Recent approaches of 2HN derived fluorophores on recognition of Al3+ ions: A review for future outlook

Development of a bisphenol A based chemosensor for Al3+ and its application in cell imaging and plant root imaging

Bisphenol A is a fluorophoric platform that is used to develop chemosensors for various species. Herein, we report a bisphenol A based Schiff-base molecule, 4,4'-(propane-2,2-diyl)bis(2-((E)-((2-hydroxy-5-methylphenyl)imino)methyl)phenol) (Me-H4L), as a selective chemosensor for Al3+. Among the several metal ions, it shows a significant increment in its fluorescence intensity (50 fold) at 535 nm in the presence of Al3+ ions. The enhanced fluorescence was attributed to the CHEFF mechanism and inhibition of CN isomerization. The limit of detection value of Me-H4L for Al3+ was determined to be 9.65 μM. Its quantum yield and lifetime increased considerably in the presence of the cation. Some theoretical calculations were performed to explain the interaction between Al3+ and the probe. Furthermore, Me-H4L was applied in cell imaging studies using animal cells and plant roots.

Salicylaldehyde built fluorescent probe for dual sensing of Al3+, Zn2+ ions: Applications in latent fingerprint, bio-imaging & real sample analysis

This Schiff base chemosensor (SNN) detected dual ions, Al3+ and Zn2+ ions selectively. Fluorescence spectrum investigations showed that Al3+ ions increased fluorescence intensity, notably at 493 nm. Introducing Zn2+ ions caused a significant blue shift of roughly ∼65 nm at a wavelength of 434 nm, resulting in a notable change in fluorescence intensity. When binding Al3+/Zn2+ ions, the SNN receptor uses three methods. Inhibition of photoinduced electron transfer (PET), excited state intramolecular proton transfer (ESIPT), and restriction of CN isomerization. The jobs plot method found that SNN + Al3+ and SNN + Zn2+ complexations had a 1:1 stoichiometry. DFT, LC-HRMS, and 1H NMR titration confirm this conclusion. The probe SNN's limit of detection (LOD) for Al3+/Zn2+ ions was 3.99 nM and 1.33 nM. Latent fingerprint (LFP), food samples, pharmaceutical products, and E. coli pathogen bio-imaging have all used the SNN probe to identify Al3+ and Zn2+ ions.

Synthesis of a super-low detection limit fluorescent probe for Al3+ and its application in fluorescence imaging of zebrafish and cells

A novel fluorescent probe N'-(2-hydroxybenzylidene)-indole-3-formylhydrazine (JHK) was designed and synthesized based on the condensation reaction of indole-3-formylhydrazine and salicylaldehyde. The probe JHK solution could highly selectively recognize Al3+ by the obvious fluorescence enhancement (288-fold) after adding Al3+. And the probe solution with Al3+ had a very high fluorescence quantum yield (89.29 %). The detection limit was calculated to be 1.135 nM, which was significantly lower than many reported detection limits, indicating that the probe JHK had pretty good sensitivity. The ratio of JHK to Al3+ (1:1) and the sensing mechanism were determined by Job's plot, 1H NMR spectra, FTIR spectra, ESI-MS and Gaussian calculation. The probe solution and medium-speed filter paper were successfully used to make test papers for more convenient detection of Al3+. Furthermore, the probe JHK had been successfully applied to the detection of Al3+ in real water, zebrafish and living cells.

Novel Flavonoid Photoswitchable "Turn-On" Fluorescent Chemosensors: Synthesis of Bromo Flavonols for Nanomolar Aluminum Ion Detection and Cellular Imaging, among Other Applications

Aluminum (Al), a non-essential element in living systems, can potentially cause chronic toxicity. Therefore, it is crucial to have a specific and sensitive method for detecting Al3+ in order to assess its risk to life. In this study, we designed and synthesized a novel fluorescent probe (IV) based on bromoflavonol. Upon binding to Al3+, probe IV exhibits a blue shift in emission and enhanced fluorescence, making it suitable for Al3+ detection. Our UV-Vis absorption and fluorescence emission spectra demonstrate that probe IV has high selectivity and sensitivity towards Al3+ while being immune to interference from other metal ions. Through fluorescence titration, we determined that the detection limit (LOD) of probe IV for Al3+ is 1.8 × 10-8 mol/L. Job's curve and 1 H NMR titration further confirmed a 1:1 binding stoichiometry between probe IV and Al3+. Additionally, using DFT (Density Functional Theory), we calculated the energy gap difference between IV and IV + Al3+ and found that the complex formed by probe IV and Al3+ is more stable than IV alone. We successfully detected Al3+ in tap water and river water from the middle regions of the Han River, achieving recoveries of over 96% using this probe. This demonstrates its potential for quantitative detection of Al3+ in environmental water samples. Moreover, we successfully used the probe for imaging Al3+ in MG63 cells, suggesting its potential application in biological imaging.

New Amino Acid-Based Thiosemicarbazones and Hydrazones: Synthesis and Evaluation as Fluorimetric Chemosensors in Aqueous Mixtures

Bearing in mind the interest in the development and application of amino acids/peptides as bioinspired systems for sensing, a series of new phenylalanine derivatives bearing thiosemicarbazone and hydrazone units at the side chain were synthesised and evaluated as fluorimetric chemosensors for ions. Thiosemicarbazone and hydrazone moieties were chosen because they are considered both proton-donor and proton-acceptor, which is an interesting feature in the design of chemosensors. The obtained compounds were tested for the recognition of organic and inorganic anions (such as AcO-, F-, Cl-, Br-, I-, ClO4-, CN-, NO3-, BzO-, OH-, H2PO4- and HSO4-) and of alkaline, alkaline-earth, and transition metal cations, (such as Na+, K+, Cs+, Ag+, Cu+, Cu2+, Ca2+, Cd2+, Co2+, Pb2+, Pd2+, Ni2+, Hg2+, Zn2+, Fe2+, Fe3+ and Cr3+) in acetonitrile and its aqueous mixtures in varying ratios via spectrofluorimetric titrations. The results indicate that there is a strong interaction via the donor N, O and S atoms at the side chain of the various phenylalanines, with higher sensitivity for Cu2+, Fe3+ and F- in a 1:2 ligand-ion stoichiometry. The photophysical and metal ion-sensing properties of these phenylalanines suggest that they might be suitable for incorporation into peptide chemosensory frameworks.

A Novel Rhodamine Probe Acting as Chemosensor for Selective Recognition of Cu2+ and Hg2+ Ions: An Experimental and First Principle Studies

Copper and Mercury ions have vital role to play in biological world as their excess or deficiency can cause different type of diseases in human being as well as biological species including plants and animals. Therefore, their detection at trace level becomes very important in term of biological. The current studies embody the fabrication, structural characterization and recognition behavior of a novel rhodamine B hydrazone formed when hydrazide of rhodamine B was condensed with 5-Allyl-3-methoxy salicylaldehyde (RBMA). RBMA was found to be responsive towards the very trace level of Cu2+ and Hg2+ among other tested cations so far. The sensing procedure is based on the classical opening of the spiroatom ring of rhodamine. The limit of detection (LOD) and binding constant is 5.35 ppm, 2.06 × 104 M-1 and 5.16 ppm, 1.26 × 104 M-1 for Cu2+ and Hg2+ ions respectively. The probable mechanism correlates the specific binding of RBMA with Cu2+ and Hg2+ ions. The 1:1 stoichiometry of RBMA with Cu2+ and Hg2+ ions have been supported by HRMS, FT-IR data, Job's plot, and binding constant data. Reversibility is well exhibited by RBMA by the involvement of CO32- ions via demetallation process. The real time application is well demonstrated by the use of paper strip test. The DFT study also carried out which agrees well with the experimental findings. The results displayed the novelty of this current work towards the trace level analysis of the Cu2+ and Hg2+ of the cations which are play the crucial role in industry.

"Lighting up" fluorescence precise recognition of Al3+ with an effective fluorescence detection using a Bisphenol A-based sensor

Although aluminum is a ubiquitous metal in the ecosystem and has numerous critical roles in both the medicinal and biological fields, human daily life is seriously threatened by its assorted harmful influences. By this virtue, tracking the amount of aluminum byrapid sensitive and selective recognition methodologies is of great importance. Based on this, a novel fluorescent chemosensor 4,4'-(propane-2,2-diyl)bis(2-(((-2-hydroxybenzylidene) hydrazineylidene)-methyl)phenol) (BFASA) capable of recognizing Al³⁺ in a medium was constructed via an easy Schiff-base reaction between bisphenol A-containing molecule and the salicylaldehyde. The metal-binding studies of BFASA indicated a drastically enhanced emission with color alteration from colorless to green establishing the utility of BFASA against monitoring of Al³⁺ and only Cu²⁺/Al³⁺ significantly enhanced the absorbance intensity of the probe solution at 433 and 406, respectively. Its ability to selectively sense Al³⁺ demonstrated "switch-on" fluorescence responses for Al³⁺ with a low detection limit (LOD) of 0.56 μM and good selectivity, and pH adaptation range (5-8). The stoichiometric ratio of BFASA against the Al³⁺ was verified by the Job's plot and TOF-MS analysis and determined as 1:2. To make the recognition process inexpensively, viable and straightforward, Smartphone application of BFASA was effectively applied to Al³⁺ sensing, which could benefit the on-site Al³⁺ recognition. In the fluorescence bio-imaging aspect, the BFASA could effectively monitor Al³⁺ in living cells.

Poly-L-aspartic acid based nonconventional luminescent biomacromolecules with efficient emission in dilute solutions for Al3+ detection

Nonconventional luminescent macromolecules exhibiting bright fluorescence or phosphorescence emission at high concentrations and solid-state have attracted significant attention due to their promising application in different fields. However, most reported nonconventional luminescent macromolecules show weak or no emission in dilute solutions, limiting their large-scale applications. Herein, nonconventional luminescent biomacromolecules with hydrophobic rigid chains, hydrophilic flexibility and inter- or intra-molecular hydrogen bonding interactions were proposed to achieve effective luminescence in dilute solutions. Poly-L-aspartic acid (PASA) with a fluorescence quantum yield of 4.6 % in a dilute solution (0.8 mg/mL) was synthesized to validate this design strategy. The fluorescence intensity of PASA solution increased with the increase of the concentration, demonstrating a clustering-triggered emission (CTE) effect. Furthermore, the fluorescence intensity significantly enhanced when adding Al³⁺ into PASA aqueous solution via the Al³⁺ recognition effect. The detection limits for Al³⁺ (1.71 × 10^-6 mol/L) meet the World Health Organization (WHO) requirements for food detection. At last, PASA solid-state samples exhibit room temperature phosphorescence emission.

Positional Isomeric Symmetric Dipodal Receptors Dangled with Rotatable Binding Scaffolds: Fluorescent Sensing of Silver Ions and Sequential Detection of l-Histidine and Their Multifarious Applications

Three simple dipodal artificial acyclic symmetric receptors, SDO, SDM, and SDP, driven by positional isomerism based on xylelene scaffolds were designed, synthesized, and characterized by ¹H NMR, ¹³C NMR, and mass spectroscopy techniques. Probes SDO, SDM, and SDP demonstrated selective detection of Ag⁺ metal ions and amino acid l-histidine in a DMSO-H₂O solution (1:1 v/v, HEPES 50 mM, pH = 7.4). The detection of Ag⁺ metal ions occurred in three ways: (i) inhibition of the photoinduced electron-transfer (PET) process, (ii) blueshifted fluorescence enhancement via the intramolecular charge-transfer (ICT) process, and (iii) restricted rotation of the dangling benzylic scaffold following coordination with a Ag⁺ metal ion. Job's plot analysis and quantum yields confirm the binding of probes to Ag⁺ in 1:1, 1:2, and 1:2 ratios with LODs and LOQs found to be 1.3 μM and 3.19 × 10^-7 M, 6.40 × 10^-7 and 2.44 × 10 ^-6 M, and 9.76 × 10^-7 and 21.01 × 10^-7 M, respectively. ¹H NMR titration, HRMS, ESI-TOF, IR analysis, and theoretical DFT investigations were also used to establish the binding stoichiometry. Furthermore, the probes were utilized for the detection of Ag⁺ ions in water samples, food samples, soil analysis, and bacterial imaging in Escherichia coli cells and a molecular logic gate was constructed.

A rhodamine based chemodosimeter for the detection of Group 13 metal ions

A new rhodamine derivative, HL-CIN, derived from a reaction between N-(rhodamine-6G)lactam-ethylenediamine (L1) and trans-cinnamaldehyde, is reported here for the colorimetric and fluorogenic sensing of Group 13 trivalent cations, namely Al³⁺, Ga³⁺, In³⁺ and Tl³⁺. The absorption intensity of the probe increases significantly at 530 nm whereas the fluorescence intensity enhances massively at 558 nm upon interaction with these metal ions. Other relevant metal ions could not impart any noticeable color change or fluorescence enhancement. The quantum yield or fluorescence life time of HL-CIN increases considerably in the presence of these Group 13 metal ions. Different spectral studies such as ESI-mass, FT-IR, ¹H and ¹³C NMR spectra, establish that HL-CIN undergoes hydrolysis in the presence of the trivalent cations and a rhodamine species in its ring opened form (i.e. N-(2-aminoethyl)-2-((6Z)-3-(ethylamino)-6-(ethylimino)-2,7-dimethyl-6H-xanthen-9-yl)benzamide, (L2)) along with cinnamaldehyde are produced. The rhodamine species in its ring opened form (L2) is responsible for the color change and strong increment in the absorbance and fluorescence of HL-CIN with Group 13 cations. Interaction between L1 and these metal ions could not produce the same outcome. It has been used in test paper strips and to detect these cations in real samples.

Fluorescent Organic Small Molecule Probes for Bioimaging and Detection Applications

The activity levels of key substances (metal ions, reactive oxygen species, reactive nitrogen, biological small molecules, etc.) in organisms are closely related to intracellular redox reactions, disease occurrence and treatment, as well as drug absorption and distribution. Fluorescence imaging technology provides a visual tool for medicine, showing great potential in the fields of molecular biology, cellular immunology and oncology. In recent years, organic fluorescent probes have attracted much attention in the bioanalytical field. Among various organic fluorescent probes, fluorescent organic small molecule probes (FOSMPs) have become a research hotspot due to their excellent physicochemical properties, such as good photostability, high spatial and temporal resolution, as well as excellent biocompatibility. FOSMPs have proved to be suitable for in vivo bioimaging and detection. On the basis of the introduction of several primary fluorescence mechanisms, the latest progress of FOSMPs in the applications of bioimaging and detection is comprehensively reviewed. Following this, the preparation and application of fluorescent organic nanoparticles (FONPs) that are designed with FOSMPs as fluorophores are overviewed. Additionally, the prospects of FOSMPs in bioimaging and detection are discussed.

Recent Advancements in Developments of Novel Fluorescent Probes: In Cellulo Recognitions of Alkaline Phosphatases

Alkaline phosphatase (ALP) is one of the vital phospho-ester bond cleaving biocatalysts that has inevitable significance in cellular systems, viz., early-stage osteoblast differentiation, cell integrity in tissues, bone mineralization, cancer biomarker, liver dysfunction, cellular osmotic pressure, protein folding and many more. Variation from optimal levels of ALP in intra and extracellular fluids can cause severe diseases, including death. Due to these reasons, ALP is considered as a vital biomarker for various preclinical and medical diagnosis. Fluorescence image-based diagnosis is the most widely used method, owing to its simplicity, robustness, non-invasive properties and excellent spatio-temporal resolution (up to the nM/pM level), as compared to conventional analytical techniques, such as the electroanalytical method, nuclear magnetic resonance (NMR) and high-performance liquid chromatography (HPLC). Most of the reviews reported for ALP’s recognition in the literature scarcely explain the structurally related, photophysical and biophysical parameters; and the sub-cellular localizations. Considering these facts, in order to enhance the opto-analytical parameters of fluorescence-based diagnostic materials at the cellular level, herein we have systematically documented recent developments in the opto-analytical capabilities of quencher-free probes for ALP, used in in vitro (biological buffers) to in cellulo conditions, along with in vivo models.