Fabrication of chitosan-based fluorescent hydrogel membranes cross-linked with bisbenzaldehyde for efficient selective detection and adsorption of Fe2

Chitosan, as a natural biomass material, is green, recyclable, sustainable and well biocompatible. The molecular chain is rich in active groups such as amino and hydroxyl groups, and its preparation of fluorescent probes has the advantages of biocompatibility and efficient detection performance. In this study, a bis(benzaldehyde) (BHD) fluorescent functional molecule was designed. Then a series of fluorescent chitosan-based hydrogel films (CSBHD) were prepared using chitosan as raw material and BHD as cross-linking agent. As a fluorescent probe for metal ions, CSBHD was able to efficiently detect Fe2+ with a linear correlation of fluorescence intensity in the range of 0-160 μM, and the limit of detection (LOD) was 0.55 μM. Moreover, it has excellent adsorption performance for Fe2+ ions, with a maximum adsorption capacity of 223.5 g/mg at 500 mg/L Fe2+ concentration. Finally, we characterised the structure and microscopic morphology of CSBHD films and found that CSBHD as a hydrogel film has a high cross-linking density, good water resistance, excellent thermal stability, strong resistance to swelling, and excellent stability in cycling tests. Hence, it has great potential for application in adsorption and detection of Fe2+ ions. It also provides a good strategy for the application of chitosan based fluorescent probe materials in environmental monitoring and heavy metal ion adsorption.

Microflow injection analysis based on modular 3D platforms and colorimetric detection for Fe(III) monitoring in a wide concentration range

A modular microflow injection analysis (microFIA) system for the determination of Fe(III) in a bioleaching reactor has been designed, developed and validated. The different modules of the analyzer (mixer, diluter, disperser and detector) were 3D-printed. Fe(III) quantification is due by measuring the color intensity of the chelate formed between Fe(III) and salicylic acid at 525 nm. The device has been designed to dilute, disperse and detect high Fe(III) concentrations in the form of an inexpensive multi-step photometric flow cell that uses an light-emitting diode (LED) as a light source and an light-dependent resistor (LDR) as a light intensity detector. This microFIA system has been shown to be suitable for automatic and continuous determination of Fe(III) in the operation of a bioreactor for the oxidation of Fe(II). The device has a good repeatability (less than 5% of coefficient of variation in the whole range of concentrations) and accuracy of around 100%. The analyzer features an exceptional wide linear range, between 25 and 6000 mg·L-1. The device was successfully applied to the determination of Fe(III) in real samples. The obtained results proved that the method is applicable for accurate, precise, rapid, and low-cost colorimetric analysis and didn't show significant differences with a conventional UV-Vis method.

L-Phenylalanine-derived pseudopeptidic bioinspired materials: Zn(II) induced fluorescence enhancement and precise tuning of self-assembled nanostructures

The pseudopeptide, owing to its intriguing, sustainable, and easily accessible multifunctional properties, has attracted significant research interest over the years. C2-symmetric pseudopeptidic chiral bioinspired materials have been developed for their selective sensitivity to Zn(II) ions via a turn-on fluorescence under physiological conditions. Moreover, these are promising soft materials for precisely tuning their self-assembled nanostructures after incubating with Zn(II), opening avenues for exploring similar effects in various peptidomimetics.

Solvent-regulated fluorescence off-on signaling of Ni(II) and Zn(II) with the formation of two mononuclear complexes with an ATP detection ability by Zn(II) assembly

The current study shows that Schiff base HL, (Z)-2,4-dibromo-6-(((piperidin-2-ylmethyl)imino)methyl)phenol, can be used successfully as a selective chemosensor for Zn(II) and Ni(II) among several competing cations in purely aqueous and semi-aqueous media. Under UV light in methanol-water (9 : 1) HEPES buffer, the receptor gives its response by changing its color to cyan color in the presence of Zn(II) and to bluish cyan color in the presence of Ni(II). Surprisingly, the chemosensor can only reliably identify Zn(II) in a hundred percent aqueous medium by changing its color to light yellow. UV and fluorescence studies in both aqueous and semi-aqueous media are used to further investigate this Zn(II) and Ni(II) recognition phenomenon. The high values of the host-guest binding constants, obtained by electronic and fluorescence titration, ensure that a strong bond exists between HL and Ni(II)/Zn(II). As anticipated, two highly luminescent mononuclear, crystalline compounds, complexes 1 and 2, have been developed by a separate reaction of HL and Zn(II)/Ni(II), and the high luminous properties are due to the occurrence of Chelation Enhanced Fluorescence (CHEF). According to the single crystal structure, the asymmetric units of both complexes consist of two deprotonated chemosensor units and one Zn(II)/Ni(II), leading to the formation of an octahedral complex. For Ni(II) and Zn(II) sensing, the predicted LOD is in the nanomolar range. Both complexes 1 and 2 are fluorescence active and studies to check their ATP detection ability, but intriguingly, only complex 2 is capable of detecting ATP in a fully aqueous solution. Finally, the live cell imaging study validates the two sensors' biosensing functionality.

Colorimetric detection of heavy metal ions with various chromogenic materials: Strategies and applications

Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions.

Poly(carbazole-co-1,4-dimethoxybenzene): Synthesis, Electrochemiluminescence Performance, and Application in Detection of Fe3+

In this study, four polycarbazole derivatives (PCMB-Ds) with different alkyl side chains were designed and synthesized via Wittig–Horner reaction. A novel solid-phase electrochemiluminescence (ECL) system was prepared by immobilizing PCMB-D on an indium tin oxide (ITO) electrode with polyvinylidene fluoride (PVDF) in the presence of tripropylamine (TPrA). It could be found that the increase in alkyl side chain length had little effect on the ECL signal of PCMB-D, while the increase in the degree of polymerization (DP) greatly enhanced the ECL signal. Furthermore, the P-3/ITO ECL sensor based on the polyoctylcarbazole derivative (P-3) with the best ECL performance was successfully constructed and detected Fe³⁺ under the optimal experimental conditions. The ECL signal steadily diminished with the increased concentration of Fe³⁺ because of the competition and complexation between Fe³⁺ and P-3 under the condition of pH 7.4. This P-3/ITO platform could realize a highly sensitive and selective detection of Fe³⁺ with a wide detection range (from 6 × 10⁻⁸ mol/L to 1 × 10⁻⁵ mol/L) and low detection limit of 2 × 10⁻⁸ mol/L, which could allow the detection of Fe³⁺ in multiple scenarios, and would have a great application prospect.

A dual-channel "on-off-on" fluorescent probe for the detection and discrimination of Fe3+ and Hg2+ in piggery feed and swine wastewater

Blue-fluorescent blood-CDs were synthesized through a one-pot hydrothermal method using a mixture of chicken blood and trisodium citrate and then explored as a fluorescent probe for detecting Fe³⁺ and Hg²⁺. The probe showed excellent selectivity and sensitivity towards Fe³⁺ and Hg²⁺ with a dramatic "on-off" fluorescence response. F^- recovered the fluorescence quenching by Fe³⁺, and Al³⁺ recovered the fluorescence quenching by Hg²⁺, showing an "off-on" fluorescence response. The blood-CDs were used as an "on-off-on" dual-channel fluorescent sensor for the detection and discrimination of Fe³⁺ and Hg²⁺ ions. The probe showed wide linear ranges for determination of Fe³⁺ (0-100 μM) and Hg²⁺ (0-120 μM) with low detection limits of 0.23 μM for Fe³⁺ and 0.17 μM for Hg²⁺. This probe was practically applied for the determination of Fe³⁺ and Hg²⁺ in piggery feed and wastewater with good recoveries. This work provides a fluorescent probe for the quantification of Fe³⁺ and Hg²⁺ in livestock feed and environmental water samples.

A novel [1,2,4]triazolo[1,5-a]pyrimidine derivative as a fluorescence probe for specific detection of Fe3+ ions and application in cell imaging

The detection of metal ions is of particular importance for monitoring environmental pollution and life metabolic activities. However, it is still a challenge to achieve Fe³⁺ detection with specific sensitivity and rapid response, especially in the presence of chelating agents for Fe³⁺ ions. Herein, a novel fluorescence probe for Fe³⁺, i.e., amide derivative of [1,2,4]triazolo[1,5-a] pyrimidine (TP, Id), was synthesized, featuring specific Fe³⁺ selectivity, rapid quenching (5 s), low limit of detection (0.82 μM), good permeability and low cytotoxicity. More importantly, Id can be used to identify and detect Fe³⁺ in the presence of existing strong chelating agents (e.g., EDTA) for Fe³⁺ ions. The results show that the as-synthesized fluorescence probe is particularly suitable as a bioimaging reagent to monitor intracellular Fe³⁺ in living HeLa cells. Furthermore, we proposed the binding mode for Id with Fe³⁺ ions and the light-emitting mechanism through high-resolution mass spectra and density function theory calculations, respectively. An Id-based test paper can be used to rapidly identify Fe³⁺. These results are expected to improve the development of new sensitive and specific fluorescent sensors for Fe³⁺.

A Novel Benzimidazole-Based Chemosensor for Fluorometric Determination of Zinc Ions

A simple and novel Schiff base chemosensor (BMHM) based on benzimidazole was synthesized. In ethanol-water (1:1, v/v) medium on varying concentrations of Zn²⁺ chemosensor exhibited a strong and quick turn on fluorescence response. The Zn²⁺ recognition was based on the Chelation-enhanced fluorescence effect. The binding constant and limit of detection for BMHM-Zn²⁺ complexation were estimated to be 7.99 × 104 M^-1 and 0.148 µM, respectively. The extreme fluorescent enhancement caused by Zn²⁺ binding in chemosensor BMHM occurred at a pH range of 6-7. The practical use of chemosensor BMHM was tested by determination of Zn²⁺ in real water samples and comparing the results with the data obtained using high resolution inductively coupled plasma mass spectrometry.

An Indole-Based Fluorescent Chemosensor for Detecting Zn2+ in Aqueous Media and Zebrafish

An indole-based fluorescent chemosensor IH-Sal was synthesized to detect Zn²⁺. IH-Sal displayed a marked fluorescence increment with Zn²⁺. The detection limit (0.41 μM) of IH-Sal for Zn²⁺ was greatly below that suggested by the World Health Organization. IH-Sal can quantify Zn²⁺ in real water samples. More significantly, IH-Sal could determine and depict the presence of Zn²⁺ in zebrafish. The detecting mechanism of IH-Sal toward Zn²⁺ was illustrated by fluorescence and UV–visible spectroscopy, DFT calculations, ¹H NMR titration and ESI mass.

All Silica Micro-Fluidic Flow Injection Sensor System for Colorimetric Chemical Sensing

This paper presents a miniature, all-silica, flow-injection sensor. The sensor consists of an optical fiber-coupled microcell for spectral absorption measurements and a microfluidic reagent injection system. The proposed sensor operates in back reflection mode and, with its compact dimensions, (no more than 200 µm in diameter) enables operation in small spaces and at very low flow rates of analyte and reagent, thus allowing for on-line or in-line colorimetric chemical sensing.

Selective detection of sulfide in human lung cancer cells with a blue-fluorescent "ON-OFF-ON" benzimidazole-based chemosensor ensemble

A completely water-soluble, high quantum yield blue-fluorescent benzimidazole derivative (AQ), containing a rigid benzimidazole-thiophene structure, was synthesized. Among 21 metal ions, the fluorescence of AQ was selectively turned off by Cu²⁺ to form an AQ-Cu²⁺ ensemble. Thereafter, the fluorescence of the AQ-Cu²⁺ ensemble was turned on by sulfide (S^2-) with high selectivity and sensitivity in pure water solution. In comparison with AQ-Ag⁺ and AQ-Hg²⁺ ensembles, AQ-Cu²⁺ was the only ensemble that was capable of detecting a sulfide anion. Also, the fluorescence intensity of AQ was linearly proportional to the concentration of Cu²⁺ and S^2-. Both Cu²⁺ and S^2- were detected within a minute in vitro. Moreover, AQ worked best in the pH range of 5-10 and had a limit of detection of 50 nM and 354 nM for Cu²⁺ and S^2- respectively. It was employed for the detection of sulfide in human lung cancer A549 cells with low cytotoxicity.

Novel benzimidazole-based conjugated polyelectrolytes: synthesis, solution photophysics and fluorescent sensing of metal ions

Two benzimidazole-based conjugated polyelectrolytes (+)-PPBIPV and (-)-PPBIPV which have opposite charges on their side chains were synthesized via Heck coupling reaction and characterized by 1H-NMR, UV-vis and PL spectroscopy. These two polyelectrolytes are both consisted of benzimidazole derivatives and phenylenevinylene units. The absorption and emission spectra reveal that the polymers both have solvent-dependency and concentration-dependency, and they exhibit aggregation effect in aqueous solution. In the respect of ion detection, the aqueous solution of (+)-PPBIPV has excellent selectivity and sensitivity for Fe3+. Moreover, Pd2+ can almost completely quench the fluorescence of (+)-PPBIPV in methanol solution, and its quenching constant KSV is 5.93×104 M-1. For (-)-PPBIPV, Sn2+ can double the fluorescence intensity of its aqueous solution, while (-)-PPBIPV has good identification for Fe3+ in methanol with a KSV = 3.44×105 M-1. Hence, two polyelectrolytes have considerable potential to become effective fluorescent sensing materials for some specific metal ions. All of the stoichiometric relationships between metal ions and conjugated polyelectrolytes were calculated using Benesi-Hildebrand equation.

A Novel Thiophene-Based Fluorescent Chemosensor for the Detection of Zn2+ and CN-: Imaging Applications in Live Cells and Zebrafish

A novel fluorescent turn-on chemosensor DHADC ((E)-3-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2,3-dihydrothiophene-2-carboxamide) has been developed and used to detect Zn2+ and CN-. Compound DHADC displayed a notable fluorescence increase with Zn2+. The limit of detection (2.55 ± 0.05 μM) for zinc ion was far below the standard (76 μM) of the WHO (World Health Organization). In particular, compound DHADC could be applied to determine Zn2+ in real samples, and to image Zn2+ in both HeLa cells and zebrafish. Additionally, DHADC could detect CN- through a fluorescence enhancement with little inhibition with the existence of other types of anions. The detection processes of compound DHADC for Zn2+ and CN- were demonstrated with various analytical methods like Job plots, 1H NMR titrations, and ESI-Mass analyses.

On-off-on relay fluorescence recognition of ferric and fluoride ions based on indicator displacement in living cells

A new boronic acid derivative functionalized with a 4-(3-(4-(4,5-diphenyl-1H-imidazole-2-yl)phenyl)-1,2,4-oxadiazol-5-yl)phenyl (IOP) moiety was synthesized for use as a sequential "on-off-on"-type relay fluorescence probe for Fe³⁺ ions and F^- ions with high selectivity and sensitivity under physiological conditions. The introduction of Fe³⁺ to IOP boronic acid (IOPBA) formed an Fe³⁺IOPBA complex, which led to quenching of the blue fluorescence intensity at 458 nm. The lowest-energy conformation of IOPBA was theoretically predicted to adopt an extended structure, and the Fe³⁺ ion in the Fe³⁺IOPBA complex was coordinated to two phenyl groups to form a π-complex. Upon addition of F^- to the Fe³⁺IOPBA complex, the original fluorescence was recovered due to formation of [FeF₆]^3‒, resulting in "on-off-on"-type sensor behavior. IOPBA showed high selectivity towards Fe³⁺ among other cations. Moreover, the Fe³⁺IOPBA complex showed specific selectivity towards F^-, with other cations and anions not interfering with detection. Both sensing processes showed 1:1 stoichiometry with binding constants of 6.87 × 10⁶ and 4.49 × 10⁶ mol^-1 L for Fe³⁺ with IOPBA and F^- with Fe³⁺IOPBA, respectively. The limits of detection for Fe³⁺ and F^- were 10 and 1 nM, respectively. The proposed method was successfully applied in real water samples. Furthermore, the probe had low cytotoxicity and was successfully used as a bioimaging reagent to detect intracellular Fe³⁺ and F^- in living HeLa cells.

Novel dual-functional fluorescent sensors based on bis(5,6-dimethylbenzimidazole) derivatives for distinguishing of Ag+ and Fe3+ in semi-aqueous medium

Three novel bisbenzimidazole derivatives have been synthesized and developed as dual-functional fluorescent sensors for the rapid and highly selective detection of Ag⁺ and Fe³⁺ ions in semi-aqueous medium with distinct spectral response for the first time. The absorption intensity is drastically decreased after the addition of Ag⁺. Contrarily, it is markedly increased upon the addition of Fe³⁺. And there is a good linear relation at low concentration of both Ag⁺ and Fe³⁺, which provides a quantitative method for their detection. Similarly, the sensors show a distinct fluorescence response towards Ag⁺ and Fe³⁺ with a different fluorescence color change under UV light. In addition, no significant changes and interference can be observed with other metal ions. The sensing mechanism studies confirm that the N atom in CN of benzimidazole ring of sensor 4a may bind with Ag⁺ or Fe³⁺ ion to form metal complex. And there is only a static quenching process for the 4-Ag⁺ complex system, but both dynamic and static quenching processes occur in the 4-Fe³⁺ complex system. Moreover, sensors 4 can steadily work in solution with a wide range of pH 4-13 and rapidly respond to Ag⁺ and Fe³⁺ with a response time of 10 s. Finally, the sensors have been successfully applied to the visual detection of Ag⁺ and Fe³⁺ not only in solution, but also in test paper.

A hydrazono-quinoline-based chemosensor sensing In3+ and Zn2+via fluorescence turn-on and ClO−via color change in aqueous solution

A multi-target sensor, based on hydrazono-quinoline, was developed for fluorescence turn-on detection of In³⁺ and Zn²⁺ and colorimetric detection of ClO⁻.

A multiple target chemosensor for the sequential fluorescence detection of Zn2+ and S2− and the colorimetric detection of Fe3+/2+ in aqueous media and living cells

A novel multiple target sensor DHIC was developed for the fluorescence detection of Zn²⁺ and S²⁻ and colorimetric detection of Fe^3+/2+. Moreover, DHIC could image sequentially Zn²⁺ and S²⁻ in living cells.

A voltammetric method for Fe(iii) in blood serum using a screen-printed electrode modified with a Schiff base ionophore

A miniaturized disposable screen-printed electrode for the detection of Fe(iii) at the micro-molar level.

Highly Sensitive Colorimetric Assay for Determining Fe3+ Based on Gold Nanoparticles Conjugated with Glycol Chitosan

A highly sensitive and simple colorimetric assay for the detection of Fe³⁺ ions was developed using gold nanoparticles (AuNPs) conjugated with glycol chitosan (GC). The Fe³⁺ ion coordinates with the oxygen atoms of GC in a hexadentate manner (O-Fe³⁺-O), decreasing the interparticle distance and inducing aggregation. Time-of-flight secondary ion mass spectrometry showed that the bound Fe³⁺ was coordinated to the oxygen atoms of the ethylene glycol in GC, which resulted in a significant color change from light red to dark midnight blue due to aggregation. Using this GC-AuNP probe, the quantitative determination of Fe³⁺ in biological, environmental, and pharmaceutical samples could be achieved by the naked eye and spectrophotometric methods. Sensitive response and pronounced color change of the GC-AuNPs in the presence of Fe³⁺ were optimized at pH 6, 70°C, and 300 mM NaCl concentration. The absorption intensity ratio (A₇₀₀/A₅₁₀) linearly correlated to the Fe³⁺ concentration in the linear range of 0-180 μM. The limits of detection were 11.3, 29.2, and 46.0 nM for tap water, pond water, and iron supplement tablets, respectively. Owing to its facile and sensitive nature, this assay method for Fe³⁺ ions can be applied to the analysis of drinking water and pharmaceutical samples.

Improved performance of Schiff based ionophore modified with MWCNT for Fe(ii) sensing by potentiometry and voltammetry supported with DFT studies

A novel potentiometric and voltammetric sensor for creating a cationic response for Fe(ii) is introduced.

Sequential detection of Fe3+/2+ and pyrophosphate by a colorimetric chemosensor in a near-perfect aqueous solution

A colorimetric chemosensor was developed for Fe^3+/2+ and pyrophosphate with low detection limit and practical application for Fe³⁺ in water samples.

Synthesis, crystal structure, photophysical property and metal ion-binding behavior of a cyclometalated platinum(ii) terpyridylacetylide with efficient π-conjugation degree

The “Donor–Phosphore–Receptor” platform as a novel building block for formation of heterotrinuclear transition metal complexes.

Silkworm feces extract improves iron deficiency anemia via suppressing hepcidin expression and promoting iron-regulatory proteins expression

In this study, we aimed to explore the preventive efficacy of SFE toward iron deficiency anemia in rats and clarify the underlying mechanisms. Findings suggest that SFE may be an efficient oral iron supplement to ameliorate iron deficiency anemia.