Highly selective colorimetric and electrochemical sensing of iron (III) using Nile red functionalized graphene film

Colorimetric detection of Fe2+ and Cr2O72- in environmental water samples based on dual-emitting RhB-embedded Zr-MOFs

Three dye-loaded tunable dual-emission colorimetric fluorescent probes RhB@UiO-66-Ph (R@U-P) were prepared by in-situ encapsulation method under solvothermal conditions. The resonance energy transfer between UiO-66-Ph and RhB made the dual emission of R@U-P easily tunable with the embedded dye content changing. The R@U-P composites achieved emission from purple light to red light, and served as probes to realize comparative detection of Fe3+, Fe2+ and Cr2O72- in water through colorimetric or quenching detection mode. Mechanism study indicates that the resonance energy transfer or electron transfer interactions between R@U-P composites and inorganic ions resulted in the relative changes of the two emission peaks and realized the selective detection of analytes. The preparation and application of R@U-P probes provide a promising strategy for the in-situ encapsulation dye to obtain two dual-emission composites for the comparative detection of Fe3+, Fe2+ and Cr2O72- in water samples.

Chitosan-based fluorescent probe for the detection of Fe3+ in real water and food samples

Iron ions play a crucial role in the environment and the human body. Therefore, developing an effective detection method is crucial. In this paper, we report CNS2, a chitosan-based fluorescent probe utilizing naphthalimide as a fluorophore. CNS2 is designed to "quench" its own yellow fluorescence through the specific binding of compounds containing enol structures to Fe3+. Studying the fluorescence lifetime of CNS2 in the presence or absence of Fe3+ reveals that the quenching mechanism is static. The presence of multiple recognition sites on the chitosan chain bound to Fe3+ gave CNS2 rapid recognition (1 min) and high sensitivity, with a detection limit as low as 0.211 μM. Moreover, the recognition of Fe3+ by CNS2 had a good specificity and was not affected by interferences. More importantly, in this study, CNS2 was successfully utilised to prepare fluorescent composite membranes and to detect Fe3+ in real water samples and a variety of food samples. The results show that the complex sample environment still does not affect the recognition of Fe3+ by CNS2. All the above experiments obtained more satisfactory results, which provide strong support for the detection of Fe3+ by the probe CNS2 in practical applications.

Schiff base fluorescent sensor with aggregation induced emission characteristics for the sensitive and specific Fe3+ detection

An aggregation induced emission based compound ((E)-4-((2-hydroxy-5-methoxybenzylidene)amino)benzoic acid) was synthesized through facile Schiff base condensation and characterized by various spectral techniques. The as-prepared compound represented a typical aggregation induced emission behavior in aqueous solution and exploited as a turn-off fluorescent sensor for Fe3+ detection in THF-H2O system (3:7, v/v) with high sensitivity and selectivity. The mechanism of the fluorescence quenching was intensively studied, which was attributed to both dynamic quenching and inner filter effect. The fluorescence probe displayed a highly broad dynamic response range (0.5-500 μM) for selective detection of Fe3+ with a limit of detection of 0.079 μM. The proposed method was successfully employed for detection and quantification of Fe3+ in human urine samples and proved to have potential for practical applications in biological field.

A sensitive "turn-on" Schiff-base fluorescent probe for the selective detection of Fe3+ and bio-imaging

A novel Schiff-base fluorescent probe, 4-(N-(2- hydroxyl-1-naphthalymethylimino)-ethylamino) -7-nitro-1,2,3-benzoxadiazole (HENB) was synthesized and utilized for spectral sensing of Fe3+ ions at neutral pH. The binding of Fe3+ to HENB in C2H5OH-HEPES buffer (1:1 v/ v, 25 mM, pH 7.2) resulted in a pronounced emission enhancement at 530 nm, which is possibly due to the inhibition of photo-induced electron transfer (PET) process as well as the chelation enhanced fluorescence (CHEF) effect. HENB shows good selectivity and sensitivity toward Fe3+ with the detection limit as low as 4.51 nM. Test strips made of HENB was used for rapid "naked-eye" detection of Fe3+ ions in aqueous medium. Moreover, HENB was successfully applied in fluorescence imaging of exogenous and endogenous Fe3+ in live Hela cells as well as zebrafish. Importantly, HENB is capable of effectively monitoring the variations of Fe3+ in living cells during ferroptosis process.

A naked-eye visible aluminium (III)-based complex fluorescence sensor for sensitive detection of mesotrione

Mesotrione, which is a kind of herbicide to control broad-leaved weeds, has been increasingly used due to its excellent selectivity, rapid process and low toxicity. However, the excessive application of mesotrione have led to widespread contamination. Herein, a turn-on competitive coordination-based fluorescent probe, 2-hydroxy-1-(9-purin)-methylidenehydrazinenaphthalene (HPM), has been successfully synthesized. HPM could effectively detect Al3+ in CH3OH/HEPES (1/9, v/v) with low limit of detection (LOD) being 0.2 µM via coordination. HPM also exhibited excellent imaging capabilities for Al3+ in living cells with low cytotoxicity. On the basis of the competitive coordination of HPM with Al3+, the [HPM-Al3+] complex could also serve as a potential fluorescence sensor for detecting mesotrione with the LOD of 0.2 µM. Furthermore, [HPM-Al3+] complex was applied for the detection of mesotrione in real samples and test paper. Finally, the mechanism of [HPM-Al3+] for sensing mesotrione was investigated deeply as well. This work designed a new convenient method for on-site detection of mesotrione without the large-scale equipment or complicated pre-treatment.

A dual-emitting Rhodamine B-encapsulated Zn-based MOF for the selective sensing of Chromium(VI)

A Rhodamine B-Zn-MOF composite (RhB-Zn-MOF) with dual emission intensity was synthesized through one pot synthesis by in-situ encapsulation of Rhodamine-B dye on a new Zn-MOF metal-organic framework [(Zn(OAc)2(4-BrIPh) (1,10-phenonthroline)(H2O)].H2O, (4-BrIPh = 4-Bromoisophthalic acid). The synthesized encapsulated material was characterized by elemental analysis, FTIR, UV-Visible spectroscopy, TGA, single crystal and powder X-ray diffraction and photoluminescence spectroscopy. The results showed that the synthesized composite, RhB-Zn-MOF could be used as an efficient probe for the selective sensing of Cr(VI) in the presence of Cr(III) as well as other metal ions.

Sulfonamide functionalized silica nano-composite: characterization and fluorescence "turn-on" detection of Fe3+ ions in aqueous samples

We have synthesized novel sulfonamide-based nano-composite (SAN) for selective and sensitive detection of Fe³⁺ ions in aqueous samples. Morphological characterization of SAN was carried out with TGA, FT-IR, UV-Vis, ninhydrin assay, FE-SEM, pXRD, BET, EDX, and elemental analysis. The sensing nature, effect of pH, sensor concentration and response time analysis were accomplished with the help of emission spectral studies and SAN was assessed as "turn-on" emission detector for the biologically important Fe³⁺ ions. Here, the LOD and LOQ were computed to be 26.68 nM and 88.93 nM, respectively, and it was found to be much lower than the permissible limit of Fe³⁺ ions in drinking water. The accuracy of the sensor (SAN) was determined by testing the aqueous samples spiked with known concentrations of Fe³⁺ ions and results demonstrated 98.00-99.66% recovery, which made SAN a reliable, selective and sensitive chemosensor for the quantification of Fe³⁺ ions in fully aqueous media.

Preparation of temperature-responsive nanomicelles with AIE property as fluorescence probe for detection of Fe3+ and Fe2

Temperature-responsive nanomicelles with aggregation induced emission (AIE) property were prepared by the host-guest complexation of ferrocene functionalized tetraphenyl (TPE-Fc) and β-cyclodextrin-poly (N-isopropylacrylamide) (β-CD-(PNIPAM)₇). The AIE chromophore TPE-Fc bound to the hydrophobic cavity of cyclodextrin serves as the core of micelles, and temperature sensitive PNIPAM serves as the shell to give the micelles good solubility. The size of the nanomicelles is about 100 nm. At the excitation wavelength of 340 nm, the strongest fluorescent emission peak was 421 nm. The introduction of cyclodextrin star polymer increased the fluorescence intensity of nanomicelles, thus improving the recognition of probe to Fe³⁺ and Fe²⁺. The fluorescent probe can quickly detect Fe³⁺ and Fe²⁺ in water within 5 min even in the presence of various interfering ions. The detection limits of Fe³⁺ and Fe²⁺ were 1.04 μM and 0.78 μM, respectively in the range of 10-90 μM. The formation of complex between the probe and Fe³⁺/Fe²⁺ was supported by Job's plot. The probe was successfully applied to the detection of Fe³⁺and Fe²⁺ in actual water sample with a good recovery. In addition, a possible sensing mechanism for the interaction of iron ions with amide bond groups of nanomicelles was proposed.

Thionine-mediated electrocatalytic reduction for electrochemical detection of EDTA-Fe(III) in soy sauce

Electrocatalytic reactions based on electron transfer mediators provide a simple and effective route for the development of convenient and sensitive electrochemical assays. Here, we report a novel electrocatalytic assay for detection of EDTA-Fe(III), which is widely used as a supplement in iron-fortified foods to reduce prevalence of iron deficiency. Unlike conventional electrochemical methods to detect Fe(III) ion, signaling mechanism of our electrocatalytic assay relies on the previously unexplored thionine-mediated electrochemical reduction of EDTA-Fe(III). This electrocatalytic detection method is sensitive for EDTA-Fe(III) detection in the linear concentration range from 10 to 750 μM with a detection limit of 2.5 μM. It is also specific enough and applicable to detection of EDTA-Fe(III) in real soy sauce samples with satisfactory recovery. The one-step electrocatalytic reduction for signal generation enables the direct and sensitive electrochemical detection of EDTA-Fe(III). We believe that this electrocatalytic assay can serve as a general platform for quantification of EDTA-Fe(III) in many EDTA-Fe(III)-fortified foods. And because thionine is increasingly used as a signal reporter in electrochemical DNA/aptamer sensors, the engineered electrocatalytic reaction of thionine-mediated electrochemical reduction of EDTA-Fe(III) will also provide a simple signal amplification means for the development of highly sensitive electrochemical biosensors.

Status and Prospects of Heterojunction-Based HEMT for Next-Generation Biosensors

High electron mobility transistor (HEMT) biosensors hold great potential for realizing label-free, real-time, and direct detection. Owing to their unique properties of two-dimensional electron gas (2DEG), HEMT biosensors have the ability to amplify current changes pertinent to potential changes with the introduction of any biomolecules, making them highly surface charge sensitive. This review discusses the recent advances in the use of AlGaN/GaN and AlGaAs/GaAs HEMT as biosensors in the context of different gate architectures. We describe the fundamental mechanisms underlying their operational functions, giving insight into crucial experiments as well as the necessary analysis and validation of data. Surface functionalization and biorecognition integrated into the HEMT gate structures, including self-assembly strategies, are also presented in this review, with relevant and promising applications discussed for ultra-sensitive biosensors. Obstacles and opportunities for possible optimization are also surveyed. Conclusively, future prospects for further development and applications are discussed. This review is instructive for researchers who are new to this field as well as being informative for those who work in related fields.

A colourimetric fluorescent probe for the sensitive detection of total iron in wine

As the iron content of wine affects the wine quality, a highly selective and simple detection method is needed to detect the iron content in wine. A colourimetric fluorescent probe (BTBAP probe) for the detection of total iron in wine was developed. The quantitative range of Fe^2+/3+ content detected with the probe was 0 to 200 μM with a limit of detection (LOD) of 1.16 μM. After 10 min of Fe^2+/3+ addition, the luminescence intensity of the BTBAP probe solution gradually decreased with increasing Fe^2+/3+ concentration. Moreover, the B and G values of the luminescence photos were linearly related to the concentration of Fe^2+/3+ (0-200 μM). BTBAP probe was successfully applied for rapid determination of the Fe^2+/3+ concentration of wine. This work demonstrates that BTBAP probe is an excellent tool for rapid determination of the total iron content of wine using only a smartphone and no other professional equipment.

Green metallochromic cellulose dipstick for Fe(III) using chitosan nanoparticles and cyanidin-based natural anthocyanins red-cabbage extract

Environmentally-friendly, cyanidin(Cy)-based anthocyanin isolated from red-cabbage served as a spectroscopic probe imprinted onto chitosan nanoparticles (CsNPs), which were in turn integrated onto cellulose paper strip (CPS) as a host matrix to develop a metallochromic solid state sensor for real-time selective determination of ferric ions in an aqueous medium. The ferric transition metal ions in aqueous environments were detected using a novel, simple, portable, fast responsive, low-cost, real-time, environmentally safe, reversible and colorimetric sensor based on chitosan nanoparticles as a hosting biopolymer and cyanidin phenol chromophore as a biomolecular probe. In order to use the cyanidin biomolecule as a pH indicator and chelating agent, it was purified from red-cabbage and added into the CsNPs biosensor film. The colorimetric shift increased in direct proportion to the ferric ion concentration. As a result, the current research that was both qualitative and quantitative was carried out. While the Cy-CsNPs-CPS sensor showed high selectivity for ferric ions, no color change was detected for other metal cations. It was discovered that the detection process occurred as a result of a coordination complex formed between the active sites of phenolic cyanidin and Fe(III) ions.

Application of a luminous intensity variation fluorescent probe for the detection of ferric ions

A luminous intensity variation fluorescent probe (Probe 1) for the detection of ferric ion was developed. The quantitative range of Fe³⁺ content detected was 0 to 600 μM with the LOD at 0.76 μM. Further, after 20 minutes of Fe³⁺ addition, the intensity of luminescence of Probe 1 solution gradually decreased with increased Fe³⁺ concentration. In addition, the B and G values of these images showed a linear relationship with Fe³⁺ concentration (0-500 μM). Probe 1 was successfully used for the rapid determination of Fe³⁺ concentration in real samples. This study demonstrates that Probe 1 is an excellent tool for the rapid determination of Fe³⁺ content in real samples using a smart phone without professional equipment.

DNA nanosensing systems for tunable detection of metal ions and molecular crypto-steganography

Various sensing platforms based on molecular or nanosystems are widely exploited through molecular diversity and specific recognition. However, it is extremely challenging to develop systems with tunable sensing ability and utilize the systems as information carriers/covers for communication and safety. Herein, DNA nanosensing systems based on cobalt oxyhydroxide (CoOOH) nanosheets were constructed for tunable detection and valence distinction of metal ions, molecular crypto-steganography, and information coding. CoOOH nanosheets absorb fluorescence-labeled single-stranded DNA with different bases and lengths, resulting in fluorescence quenching. The binding priority of bases with CoOOH nanosheets was guanine (G) > cytosine (C) > adenine (A) ≈ thymine (T) and the short chain excelled long chain. Due to the differences in the interaction among CoOOH, DNA, metal ions and variability of DNA bases, various DNA-CoOOH nanosystems have significantly different selective response patterns (that is selectivity) to metal ions and tunable linear ranges to Fe³⁺, Hg²⁺, Cr³⁺. Interestingly, by utilizing their molecular diversity, recognition, selective patterns, DNA-CoOOH sensing systems can be served as doubly cryptographic and steganographic systems to implement information encoding, encryption, and hiding and to reversely improve the selectivity of metal ions. This study provides an idea and platform for adjustable detection and valence distinction of metal ions, and gives a set of "molecular programming languages" for designing intelligent programmable sensing and molecular information communication and safety systems.

Conjugated microporous organic polymer as fluorescent chemosensor for detection of Fe3+ and Fe2+ ions with high selectivity and sensitivity

A conjugated microporous organic polymer (TPA-Bp) comprised of triphenylamine (TPA) and 2,2'-bipyridine-5,5'-diformaldehyde (Bp) was prepared via the Schiff-base reaction under ambient conditions. TPA-Bp is an amorphous and microporous spherical nanoparticle with very high stability. TPA-Bp suspension in DMF displayed strong fluorescence emission and selective fluorescence quenching response towards Fe³⁺ and Fe²⁺ ions. The fluorescence intensity of TPA-Bp at 331 nm presents linear relationship with the concentrations of both Fe³⁺ and Fe²⁺ with low detection limits of 1.02 × 10^-5 M for Fe³⁺ and 5.37 × 10^-6 M for Fe²⁺. The results of X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR) confirm the selective coordination of N atoms of pyridine unit with Fe ions. The fluorescence quenching of TPA-Bp upon the addition of Fe³⁺/Fe²⁺ ions can be attributed to the absorption competition quenching (ACQ) mechanism and the energy transfer between TPA-Bp and Fe³⁺/Fe²⁺ ions. This work demonstrates that the conjugated microporous polymers are promising candidates as luminescent sensor for detection of the special analytes in practical applications.

Curauá-derived carbon dots: Fluorescent probes for effective Fe(III) ion detection, cellular labeling and bioimaging

This study reports the generation of curauá-derived carbon dots (C-dots) and their suitability for Fe(III) detection, bioimaging and FACS analysis. C-dots were generated from curauá (Ananas erectifolius) fibers by a facile one-step hydrothermal approach. They exhibited graphite-like structure with a mean diameter of 2.4 nm, high water solubility, high levels of carboxyl and hydroxyl functional groups, excitation-dependent multicolor fluorescence emission (in the range 450 nm - 560 nm) and superior photostability. C-dots were highly selective and effective for the detection of ferric Fe(III) ion in an aqueous medium with a detection limit of 0.77 μM in the linear range of 0-30 μM, a value much lower than the guideline limits proposed by the World Health Organization (WHO). In biological cell systems, C-dots were very well tolerated by B16F1 mouse melanoma and J774.A1 mouse macrophages cell lines, both of which effectively internalized C-dots in their cytoplasmic compartment. Finally, C-dots were effective probes for long-term live cell imaging experiments and multi-channel flow cytometry analysis. Collectively, our findings demonstrate that curauá-derived C-dots serve as versatile and effective natural products for Fe(III) ion sensing, labeling and bioimaging of various cell types. This study adds novel C-dots to the library of carbon-based probes and paves the way towards a sustainable conversion of a most abundant biomass waste into value-added products.

A Multifunctional 3D Supermolecular Co Coordination Polymer With Potential for CO2 Adsorption, Antibacterial Activity, and Selective Sensing of Fe3+/Cr3+ Ions and TNP

A 3D supermolecular structure [Co₃(L)₂ (2,2′-bipy)₂](DMF)₃(H₂O)₃ 1) (H₃L = 4,4′,4″-nitrilotribenzoic acid) has been constructed based on H₃L, and 2,2′-bipy ligands under solvothermal conditions. Compound 1 can be described as a (3, 6)-connected kgd topology with a Schläfli symbol (4³)₂(4⁶.6⁶.8³) formed by [Co₃(CO₂)₆] secondary building units. The adsorption properties of the activated sample 1a has been studied; the result shows that 1a has a high adsorption ability: the CO₂ uptakes were 74 cm³·g⁻¹ at 273 K, 50 cm³·g⁻¹ at 298 K, the isosteric heat of adsorption (Q_st) is 25.5 kJ mol⁻¹ at zero loading, and the N₂ adsorption at 77 K, 1 bar is 307 cm³ g⁻¹. Magnetic measurements showed the existence of an antiferromagnetic exchange interaction in compound 1, besides compound 1 exhibits effective luminescent performance for Fe³⁺/Cr³⁺ and TNP.

Selective colorimetric sensing of deferoxamine with 4-mercaptophenol- and mercaptoacetic acid-functionalized gold nanoparticles via Fe(iii) chelation

The multidentate deferoxamine ligand can selectively aggregate the Fe(iii)-attached AuNPs@(4MP–MAA) colorimetric nanoprobe, whereas other bidentate iron chelators cannot bridge the nanoparticles.

New water-soluble colorimetric pH and metal ione sensor based on graphene quantum dot modified with alizarine red S

A new colorimetric sensor was designed for the screening pH changes in solutions, as well as, detection of some cations. The sensor preparation includes the chemical binding of alizarine red S (ARS) as a sensor of pH and cation to graphene quantum dots (GQD). Loading ARS on GQD led to the formation of water soluble sensor which finally responded to the colorimetric detection of some cations in water. Solubility and stability of the sensor in water indicate that the sensor is an ideal system for the biological and environmental applications. To demonstrate the applicability of the new sensor, the colorimetric responds of sensor were examined for some cations including Fe³⁺, Co²⁺, Ca²⁺, As³⁺, Cd²⁺, Hg²⁺, Pb²⁺, Sn²⁺, Al³⁺, and Cr³⁺. The colorimetric detections of all the ions were performable individually in a solution. In addition, GQD-ARS as a colorimetric sensor detected Co²⁺ at pH < 0.6 with limit of quantification 0.08 mM and Fe³⁺ at 0.6 < pH < 4.0 with limit of quantification 0.03 mM in the mixture of cations.

A built-in self-calibrating luminescence sensor based on RhB@Zr-MOF for detection of cations, nitro explosives and pesticides

A RhB@Zr-MOF composite with dual-emission properties was successfully constructed, which comprises a zirconium-based metal-organic framework and the luminescent dye molecule, Rhodamine B (RhB), embedded via the encapsulation method. The fluorescence intensity ratio of the two emissions was found to be ca. 370 nm/590 nm for RhB@Zr-MOF. The fluorescence intensity values of the two emissions of RhB@Zr-MOF can also be affected by the structures of analytes containing different organic groups. Due to the existence of the dual-emission properties in RhB@Zr-MOF, the relative fluorescence intensity of the emission peaks was introduced as a detection index instead of absolute fluorescence intensity. RhB@Zr-MOF, which possesses the characteristics of a built-in self-calibrating fluorescence sensor, was investigated for detecting cations, nitroaromatics and pesticides. Aside from high sensitivity and selectivity, recyclability is the most important property for sensing pesticides. This work shows that RhB@Zr-MOF can maintain its stability after 5 cycles of detecting nitenpyram, with LOD of 0.2 μM. These results demonstrate that dye@MOFs with dual-emission properties can be employed as multifunctional fluorescence sensors for different types of analytes, and that RhB@Zr-MOF provides a new paradigm for analyte sensing.

Detecting Ferric Iron by Microalgal Residue-Derived Fluorescent Nanosensor with an Advanced Kinetic Model

Biomass-derived carbon quantum dots (CQDs) are attractive to serve as fluorescent nanosensors owing to their superior environmental compatibility and biocompatibility. However, the detection range has been limited, only in partial agreement with the experimental data. Thus, an advanced kinetic model for quantifying the fluorescence quenching over a wide range is on demand. Here, we describe a nanosensor for Fe(Ⅲ) detection in real waters, which is developed via microalgal residue-derived CQDs with an advanced kinetic model. The multiple-order kinetic model is established to resolve the incoherence of previous models and unveil the entire quenching kinetics. The results show that the detection range of Fe(Ⅲ) can reach up to 10 mM in the high detection end. The newly obtained kinetic model exhibits satisfactory fittings, clearly elucidating a dynamic quenching mechanism. This work provides a new insight into CQDs-based detection of heavy metals in real water samples by establishing an innovative multiple-order kinetic model.

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Microalgal residue-derived carbon dots synthesized by hydrothermal method are introduced

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An advanced kinetic model with wide concentration applicability is developed

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Waste biomass-derived Fe(Ⅲ) nanosensor is applied in accurate detection of actual water

Two luminescent dye@MOFs systems as dual-emitting platforms for efficient pesticides detection

Pesticides, which can accumulate in soil, water, animals and plants, are essential to world agriculture. Developing a method that can efficiently and quickly detect toxic pesticides is of importance but still a challenge. Here, two luminescent dye@MOFs systems, Rho B@1 and Rho 6G@1, were successfully fabricated based on [Cd₂(tib)(btb)(H₂O)₂]∙NO₃∙2DMF (1). This work is the first use of two fluorescent sensors as dual-emitting platforms for detecting pesticides. As a result, the fluorescence intensity ratios between the two main emissions can be tuned using the concentrations of the dye solutions, and the emissions are at 370 nm/606 nm and 370 nm/590 nm for Rho B@1 and Rho 6G@1, respectively. The intensities of the two main emissions of Rho B@1 and Rho 6G@1 are also influenced by the chemical structures of pesticides with electron-withdrawing groups. It is important that high sensitivity and selectivity for sensing pesticides must have good recyclability. Rho B@1 and Rho 6G@1 can still remain stable regarding the detection of nitenpyram even after 5 cycles, with LODs of 0.48 nM for Rho B@1 and 3 nM for Rho 6G@1, which indicate that these two luminescent dye@MOFs systems are excellent fluorescence probe candidates for the selective detection of pesticides.

Two novel rhodamine-based fluorescent probes for the rapid and sensitive detection of Fe3+: Experimental and DFT calculations

Fe³⁺ ions play an important role in both biological and environmental field. In this work, two novel rhodamine-based colorimetric and fluorescent probes (RBA2 and RBA3) were designed and synthesized for the efficient detection of Fe³⁺. Upon the addition of Fe³⁺, the fluorescence intensity of RBA2 and RBA3 enhanced 108-fold and 222-fold, respectively. RBA2 and RBA3 exhibited a low detection limit which could achieve 12.8 nM and 11.0 nM. In addition, the binding modes of RBA2 and RBA3 with Fe³⁺ were proved to be 1:1 stoichiometry in the complexes by Job's plot, ESI-MS and ¹H NMR results. The complexing ability of RBA3 with Fe³⁺ excessed to that of RBA2 that was determined by the binding association constants, and highly consistent with DFT calculations results. Furthermore, RBA2 and RBA3 were further utilized to detect Fe³⁺ in living cells and real water samples, indicating their promising prospects in biological and environmental field.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Development of rhodamine-based fluorescent probes for sensitive detection of Fe3+ in water: spectroscopic and computational investigations

Four novel rhodamine-based fluorescent probes (RE1–RE4) were designed and synthesized for sensitive detection of Fe³⁺ in water.

Evaluation of Micronutrient Sensors for Food Matrices in Resource-Limited Settings: A Systematic Narrative Review

In resource-limited settings, mass food fortification is a common strategy to ensure the population consumes appropriate quantities of essential micronutrients. Food and government organizations in these settings, however, lack tools to monitor the quality and compliance of fortified products and their efficacy to enhance nutrient status. The World Health Organization has developed general guidelines known as ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end-users) to aid the development of useful diagnostic tools for these settings. These guidelines assume performance aspects such as sufficient accuracy, reliability, and validity. The purpose of this systematic narrative review is to examine the micronutrient sensor literature on its adherence towards the ASSURED criteria along with accuracy, reliability, and validation when developing micronutrient sensors for resource-limited settings. Keyword searches were conducted in three databases: Web of Science, PubMed, and Scopus and were based on 6-point inclusion criteria. A 16-question quality assessment tool was developed to determine the adherence towards quality and performance criteria. Of the 2,365 retrieved studies, 42 sensors were included based on inclusion/exclusion criteria. Results showed that improvements to the current sensor design are necessary, especially their affordability, user-friendliness, robustness, equipment-free, and deliverability within the ASSURED criteria, and accuracy and validity of the additional criteria to be useful in resource-limited settings. Although it requires further validation, the 16-question quality assessment tool can be used as a guide in the development of sensors for resource-limited settings.

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.

Green synthesis of fluorescent carbon dots from Borassus flabellifer flowers for label-free highly selective and sensitive detection of Fe3+ ions

Fluorescent carbon dots were derived from Borassus flabellifer flowers by thermal pyrolysis method and used for label-free highly selective and sensitive detection of Fe³⁺ ions.

Flexible Graphene-Based Wearable Gas and Chemical Sensors

Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating flexible gas sensors for the detection of various hazardous gases, including nitrogen dioxide (NO₂), ammonia (NH₃), hydrogen (H₂), hydrogen sulfide (H₂S), carbon dioxide (CO₂), sulfur dioxide (SO₂), and humidity in wearable technology, is discussed. In addition, applications of graphene-based materials are also summarized in detecting toxic heavy metal ions (Cd, Hg, Pb, Cr, Fe, Ni, Co, Cu, Ag), and volatile organic compounds (VOCs) including nitrobenzene, toluene, acetone, formaldehyde, amines, phenols, bisphenol A (BPA), explosives, chemical warfare agents, and environmental pollutants. The sensitivity, selectivity and strategies for excluding interferents are also discussed for graphene-based gas and chemical sensors. The challenges for developing future generation of flexible and stretchable sensors for wearable technology that would be usable for the Internet of Things (IoT) are also highlighted.