A novel phenolphthalein-based fluorescent sensor for Al3+ sensing in drinking water and herbal tea samples

Chemically modified graphitic carbon nitride nanosheets for the selective turn-off fluorescence detection of Al(III) ions in crabs (Brachyura)

The selective and sensitive detection of Al(III) is critically important for human health since the level of Al(III) is an indicator of many diseases in humans. Herein, we developed a simple and sensitive fluorescent sensor for the detection of Al(III) in an aqueous solution based on the fluorescence of hydroxyl-functionalized graphitic carbon nitride nanosheets (HO/g-CN). OH/g-CN nanosheets were synthesized via the thermal pyrolysis of 1,3,5-triazine-2,4,6-triamine (as raw material) at 550 °C for 2 hours, followed by thermal alkali treatment at 730 °C for 2 min. The fluorescence of HO/g-CN at 377 nm (at 290 nm excitation) can be quenched by Al(III) effectively and selectively, and the linear relationship between the concentration of Al(III) and fluorescence intensity is in the range of 1.85-14.82 μM with a detection limit of 0.272 μM. The fluorescence turn-off effect of the Al(III) ion on the prepared HO/g-CN nanosheets could be attributed to the presence of oxygen- and nitrogen-containing functional groups on the surface of HO/g-CN that have chelating interactions with Al(III), leading to quenching. The surface functional groups of OH/g-CN were confirmed using different characterization techniques (FTIR, EDX, and XPS). Moreover, the prepared HO/g-CN exhibited remarkable long-term fluorescence stability in water (>30 days) and minimal toxicity. Importantly, a prepared novel fluorescent sensor (HO/g-CN) was successfully applied for the detection and determination of Al(III) in commercially available crab (Brachyura) samples.

Toward Sensitive and Reliable Immunoassays of Marine Biotoxins: From Rational Design to Food Analysis

Marine biotoxins are metabolites produced by algae that can accumulate in shellfish or fish and enter organisms through the food chain, posing a serious threat to biological health. Therefore, accurate and rapid detection is an urgent requirement for food safety. Although various detection methods, including the mouse bioassay, liquid chromatography-mass spectrometry, and cell detection methods, and protein phosphatase inhibition assays have been developed in the past decades, the current detection methods cannot fully meet these demands. Among these methods, the outstanding immunoassay virtues of high sensitivity, reliability, and low cost are highly advantageous for marine biotoxin detection in complex samples. In this work, we review the recent 5-year progress in marine biotoxin immunodetection technologies such as optical immunoassays, electrochemical immunoassays, and piezoelectric immunoassays. With the assistance of immunoassays, the detection of food-related marine biotoxins can be implemented for ensuring public health and preventing food poisoning. In addition, the immunodetection technique platforms including lateral flow chips and microfluidic chips are also discussed. We carefully investigate the advantages and disadvantages for each immunoassay, which are compared to demonstrate the guidance for selecting appropriate immunoassays and platforms for the detection of marine biotoxins. It is expected that this review will provide insights for the further development of immunoassays and promote the rapid progress and successful translation of advanced immunoassays with food safety detection.

Recent Developments in Colorimetric and Fluorometric Detection Methods of Trivalent Metal Cations (Al3+, Fe3+ and Cr3+) Using Schiff Base Probes: At a Glance

This review basically concerned with the application of different Schiff bases (SB) based fluorimetric (turn-off and turn-on) and colorimetric chemosensors for the detection of heavy metal cations particularly Al(III), Fe(III), and Cr(III) ions. Chemosensors based on Schiff bases have exhibited outstanding performance in the detection of different metal cations due to their facile and in-expensive synthesis, and their excellent coordination ability with almost all metal cations and stabilize them in different oxidation states. Moreover, Schiff bases have also been used as antifungal, anticancer, analgesic, anti-inflammatory, antibacterial, antiviral, antioxidant, and antimalarial etc. The Schiff base also can be used as an intermediate for the formation of various heterocyclic compounds. In this review, we have focused on the research work performed on the development of chemosensors (colorimetric and fluorometric) for rapid detection of trivalent metal cations particularly Al(III), Fe(III), and Cr(III) ions using Schiff base as a ligand during 2020-2022.

A portable front face fluorescent system for in situ detection of aluminum in flour foods

A simple and rapid method for in situ detection of aluminum in flour food was developed by using a self-made portable front face fluorescent system (PFFFS). The effects of pH, temperature, reaction time, protective agent and masking agent on the detection of Al³⁺ were investigated. The use of fluorescent probe protective agent, interfering ion masking agent, multi-point collection measurements and the working curves based on the analyte content in the real samples makes the present method have high accuracy, selectivity and reliability for in situ detection of Al³⁺ in flour foods. By comparison with the ICP-MS the accuracy and reliability of the present method were verified. The results showed that when 97 real samples were analyzed the Al³⁺ content values obtained by the present method and those obtained by ICP-MS method reached a highly significant correlation, with r ranging from 0.9747 to 0.9844. The self-made PFFFS combined with fluorescent probe does not require sample digestion, and can quickly detect Al³⁺ in flour food within 10 min. Therefore, the present method based on using FFFS has good practical application value for in-situ rapid detection of Al³⁺ in flour foods.

A cyanobiphenyl-based fluorescent ''lighting-up'' sensor for highly selective and sensitive recognition of Al3+: Theoretical, practical and bioimaging studies

The recognition of toxic Al³⁺ in foods and biosystems has of great interest to researchers. Herein, a novel cyanobiphenyl-based chemosensor CATH (E)-N'-((4'-cyano-4-hydroxy-[1,1'-biphenyl]-3-yl)methylene)thiophene-2-carbohydrazide was fabricated and shown to recognize Al³⁺ in HEPES buffer:EtOH (90:10, v:v, pH = 7.4) by ''lighting-up'' fluorescence sensing. The CATH evidenced high sensitivity (LOD = 13.1 nM) and excellent selectivity to Al³⁺ over competing cations. The Job's plot, TOF-MS and theoretical computation studies were performed to probe the binding mechanism of Al³⁺ to CATH. Additionally; CATH was successfully utilized to practical applications and employed to recover of Al³⁺ from different food samples. More importantly, it was employed to intracellular Al³⁺ detection in living cells including THLE2 and HepG2.

Two novel fluorescent probes based on quinolinone for continuous recognition of Al3+ and ClO. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023;300:122917. [PMID: 37269662 DOI: 10.1016/j.saa.2023.122917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

On the basis of classical Schiff base reaction, two novel and efficient fluorescent probes (DQNS, DQNS1) were designed and synthesized by introducing Schiff base structure into dis-quinolinone unit for structural modification, which can be used to detect Al³⁺ and ClO^-. Because the power supply capacity of H is weaker than that of methoxy, DQNS shows better optical performance: a large Stokes Shift (132 nm), identify Al³⁺ and ClO^- with high sensitivity and selectivity, low detection limit (29.8 nM and 25 nM) and fast response time (10 min and 10 s). Through the working curve and NMR titration experiment, the recognition mechanism of Al³⁺ and ClO^- (PET and ICT) probes are confirmed. Meanwhile, it is speculated that the probe has continuity for the detection of Al³⁺ and ClO^-. Furthermore, DQNS detection of Al³⁺ and ClO^- was applied to real water samples and living cell imaging.

A novel water-soluble flavonol-based fluorescent probe for highly specific and sensitive detection of Al3+ and its application in onion and zebrafish

A novel and simple turn-on fluorescence probe (HD) for Al³⁺ detection was successfully developed based on flavonol derivatives. This probe exhibited a significantly enhanced fluorescence response toward Al³⁺ in aqueous solution which could be observed by naked-eye from poor fluorescence to strong light green emission. The probe HD displays highly specific detection for Al³⁺ over other competitive metal ions, and the detection limit of probe HD for Al³⁺ was determined to be 2.57 × 10^-8 M, which are much lower than the World Health Organization (WHO) guideline value for drinking food/water. The binding stoichiometry of probe HD with Al³⁺ was determined to be 1:1 according to Job's plot and ESI-HRMS analysis, and the binding constant was calculated to be 2.01 × 10⁴ M^-1. The probe HD exhibited high selectivity, high sensitivity, good anti-interface ability, and wide pH application range as well as the quantitative determination in the detection of Al³⁺. The coordination mechanism of probe HD with Al³⁺ was supported by density functional theory (DFT) calculations and HRMS analysis. In addition, the probe HD was found to have good cell permeability and could be applied for live-cell imaging to detect Al³⁺ in onions and zebrafish.

Rewritable acidochromic papers based on oxazolidine for anticounterfeiting and photosensing of polarity and pH of aqueous media

Oxazolidine is a new category of stimuli-chromic organic compounds with unique characteristics in response to polarity, pH changes, water, light, and metal ions that were well-known as solvatochromism, acidochromism, hydrochromism, photochromism, and ionochromism, respectively. Therefore, oxazolidine derivatives have been developed for their potential applications in chemosensors, anticounterfeiting, and rewritable hydrochromic papers. In this study, various oxazolidine derivatives containing hydroxyl and naphthalene substituted groups were synthesized by using two different indolenine compounds. The synthesized oxazolidine derivatives were used for investigation of solvatochromism in different solvents, and also acidochromism in various pHs by using UV–Vis and fluorescence spectroscopies. In addition, the oxazolidine derivatives were coated on cellulosic papers using a layer-by-layer strategy to develop rewritable acidochromic papers for printing of security tags on cellulosic papers by using acidic and alkaline solutions as water-based inks. Therefore, the developed rewritable acidochromic papers could be used as security papers.

A dimedone-phenylalanine-based fluorescent sensor for the detection of iron (III), copper (II), L-cysteine, and L-tryptophan in solution and pharmaceutical samples

The development of fluorescence molecules for the fast and effective detection of L-tryptophan (L-Trp) has attracted a lot of attention because it is an important amino acid for baby growth, nitrogen equilibrium in adults, improving sleep, and mood regulation. A dimedone-phenylalanine-based chiral sensor (SDPA) was synthesized and exhibited a strong fluorescence quenching by Fe³⁺ and Cu²⁺ in a water/DMSO (3/7) solution with a detection limit of 2.29 × 10^-6 M and 6.37 × 10^-6 M, respectively. The factors affecting fluorescence sensings, such as the pH and competing cations, were studied. The sensor can be reused at least five times after being treated with EDTA. The Job plot, ESI-MS spectra, ¹H NMR spectra, absorbance, and fluorescence titration experiments were investigated to study the mechanism of SDPA-Fe³⁺ and SDPA-Cu²⁺ complexation. The SDPA-Cu²⁺ complex can detect L-tryptophan and L-cysteine at trace levels by turn-on fluorescence with a detection limit of 9.35 × 10^-6 M and 8.86 × 10^-6 M, respectively. Moreover, applying the SDPA-Cu²⁺ complex for quantitative analysis of L-tryptophan in real sleep-improving capsules resulted in good recovery. The L-tryptophan level of the Elining capsule was determined at 190.8 ± 10.5 mg/g (mg L-tryptophan/g medicine), which is close to the announced quantity of 180 mg/g. Besides, the SDPA-Cu²⁺ complex can selectively detect free L-Try molecules and L-Try residues in proteins.

A new and efficient diaminopyrimidine-based colorimetric and fluorescence chemosensor for the highly selective and sensitive detection of Cu2+ in aqueous media and living cells

In this paper, a new and effective diaminopyrimidine-based chemosensor (DAPCS) was developed for the highly selective and ultra-sensitive detection of Cu²⁺ ion in aqueous media and living cell. Characterization and structure determining of DAPCS was determined by UV-Vis, FTIR and NMR analyses. It is observed that DAPCS and Cu (II) forms a ligand to metal charge transfer (LMCT) complex which produces distinguishable red color. The results also indicate that the DAPCS easily interacts with Cu²⁺ ion to form a 1:1 stoichiometry complex (DAPCS -Cu²⁺), resulting in a bathochromic shift in absorption maximum (429 nm to 449 nm) and remarkable quenching fluorescence intensity at the wavelength of 501 nm in DMSO-H₂O solution. Furthermore, the detection limit of DAPCS towards Cu²⁺ was calculated to be 3.19 µM. Meanwhile, DAPCS was applied as fluorescent probe for detection of Cu²⁺ ions with the detection limit of 0.014 µM. The optimal pH range of probe DAPCS for quantitative analysis of Cu²⁺ ions was 9-11, which renders it suitable for detection of Cu²⁺ under physiological conditions. Additionally, the DAPCS could be applied to detect Cu²⁺ in real water samples and in HeLa cells, indicating the practical uses of DAPCS in real analyses.

Novel dual-emissive fluorescent immunoassay for synchronous monitoring of okadaic acid and saxitoxin in shellfish

In this work, we present a novel dual-emissive fluoroimmunoassay for synchronous monitoring of okadaic acid (OA) and saxitoxin (STX) using multicolor fluorescent labels composed of sulfur, phosphorous co-doped graphene quantum dots (S, P-GQDs), and ovalbumin (OVA)-coated gold nanoparticles (OVA-AuNPs). The novel OVA-AuNPs were prepared by the reduction of chloroauric acid under alkaline conditions using OVA as a reducing agent. Both S, P-GQDs and OVA-AuNPs exhibit bright fluorescence, more importantly, a large emission wavelength difference (Δλ = 156 nm) under an excitation of 400 nm and relatively independent fluorescence behavior, which are essential to realizing the dual-signal marks in a directly mixing system. Using a competitive fluorescence-linked immunosorbent assay (cFLISA) format, the dual-emissive cFLISA was successfully utilized to measure OA and STX contents in Alectryonella plicatula (commonly named as fingerprint oyster) and the detection results were in good agreement with the commercial enzyme-linked immunosorbent assay (ELISA) kits.

Fabrication and sensing properties of phenolphthalein based colorimetric and turn-on fluorogenic probe for CO32- detection and its living-cell imaging application

Herein, an easy assembled colorimetric and ''turn-on'' fluorescent sensor (probe P4SC) based on phenolphthalein was developed for carbonate ion (CO₃^2-) sensing in a mixture of EtOH/H₂O (v/v, 80/20, pH = 7, Britton-Robinson buffer) media. The probe P4SC demonstrated high sensitive and selective monitoring toward CO₃^2- over other competitive anions. Interaction of CO₃^2- with the probe P4SC resulted in a significant increment in emission intensity at λ_em = 498 nm (λ_ex = 384 nm) due to the strategy of blocking the photo induced electron transfer (PET) mechanism. ¹H NMR titration and Job's methods, as well as the theoretical study were carried out to support the probable stoichiometry of the reaction (1:2) between P4SC and CO₃^2-. The binding constant of the probe P4SC with CO₃^2- was calculated as 2.56 × 10¹⁰ M^-2. The probe P4SC providing rapid response time (~0.5 min) with a satisfactorily low detection limit (14.7 nM) may be useful as a valuable realistic sensor. The imaging studies on the liver cancer cells (HepG2) shows the great potential of the probe P4SC for the sensation of intracellular CO₃^2- anions. Furthermore, the satisfactory recovery and RSD values obtained for water application confirming that the probe P4SC could be applied to sensing of CO₃^2- ion.

A fluorescence based immunochromatographic sensor for monitoring chlorpheniramine and its comparison with a gold nanoparticle-based lateral-flow strip

Chlorpheniramine (CPM) is an illegal additive found in herbal teas and health foods, and its excessive intake can cause health problems. In this study, a CPM monoclonal antibody (mAb) was developed based on a new type of hapten. The mAb was found to belong to the IgG2b subclass and showed high sensitivity and specificity when used in ELISA, with a half-maximal inhibitory concentration (IC₅₀) of 0.98 ng mL^-1 and cross-reactivity (CR) values below 1.8% when compared to antiallergic drugs. Based on the mAb produced, a fluorescent microsphere-based immunochromatographic strip assay (FM-ICS) and a gold nanoparticle-based immunochromatographic strip assay (GNP-ICS) were developed for the rapid and sensitive detection of CPM in herbal tea samples. Under optimal conditions, the cut-off values for the FM-ICS and GNP-ICS were 10 ng mL^-1 and 100 ng mL^-1, respectively, in herbal tea samples. The FM-ICS exhibited a higher sensitivity than GNP-ICS, but both could produce results within 15 min. In addition, a variety of high-throughput rapid immunoassay formats could be implemented based on this mAb for use as a convenient and reliable tool for the determination of CPM exposure in foods and the environment.

1,8-Naphthalimide appended propiolate-based fluorescent sensor for selective detection of cysteine over glutathione and homocysteine in living cells

A novel 1,8-naphthalimide-based fluorogenic chemoprobe NASP was designed and developed as a sensor platform for the selective detection of biologically important cysteine over glutathione and homocysteine in living-cells.