Development of an azo-naphthol-based probe for detecting hypochlorite (ClO−) via color change in aqueous solution

A fast and sensitive colorimetric sensor for residual chlorine detection made with oxidized cellulose

Residual chlorine from widespread disinfection processes forms byproducts in water that are harmful to humans and ecosystems. Portable sensors are essential tools for the on-site monitoring of residual chlorine in environmental samples. Here, an inexpensive colorimetric sensor was developed by grafting via amidation the chromogen orthotolidine (OTO) to the surface of a TEMPO-oxidized cellulose filter paper (O-TOFP). A thorough characterization of the sensor strip demonstrated that it was highly stable and that it could be stored for a long period before usage. O-TOFP had a fast response time of 30 s, was highly selective for residual chlorine ions (ClO-) with an accuracy of at least 95 %, and exhibited an excellent limit of detection of only 0.045 mg/L when combined with smartphone image acquisition. With its many positive features, the easy-to-use and robust O-TOFP sensor described here could become a useful tool for the determination of residual chlorine in different water samples.

Fast and easy detection of hypochlorite by a smartphone-based fluorescent turn-on probe: Applications to water samples, zebrafish and plant imaging

We have developed a fluorescent probe DBT-Cl ((E)-2-(2-(4-(diphenylamino)benzylidene) hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) for ClO- with an aggregation-induced emission (AIE) strategy depending on solvent polarity. DBT-Cl possessed a prominent solvatochromic emission property with intramolecular charge transfer (ICT) from the TPA (triphenylamine) to the amide group, which was studied by spectroscopic analysis and DFT calculations. These unique AIE properties of DBT-Cl led to the recognition of ClO- with high fluorescent selectivity. DBT-Cl quickly detected ClO- in less than 1 sec with a fluorescent color change from green to cyan. DBT-Cl had a low detection limit of 9.67 μM to ClO-. Detection mechanism of DBT-Cl toward ClO- was illustrated to be oxidative cleavage of DBT-Cl by 1H NMR titrations, ESI-mass, and DFT calculations. We established the viability for dependable detection of ClO- in actual water samples, as well as zebrafish and plant imaging. In particular, DBT-Cl was capable of easily monitoring ClO- through a smartphone application. Therefore, DBT-Cl assured a promising approach for a fast-responsive and multi-applicable ClO- probe in environmental and living organism systems.

Ex_g-C3N4 as a novel fluorescent probe for sensitive detecting ClO- in water samples with portable test strip

Excessive hypochlorite (ClO^-) is easy to form residues in water, which will seriously endanger human health and environmental pollution. Therefore, it is essential to develop a sensitive fluorescent sensor to detect ClO^- in water. Herein, a simple and economical fluorescent probe for the detection of ClO^- was designed by highly exfoliated graphite-like carbon nitride (Ex_g-C₃N₄). The results showed that Ex_g-C₃N₄ had obvious fluorescence quenching effect on ClO^- with high selectivity and anti-interference ability, which was feasible for making probes for detecting ClO^- in water. Sensing experiments showed that the Ex_g-C₃N₄ probe had the detection limit of 5.56 nM while the detection range was 0-62 mM in water. Moreover, the fast response time of Ex_g-C₃N₄ was less than 30 s, illustrating the superior sensitivity. Besides, the fluorescence sensing experiment was carried out in various liquid conditions, which demonstrated that Ex_g-C₃N₄ probe had outstanding detecting application in natural environment. A portable fluorescent test strip for rapid detecting ClO^- was successfully developed. The response of the probe on test strip towards ClO^- was investigated, and the detection limit (0.1 μM) is low enough to meet the safety requirements in tap water. Furthermore, the quenching mechanism of Ex_g-C₃N₄ probe was also discussed.

Green-emitting carbon quantum dots as a dual-mode fluorescent and colorimetric sensor for hypochlorite

In this work, green-emitting carbon quantum dots were successfully prepared through a facile one-step solid-state reaction method. The obtained green-emitting carbon dots (G-CDs) showed good fluorescence stability in NaCl aqueous solution and different pH values. Moreover, the G-CDs showed high sensitivity and selectivity for detecting hypochlorite by both fluorometry and colorimetry. Under the optimized condition, a highly sensitive detection of hypochlorite was established in the range of 0.2-100 μM and 10-150 μM for fluorescent and colorimetric methods, respectively. The corresponding limits of detection (LOD) were 0.0781 μM and 1.82 μM, respectively. Therefore, the G-CDs were successfully applied to determinate hypochlorite in actual water samples. In addition, a paper-based sensor loading with the G-CDs was also developed for rapid visual detection of hypochlorite. The results suggested that the G-CDs could be a promising candidate to detect hypochlorite.

A Flexible Chemosensor Based on Colorimetric and Fluorescent Dual Modes for Rapid and Sensitive Detection of Hypochlorite Anion

A flexible chemosensor has been developed based on colorimetric and fluorescent dual modes using tetraphenylethylene-centered tetraaniline (TPE4A) for rapid and sensitive detection of hypochlorite anion. The fluorescent probe TPE4A exhibits a unique aggregation-induced emission (AIE) character which is proved by a blue shift of the fluorescent peak from 544 to 474 nm with the water equivalents increasing. With the addition of hypochlorite in solution, the absorbance of the probe changes and the responding fluorescence color can be observed to change from light green to purple. The detection limit of hypochlorite is 1.80 × 10-4 M in solution, and the visual detection limit is 1.27 µg/cm2 with the naked eye for the flexible paper-based chemosensor. The proposed flexible chemosensors show a good selectivity and sensitivity which has great potential for effective detection of hypochlorite anions without any spectroscopic instrumentation.

One-step construction of a novel AIE probe based on diaminomaleonitrile and its application in double-detection of hypochlorites and formaldehyde gas

A novel and efficient probe with AIE property was designed and synthesized for application in double-detection of hypochlorites and formaldehyde gas.