A ratiometric fluorescence platform for on-site screening meat freshness

Meat freshness is related to food safety and human health. Developing a simple and effective method for on-site detection of meat freshness is essential to ensure food safety. This study aimed to explore a ratiometric fluorescence platform for on-site screening of meat freshness. We synthesized a series of benzothiazole-based fluorescent compounds (BM, BHM and BTH), each with different recognition groups for detecting meat freshness biomarkers cadaverine (Cad) and putrescine (Pte). The optimized 2-(2'-hydroxyphenyl-3-aldehyde-5-1,3-indanedione) benzothiazole (BTH) demonstrated a noticeable color and fluorescence change, a fast response (<15 min), and high selectivity and sensitivity (LOD = 70 nM) to Cad. Portable test strips based on BTH were prepared for rapid visual detection of meat freshness, which exhibited visible color and fluorescen color changes to Cad and Pte. Furthermore, a portable smartphone-based fluorescence device integrated with a self-programmed Python program was fabricated and used on-site to monitor Cad and Pte within 5 min. The BTH-loaded portable test strips were successfully employed as low-cost, high-contrast, fast-response, and smartphone-adaptable fluorescent labels for detecting Cad and Pte in meat samples under different temperatures (25 °C, 4 °C, and -20 °C). This enabled consumers and food supply chain stakeholders to quickly and visually monitor the meat freshness in real beef, chicken, and pork products.

Construction of a ratiometric fluorescent sensing platform based on near-infrared carbon dots for organophosphorus pesticides detection

In this work, a convenient ratiometric fluorescent platform was designed to measure organophosphorus pesticides (OPs) based on acetylcholinesterase (AChE), acetylthiocholine (ATCh), manganese dioxide nanosheets (MnO₂), near-infrared carbon dots (RCDs) and o-phenylenediamine (OPD). In this platform, a direct oxidation of OPD by MnO₂ generated the luminescent product 2,3-diaminophenolazine (DAP) through intrinsic oxidase activity, while RCDs served as a fluorescent reference indicator. In the presence of AChE and ATCh, the enzymatic hydrolysate thiocholine (TCh) would reduce MnO₂ nanosheets to Mn²⁺, leading to the quenching of DAP fluorescence. On the other hand, OPs can inhibit the catabolism of ATCh by AChE thus acting as a recognizer of OPs. According to these reactions, OPs were quantitatively analyzed by the intensity ratio of fluorescence emitted from RCDs and DAP (F₅₆₀/F₆₇₆). The constructed platform can detect OPs with the range of 0.2-0.6 μM with a detection limit of 4.3 nM. Figure A ratiometric fluorescent probe based on carbon dots was obtained and using it to determine the concentration of organophosphorus pesticides.

A facile fluorescence platform for chromium and ascorbic acid detection based on "on-off-on" strategy

In this paper, a facile and rapid fluorescence "on-off-on" strategy for the detection of chromium (Cr(VI)) and ascorbic acid (AA) was developed, which was based on the water-soluble carbon dots (CDs). The CDs was synthesized by a microwave-assisted treatment of L-tartaric acid, citric acid, and urea. The CDs have many advantages, such as high fluorescence quantum yield (20.5%) and good fluorescence stability. Based on inner filter effect (IFE) and static quenching, the fluorescence of the CDs can be quenched by Cr(VI) quickly; while the reduction of IFE and reducing action can make the fluorescence of the CDs recover by AA efficiently. Moreover, under the optimal experimental conditions, the CDs had a good detection performance for Cr(VI) in the range of 0.8 ∼ 189 µM with the limit of detection (LOD) of 0.16 µM. The linear detection for AA was ranged from 0.43 to 25.7 µM with a LOD of 0.1 µM. More importantly, the as-constructed fluorescence detecting platform was successfully applied for Cr(VI) and AA detection in the environmental samples and fruit samples, respectively. In addition, the application potential of the CDs in fluorescent films and anti-counterfeiting materials was further discussed in detail. This work will provide a novel idea for designing a portable sensor based on the CDs to quickly and sensitively detect Cr(VI) and AA.