Ratiometric sensors with selective fluorescence enhancement effects based on photonic crystals for the determination of acetylcholinesterase and its inhibitor.

Ratiometric fluorescent sensors are powerful tools for quantitative analyses. However, gold nano-clusters (AuNCs) as typical fluorophores in ratiometric sensors have some disadvantages, such as low luminous efficiency. In this study, a highly sensitive ratiometric fluorescence sensor was fabricated by the combination of AuNCs and fluorescein (FL), and the photonic crystals (PhCs) were used to selectively enhance the fluorescence intensity of AuNCs. This fluorescence sensor was used for the sensitive detection of acetylcholinesterase (AChE) and its inhibitor paraoxon. AChE can catalyze the hydrolysis of acetylthiocholine (ATCh) to form thiocholine (TCh), which can induce the fluorescence quenching of AuNCs while having no obvious influence on the fluorescence intensity of FL. AChE can be determined in the range from 0.1 to 25 mU mL-1 with a limit of detection (LOD) of 0.027 mU mL-1, and paraoxon can be determined in the range of 0.06 to 60 ng mL-1 with a LOD 0.025 ng mL-1. This method, as a new way to selectively improve the fluorescence signal of one of the fluorophores in the ratiometric sensor, would be a promising strategy for the sensitive determination of AChE and its inhibitor.