A Sensor Array for the Nanomolar Detection of Azo Dyes in Water

Construction of fluorescent sensor array with nitrogen-doped carbon dots for sensing Sudan Orange G and identification of various azo compounds

In this study, nitrogen-doped carbon dots (N-CDs) were facilely fabricated by one-pot hydrothermal method with levulinic acid and triethanolamine. A fluorescent sensor array was established for identifying azo compounds including Sudan Orange G (SOG), p-diaminoazobenzene, p-aminoazobenzene, azobenzene and quantitative detection of SOG. Experimental results revealed that azo compounds could quench the fluorescent intensity of N-CDs. Owing to various azo compounds showing different affinities to N-CDs, the sensor array exhibited different fluorescence quenching changes, which were further analyzed with principal component analysis to discriminate azo compounds. The sensor array was able to differentiate and recognize diverse concentrations of azo compounds from 0.25 to 2 mg/L. Simultaneously, a variety of factors affecting the detection of SOG were optimized. Under the optimized conditions, the sensor showed excellent stability and sensitivity. The sensor possessed marvelous linearity in the range of 0.1-1 mg/L and 1-4 mg/L and the detection limit was 27.82 μg/L. Spiked recoveries of 90.8-98.2 % were attained at spiked levels of 0.2 mg/L and 1 mg/L, demonstrating that the constructed fluorescence sensor was dependable and feasible for sensing SOG in environmental water samples.

CsPbBr3 perovskite quantum dot decorated ZIF-8 MOF: a selective dual recognition fluorometric visual probe for 4-nitroaniline and rhodamine blue

The uses of highly luminescent perovskite quantum dots in real analytical detection were limited by their supersensitive nature. Here, we have designed a CsPbBr3 perovskite based fluorometric sensor by integrating them with a zeolitic imidazole framework (ZIF-8) via an in situ one step technique and established its stability in aqueous and other polar solvents. The CsPbBr3@ZIF-8 luminescence sensor functioned excellently for the trace detection of 4-nitroaniline and rhodamine blue dye molecules with a detection limit value of 8.367 ppb and 0.088 ppm, respectively. A comprehensive investigation found that the quenching of the fluorescence signal occurred via fluorescence resonance energy transfer (FRET) for rhodamine blue dye and a H-bonding interaction induced trap density mediated quenching mechanism was responsible for 4-NA detection. The potential of this suggested sensor as a cheap portable test paper probe for analyte detection was also explored. This study introduces CsPbBr3 as a cutting-edge sensing platform for industrial pollutants such as dye molecules and nitroaromatics.

Synthesis of efficient light harvesting Cr, N Co-doped TiO2 nanoparticles for enhanced visible light photocatalytic degradation of xanthene dyes; eosin yellow and rose bengal

To solve the problem of water pollution, using environment friendly and cost effective method in short time is the need of hour. In this work, chromium (Cr) and nitrogen (N) co-doped TiO2 nanoparticles were synthesized and were used for the photocatalytic degradation of dyes under visible light. The synergistic effect of metal and non-metal co-dopants added would result in appropriate reduction of band gap {from 3.2 eV of TiO2 to 2.67 eV}, decrease in recombination rate of charge carriers by trapping electrons and holes, and in better light harvesting capacity. Nanoparticles were synthesized by sol-gel method and characterized using ultraviolet-visible (UV-VIS) spectroscopy, fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), zeta potential, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, field emission scanning electron microscopy (FE-SEM), and RAMAN spectroscopy. Eosin yellow (EY) and rose bengal (RB) were subjected to photocatalytic degradation under solar light to check the photocatalytic activity of the synthesized nanoparticles. Effects of dye concentration, the concentration of nanoparticles, time, and pH were investigated to optimize the parameters. The results obtained were remarkable for 20 ppm EY solution took 10 min using 1 gL-1 NPs at pH 3 and 10 ppm RB solution took 5 min using 0.75 gL-1 NPs at pH 5.78 (original pH) for complete degradation. Kinetics studies were also performed and both dyes followed pseudo-second-order kinetics with R2 values 0.99312 and 0.99712 for EY and RB, respectively. The study of degraded products was conducted using high-performance liquid chromatography (HPLC) hyphenated with electron spray ionization mass spectroscopy (ESI-MS) (LC-MS) and possible degradation pathways were made for both dyes. A reusability test was also performed showing the efficiency of the particles was up to 88% after 3 cycles of use. These notable results can be attributed to the efficient removal of organic pollutants using the proposed dopants in this study.

Aggregation-induced bimodal excitation of nitrogen-doped carbon dots for ratiometric sensing of new coccine and solid-state multicolor lighting

Trace detection of foodstuff pigments have gained increasing attention because of their close association with biological and environmental processes. Herein, we propose an innovative bimodal excitation nitrogen-doped carbon dots (N-CDs) for ratiometric sensing of new coccine (NC) pigment, which are synthesized by using melamine and o-phenylenediamine as precursors via solvothermal treatment. With the increase of the N-CDs concentration, N-CDs exhibit not only a concentration-dependent tunable color behavior, but also a novel aggregation-induced bimodal excitation phenomenon. Considering this distinctive bimodal excitation behavior, a ratiometric sensor based on N-CDs has been developed for the detection of the NC in different organic solvents due to the inner filter effect and fluorescence resonance energy transfer. The intensity ratio of two excitation signals is linear with the NC concentration in the range of 0.032-100 µM, and the limit of detection is as low as 32.1 nM. Meanwhile, we realize the design of multicolor-emission N-CDs/polymer films. All in all, this work presents a novel kind view of the mechanism of distinctive bimodal excitation of N-CDs, and further proposes an innovative ratiometric method for the screening analysis of NC in food samples and environmental pollutants.

Printed 384-Well Microtiter Plate on Paper for Fluorescent Chemosensor Array in Food Analysis

We propose a printed 384-well microtiter paper-based fluorescent chemosensor array device (384-well microtiter PCAD) to simultaneously categorize and discriminate saccharides and sulfur-containing amino acids for food analysis. The 384-well microtiter PCAD required 1 μL/4 mm 2 of each well can allow high-throughput sensing. The device embedded with self-assembled fluorescence chemosensors displayed a fingerprint-like response pattern for targets, the image of which was rapidly captured by a portable digital camera. Indeed, the paper-based chemosensor array system combined with imaging analysis and pattern recognition techniques successfully not only categorized saccharides and sulfur-containing amino acids but also classified mono- and disaccharide groups. Furthermore, the quantitative detectability of the printed device was revealed by a spike recovery test for fructose and glutathione in a diluted freshly made tomato juice. We believe that the 384-well microtiter PCAD using the imaging analysis system will be a powerful sensor for multi-analytes at several categorized groups in real samples.

Advances in Optical Sensors for Persistent Organic Pollutant Environmental Monitoring

Optical chemical sensors are widely applied in many fields of modern analytical practice, due to their simplicity in preparation and signal acquisition, low costs, and fast response time. Moreover, the construction of most modern optical sensors requires neither wire connections with the detector nor sophisticated and energy-consuming hardware, enabling wireless sensor development for a fast, in-field and online analysis. In this review, the last five years of progress (from 2017 to 2021) in the field of optical chemical sensors development for persistent organic pollutants (POPs) is provided. The operating mechanisms, the transduction principles and the types of sensing materials employed in single selective optical sensors and in multisensory systems are reviewed. The selected examples of optical sensors applications are reported to demonstrate the benefits and drawbacks of optical chemical sensor use for POPs assessment.

Cell-Based Chemical Safety Assessment and Therapeutic Discovery Using Array-Based Sensors

Synthetic chemicals are widely used in food, agriculture, and medicine, making chemical safety assessments necessary for environmental exposure. In addition, the rapid determination of chemical drug efficacy and safety is a key step in therapeutic discoveries. Cell-based screening methods are non-invasive as compared with animal studies. Cellular phenotypic changes can also provide more sensitive indicators of chemical effects than conventional cell viability. Array-based cell sensors can be engineered to maximize sensitivity to changes in cell phenotypes, lowering the threshold for detecting cellular responses under external stimuli. Overall, array-based sensing can provide a robust strategy for both cell-based chemical risk assessments and therapeutics discovery.

The oxidative degradation of Calmagite using added and in situ generated hydrogen peroxide catalysed by manganese(II) ions: Efficacy evaluation, kinetics study and degradation pathways

Manganese (II) ions (Mn(II)) catalyse the oxidative degradation of Calmagite (CAL, 2-hydroxy-1-(2-hydroxy-5methylphenylazo)-4-naphthalenesulfonic acid) at room temperature using added and in situ generated hydrogen peroxide (H₂O₂), using 1,2-dihydroxybenzene-3,5-disulfonate, disodium salt and monohydrate (Tiron) as the co-catalyst for the in situ generation of H₂O₂. The percentage of CAL degradation with the in situ generated H₂O₂ was 91.1 % after 30 min which is lower than that in the added H₂O₂/Mn(II) system (96.0 %). A one-eighth-lives method was applied to investigate the kinetic parameters in the added H₂O₂ system, with and without Mn(II), involving phosphate, carbonate, and two biological buffers at different pHs. Percarbonate (HCO₄^-) was found to be the main reactive species for CAL degradation in the added H₂O₂ system buffered by carbonate in the absence of Mn(II). Manganese (IV) = O (Mn(IV) = O) and manganese(V) = O (Mn(V) = O) are the main reactive species in the added H₂O₂/Mn(II) system buffered by carbonate and non-carbonate buffers respectively. pH 8.5 was the optimum pH for CAL degradation when buffered by carbonate, while pH 10.0 is the best pH for the systems not using carbonate buffer. Using a high performance liquid chromatography/electrospray ionisation mass spectrometer (HPLC/ESI-MS), the degradation intermediates of CAL were identified as 1-amino-2-naphthol-4-sulfonate ion, 1-amino-2-naphthol-4-sulfinic ion, 1-amino-2-naphthol, and 1-nitroso-2-naphthol.

Terthiophene-functionalized mesoporous silica-based fluorescence sensor for the detection of trace methyl orange in aqueous media

A terthiophene-functionalized mesoporous SBA-15 silica, i.e., TTU-SBA-15, was successfully developed and used as a highly selective and ultrasensitive fluorescence sensor for methyl orange (MO) detection. When the concentration of MO was increased, the fluorescence emission intensity of TTU-SBA-15 suspensions at 452 nm gradually decreased at an excitation wavelength of 368 nm, and the color of the suspension solutions changed obviously from blue to dark under 365 nm UV light. The fluorescence intensity at 452 nm was linearly proportional to the concentration of MO in the range 0.20 - 2.0 μM, with a detection limit of 0.092 μM. Competitive pollutants, variations in pH, and sample recycling had subtle or negligible effects on the detection of MO. TTU-SBA-15 was applied to the determination of MO in tap water, and recoveries from spiked samples were in the range 98.3 - 103.0%. This study provides a convenient and effective strategy to realize highly sensitive and selective sensors that could target dyes via the functional modification of mesoporous materials.

Green preparation of carbon dots from Momordica charantia L. for rapid and effective sensing of p-aminoazobenzene in environmental samples

p-Aminoazobenzene (pAAB) is a hazardous azo dye that causes considerable harm to human health and the environment. The development of novel and sensitive sensors for the rapid detection of pAAB is in high demand. In this study, a simple fluorescent sensor for pAAB detection is designed based on carbon dots (CDs) which are prepared using green carbon source of Momordica charantia L. via a facile hydrothermal approach. The fluorescence spectra of CDs exhibit considerable overlap with the absorption band of pAAB, and the fluorescence is specifically suppressed in the presence of pAAB ascribed to the inner filter effect. Good and wide linearity is observed in the pAAB concentration range of 0.01-12.5 μg mL^-1 with a lower detection limit of 3.9 ng mL^-1. The established method achieves good results with a rapid analysis of pAAB in different practical water and soil samples. The as-constructed fluorescent sensor provides a simple, rapid, economical and eco-friendly platform and possesses prospective applications for the effective, selective and sensitive detection of pAAB in the environmental field.

Fluorescence-Based Sensing of Pesticides Using Supramolecular Chemistry

The detection of pesticides in real-world environments is a high priority for a broad range of applications, including in areas of public health, environmental remediation, and agricultural sustainability. While many methods for pesticide detection currently exist, the use of supramolecular fluorescence-based methods has significant practical advantages. Herein, we will review the use of fluorescence-based pesticide detection methods, with a particular focus on supramolecular chemistry-based methods. Illustrative examples that show how such methods have achieved success in real-world environments are also included, as are areas highlighted for future research and development.

Effect of curvature and placement of donor and acceptor units in cycloparaphenylenes: a computational study

Cycloparaphenylenes have promise as novel fluorescent materials. However, shifting their fluorescence beyond 510 nm is difficult. Herein, we computationally explore the effect of incorporating electron accepting and electron donating units on CPP photophysical properties at the CAM-B3LYP/6-311G** level. We demonstrate that incorporation of donor and acceptor units may shift the CPP fluorescence as far as 1193 nm. This computational work directs the synthesis of bright red-emitting CPPs. Furthermore, the nanohoop architecture allows for interrogation of strain effects on common conjugated polymer donor and acceptor units. Strain results in a bathochromic shift versus linear variants, demonstrating the value of using strain to push the limits of low band gap materials.

Effect of the Heteroaromatic Antenna on the Binding of Chiral Eu(III) Complexes to Bovine Serum Albumin

The cationic enantiopure (R,R) and luminescent Eu(III) complex [Eu(bisoQcd)(H₂O)₂] OTf (with bisoQcd = N,N′-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate and OTf = triflate) was synthesized and characterized. At physiological pH, the 1:1 [Eu(bisoQcd)(H₂O)₂]⁺ species, possessing two water molecules in the inner coordination sphere, is largely dominant. The interaction with bovine serum albumin (BSA) was studied by means of several experimental techniques, such as luminescence spectroscopy, isothermal titration calorimetry (ITC), molecular docking (MD), and molecular dynamics simulations (MDS). In this direction, a ligand competition study was also performed by using three clinically established drugs (i.e., ibuprofen, warfarin, and digitoxin). The nature of this interaction is strongly affected by the type of the involved heteroaromatic antenna in the Eu(III) complexes. In fact, the presence of isoquinoline rings drives the corresponding complex toward the protein superficial area containing the tryptophan residue 134 (Trp134). As the main consequence, the metal center undergoes the loss of one water molecule upon interaction with the side chain of a glutamic acid residue. On the other hand, the similar complex containing pyridine rings ([Eu(bpcd)(H₂O)₂]Cl with bpcd = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate) interacts more weakly with the protein in a different superficial cavity, without losing the coordinated water molecules.

The effect of the antenna moiety on the interaction of two new luminescent Eu(III) complexes with BSA was studied. Results show that the complexes can be conveniently exploited as optical probes for albumin serum proteins by means of opposite mechanisms (switch-on−off of the luminescent signal).