Zinc(II) salphen complex-based fluorescence optical sensor for biogenic amine detection

Colorimetric and fluorometric bimodal amine chemosensor based on deprotonation-induced intramolecular charge transfer: Application to food spoilage detection

Amine derivatives are signature organic compounds generated from rotten protein food. Thus, sensitive detection of the presence of amines in protein foods can be a critical technique for monitoring their quality. In this study, we develop an organic chemosensor probe, 4-(2-(3-(dicyanomethylene)- 5,5-dimethylcyclohex-1-en-1-yl)vinyl)-N,N-diethylbenzenaminium chloride (DEAH), to effectively detect amines through discernible bimodal (colorimetric and fluorometric) changes. By exploiting the amine-triggered intramolecular charge transfer behavior, DEAH exhibits rapid color changes (<1 s) with an excellent detection limit (36.9 nM) and also fluorescence turn-on in response to amine gas. Moreover, it possesses detection capabilities in versatile conditions, including solutions, solids, and coated films, suggesting its practical applicability. In particular, DEAH shows dramatic color change from yellow to violet with exceptional color difference (△Eab) over 98, repeatable usability, and excellent selectivity to amines. Based on these compelling advantages, we successfully demonstrate real-time monitoring of amine gas generated from spoiled protein foods using DEAH-coated films.

Material Breakthroughs in Smart Food Monitoring: Intelligent Packaging and On-Site Testing Technologies for Spoilage and Contamination Detection

Despite extensive commercial and regulatory interventions, food spoilage and contamination continue to impose massive ramifications on human health and the global economy. Recognizing that such issues will be significantly eliminated by the accurate and timely monitoring of food quality markers, smart food sensors have garnered significant interest as platforms for both real-time, in-package food monitoring and on-site commercial testing. In both cases, the sensitivity, stability, and efficiency of the developed sensors are largely informed by underlying material design, driving focus toward the creation of advanced materials optimized for such applications. Herein, a comprehensive review of emerging intelligent materials and sensors developed in this space is provided, through the lens of three key food quality markers - biogenic amines, pH, and pathogenic microbes. Each sensing platform is presented with targeted consideration toward the contributions of the underlying metallic or polymeric substrate to the sensing mechanism and detection performance. Further, the real-world applicability of presented works is considered with respect to their capabilities, regulatory adherence, and commercial potential. Finally, a situational assessment of the current state of intelligent food monitoring technologies is provided, discussing material-centric strategies to address their existing limitations, regulatory concerns, and commercial considerations.

A comprehensive review of the spoilage of shrimp and advances in various indicators/sensors for shrimp spoilage monitoring

Shrimp is a popular internationally traded shellfish due to its unique taste, texture, and nutritional value. Shrimp is highly perishable because it has enough free amino acids, high moisture levels, non-nitrogenous compounds used for microbial growth, and melanosis. Shrimp spoilage after death is caused by various reasons, like autolysis (endogenous proteinases actions during shrimp storage), growth of spoilage microorganisms, ATP degradation, melanin formation, and lipid peroxidation. A microbial byproduct, total volatile basic nitrogen, is one of the major reasons for the generation of foul odors from shrimp spoilage. Shrimp freshness monitoring is crucial for market sellers and exporters. Traditional methods for estimating shrimp freshness are expensive and inaccessible to the general public. Sensors are rapid, sensitive, selective, and portable food toxins' detection tools, devoid of expensive instruments, skilled people, sample pretreatment, and a long detection time. This review addresses shrimp spoilage causes. The mechanisms of different stages of shrimp spoilage after death, like rigor mortis, dissolution of rigor mortis, autolysis, and microbial spoilage mechanisms, are discussed. This review highlights the last five years' advances in shrimp freshness detection sensors and indicators like colorimetric pH indicators, fluorescence sensors, electronic noses, and biosensors, their working principles, and their sensitivities. Commercially available indicators and sensors for shrimp spoilage monitoring are also discussed. A review highlighting the applications of the different sensors and indicators for monitoring shrimp freshness is unavailable to date. Challenges and future perspectives in this field are explained at the end.

pH-Responsive strips integrated with resazurin and carbon dots for monitoring shrimp freshness

Carbon dots (CDs) were synthesized via a one-step hydrothermal approach using tangerine peel (Tan) and resazurin (Res) to fabricate biocompatible indicators for food freshness. The CDs' pH-responsive mechanism, morphology, zeta potential, XPS, and optical and fluorescence analysis were investigated. The as-prepared tangerine peel/resazurin carbon dots (Tan/Res CDs) exhibited pH-responsive emission that changed from yellow to orange as the pH value increased. The Tan/Res CDs showed the sensing ability of ammonia with a detection limit of 0.84 μM by proportionally losing fluorescence intensity as the concentration increased from 1 to 100 μM. The CDs were coated onto paper strips to impart biogenic amine (BAs) detection for pH-responsive intelligent monitoring of packaged foods. The Tan/Res CDs paper-based indicator exhibited an impressive color change from yellow to brown during the detection of ammonia vapor. The indicator also showed the ability to detect BAs through a color change, demonstrating the ability to monitor the freshness of shrimp in situ. Additionally, the efficacy of the Tan/Res CDs indicator is validated by total volatile basic nitrogen (TVB-N), providing customers and suppliers with a simple, inexpensive, and portable tool to monitor the freshness of seafood in real-time.

Recent Progress of Fluorescence Sensors for Histamine in Foods

Biological amines are organic nitrogen compounds that can be produced by the decomposition of spoiled food. As an important biological amine, histamine has played an important role in food safety. Many methods have been used to detect histamine in foods. Compared with traditional analysis methods, fluorescence sensors as an adaptable detection tool for histamine in foods have the advantages of low cost, convenience, less operation, high sensitivity, and good visibility. In terms of food safety, fluorescence sensors have shown great utilization potential. In this review, we will introduce the applications and development of fluorescence sensors in food safety based on various types of materials. The performance and effectiveness of the fluorescence sensors are discussed in detail regarding their structure, luminescence mechanism, and recognition mechanism. This review may contribute to the exploration of the application of fluorescence sensors in food-related work.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Highly selective and sensitive colorimetric/fluorometric dual mode detection of relevant biogenic amines

Biogenic amines are involved in physiological roles in living organisms, but their excessive production or intake can induce undesired toxicological effects. As biogenic amines can be found in the process of food spoilage, they are considered an indicator of food quality and freshness, and their detection is of crucial importance in food safety. In this contribution, we report the fast and direct colorimetric and fluorometric sensing of biogenic amines by means of a dinuclear Zn(ii) Schiff-base complex. The selective and sensitive detection involves the formation of stable adducts between the dinuclear complex, acting as the Lewis acidic molecular tweezer, and biogenic di- or polyamines. The selectivity towards biogenic amines, even in the presence of common aliphatic, primary, secondary, or tertiary monoamines, heterocyclic amines, and amino acids, is demonstrated by competitive experiments. The quantitation of histamine in a fish matrix is easily achieved using a standard extraction procedure followed by simple colorimetric or fluorometric measurements.

Schiff base complex/TiO2 chemosensor for visual detection of food freshness level

Histamine is one of the important biomarkers for food spoilage in the food sectors. In the present study, a rapid and simple analytical tool has been developed to detect histamine as an indirect strategy to monitor food freshness level. Optical histamine sensor with carboxyl-substituted Schiff base zinc(II) complex with hydroxypropoxy side chain deposited onto titanium dioxide nanoparticles was fabricated and was found to respond successfully to histamine. The Schiff base zinc(II) complex-histamine binding generated an enhancement of the fluorescent signal. Under the optimal reaction condition, the developed sensor can detect down to 2.53 × 10^-10 M in the range of between 1.0 × 10^-9 and 1.0 × 10^-5 M (R² = 0.9868). Selectivity performance of the sensor towards histamine over other amines was confirmed. The sensor also displayed good reproducibility performances with low relative standard deviation values (1.45%-4.95%). Shelf-life studies suggested that the developed sensor remains stable after 60 days in histamine detection. More importantly, the proposed sensor has been successfully applied to determine histamine in salmon fillet with good recoveries. This strategy has a promising potential in the food quality assurance sectors, especially in controlling the food safety for healthy consumption among consumers.

A simple "turn-on" fluorescence sensor for salicylaldehyde skeleton based on switch of PET-AIE effect

The selective detection of salicylaldehyde skeleton is of great significance in phytochemistry and biological research but rarely reported. In this research, a simple and highly selective "turn-on" fluorescence sensor (CDB-Am) for salicylaldehyde skeleton was developed based on switch of photoinduced electron transfer (PET) and aggregation-induced emission (AIE). CDB-Am bearing amino-cyanodistyrene structure responded to salicylaldehyde in the range of 3.1 to 40 μM with a detection limit of 0.94 μM. The sensing process of formation of Schiff-base adduct CDB-SA was confirmed by ¹H NMR, MS, and FT-IR spectra, revealing that a recovered AIE property accounted for the turn-on fluorescence response of CDB-Am and the intramolecular hydrogen bonding played a crucial role in the disruption of PET process. This sensing ability was successfully applied for both fluorescence qualitative test of salicylaldehyde skeleton on TLC analysis and quantitative detection of salicylaldehyde skeleton with good accuracy in the root bark of Periploca sepium, suggesting the extensive applications in phytochemistry and traditional Chinese herbal medicine. Furthermore, CDB-Am exhibited the first excellent fluorescence imaging ability in detecting salicylaldehyde skeleton in a living system. This work supplied a new strategy of preparing a novel "turn-on" fluorescence probe for detecting salicylaldehyde skeleton in complex environments and living bodies.

A review on chemical and electrochemical methodologies for the sensing of biogenic amines

Biogenic amines (BA) are biomolecules of low molecular weight with organic basic functionalities (amine group) that are formed by the microbial decarboxylation of amino acids of fermented food/beverages. Hence BAs are an important indicator in estimating the freshness and quality of meat, seafood, and industrial food products with high protein content. The reaction of BAs with nitrites available in certain meat products forms nitrosoamine, a carcinogenic compound. Hence BAs are in general considered to be a food hazard and monitoring the level of BAs in food samples becomes crucial as their high concentrations may lead to health problems. This review offers an overview of the available chemical and electrochemical methods that are typically used for the sensing of BAs in food samples. Certain compounds are known to selectively interact with BAs via chemical or non-covalent interactions and these interactions are often accompanied by fluorescence or visible color changes (sometimes visual detection) that could be monitored/assessed using a fluorescence spectrophotometer or UV-vis spectrophotometer (colorimetric methods). The colorimetric methods are limited by sensitivity and selectivity as they are based on straight-forward chemical reactions. In the case of electrochemical sensing of BAs, mediators are often used which undergo oxidation/reduction to produce intermediates that could interact with BAs accompanied by changes in their electrochemical potential. Overall, this review summarizes the available chemical and electrochemical strategies towards the sensing of BAs with a discussion on further prospects.

Construction of a Hydrogel Pectin-Based Triglyceride Optical Biosensor with Immobilized Lipase Enzymes

A novel and simple optical biosensor to detect triglycerides (TGs) has been successfully constructed by using pectin hydrogel membrane as the indicator pH and chromoionophore ETH 5294 (CI), with lipase as the catalyst. The enzymatic working system against TGs releasing H⁺ ions will affect the color absorbance of CI. The characterization results show that a TG biosensor has the optimum condition and sensitivity at the phosphate buffer concentration of 50 mM, pH 7, and enzyme loading of 60 μg. The biosensor works at the tripalmitin (TP) concentration range of 100–400 mg/dL. With the sensitivity of 0.001 (∆A/(mg/dL)), the biosensor response reaches stability after five minutes, and the limit of detection (LOD) of the TG optical biosensor is 15 mg/dL. Relative standard deviation (RSD) in a reproducibility test was 2.5%, with a 15-day lifespan.