Nanosized ion-imprinted polymer doped with Alizarin Red S for separation and quantification of zinc(II) prior to its determination by electrothermal AAS

High quantum yield copper nanoclusters integrated with nitrogen-doped carbon dots for off-on ratiometric fluorescence sensing of S2- and Zn2

Pursuing nanomaterials with high fluorescence quantum yields is of great significance in the fields of bioimaging, medical diagnosis, and food safety monitoring. This work reports on orange-emitting aggregation-induced emission (AIE) copper nanoclusters (Cu NCs) integrated with blue-emitting nitrogen-doped carbon dots (N-CDs), which enables highly sensitive detection of S2- and Zn2+ ions through an off-on ratiometric fluorescence method. The highly emissive Cu NCs was doped by Ce3+ with a high quantum yield of 51.30 % in aqueous solution. The S2- can induce fluorescence quenching of AIE Cu NCs/N-CDs from orange to blue, while Zn2+ can restore the orange fluorescence. The probe provided linear detection ranges of 0.5-170 μM for S2- and 0.05-200 μM for Zn2+, with detection limits of 0.17 μM and 0.02 μM, respectively. Moreover, a smartphone assistant ratiometric fluorescent test strips were developed for the rapid and visual detection of S2- and Zn2+. The AIE Cu NCs/N-CDs probe exhibited diverse fluorescence color responses, high fluorescence stability, and low cytotoxicity. The ratiometric system was successfully applied to the detection of S2- and Zn2+ in real water samples as well as in cellular and living imaging, demonstrating its potential in biochemical analysis and food safety monitoring.

A ratiometric fluorescence strategy based on inner filter effect for Cu2+-mediated detection of acetylcholinesterase

A novel ratiometric fluorescence strategy for detection of acetylcholestinerase (AChE) is proposed based on carbon nitride quantum dots (g-CNQD) and the complex (PA) formed between phenylboronic acid (PBA) and alizarin red S (ARS). PA showed fluorescence at 598 nm and quenched the fluorescence of g-CNQD at 438 nm. Through UV-visible absorption, fluorescence, and fluorescence lifetime measurements, the quenching effect was demonstrated as inner filter effect (IFE). When Cu²⁺ was added, the coordination of ARS and Cu²⁺ decreased the fluorescence of PA at 598 nm and recovered that of g-CNQD at 438 nm. In the presence of AChE it catalyzed the hydrolysis of acetylthiocholine (ATCh) to produce thiocholine (TCh) which competed with ARS for binding to Cu²⁺; thus, the fluorescence at 598 nm increased and that at 438 nm decreased again. Under the mediation of Cu²⁺, the fluorescence ratio F₅₉₈/F₄₃₈ of PA-CNQD probe had good linear relationship with AChE concentration in the range 0.5-15 mU/mL with a detection limit of 0.36 mU/mL. The method was successfully applied to the determination of AChE in human serum and the screening of inhibitors.