Aggregation-Induced Emission Fluorophore-Incorporated Curcumin-Based Ratiometric Nanoprobe for Hypochlorite Detection in Food Matrices

AIE fluorescent nanozyme-based dual-mode biosensor for analysis of the bioactive component hypoxanthine in meat products

The development of facile, low-cost reliable, and precise onsite assays for the bioactive component hypoxanthine (Hx) in meat products is significant for safeguarding food safety and public health. Herein, we proposed a smartphone-assissted aggregation-induced emission (AIE) fluorogen tetraphenylethene (TPE)-incorporated amorphous Fe-doped phosphotungstates (Fe-Phos@TPE) nanozyme-based ratiometric fluorescence-colorimetric dual-mode biosensor for achieving the onsite visual detection of Hx. When the Hx existed, xanthine oxidase (XOD) catalyzed Hx into H2O2 to be further catalyzed into •OH by the prominent peroxidase activity of Fe-Phos@TPE at pH = 6.5, resulting in the oxidization of nonfluorescent o-phenylenediamine (OPD, naked-eye colorless) to be yellow fluorescent emissive 2,3-diaminophenazine (DAP, naked-eye dark yellow) at 550 nm as well as the intrinsic blue fluorescence of Fe-Phos@TPE at 440 nm to be decreased via inner-filter effect (IFE) action, thereby realizing a multi-enzyme cascade catalytic reaction at near-neutral pH to overcome the traditional acidity dependence-induced time-consuming and low sensitivity troublesome.

Tb3+ assisted dithioerythritol stabilized copper nanocluster with AIE behavior for ratiometric fluorescent determination of fluoroquinolones

BACKGROUND

Fluoroquinolones (FQs) are widely used in livestock and poultry industry because of their satisfactory effects in preventing and treating bacterial infection. However, due to irrational use and poor biodegradability, FQs can easily remain in food animals and further enter the human body through the food chain. Therefore, accurate and sensitive detection of FQs residues in animal-origin food is significant. The traditional methods commonly used for FQs detection have some limitations. Ratiometric fluorescence detection technology has the advantages of fast, sensitive, self-correcting, and easy visualization. However, the reports on the use of ratiometric fluorescence probes for FQs detection are limited.

RESULTS

In this work, a novel probe was proposed for ratiometric fluorescent analysis of FQs. In this probe, the fluorescence of dithioerythritol stabilized copper nanoclusters (DTE-Cu NCs) was significantly enhanced due to the Tb3+ triggered aggregation-induced emission effect. FQs bound Tb3+ in Tb3+/DTE-Cu NCs through carboxyl and carbonyl groups, so that Tb3+ was effectively sensitized to emit green fluorescence. However, the red fluorescence of DTE-Cu NCs was not interfered. The fluorescence of the probe transformed from red to green with the increase of FQs concentration. Using norfloxacin (NOR), difloxacin (DIF), and enrofloxacin (ENR) as FQs simulants, this probe showed a sensitive linear response ranged from 0.025 to 22.5 μM, with the limits of detection of 9.6 nM, 9.3 nM, and 7.7 nM. The application potential for FQs detection was verified via a standard addition assay of egg samples with the recovery rate of 90.4 %-114.7 %.

SIGNIFICANT

The fluorescence probe based on Tb3+/DTE-Cu NCs is expected to realize the ratiometric fluorescence sensitive detection of FQs. The establishment of this simple, effective, and rapid detection platform opens up a new way for the detection of FQs residues in animal-origin foods, and also provides a new idea for the design of rapid detection platforms for other hazard factors.

Fluorescent and smartphone imaging detection of tetracycline residues based on luminescent europium ion-functionalized the regular octahedral UiO-66-NH2

Antibiotic residues cause extensive damage to food security, thus arousing serious concerns. Hence, rapid and sensitive detection of antibiotic residues is crucial to food safety. This study aimed to propose a portable, visual, intelligent and rapid method for tetracycline detection. We developed a ratiometric fluorescent sensor based on the Eu3+-functionalized regular octahedral UiO-66-NH2 material. The developed sensor could quantify tetracycline in the concentration range of 0.5-200 μM with a detection limit as low as 0.2 μM under the optimum conditions. Furthermore, the analytical results obtained using the designed sensor in the actual samples were basically consistent with those obtained using high-performance liquid chromatography. Based on these achievements, a smartphone application-integrated fluorescent testing paper was designed for facile, intelligent, and visual detection of tetracycline. The integrated portable sensor not only saved cost and time for testing but also provided a forward-looking approach to fast, sensitive detection of antibiotic residues.

Silver metallization-triggered liposome-embedded AIE fluorophore for dual-mode detection of biogenic amines to fight food freshness fraud

To combat food freshness fraud, it is urgent to develop a method which could realize the detection of biogenic amines (BAs) present in food. In our study, we developed a colorimetric and ratiometric fluorescence dual-mode sensor which integrated with silver metallization-based response system of AIE liposome + OPD + RSM + Ag+ toward BAs in foods for fighting freshness fraud. With the hydrolysis from the alkaline of BAs to resorcinol monoacetate (RSM), the production resorcinol (RS) could metallize silver ion (Ag+) to silver atoms (Ag0) which could lead to a BAs concentration-dependent decrease of the oxidation product 2,3-diaminophenothiazine (DAP) of Ag+ to o-phenylenediamine (OPD). As a result, the dual-mode sensor has a low detection limit and wide linear range in the spiked detection of soy products, pork and milk samples for BAs. Thus, providing a reliable method for food safety and forestalling food freshness fraud.

Hypochlorous acid-activated near-infrared fluorescent probe for in vivo/exogenous detection and dairy toxicity evaluation

Oxidative stress has been reported to be closely associated with many diseases, and an excessive overdose of hypochlorite (ClO^-) can also induce stress-related diseases. In this study, we designed and synthesized a NIR probe, named W-1a based on computational analysis of DCM (4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) derivatives for specific detection of ClO^-. The probe exhibited dual fluorescence and colorimetric sensing with a response time of <1 min and a detection limit of 0.15 μM. Additionally, the probe was successfully applied for fluorescence imaging of ClO^- at the cellular level and ebrafish endogenous/exogenous ClO^- assay and dairy toxicity assessment. Thus, we present a potential method for developing an efficient and reliable detection of ClO^- in early stage using near-infrared dyes.

Highly sensitive fluorescent probes for selective detection of hypochlorite: Applications in blood serum and cell imaging

Being one of the vital reactive oxygen species (ROS), abnormal level of hypochlorite ion (ClO^-) may pose detrimental threats to living organisms. Therefore, highly selective, and rapid monitoring of ClO^- in living system is of prime importance to protect living organisms from its harmful effects. In this regard, design of synthetic fluorescent probes for ClO^- has garnered considerable attention. However less fluorescence emission in aggregated state and less photostability of several existing probes for ClO^- inspired us to design aggregation induced emission (AIE) active fluorescent probes SH1 and SH2. Probes were rationally designed by introducing thiourea moiety that selectively reacted through desulfurization reaction and resulted in highly selective detection of ClO^-. Hypochlorite induced desulfurization reaction was validated through ¹H NMR titration and DFT studies. Fine tuning of probes SH1 and SH2 prompted highly sensitive nanoscale (55 nM and 77 nM) and rapid (15 and 35 sec) detection of ClO^-. Probe SH1 displayed less cytotoxic effect to live cells before it was successfully applied for bioimaging of ClO^- in live MCF-7 cells. Moreover, probes displayed excellent sensing potential for ClO^- in blood serum and real water samples. Advantageously, probe coated portable fluorescent films were fabricated for the easy and fast monitoring of ClO^-. Of note, this work offers excellent design strategy for highly selective detection of ClO^- that may lead to clinical trials.

Nanoassemblies Based on a Cationic Perylene Diimide Derivative and Sodium Dodecyl Sulfate: A Simple Fluorescent Platform for Efficient Analysis of Aflatoxin B1

Aflatoxin B₁ (AFB₁) is a kind of potently carcinogenic fungal metabolite in food threatening human health, and it is crucial and challenging to develop advanced nonimmune approaches for AFB₁ determination. Addressing this challenge, we successfully constructed a nanoassembly (PdE-PDI/SDS) by noncovalently coupling a cationic perylene diimide derivative (PdE-PDI) and sodium dodecyl sulfate (SDS), exhibiting high-density charges and a specific surface area for rapid sensing of AFB₁. The large electronic conjugate structure and rigid plane of PdE-PDI enable it to form more stable σ-π, π-π coordination, and hydrogen bonds with AFB₁. Additionally, the introduction of SDS significantly amplifies noncovalent interactions and enhances the quenching efficiency of PdE-PDI toward AFB₁. The proposed PdE-PDI/SDS exhibited excellent specificity to AFB₁ and showed dosage-sensitive detection with detection limit as low as 0.74 ng mL^-1. Finally, the PdE-PDI/SDS was successfully applied in cereal samples with good recoveries from 94.61 to 109.92%. To our knowledge, this is the first time a fluorescent strategy from the point of self-assembly for AFB₁ determination is reported, which holds great promise for wide applications of perylene diimide derivative in food safety.

A Reaction-Based Ratiometric Bioluminescent Platform for Point-of-Care and Quantitative Detection Using a Smartphone

Fluorescent probes have emerged as powerful tools for the detection of different analytes by virtue of structural tenability. However, the requirement of an excitation source largely hinders their applicability in point-of-care detection, as well as causing autofluorescence interference in complex samples. Herein, based on bioluminescence resonance energy transfer (BRET), we developed a reaction-based ratiometric bioluminescent platform, which allows the excitation-free detection of analytes. The platform has a modular design consisting of a NanoLuc-HaloTag fusion as an energy donor, to which a synthetic fluorescent probe is bioorthogonally labeled as recognition moiety and energy acceptor. Once activated by the target, the fluorescent probe can be excited by NanoLuc to generate a remarkable BRET signal, resulting in obvious color changes of luminescence, which can be easily recorded and quantitatively analyzed by a smartphone. As a proof of concept, a fluorescent probe for HOCl was synthesized to construct the bioluminescent system. Results demonstrated the system showed a constant blue/red emission ratio which is independent to the signal intensity, allowing the quantification of HOCl concentration with high sensitivity (limit of detection (LOD) = 13 nM) and accuracy. Given the universality, this reaction-based bioluminescent platform holds great potential for point-of-care and quantitative detection of reactive species.

A fluorescent biosensor for Cd2+ detection in water samples based on Cd2+-fueled wheel DNAzyme walker and its logic gate applications

A fluorescent biosensor was developed for Cd²⁺ detection based on a Cd²⁺-fueled wheel DNAzyme walker. Cd²⁺ can activate the wheel to roll along the DNA walking tracks through DNAzyme cleavage and toehold-mediated strand displacement. The substrate strand was modified with BHQ and Cy5. Through continuous cleavage reactions toward the substrate strands, a high fluorescence signal can be obtained. The biosensor is ultrasensitive, and the detection limit is 0.2 pM (S/N = 3). The fluorescent assay is robust and has been applied to the determination of Cd²⁺ in real water samples with good accuracy and reliability. Using Cd²⁺, Pb²⁺, and Hg²⁺ as the three inputs, we also construct a concatenated AND logic gate. The input combination of (111) can produce an output of 1. Other input combinations produce an output of 0. Our proposed detection platform and logic system hold great promise for the ultrasensitive and intelligent sensing of different heavy metal ions in water samples.

An optical strategy for detecting hypochlorite in vitro and cells with high selectivity and stability based on a lanthanide-doped upconversion probe

The excessive use of sodium hypochlorite disinfectant for preventing COVID-19 can be harmful to the water environment and humans. More importantly, owing to hypochlorite being a biomarker of immune responses in living organisms, its abnormal production can damage nucleic acids and protein molecules, eventually causing many diseases (even cancer). Exploring a reliable, rapid, and non-invasive method to monitor the hypochlorite level in vitro and in cells can be significant. Herein, we report a novel ratiometric fluorescence sensing strategy based on Astrazon Brilliant Red 4G dye-sensitized NaGdF₄:Yb³⁺, Er³⁺@NaYF₄ core–shell upconversion nanoparticles (UCNPs@ABR 4G). Based on the combination mechanism of the fluorescent resonant energy transfer effect (FRET) and redox, a linear model of fluorescence intensity ratio and hypochlorite concentration was constructed for a fast response and high selectivity monitoring of hypochlorite in vitro and in vivo. The detection limit was calculated to be 0.39 μM. In addition, this sensing strategy possessed good stability and circularity, making it valuable both for the quantitative detection of hypochlorite in water and for the visualization of intracellular hypochlorite. The proposed optical probe is promising for the efficient and stable non-invasive detection of hypochlorite.

The excessive use of sodium hypochlorite disinfectant for preventing COVID-19 can be harmful to the water environment and humans.