Multicolor hydrogen sulfide sensor for meat freshness assessment based on Cu2+-modified boron nitride nanosheets-supported subnanometer gold nanoparticles

A portable/miniaturized analytical kit for on-site analysis: Chemical vapor generation-visual colorimetric and smartphone RGB dual-mode for detection of sulfide ion in water and food additives

Chemical vapor generation (CVG) was used as a gaseous sample introduction technique for the visual/smartphone RGB readout colorimetric system, with the advantages of efficient matrix elimination and high vapor generation efficiency, this analytical system exhibits a good selectivity and sensitivity. Sulfide ion (S2-) in solution was transformed to its volatile form (H2S), the generated H2S reacted with a silver-containing metal organic framework (Ag-BTC) selectively, Ag2S was thus generated. Ag-BTC (fabricated on paper sheet) changed from white to dark brown, the color variance was identified by smartphone and naked-eye simultaneously. Under the optimized conditions, a limit of detection of 0.02 μg/mL was obtained by naked-eye. Several water samples and commercial food additives were analyzed for confirming its accuracy and potential application for on-site detection, recoveries ranging 94-110 % were obtained. To meet the demand of on-site analysis of S2-, this colorimetric system was integrated in a portable/miniaturized analytical kit. It is an easy-used, affordable and portable analytical kit for S2- detection in field.

Research progress of chilled meat freshness detection based on nanozyme sensing systems

It is important to develop rapid, accurate, and portable technologies for detecting the freshness of chilled meat to meet the current demands of meat industry. This report introduces freshness indicators for monitoring the freshness changes of chilled meat, and systematically analyzes the current status of existing detection technologies which focus on the feasibility of using nanozyme for meat freshness sensing detection. Furthermore, it examines the limitations and foresees the future development trends of utilizing current nanozyme sensing systems in evaluating chilled meat freshness. Harmful chemicals are produced by food spoilage degradation, including biogenic amines, volatile amines, hydrogen sulfide, and xanthine, which have become new freshness indicators to evaluate the freshness of chilled meat. The recognition mechanisms are clarified based on the special chemical reaction with nanozyme or directly inducting the enzyme-like catalytic activity of nanozyme.

A Visual Color Response Test Paper for the Detection of Hydrogen Sulfide Gas in the Air

Hydrogen sulfide (H2S) is widely found in oil and natural gas wells and industrial wastewater tanks. Owing to its high toxicity, the monitoring and detection of H2S in the air is essential. However, recent techniques for the quantitative detection of H2S gas suffer from limitations such as high cost, complicated operation, and insufficient sensitivity, preventing their practical application in industry. Thus, we have developed a portable test paper for real-time and inexpensive monitoring of H2S gas by color changes. The test paper had a significantly low H2S detection limit of 200 ppb, which is considered safe for humans. Moreover, the color of the test paper did not change noticeably when exposed to CO2, N2, O2, and air environments, indicating that the test paper is selective for H2S gas and can be stored for a long time. In addition, we fitted a color difference linear model between the color difference values (ΔE) and the concentrations of H2S gas. The establishment of the linear model substantiates that the test paper can provide accurate intensity information when detecting H2S gas leakage.

Engineered nanomaterials-based sensing systems for assessing the freshness of meat and aquatic products: A state-of-the-art review

Meat and aquatic products are susceptible to spoilage during distribution, transportation, and storage, increasing the urgency of freshness evaluation. Engineered nanomaterials (ENMs) typically with the diameter in the range of 1-100 nm exhibit fascinating physicochemical properties. ENMs-based sensing systems have received extensive attention for food freshness assessment due to the advantages of being fast, simple, and sensitive. This review focuses on summarizing the recent application of ENMs-based sensing systems for food freshness detection. First, chemical indicators related to the freshness of meat and aquatic products are described. Then, how to apply the ENMs including noble metal nanomaterials, metal oxide nanomaterials, carbon nanomaterials, and metal-organic frameworks for the construction of different sensing systems were described. Besides, the recent advance in ENMs-based colorimetric, fluorescent, electrochemical, and surface-enhanced Raman spectroscopy sensing systems for assessing the freshness of meat and aquatic products were outlined. Finally, the challenges and future research perspectives for the application of ENMs-based sensing systems were discussed. The ENMs-based sensing systems have been demonstrated as effective tools for freshness evaluation. The sensing performance of ENMs employed in different sensing systems depends on their composition, size, shape, and stability of nanoparticles. For the real application of ENMs in food industries, the risks and regulatory issues associated with nanomaterials need to be further considered. With the continuous development of nanomaterials and sensing devices, the ENMs-based sensors are expected to be applied in-field for rapid detection of the freshness of meat and aquatic products in the future.

Dual-Signaling Photoelectrochemical Biosensor Based on Biocatalysis-Induced Vulcanization of Bi2MoO6 Nanosheets

A magnetic-assisted photoelectrochemical (PEC) and colorimetric (CL) dual-modal biosensing platform with high precision was established to monitor prostate-specific antigen (PSA) based on Bi₂MoO₆ nanosheets (BMO) by coupling the aptamer-guided hybridization chain reaction (HCR) with the hydrolysate-induced vulcanization reaction of Bi₂MoO₆ nanosheets. Upon addition of PSA, trigger DNA (tDNA) was released by the interaction between the target analyte and the aptamer and then further hybridized with anchor DNA (aDNA) conjugated on magnetic beads (MBs). The as-released tDNA initiated the target-assisted HCR in the presence of two alternating hairpin sequences (Bio-H1 and Bio-H2) to produce nicked long double-stranded DNA on the surface of MBs, where numerous alkaline phosphatase (ALP) enzymes could assemble with MBs through the biotin-avidin reaction, resulting in the hydrolysis of sodium thiophosphate (TP) to H₂S. The as-produced H₂S reacted with BMO to form vulcanized BMO (BMO-S), thus leading to obvious enhanced PEC performance under visible light with the color change from light yellow to brown. Having optimized the test conditions, the magnetic-assisted biosensing system holds a good quantitative diagnosis sensitivity area in a range of 5.0 pg mL^-1-100 ng mL^-1 with a calculated detection limit down to 3.5 pg mL^-1. Meanwhile, a visual colorimetric assay on basis of the change in the color of the materials was also realized. Given the exceptional performance of the constructed biosensor, it may possess great promise as an advanced bioanalytical tool for practical applications.

A sensitive colorimetric hydrogen sulfide detection approach based on copper-metal-organic frameworks and a smartphone

In this study, we demonstrate a colorimetric approach for the detection of hydrogen sulfide (H₂S) in water samples with high sensitivity. Firstly, copper-metal-organic frameworks (Cu-MOFs) were synthesized by ultrasonic-assisted hydrothermal method, presenting a maximum absorption peak at 700 nm. It was found that Cu-MOFs could react with H₂S to form a copper-sulfur complex along with a decrease of the absorption peak at 700 nm and a visible color change from blue to tan. Under the optimal reaction conditions, the absorption intensity at 700 nm was linear with H₂S concentration in a range of 0.05-2 mM (R² = 0.9928), providing a detection limit of 22 μM. Furthermore, the method was successfully applied to the detection of H₂S in lake water samples with a recovery rate between 94.4% and 112.6%. In addition, a practical and portable device for on-site H₂S detection was designed by using agarose hydrogels, and a simple colorimetric detection method based on a smartphone was developed. This analytical method showed good selectivity for H₂S compared to other interfering substances, and the feasibility of the agarose hydrogel-based device was proved by the determination of H₂S in real lake water samples.