A novel and fast responsive turn-on fluorescent probe for the highly selective detection of Cd2+ based on photo-induced electron transfer

Carbon Dots Employed for the Detection of Ranitidine and Elaborating the Detecting Mechanism

Carbon dots (CDs) has been widely utilized in multiple fields, especially towards kinds of drug analyses, owing to its superior optical properties and satisfactory stability. Herein, we rapidly synthesized one kind of soluble bright-blue fluorescent CDs through a facile microwave method, while disodium ethylenediaminetetraacetic acid and phosphoric acid served as the raw materials. Importantly, introducing ranitidine into these CDs resulted in its decreased fluorescence, and thus an innovative method of detecting ranitidine was successfully established, which showed the favorable selectivity and anti-interference ability. With the optimal conditions, the standard curve diagram of F0/F against concentration of ranitidine was linear in the range of 6-2000 µM with a correlation coefficient of 0.9833, and the limit of detection (LOD) was calculated to be 4.2 µM. Meanwhile, we also explored the detecting mechanism of ranitidine by CDs, and elaborated that as the internal filtration effect. Consequently, we may broaden the avenues of detecting ranitidine on the basis of CDs.

Dual Fluorimetric Sensor for Tandem Detection of Cadmium and Cysteine: An Approach for Designing a Molecular Keypad Lock System

A fluorimetric sensor for dual and sensitive detection of Cd2+ ion and Cysteine (based on 2-picolylamine platform) was developed.The sensor was designed and synthesized by simple condensation method and characterized by using common spectroscopic methods. The observations made from the kinetics of absorption and emission profile shows that probe Pdac behaves as ''ON-OFF'' fluorescent quenching sensor for cadmium ions. The probe exhibit selectivity in fluorescence quenching behaviour over other competitive metal ions, and also the Pdac-Cd2+ ensemble behave as an efficient ''OFF-ON'' type sensor for an essential amino acid Cysteine. Moreover, this dual sensing nature of the sensor makes it successfully applied for the designing of a molecular keypad lock system.

Thiophene derived sky-blue fluorescent probe for the selective recognition of mercuric ion through CHEQ mechanism and application in real time samples

A vibrant blue organic luminescent material with enhanced photophysical properties is in great demand for the generation of optoelectronic devices and luminescent sensors. In this context, the thiophene-benzimidazole probe TH-IMI was designed and synthesized by a simple condensation reaction. The synthesized probe has shown excellent photophysical properties like high FL intensity, a high quantum yield of 90% in the solution phase, a low optical bandgap of 2.84 eV, positive solvatochromic effect in emission spectra and Disaggregation Caused Quenching Effect (DCQE). Such a high luminescent probe was employed for the recognition of mercuric ions in the solution phase, solid state detection, and in tracking mercury in green gram sprouts. UV-visible absorption and emission spectra, 1H NMR titration, IR spectroscopic and ESI-MS techniques confirmed that the probe underwent a fluorescence quenching response via the CHEQ effect upon exposure to Hg2+. The stoichiometry was found to be 1:1 through Job's plot and has a fast response rate and relatively low limit of detection of about 6.13 × 10-11 M in a linear range between 0 and 110 µL.

Recent Progress on Fluorescent Probes in Heavy Metal Determinations for Food Safety: A Review

One of the main challenges faced in food safety is the accumulation of toxic heavy metals from environmental sources, which can sequentially endanger human health when they are consumed. It is invaluable to establish a practical assay for the determination of heavy metals for food safety. Among the current detection methods, technology based on fluorescent probes, with the advantages of sensitivity, convenience, accuracy, cost, and reliability, has recently shown pluralistic applications in the food industry, which is significant to ensure food safety. Hence, this review systematically presents the recent progress on novel fluorescent probes in determining heavy metals for food safety over the past five years, according to fluorophores and newly emerging sensing cores, which could contribute to broadening the prospects of fluorescent materials and establishing more practical assays for heavy metal determinations.

A Colorimetric Distinct Color Change Cu(II) 4-{[1-(2,5-dihydroxyphenyl)ethylidene]amino}-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one Chemosensor and its Application as a Paper Test Kit

In the current research work "4-{[1-(2,5-dihydroxyphenyl)ethylidene]amino}-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one" chemosensor (C1) synthesized by condensation reaction using "4-amino-1,2-dihydro-1,5-dimethyl-2-phenylpyrazol-3-one" and "2,5-dihydroxy actophenone" was used as the effective sensor of metal ion. The C1 shows absorption peak at 326 nm due to the C = C bond (π-π* transition), while the absorption peak at 364 nm is caused by the C = O bond (n-π* transition). In the presence of copper, C1 only demonstrated a redshift in absorption peak from 364 to 425 nm. Even in the presence of other competing metal ions, the hypsochromic shift of the absorption band and the quenching of the fluorescence emission intensity were different for detecting Cu²⁺, in CH₃OH-H₂O (v/v = 6:4). The capacity of the C1 to bind with Cu²⁺ was further proved using DFT simulations. The complex C1 + Cu²⁺ has a HOMO-LUMO energy gap of 2.8002 eV, which is lesser than C1 (2.9991 eV) showing improvement in the stability of the C1 + Cu²⁺ complex. Using the Benesi-Hildebrand and Scatchard plots, calculated Kb values were to be 47,340 and 48369 M^-1 respectively, showing the creation of stable complexation between Cu²⁺ and C1 with 1:1 stoichiometry. The limit of detection (LOD) for Cu²⁺ ion was 649 nM. Strip sheets were also built and tested to detect varying amounts of Cu²⁺ in aqueous solution, and their color change suggested that they might be used for on-site Cu²⁺ detection in polluted water.

Thiazole-Formulated Azomethine Compound for Three-Way Detection of Mercury Ions in Aqueous Media and Application in Living Cells

Heavy metal ions are extremely poisonous and cause long-term harm to living organisms. Among these ions, mercury is the most toxic metal and has no notorious purpose in the human body. In this regard, an elegant azomethine thiazole compound AM1 was synthesized, and it was found to be highly sensitive to three-way detection of mercury ions with detection limits of 0.1126 × 10^-9 M (FL) and 0.64 × 10^-6 M (UV-vis). AM1 highlighted the capability to detect mercury ions through the colorimetric method, the fluorometric method, and via the naked eye in three-way detection. In addition, the structure of AM1 was confirmed by single-crystal X-ray diffraction studies and crystallized in a monoclinic crystal system with a P21/c space group, and it shows numerous noncovalent interactions in the crystal packing. The high sensitivity of AM1 to Hg²⁺ ions was imputed to the quenching mechanism and was estimated by Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (¹H-NMR), high-resolution mass spectrometry (HRMS), ultraviolet-visible (UV-vis) absorbance, fluorescence (FL) emission, Job's plot, B-H plot, and DFT calculation. Naked eye color change of AM1 solution to yellow and turn-off FL by the addition of mercury ion is due to complex formation. In addition to mercury ions, the sensor displayed a new absorption peak at around 240 nm. Furthermore, an AM1-coated test strip is used as the solid support sensor, and real-time detection of Hg²⁺ ions in the HeLa cell line by fluorescence microscopy is performed.

Recent progress in cadmium fluorescent and colorimetric probes

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms. Therefore, its detection is of great significance in the fields of biology, environment and medicine. Fluorescent probe has been a powerful tool for cadmium detection because of its convenience, sensitivity, and bioimaging capability. In this paper, we reviewed 98 literatures on cadmium fluorescent sensors reported from 2017 to 2021, classified them according to different fluorophores, elaborated the probe design, application characteristics and recognition mode, summarized and prospected the development of cadmium fluorescent and colorimetric probes. We hope to provide some help for researchers to design cadmium fluorescent probes with higher selectivity, sensitivity and practicability.

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms.

A simple fluorescent probe for detection of Ag+ and Cd2+ and its Cd2+ complex for sequential recognition of S2

In this study, we designed and synthesized a simple probe 2-(8-((8-methoxyquinolin-2-yl)methoxy)quinolin-2-yl)benzo[d]thiazole (DQT) for detection of Ag⁺ and Cd²⁺ in a CH₃OH/HEPES (9 : 1 v/v, pH = 7.30) buffer system. Its structure was characterized by NMR, ESI-HR-MS and DFT calculations, and its fluorescence performance was also investigated. Probe DQT showed fluorescence quenching in response to Ag⁺ and Cd²⁺ with low detection limits of 0.42 μM and 0.26 μM, respectively. Importantly, the complexation of the probe with Cd²⁺ resulted in a red shift from blue to green, making it possible to detect Ag⁺ and Cd²⁺ by the naked eye under an ultraviolet lamp. The DQT-Cd²⁺ complex could be used for sequential recognition of S^2-. The recovery response could be repeated 3 times by alternate addition of Cd²⁺ and S^2-. A filter paper strip test further demonstrated the potential of probe DQT as a convenient and rapid assay.

A new bio-compatible Cd2+-selective nanostructured fluorescent imprinted polymer for cadmium ion sensing in aqueous media and its application in bio imaging in Vero cells

Schematic representation of Cd²⁺ recognition by the imprinted polymer and fluorescence signal creation as a result of the mentioned recognition process.