Colorimetric Sensor Based on Ag-Fe NTs for H2S Sensing

Visual tracking of real-time freshness of fish using an agar hydrogel colorimetric indicator containing CuNPs/NCQDs

A simple, selective, and affordable dual fluorescence-colorimetric indicator for hydrogen sulfide was developed based on a complex of copper nanoparticles and N-doped carbon quantum dots (CuNPs/NCQDs). Real-time and visual freshness tracking of fish was done using a colorimetric indicator by incorporating CuNPs/NCQDs into agar hydrogel (AH-CuNPs/NCQDs). The fluorescence response of the CuNPs/NCQDs solution is quenched upon exposure to H2S. The field-emission scanning electron microscopy image of the AH-CuNPs/NCQDs film revealed a unified structure. The prepared indicator exhibited a good and irreversible response to H2S, with a LOD of 91.36 and a LOQ of 276.86 μM, based on the localized surface plasmon resonance (LSPR) mechanism. The X-ray photoelectron spectrometer and Fourier transform infrared spectrometer results confirmed the formation of a CuS bond in the colorimetric indicator exposed to fish spoilage. The prepared indicator demonstrated good stability and remained unaffected by pH or other volatile compounds. Notably, there was a strong correlation between ΔΕ and fish freshness parameters (pH, TV-BN, and TVC). Light green, pale yellow, and dark yellow colors, respectively, indicated freshness, semi-freshness, and spoilage of fish during storage in the refrigerator. Overall, the prepared indicator can be effectively used for detecting spoilage in meat products as a highly sensitive freshness indicator.

Digitalization of Colorimetric Sensor Technologies for Food Safety

Colorimetric sensors play a crucial role in promoting on-site testing, enabling the detection and/or quantification of various analytes based on changes in color. These sensors offer several advantages, such as simplicity, cost-effectiveness, and visual readouts, making them suitable for a wide range of applications, including food safety and monitoring. A critical component in portable colorimetric sensors involves their integration with color models for effective analysis and interpretation of output signals. The most commonly used models include CIELAB (Commission Internationale de l'Eclairage), RGB (Red, Green, Blue), and HSV (Hue, Saturation, Value). This review outlines the use of color models via digitalization in sensing applications within the food safety and monitoring field. Additionally, challenges, future directions, and considerations are discussed, highlighting a significant gap in integrating a comparative analysis toward determining the color model that results in the highest sensor performance. The aim of this review is to underline the potential of this integration in mitigating the global impact of food spoilage and contamination on health and the economy, proposing a multidisciplinary approach to harness the full capabilities of colorimetric sensors in ensuring food safety.

Recent advancements in chemosensors for the detection of food spoilage

The need for reliable sensors has become a major requirement to confirm the quality and safety of food commodities. Chemosensors are promising sensing tools to identify contaminants and food spoilage to ensure food safety. Chemosensing materials are evolving and becoming potential mechanisms to enable onsite and real-time monitoring of food safety. This review summarizes the information about the basic four types of chemosensors (colorimetric, optical, electrochemical, and piezoelectric) employed in the food sector, the latest advancements in the development of chemo-sensing mechanisms, and their food applications, with special emphasis on the future outlook of them. In this review, we discuss the novel chemosensors developed from the year 2018 to 2022 to detect spoilage in some common types of food like fish, meat, milk, cheese and soy sauce. This work will provide a fundamental step toward further development and innovations of chemosensors targeting different arenas in the food industry.

Facile Synthesis of Ag NP Films via Evaporation-Induced Self-Assembly and the BA-Sensing Properties

Herein, we design and prepare large-area silver nanoparticle (Ag NP) films based on evaporation-induced self-assembly, which offers the visual and real-time detection of chilled broiler meat freshness. The color change is based on the fact that an increase in the biogenic amine (BA) concentration causes a change in the absorption wavelength of Ag NPs caused by aggregation and etch of the Ag NPs, resulting in a yellow to brown color change, thus enabling a naked-eye readout of the BA exposure. The Ag NP films exhibit a rapid, sensitive, and linear response to BAs in a wide detection range of 2 µM to 100 µM. The Ag NP films are successfully applied as a quick-response, online, high-contrasting colorimetric sensor for visual detection of the freshness of chilled broiler meat.