Search Results (60)

In recent years, in the field of bioanalysis, the use of saliva as a biological fluid for the determination of biomarkers has been proposed. Saliva analysis stands out for its simplicity and non-invasive sampling. This paper proposes a method for the dual determination of ammonium and hydrogen sulfur in saliva using two colorimetric chemosensors. The ammonia reacts with 1,2-Naftoquinone 4 sulphonic acid (NQS) entrapped in polydimethylsiloxane (PDMS) and the hydrogen sulfide with AgNPs retained in a nylon membrane. The color changed from orange to brown in the case of ammonia chemosensors and from yellow to brown in the H₂S. The experimental conditions to be tested have been established. Both analytes have been determined from their gaseous form; these are ammonia from ammonium and hydrogen sulfur from hydrogen sulfur. Good figures of merit have been obtained by using both measuring strategies (reflectance diffuse and digitalized images). The acquired results show that both sensors can be used and provide good selectivity and sensitivity for the determination of these biomarkers in saliva. Both measurement strategies have provided satisfactory results for the real saliva samples (n = 15). Recoveries on spiked samples were between 70% and 100%. This methodology can lead to possible in situ diagnosis and monitoring of certain diseases and pathologies related with NH₄⁺ and/or H₂S, in a fast, simple, cheap and non-invasive way. Full article

A tert-butyldiphenylsilyl-containing polyimide (PI-OSi) has been established as a colorimetric and ratiometric chemosensor for rapid detecting fluoride ions (F⁻). The UV-vis absorbance ratio value (A₃₂₂/A₂₈₈) of PI-OSi in a DMF solution displays a wide linear range change to F⁻ concentrations with a detection limit (DL) value of 2.13 μM. Additionally, adding incremental amounts of F⁻ to a DMF solution of PI-OSi shows an immediate color change to yellow and finally to green from colorless. More interestingly, the resulting PI-OSi plus F⁻ system (PI-OSi·F) could detect trace water in DMF. The A₂₉₂/A₃₂₂ value of PI-OSi·F almost linearly increases with low water content, which suggests convenient quantitative sensing of trace water content in DMF. The DL value of PI-OSi·F for sensing water in DMF is determined to be 0.00149% (v/v). The solution color of PI-OSi·F returns to colorless when the water content increases, indicating that PI-OSi·F can conveniently estimate water content in DMF by naked-eye detection. The detection mechanisms confirmed by an ¹H NMR study and a DFT calculation involve a F⁻-induced desilylation reaction of PI-OSi to form phenolate anion followed by protonation with trace water. Finally, PI-OSi film was fabricated for the colorimetric detection of F⁻ and water in CH₃CN. Full article

Due to the extreme toxicity of cyanide in biological systems and its widespread presence in the environment, great efforts have been focused on developing sensitive and selective methods for cyanide detection. In this regard, sulfo-cyanine dye 1 was evaluated as a colorimetric and fluorimetric probe for various anions. Chemosensing studies revealed that this compound exhibited remarkable selectivity and sensitivity for CN⁻ in acetonitrile solution, with a marked colour change from cyan to colourless and fluorescence emission switched off. The detection limit was estimated to be as low as 0.45 μM, and the binding mode was studied using NMR techniques. Full article

Developing colorimetric devices for detecting chemical species is essential in many fields; nevertheless, developing effective chemosensors for many heavy and transition metal ions remains an important issue. As a result, in recent years, the use of colorimetric sensors for the selective and sensitive detection of metal ions has grown in popularity. Pyrazolones and their derivatives are heterocyclic compounds that have attracted interest due to their biological and pharmacological features. As a result, they have been used in various areas, including agriculture, medicine, organic synthesis, and analytical chemistry. However, the potential for chemosensing has yet to receive much attention. In this study, thiomethyl-substituted (4Z)-4-[(pyrazol-4-yl)methylene]pyrazolone was synthesized, and its ability to act as an optical chemosensor for several metals was evaluated. According to preliminary results, this molecule could be an optical chemosensor to detect Fe³⁺, Sn²⁺, and Al³⁺. Full article

Hydrogen peroxide (H₂O₂) is an aqueous solution that is widely used for oxidation, disinfection and sterilization, and its detection is very important in the fields of biological health and environment. The main detection methods of H₂O₂ include colorimetric, electrochemical, enzymatic and fluorescence analysis. However, due to the influence of moisture and oxidation, it is very difficult to realize simple, convenient, real-time and efficient detection technology for hydrogen peroxide vapor (HPV). Recently, our group proposed adding ammonium titanyl oxalate (ATO) to the sensing film composite system to prepare a chemosensor based on PEDOT:PSS-ATO/PEDOT composite film. The limit of detection (LOD) of the film was 1.0 ppm, and the linear trend was in the range of 1.0 ppm to 10.5 ppm. We then explored the influence of various material systems on its HPV sensing performance, which exhibited both electrical and colorimetric responses. This study was expected to realize a practical HPV sensor as well as promote the further application of PEDOT-based composites in the field of chemosensors. Full article

Industrial activity has raised significant concerns regarding the widespread pollution caused by metal ions, contaminating ecosystems and causing adverse effects on human health. Therefore, the development of sensors for selective and sensitive detection of these analytes is extremely important. In this regard, an azo dye, Dabcyl 2, was synthesised and investigated for sensing metal ions with environmental and industrial relevance. The cation binding character of 2 was evaluated by colour changes as seen by the naked eye, UV-Vis and ¹H NMR titrations in aqueous mixtures of SDS (0.02 M, pH 6) solution with acetonitrile (99:1, v/v). Out of the several cations tested, chemosensor 2 had a selective response for Pd²⁺, Sn²⁺ and Fe³⁺, showing a remarkable colour change visible to the naked eye and large bathochromic shifts in the UV-Vis spectrum of 2. This compound was very sensitive for Pd²⁺, Sn²⁺ and Fe³⁺, with a detection limit as low as 5.4 × 10⁻⁸ M, 1.3 × 10⁻⁷ M and 5.2 × 10⁻⁸ M, respectively. Moreover, comparative studies revealed that chemosensor 2 had high selectivity towards Pd²⁺ even in the presence of other metal ions in SDS aqueous mixtures. Full article

A 1,2,3-triazole-based chemosensor is used for selective switching in logic gate operations through colorimetric and fluorometric response mechanisms. The molecular probe synthesized via “click chemistry” resulted in a non-fluorescent 1,4-diaryl-1,2,3-triazole with a phenol moiety (PTP). However, upon sensing fluoride, it TURNS ON the molecule’s fluorescence. The TURN-OFF order occurs through fluorescence quenching of the sensor when metal ions, e.g., Cu²⁺, and Zn²⁺, are added to the PTP-fluoride ensemble. A detailed characterization using Nuclear Magnetic Resonance (NMR) spectroscopy in a sequential titration study substantiated the photophysical characteristics of PTP through UV-Vis absorption and fluorescence profiles. A combination of fluorescence OFF-ON-OFF sequences provides evidence of 1,2,3-triazoles being controlled switches applicable to multimodal logic operations. The “INH” gate was constructed based on the fluorescence output of PTP when the inputs are F⁻ and Zn²⁺. The “IMP” and “OR” gates were created on the colorimetric output responses using the probe’s absorption with multiple inputs (F⁻ and Zn²⁺ or Cu²⁺). The PTP sensor is the best example of the “Write-Read-Erase-Read” mimic. Full article

Optical chemosensors are a practical tool for the detection and quantification of important analytes in biological and environmental fields, such as Cu²⁺ and Fe³⁺. To the best of our knowledge, a BODIPY derivative capable of detecting Cu²⁺ and Fe³⁺ simultaneously through a colorimetric response has not yet been described in the literature. In this work, a meso-triphenylamine-BODIPY derivative is reported for the highly selective detection of Cu²⁺ and Fe³⁺. In the preliminary chemosensing study, this compound showed a significant color change from yellow to blue–green in the presence of Cu²⁺ and Fe³⁺. With only one equivalent of cation, a change in the absorption band of the compound and the appearance of a new band around 700 nm were observed. Furthermore, only 10 equivalents of Cu²⁺/Fe³⁺ were needed to reach the absorption plateau in the UV-visible titrations. Compound 1 showed excellent sensitivity toward Cu²⁺ and Fe³⁺ detection, with LODs of 0.63 µM and 1.06 µM, respectively. The binding constant calculation indicated a strong complexation between compound 1 and Cu²⁺/Fe³⁺ ions. The ¹H and ¹⁹F NMR titrations showed that an increasing concentration of cations induced a broadening and shifting of the aromatic region peaks, as well as the disappearance of the original fluorine peaks of the BODIPY core, which suggests that the ligand–metal (1:2) interaction may occur through the triphenylamino group and the BODIPY core. Full article

Four naphthalenediimide colorimetric pH indicators were synthesized with N,N-dimethylethyleneamine at the imide positions and with 5- to 7-membered heterocyclic rings at the bay positions, namely pyrrolidine, morpholine, piperidine and azepane. The pH indicators are constructed in a modular receptor–spacer–fluorophore–spacer–receptor format based on a photoinduced electron transfer (PET) design. The compounds were studied by UV–visible absorption and steady-state fluorescence spectroscopy in 1:1 (v/v) methanol/water. Brilliant colour changes are observed between pH 2 and 4 due to an internal charge transfer (ICT) mechanism. Fluorescence turn-on enhancements range from 10–37 fold; however, the maximum fluorescence quantum yield in the presence of acid is <0.004, which is below naked eye detection. Hence, from the viewpoint of a human observer, these chemosensors function as colorimetric YES logic gates, and fluorimetric PASS 0 logic gates. Full article

The precise control and monitoring of pH values remain critical for many chemical, physiological and biological processes. Perylene diimide (PDI)-based molecules and materials exhibit excellent thermal, chemical and photochemical stability, unique UV-vis absorption and fluorescent emission properties, low cytotoxicity, as well as intrinsic electron-withdrawing (n-type semiconductor) nature and impressive molecular assembly capability. These features combined enable promising applications of PDIs in chemosensors via optical signal modulations (e.g., fluorescent or colorimetric). One of the typical applications lies in the probing of pH under various conditions, which in turn helps monitor the extracellular (environmental) and intracellular pH change and pH-relying molecular recognition of inorganic or organic ions, as well as biological species, and so on. In this review, we give a special overview of the recent progress in PDI-based optical chemosensors for pH probing in various aqueous and binary water–organic media. Specific emphasis will be given to the key design roles of sensing materials regarding the architectures and the corresponding sensing mechanisms for a sensitive and selective pH response. The molecular design of PDIs and structural optimization of their assemblies in order to be suitable for sensing various pH ranges as applied in diverse scenarios will be discussed in detail. Moreover, the future perspective will be discussed, focusing on the current key challenges of PDI-based chemosensors in pH monitoring and the potential approach of new research, which may help address the challenges. Full article

Hydrogen peroxide (H₂O₂) is commonly used as an oxidizing, bleaching, or antiseptic agent. It is also hazardous at increased concentrations. It is therefore crucial to monitor the presence and concentration of H₂O₂, particularly in the vapor phase. However, it remains a challenge for many state-of-the-art chemical sensors (e.g., metal oxides) to detect hydrogen peroxide vapor (HPV) because of the interference of moisture in the form of humidity. Moisture, in the form of humidity, is guaranteed to be present in HPV to some extent. To meet this challenge, herein, we report a novel composite material based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) doped with ammonium titanyl oxalate (ATO). This material can be fabricated as a thin film on electrode substrates for use in chemiresistive sensing of HPV. The adsorbed H₂O₂ will react with ATO, causing a colorimetric response in the material body. Combining colorimetric and chemiresistive responses resulted in a more reliable dual-function sensing method that improved the selectivity and sensitivity. Moreover, the composite film of PEDOT:PSS-ATO could be coated with a layer of pure PEDOT via in situ electrochemical synthesis. The pure PEDOT layer was hydrophobic, shielding the sensor material underneath from coming into contact with moisture. This was shown to mitigate the interference of humidity when detecting H₂O₂. A combination of these material properties makes the double-layer composite film, namely PEDOT:PSS-ATO/PEDOT, an ideal sensor platform for the detection of HPV. For example, upon a 9 min exposure to HPV at a concentration of 1.9 ppm, the electrical resistance of the film increased threefold, surpassing the bounds of the safety threshold. Meanwhile, the colorimetric response observed was 2.55 (defined as the color change ratio), a ratio at which the color change could be easily seen by the naked eye and quantified. We expect that this reported dual-mode sensor will find extensive practical applications in the fields of health and security with real-time, onsite monitoring of HPV. Full article

A dinitrophenol-based colorimetric chemosensor sequentially sensing Cu²⁺ and S²⁻, HDHT ((E)-2-(2-(2-hydroxy-3,5-dinitrobenzylidene)hydrazineyl)-N,N,N-trimethyl-2-oxoethan-1-aminium), was designed and synthesized. The HDHT selectively detected Cu²⁺ through a color change of yellow to colorless. The calculated detection limit of the HDHT for Cu²⁺ was 6.4 × 10⁻² μM. In the interference test, the HDHT was not considerably inhibited by various metal ions in its detection of Cu²⁺. The chelation ratio of the HDHT to Cu²⁺ was determined as 1:1 by using a Job plot and ESI-MS experiment. In addition, the HDHT–Cu²⁺ complex showed that its color selectively returned to yellow only in the presence of S²⁻. The detection limit of the HDHT–Cu²⁺ complex for S²⁻ was calculated to be 1.2 × 10⁻¹ μM. In the inhibition experiment for S²⁻, the HDHT–Cu²⁺ complex did not significantly interfere with other anions. In the real water-sample test, the detection performance of the HDHT for Cu²⁺ and S²⁻ was successfully examined. The detection features of HDHT for Cu²⁺ and the HDHT–Cu²⁺ for S²⁻ were suggested by the Job plot, UV–Vis, ESI-MS, FT-IR spectroscopy, and DFT calculations. Full article

In this work, two Schiff-base-based chemosensors L1 and L2 containing electron-rich quinoline and anthracene rings were designed. L1 is AIEE active in a MeOH-H₂O solvent system while formed aggregates as confirmed by the DLS measurements and fluorescence lifetime studies. The chemosensor L1 was used for the sensitive, selective, and reversible ‘turn-on’ detection of Al³⁺ and Ga³⁺ ions as well as Aspartic Acid (Asp). Chemosensor L2, an isomer of L1, was able to selectively detect Ga³⁺ ion even in the presence of Al³⁺ ions and thus was able to discriminate between the two ions. The binding mode of chemosensors with analytes was substantiated through a combination of ¹H NMR spectra, mass spectra, and DFT studies. The ‘turn-on’ nature of fluorescence sensing by the two chemosensors enabled the development of colorimetric detection, filter-paper-based test strips, and polystyrene film-based detection techniques. Full article

Long-term use of norfloxacin (NOR) will cause NOR residues in foods and harm human bodies. The determination of NOR residues is important for guaranteeing food safety. In this study, a simple, selective, and label-free colorimetric chemosensor for in situ NOR detection was developed based on Fe₃O₄ magnetic molecularly imprinted nanoparticles (Fe₃O₄ MMIP NPs). The Fe₃O₄ MMIP NPs showed good peroxidase-like catalytic activity to 3,3′,5,5′-tetramethylbenzidine (TMB) and selective adsorption ability to NOR. The colorimetric chemosensor was constructed based on the Fe₃O₄ MMIP NPs-H₂O₂-TMB reaction system. The absorbance differences were proportional to the concentrations of NOR in the range of 10–300 ng/mL with a limit of detection at 9 ng/mL. The colorimetric chemosensor was successfully applied to detect NOR residue in milk. The recovery range was 78.2–95.81%, with a relative standard deviation of 2.1–9.88%. Together, the proposed colorimetric chemosensor provides a reliable strategy for the detection of NOR residues in foods. Full article