quenched the fluorescence of UCNPs. Upon addition of acetylthiocholine (ACh) and cDNA-modified AChE (cDNA-AChE), cDNA-AChE was assembled with aptamer functionalized FITC-modified UCNPs (UCNPs-FITC-aptamer), and the product of catalytic hydrolysis (acetic acid) changed the pH of the microenvironment surrounding UCNPs, causing the quenched fluorescence restored. The specific recognition of aptamer to SDZ broke the assembly composition, and reduced the recovery of fluorescence response signal. The linear relationship was achieved over the concentration range from 0.1 to 100 ng/mL and the limit of detection (LOD) was 0.031 ng/mL. In addition, the developed biosensor exhibited satisfactory results with (p > 0.05) enzyme-linked immunosorbent assay (ELISA). The excellent performance of the proposed biosensor confirmed the enormous potential to detect SDZ residuals in aquatic products.