Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Coumarin-Based Small-Molecule Fluorescent Chemosensors.

Pt activated SnO2 nanoparticle clusters were synthesized by a simple solvothermal method. The structure, morphology, chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption studies, respectively. The SnO2 nanoparticle cluster matrix consists of tens of thousands of SnO2 nanoparticles with an ultra-small grain size estimated to be 3.0 nm. And there are abundant random-packed wormhole-like pores, caused by the inter-connection of the SnO2 nanoparticles, throughout each cluster. The platinum element is present in two forms including metal (Pt) and tetravalent metal oxide (PtO2) in the Pt activated SnO2 nanoparticle clusters. The as-synthesized pure and Pt activated SnO2 nanoparticle clusters were used to fabricate gas sensor devices. It was found that the gas response toward 500 ppm of ammonia was improved from 6.48 to 203.44 through the activation by Pt. And the results indicate that the sensor based on Pt activated SnO2 not only has ultrahigh sensitivity but also possesses good response–recovery properties, linear dependence, repeatability, selectivity and long-term stability, demonstrating the potential to use Pt activated SnO2 nanoparticle clusters as ammonia gas sensors. At the same time, the formation mechanisms of the unique nanoparticle clusters and highly enhanced sensitivity are also discussed.

Nanoparticle cluster gas sensor: Pt activated SnO2 nanoparticles for NH3 detection with ultrahigh sensitivity.

This paper reports metal oxide (MOx)-decorated graphene-based sensor array combining with back-propagation (BP) neural network toward the detection of indoor air pollutant exposure. Tin dioxide (SnO 2 ) nanospheres and copper oxide (CuO) nanoflowers-decorated graphene were used as candidates for formaldehyde and ammonia gas sensing, respectively. The as-synthesized sensing materials were characterized in terms of their nanostructural, morphological and compositional features by SEM, Raman spectra, and XRD. The sensor array was fabricated via one-step hydrothermal route and layer-by-layer (LbL) self-assembly technique on the substrate with interdigital microelectrodes. The sensing properties of MOx/graphene composite toward the mixture gas of ammonia and formaldehyde, such as dynamic response, sensitivity, response/recovery time, and stability, were investigated at room temperature. And furthermore, this work successfully achieved the recognition and quantitative prediction of components in the gas mixture of formaldehyde and ammonia through the combination of MOx/graphene-based sensor array and neural network-based signal processing technologies.

Quantitative detection of formaldehyde and ammonia gas via metal oxide-modified graphene-based sensor array combining with neural network model

High sensitivity ammonia gas sensor based on Ag/ZnO composite (SZO) nanostructures and their structural, optical, morphological and gas sensing properties were investigated. Field- emission scanning electron microscopy and high- resolution transmission electron microscopy revealed that pure ZnO flower-like nanorods transformed into nanoellipsoids upon adding of silver (Ag). Scanning transmission electron microscopy (STEM) analysis showed clear flower-like morphology of Ag/ZnO composite. STEM-mapping measurement showed that Zn, Ag and O were homogeneously distributed. The ammonia gas sensing analysis revealed that the Ag/ZnO (6 wt%) showed higher gas response compared with other content of Ag wt%. Ag/ZnO (6 wt%) exhibited the highest response of 29.5 when exposed to 100 ppm ammonia gas. Interestingly, Ag/ZnO (6 wt%) possessed good response and recovery property of 13 and 20 s at low concentration of ammonia at 10 ppm, respectively. The mechanism of gas sensing and enhanced gas response of pure ZnO and Ag/ZnO composite was discussed.

Sensitivity enhancement of ammonia gas sensor based on Ag/ZnO flower and nanoellipsoids at low temperature

Recently, there is an increasing interest in ammonia sensing and detection for a wide range of applications, including food, automotive, chemical, environmental, and medical sectors. A major challenge is to obtain selective, sensitive and environmentally stable sensing polymer/chemical materials that can meet the stringent performance requirements of these application areas. Among various polymer-based sensing materials, polyaniline has emerged as a preferred choice owing to its cost-effectiveness, facile preparation steps, and superior sensing performance towards ammonia. In this review, advances in polyaniline based ammonia detection sensors are summarized, with a special focus on progresses in polyaniline modification techniques to achieve enhanced sensing performance. These techniques utilize interfacial and high dilution syntheses, multifunctional dopants, template synthesis, self-oxidizing template synthesis, etc. , methods. Most up-to-date developments in combining polyaniline with other ammonia sensing materials, including polyaniline nanocomposites with metal oxides, graphene, carbon nanotubes and other carbon nanomaterials, are included. These novel nanocomposites have special capabilities of forming p - n nanojunctions or electron interphase interactions for superior detection sensitivity and selectivity. In addition, existing challenges toward understanding, reproducing, and optimizing the design of polyaniline based ammonia sensors are discussed.

A review on advances in application of polyaniline for ammonia detection

ODAP (N-oxalyl-L-2,3-diaminopropionic acid) is present in the seeds of grass pea. In this study, variation of total ODAP accumulation in leaves throughout the crop growth starting from 40 days after sowing to maturity, and the distribution pattern of ODAP in different plant parts including the seeds at the mature stage was analyzed. Five grass pea accessions were evaluated for two subsequent growing seasons in one location of ICARDA, Aleppo (Syria). The results found that the rate of accumulation of total ODAP varied during plant development. Increased rates of synthesis were noticed in young leaves of grass pea. The highest total ODAP content in leaves was noted in the early growth stage (40–50 days after sowing). Mean total ODAP content in leaves ranged from 0.17 to 0.96 percent during 2010–2011 and from 0.19 to 1.28 percent during 2011–2012. During maturity, the total ODAP content was lowest in the seeds than in leaves, stems, pod cover, seed coat, and cotyledons. The ranges of total ODAP content were 0.13 (seed)–0.34 (stem), 0.20 (seed)–1.01 (leaf), 0.22 (seed)–0.62 (leaf), 0.21 (seed)–0.66 (leaf), and 0.21 (seed)–0.78 (leaf) percent in B387, B222, B390, Bio-520, and B587 accessions, respectively, during maturity. The results indicated that the rate of accumulation and synthesis of total ODAP varied during the plant lifespan. The lowest total ODAP content of leaves was observed after 130 days of sowing. The lower total ODAP content after the early vegetative stage of grass pea plants makes them suitable as a feed.

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Neurotoxin (N-Oxalyl-L-α,β-Diamino Propionic Acid) Content in Different Plant Parts of Grass Pea (Lathyrus sativus L.) Spanning Seedling to Maturity Stage: Does It Increase over Time?

Jitendra Kumar

Papers

Neurotoxin (N-Oxalyl-L-α,β-Diamino Propionic Acid) Content in Different Plant Parts of Grass Pea (Lathyrus sativus L.) Spanning Seedling to Maturity Stage: Does It Increase over Time?