Target-modulated UCNPs-AChE assembly equipped with microenvironment-responsive immunosensor

A fluorescence resonance energy transfer (FRET)-labeled microenvironment-responsive immunosensor modulated by acetylcholinesterase (AChE) was designed to improve the sensitivity toward Aflatoxin B1 (AFB1). Specifically, the fluorescence of functional up-conversion nanoparticles (UCNPs) was quenched strongly by pH-sensitive dye fluorescein isothiocyanate (FITC). The immune-recognition-driven UCNPs-AChE assembly allows the reduction of microenvironment pH around the surface of UCNPs. This occurrence quenched the fluorescence of functional UCNPs, thereby achieving quantitative determination of AFB1. The pre-constructed FRET system (functional UCNPs) minimized the spatial distance between UCNPs and FITC, enhancing the effective FRET quenching. The quenching efficiency reached 95%. At the same time, the trace target-induced AChE archived functional UCNPs, thereby destroyed most UCNP-FITC (FRET system) for signal amplification. The AFB1 LODs were as low as 0.003 nM. We expect that the FRET-labeled microenvironment-responsive immunosensor will make up-conversion fluorescence sensing more efficient for future research.