On‐Site Detection for Hazardous Materials in Chemical Accidents

Fast detection of tryptamine in meat products with azide-functionalized covalent organic frameworks confined in molecularly imprinted polymers

Tryptamine is a biogenic amine that affects organoleptic quality through the generation of off-odours in foods. Herein, imine-based covalent organic frameworks (COFs) were synthesized via Schiff base reactions and postmodified with click chemistry to generate azide-functionalized COFs with tunable azide units on the walls. The combination of molecular imprinting with COFs enabled the specific recognition of the targets. The resulting optosensing system (azide-functionalized COFs@MIPs) was used as a sample-to-answer analyser for detecting tryptamine (detection time within 10 min). A linear relationship was observed for the fluorescence response to tryptamine concentrations in the range of 3-120 μg L-1, with a limit of detection of 1.74 μg L-1. The recoveries for spiked samples were satisfactory, with relative standard deviations <9.90%. The optosensing system is a potential tool for the quantitative detection of tryptamine in meat products because of its lower cost, shorter processing time, and simpler processing steps compared to conventional chromatographic techniques.

A dual emitting CsPbBr3/Eu-BDC composite as a ratiometric photoluminescent turn-on probe for aliphatic amine sensing

The impressive photoluminescence properties of all inorganic cesium lead halide perovskite quantum dots (PeQDs) make them highly intriguing for fluorescence chemosensor applications. Herein, a ratiometric dual emitting perovskite-based sensor was designed by synthesizing fluorescent CsPbBr3 PeQDs in situ within a matrix of Eu-BDC (Eu(III) benzene-1,4-dicarboxylate). The results presented here establish the suggested sensor's quick and selective turn-on PL response to volatile primary aliphatic amine derivatives. In the presence of amines, the designed CsPbBr3/Eu-BDC sensor exhibits an enhancement of the PL signal of CsPbBr3 at 518 nm and the Eu-BDC signal at 615 nm served as a standard for constructing the ratiometric sensing system. Thereby, a visual color change from red to green was observed with the incremental addition of methylamine to the probe. A low detection limit of 0.083 ppm was determined for methylamine. In both the solution and vapor phases, this ratiometric sensor responds to a variety of primary aliphatic amines with very quick and strong fluorescence. Moreover, the sensor was effectively used for monitoring meat spoilage owing to the emission of biogenic amine vapor from meat products.

Rare Earth -MOFs: From Synthesis to Their Deployment for Amine-Sensing Application in Aqueous Media

The pursuit of developing sensors, characterized by their fluorescence-intensity enhancement or "turn-on" behavior, for accurately detecting noxious small molecules, such as amines, at minimal levels remains a significant challenge. Metal-organic frameworks (MOFs) have emerged as promising candidates as sensors as a result of their diverse structural features and tunable properties. This study introduces the rational synthesis of a new highly coordinated (6,12)-connected rare earth (RE) alb-MOF-3, by combining the nonanuclear 12-connected hexagonal prismatic building units, [RE9(μ3-O)2(μ3-X)12(OH)2(H2O)7(O2C-)12], with the 6-connected rigid trigonal prismatic extended triptycene ligand. The resulting Y-alb-MOF-3 material is distinguished by its high microporosity and Brunauer-Emmett-Teller surface area of approximately 1282 m2/g, which offers notable hydrolytic stability. Remarkably, it demonstrates selective detection capabilities for primary aliphatic amines in aqueous media, as evidenced by fluorescence turn-on behavior and photoluminescence (PL) titration measurements. This work emphasizes the potential of MOFs as sensors in advancing their selectivity and sensitivity toward various analytes.

Core-satellite-satellite hierarchical nanostructures: assembly, plasmon coupling, and gap-selective surface-enhanced Raman scattering

The plasmonic properties of gold nanoparticles (AuNPs), such as color tunability, electric field generation, hot carrier generation, and localized heating, are significantly enhanced in the nanogaps between AuNPs. Therefore, the creation and control of nanogaps are key to developing advanced plasmonic nanomaterials. Most AuNP nanoassemblies, including dimers, trimers, and core-satellites, have a single type of nanogap within the assembly. In this study, we construct core-satellite-satellite (CSS) hierarchical, fractal-like nanostructures featuring two types of nanogaps, namely first generation nanogaps (Gap1) between the core and first satellite (Sat1) AuNPs and second generation nanogaps (Gap2) between Sat1 and second satellite (Sat2) AuNPs. The sequential and alternating immersion of glass slides in different-sized AuNPs and linkers forms CSS with perfect yield. The UV-vis spectroscopy, combined with charge density distribution calculations, reveals the nature of the plasmon coupling between the AuNPs that constitute CSS nanoassemblies. The plasmon coupling can be tuned by independently varying Gap1 and Gap2. Furthermore, we explore the electric field amplification in Gap1 and Gap2 by comparing the surface-enhanced Raman scattering signal intensity selectively from each nanogap. This new type of nanostructure provides a great flexibility to control and enhance the plasmonic properties of noble metal nanoparticles.

Fluorescence turn on amine detection in a cationic covalent organic framework

Ionic covalent organic frameworks (iCOFs) are new examples of porous materials and have shown great potential for various applications. When functionalized with suitable emission sites, guest uptake via the ionic moieties of iCOFs can cause a significant change in luminescence, making them excellent candidates for chemosensors. In here, we present a luminescence sensor in the form of an ionic covalent organic framework (TGH⁺•PD) composed of guanidinium and phenanthroline moieties for the detection of ammonia and primary aliphatic amines. TGH⁺•PD exhibits strong emission enhancement in the presence of selective primary amines due to the suppression of intramolecular charge transfer (ICT) with an ultra-low detection limit of 1.2 × 10^‒7 M for ammonia. The presence of ionic moieties makes TGH⁺•PD highly dispersible in water, while deprotonation of the guanidinium moiety by amines restricts its ICT process and signals their presence by enhanced fluorescence emission. The presence of ordered pore walls introduces size selectivity among analyte molecules, and the iCOF has been successfully used to monitor meat products that release biogenic amine vapors upon decomposition due to improper storage.

Ionic covalent organic frameworks (iCOFs) are new examples of porous materials and show great potential for various applications. Here, the authors demonstrate functionalization of an iCOFs with suitable emission sites and application as chemosensor for amine detection with high sensitivity which can be used to monitor meat spoilage.

Reversal of a Fluorescent Fluoride Chemosensor from Turn-Off to Turn-On Based on Aggregation Induced Emission Properties

Here we present a new approach for the development of fluoride chemosensors taking advantage of aggregation induced emission (AIE) properties. Although AIE-based chemosensors have been described, they rely primarily on the analyte causing aggregation and hence fluorescence. We propose a new concept in the use of AIE for the development of fluorescent sensors. Our hypothesis is based on the fact that a turn-off chemosensor in solution can be transformed into turn-on in the solid state if the properties of ACQ and AIE are properly combined between the fluorescent molecules involved. To demonstrate this hypothesis, we have selected a fluorescent chemosensor for the fluoride anion with a conjugated structure of bis(styryl)pyrimidine that, while showing turn-off behavior in solution, becomes turn-on when it is brought to the solid state. We have also combined it with the advantages of a detection system based on the microfluidic paper-based analytical devices (μPAD). The system is fully characterized spectroscopically both in solution and in the solid state, and quantum mechanical calculations were performed to explain how the sensor works. The prepared device presents a high sensitivity, with no interference and with an LoD and LoQ that allow determination of fluoride concentrations in water 2 orders of magnitude below the maximum allowed by WHO.

A water-soluble azobenzene-dicyano pendant polymeric chemosensor for the colorimetric detection of cyanide in 100% aqueous media and food samples

A polymeric chemosensor (P1) was developed for the colorimetric detection of cyanide in aqueous media and cyanogenic food samples.