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Highlights • A dynamic multichannel colorimetric sensor array is developed for highly effective discrimination of ten explosives. • This sensor array efficiently discriminates among individual explosive and binary explosive mixtures. • The explosive discrimination capacity is not sacrificed in real pond and lake water samples. Abstract We present a dynamic multichannel colorimetric sensor array for highly effective discrimination of ten explosives, including 2,4-dinitrotoluene, picric acid, hexahydro-1,3,5-trinitro-1,3,5-triazine, 3-nitro-1,2,4-triazol-5-one, hexanitrohexaazaisowurtzitane, 2,6-diamino-3,5-dinitropyrazine-1-oxide, 1,1-diamino-2,2-dinitroethene, 4-nitrophenol, nitroguanidine, and 2,4-dinitrophenol. This sensor array is based on the fact that the reduction of indigo carmine by dithiothreitol generates semi-leucoindigo carmine and leucoindigo carmine at the different reaction time, resulting in abundantly available absorption peaks at 456 nm, 504 nm, 552 nm, 612 nm, 754 nm, and 906 nm as the sensing elements. Because of the presence of the supramolecular interactions and chemical reactions between explosives and indigo carmine, the distinct absorbance responses to each explosive are created as an analytical fingerprint to discriminate and identify ten explosives. The present colorimetric sensor array can efficiently discriminate individual explosive at a concentration of 1.5 μM and binary explosive mixtures. Additionally, this sensor array has the capability to identify individual explosive in real water samples. [ABSTRACT FROM AUTHOR]

We report a colorimetric nanoparticle array for discrimination of five organic antifreezes containing ethylene glycol (EG), formamide (FA), ethanol (EtOH), glycerin (Gly), and polyethylene glycol (PEG). Silver nanopartciles, gold nanoparticles, and Prussian blue nanoparticles are employed to be three sensing elements due to their unique optical absorption properties. The organic antifreezes can alleviate the aggregation of three nanoparticles after a freeze-thawing cycle. Based on the different freezing resistances of various antifreezes, the sensor array shows a unique colorimetric pattern of absorbance variations for each antifreeze, which is further analyzed by principal component analysis (PCA). The present sensor array has the capacity to differentiate antifreezes and their mixtures at a concentration as low as 50 mM. Moreover, the sensor array can also discriminate organic antifreezes in real water sample. Additionally, a high accuracy (100%) examination of 30 unknown samples is achieved. [ABSTRACT FROM AUTHOR]

We report that graphitic carbon nitride (g-C 3 N 4 ) nanosheets can enhance the chemiluminescence (CL) of luminol and hydrogen peroxide (H 2 O 2 ) system. The reaction mechanism of the luminol-H 2 O 2 -g-C 3 N 4 nanosheets system was investigated by CL spectrum, UV–vis absorption spectroscopy, and radical scavengers. The g-C 3 N 4 nanosheets-enhanced CL mechanism was attributed to the fact that g-C 3 N 4 nanosheets were able to catalyze the decomposition of H 2 O 2 to form reactive hydroxyl radical. The produced hydroxyl radical further reacted with luminol and H 2 O 2 anion, generating a light emission. Moreover, 2,4,6-trinitrotoluene (TNT) was observed to inhibit the CL effectively. On this basis, a sensitive and selective sensing approach was successfully developed for the detection of TNT. The linearity ranged from 1 pM to 1 nM with a detection limit of 0.75 pM based on a signal-to-noise ratio of 3. This sensitivity increased about six orders of magnitude over that of g-C 3 N 4 nanosheets-based fluorescence sensor. [ABSTRACT FROM AUTHOR]

Dendritic Au–Ag bimetallic nanoparticles with chemiluminescence (CL) activity were synthesized by the seed-assisted approach for the first time. In this approach, luminol (CL reagent) as reducing agent was employed to reduce chloroauric acid in the presence of silver nanoparticles seeds to form dendritic Au–Ag bimetallic nanoparticles. The as-prepared dendritic Au–Ag bimetallic nanoparticles had well defined dendritic morphology with an average diameter of 60 nm. Moreover, the obtained bimetallic nanoparticles could react with hydrogen peroxide that was generated by the enzymatic oxidation between d -glucose and glucose oxidase (GOx), producing a strong CL emission in the presence of horseradish peroxidase as an effective CL catalyst. On this basis, a sensitive and selective assay was proposed for the detection of d -glucose. The d -glucose could be determined by CL signal in the range from 1 μM to 1 mM with a detection limit of 0.4 μM. This work not only prepared a novel functionalized nanomaterial, but also provided a new assay for the detection of d -glucose with high sensitivity and reproducibility. [ABSTRACT FROM AUTHOR]

• A series of colorimetric methods for visual detection of atmospheric sulfate formation-involved substances are built. • These detection systems determine SO2 with detection limit of 50 ppb. • The present analytical approaches are useful for studying the atmospheric sulfate formation and environmental monitoring. The ongoing urban air pollution has resulted in an increased demand for detecting atmospheric sulfate formation-involved substances. Here, we present a series of colorimetric assays based on plasmonic MoO 3-x nanosheets for visual colorimetric detection of atmospheric sulfate formation-involved substances, including hydrogen peroxide (H 2 O 2), Fe2+/Fe3+, bisulfite (HSO 3 −), and sulfur dioxide (SO 2). We show that the plasmonic MoO 3-x nanosheets with blue color can be oxidized by hydroxyl radicals (OH) generated by the Fenton reaction between Fe2+/Fe3+ and H 2 O 2 to produce colorless MoO 3 nanosheets, resulting in a distinct absorbance change. However, when HSO 3 −/SO 2 is introduced, the OH will react with them to yield sulfate, which inhibits the oxidation of MoO 3-x nanosheets, leading to the color recovery. Using these detection systems, we determine H 2 O 2 , Fe2+, Fe3+, and HSO 3 − with detection limits of 60 nM, 50 nM, 400 nM, and 1 μM, respectively. Especially, SO 2 is selectively assayed with an ultralow detection limit, down to 50 ppb level. In addition, the present colorimetric assay is further utilized to detect SO 2 in real air with a good accuracy to demonstrate the practicality of the colorimetric method. [ABSTRACT FROM AUTHOR]

• A radical reaction-based visual colorimetric assay for SO 2 and SO 3 2− is presented. • This colorimetric assay exhibits a 60–650 μM and 30–70 ppm linear ranges for detection of SO 3 2− and SO 2 , respectively. • The specific radical detection guarantees that the present colorimetric assay has a good anti-interference ability over common inorganic ions and gases. Rapid, reliable, and highly selective detection of SO 2 and its derivatives has an especially important practical significance in terms of environmental monitoring and human health. In this study, we describe a novel Co2+ triggered radical reaction pathway for visual colorimetric detection of SO 2 and SO 3 2−. The reaction between Co2+ and SO 2 or SO 3 2− with the assistance of dissolved oxygen produces highly active sulfate radical, leading to the oxidation of o-phenylenediamine (OPD). The oxidation products containing 2,3-dinitro-phenazinemethane, OPD dimer, and OPD trimer show strong UV–vis absorption. Consequently, SO 2 and SO 3 2− are quantitatively determined using the Co2+-OPD colorimetric detection system. This colorimetric assay exhibits a 60–650 μM and 30–70 ppm linear ranges for detection of SO 3 2− and SO 2 , respectively. The corresponding limit of detection is calculated to be 4.07 μM and 1.26 ppm for SO 3 2− and SO 2. What is more, a distinct color change can be found at a SO 3 2− concentration of 50 μM by the naked-eye observation. The specific radical detection guarantees that the present colorimetric assay has a good anti-interference ability over common inorganic ions and gases. [ABSTRACT FROM AUTHOR]

• A formic acid-assisted photolysis of UO 2 2+ initiated chromogenic reaction is fabricated for colorimetric detection of UO 2 2+. • This colorimetric assay realizes visualization of UO 2 2+ at a concentration of 0.5 μM. • It possesses excellent selectivity over common inorganic ions with even 50-fold higher concentration than UO 2 2+. Current strategies for visual detection of uranyl ion (UO 2 2+) often require DNAzymes and organophosphorus receptors as well as various nanomaterials that may affect the selectivity, sensitivity, and accuracy in a complicated environment. Here, we circumvent these drawbacks by introducing a formic acid (FA)-assisted photolysis of UO 2 2+ initiated chromogenic reaction for specific recognition element-free colorimetric detection of UO 2 2+. The colorless 2, 2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) is oxidized by the superoxide anion from the photolysis of UO 2 2+ to generate green ABTS radical, which enables the determination of UO 2 2+ at a concentration of 0.5 μM with the naked eye. The present colorimetric assay is able to determine concentrations of UO 2 2+ from 0.1 to 100 μM, with a limit of detection as low as 0.01 μM. Impressively, the specific recognition element-free colorimetric assay possesses excellent selectivity over common inoganic ions with even 50-fold higher concentration than UO 2 2+. In addition to good sensitivity and selectivity, this colorimetric assay is also capable of determining UO 2 2+ in natural water samples with satisfactory recoveries. [ABSTRACT FROM AUTHOR]

A novel, label-free, and low-cost colorimetric assay is developed for the detection of hydrazine with high-selectivity and excellent sensitivity using MnO 2 nanosheets as probes. It is first time demonstrated that MnO 2 nanosheets can be used as colorimetric probes for environmental analysis. In the absence of hydrazine, MnO 2 nanosheets exhibit a strong ultraviolet–visible (UV–vis) absorption peak at 370 nm due to the d-d transition. Once hydrazine is introduced, MnO 2 nanosheets will be reduced to Mn(OH) 2 nanoparticles, and the absorbance at 370 nm decreases remarkably. In this case, a distinct color change from yellow to colorless can be observed, which is dependent on the concentration of hydrazine. The signal change can allow colorimetric detection of hydrazine. The assay offers a good linear range from 0.5 μM to 20 μM and a detection limit of 0.4 μM for hydrazine. The lowest detection concentration by the naked eye is as low as 11 μM. Additionally, the developed assay was successfully applied for the colorimetric detection of hydrazine in environmental water samples. [ABSTRACT FROM AUTHOR]

Surfactants that are organized self-assembly to form micelles have been widely utilized for detection of several analytes. However, the surfactants only provide a hydrophobic space, which does not involve the molecular recognition process. Here, we report a surfactant-involved colorimetric assay for visual and sensitive detection of fentanyl (FTN), a third-generation new psychoactive substance. It is found that sodium dodecyl sulfate (SDS) simultaneously enhance the halogen-bonding interaction between Rose Bengal (RB) as the probe and FTN as well as stabilize the RB-FTN complex. This molecular recognition induces the intermolecular charge transfer, generating a significant redshift in the absorption band of RB and accompanying a distinct color change from red to purple. This assay possesses an ultrahigh response speed (within 1 min), and the limit of detection is calculated to be as low as 0.1 mg·L−1. It also shows good selectivity and application potential. The recovery rates of real samples are between 92.5% and 110%, suggesting that it is suitable for rapid and accurate analysis of food samples such as mineral water, orange juice and cocktail. The current strategy can be further exploited in surfactant enhanced detection applications for other substances. • A new surfactant-involved colorimetric detection strategy is proposed for visual detection of fentanyl (FTN). • The limit of detection of this assay for FTN is down to 0.1 mg·L−1. • This assay allows for accurate analysis of FTN in food samples within 1 min. [ABSTRACT FROM AUTHOR]