Simultaneous determination of cadmium and iron in different kinds of cereal flakes using high-resolution continuum source atomic absorption spectrometry

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.

Sensitive detection of cadmium ions based on a quantum-dot-mediated fluorescent visualization sensor

A sensitive ratiometric fluorescent sensor for detecting cadmium ions (Cd2+) was constructed based on carbon quantum dots (CQDs)/CdTe quantum dots (CdTe QDs). Red fluorescence (from CdTe QDs) played the role of the signal response and blue fluorescence (from CQDs) served as a reference probe without a color change. The fluorescent sensor showed high selectivity and sensitivity to Cd2+ with a limit of detection (LOD) of 0.018 μM and a range from 0.1 μM to 23 μM. The proposed method was successfully applied to the determination of Cd2+ in real rice samples. In addition, a fluorescent sensor integrated with a smartphone platform was further designed for the visualized and quantitative detection of Cd2+. This work might extend the range of visualization analysis strategies and provide new insights into the rapid quantitative, portable and sensitive detection of Cd2+ in real-time and on-site applications.

The Effect of Flake Production and In Vitro Digestion on Releasing Minerals and Trace Elements from Wheat Flakes: The Extended Study of Dietary Intakes for Individual Life Stage Groups

This thorough study analyses the amounts of 43 minerals and trace elements in non-traditional wheat grains, flakes, and undigested flake portions using ICP-MS and establishes declines in their respective contents after the flake production. It also identifies appropriate dietary intakes, in vitro digestibility values, retention factors, and metal pollution indexes. The element contents in wheat flakes are lower than in wheat grains after the hydrothermal treatment process, and their declines are: Na (48-72%), Ce (47-72%), Sr (43-55%), Tl (33-43%), Ti (32-41%), U (31-44%), Ho (29-69%), Cr (26-64%), Zr (26-58%), Ag (25-52%), and Ca (25-46%). The flakes significantly contributed to the recommended dietary intake or adequate intake of particular elements for men of all categories as follows: Mn (143%) > Mo > Cu > Mg ≥ Cr > Fe (16%); for women: Mn (up to 183%) > Mo > Cu > Cr ≥ Mg > Fe (7-16%); for pregnant women aged 19-30: Mn (165%) > Mo > Cu > Mg > Cr (25%); and finally, for lactating women: Mn (127%) > Mo > Cu > Mg > Cr (17%). The contributions to the provisional tolerable weekly or monthly intakes of all toxic elements were established as being within the official limits. The daily intakes for non-essential elements were also calculated. The retention factors were calculated to assess the element concentrations in the undigested part using the digestibility values (87.4-90.5%). The highest retention factors were obtained for V (63-92%), Y (57-96%), Ce (43-76%), Pb (34-58%), Tl (32-70%), Ta (31-66%), and Ge (30-49%). K, Mg, P, Zn, Ba, Bi, Ga, Sb, Cu, Ni, and As appear to be released easily from flake matrices during digestion. The metal pollution index has been confirmed as being lower for non-traditional wheat flakes when compared with grains. Importantly, 15-25% of the metal pollution index assessed for native flakes remains in the undigested flake portion after in vitro digestion.

Stalk-derived carbon dots as nanosensors for Fe3+ ions detection and biological cell imaging

Introduction: Iron is one of the most important needed elements for the growth and reproduction of living organisms. The detection of iron levels is important and developing fluorescent probes with excellent sensitivity for Fe³⁺ ions is of great significance. Carbon dot (CDs) is a new type of fluorescent nanomaterial based on abundant and low-cost carbon elements. The use of widely distributed renewable agricultural waste straw as a carbon precursor to prepare CDs sensor can not only reduce the pollution caused by burning straw to the atmospheric environment, but also achieve the transformation of resources from waste to treasure. Methods: In this study, CDs were obtained from corn stalk powder by pyrolysis and microwave process. The sensitivity and linear response range of CDs sensor was studied through analyzing the effect of different Fe³⁺ ions concentrations on the fluorescence quenching. The application of CDs in biological cell imaging was investigated using HGC-27 cells. Results: The fluorescence quenching showed a good linear relationship with the Fe3+ concentration in the range from 0 to 128 μM, and a low detection limit of 63 nM. In addition, the CDs have high recognition for Fe3+ ions. Meanwhile, the CDs have a low cytotoxicity and desirable biocompatibility, allowing the multicolor living cell imaging. Conclusion: The prepared CDs can be used as fluorescent sensors for the selective detection of Fe³⁺ ions and biological cell imaging. Our results supported that the conversion of agricultural waste into carbon nanomaterials has great potential to be developed.

Sensing Cd(II) Using a Disposable Optical Sensor Based on a Schiff Base Immobilisation on a Polymer-Inclusion Membrane. Applications in Water and Art Paint Samples

A disposable colour-changeable optical sensor based on an interesting polymer inclusion-membrane (PIM) was designed to determine Cd(II) ions in aqueous medium. The Schiff base 2-acetylpyridine benzoylhydrazone (2-APBH) immobilised on the polymer membrane was used as a sensing molecule. The amounts of the PIM components were optimised by a 3² fractional factorial design with two central points and two blocks. The best optical sensor composition consisted of 2.5 g of poly(vinylchloride) (PVC) as a base polymer, 3 mL of tributyl phosphate (TBP) as a plasticiser, and 0.02 g of 2-APBH as a reagent. The sensor showed a good linear response in the range from 0.02 mg L⁻¹ (limit of detection) to 1 mg L⁻¹ of Cd(II) under the following experimental conditions: pH 9.5 (adjusted using ammonium chloride buffer solution at 0.337 mol L⁻¹), 60 min of exposure time plus 2 min of sonication (pulses at 2 s intervals), and 10 min of short-term stability. The relative standard deviation of the method was determined to be 4.04% for 0.4 mg L⁻¹ of Cd(II). The optical sensor was successfully applied to the determination of Cd(II) in natural-water and art-paint samples.

Cheap and sensitive polymer/bismuth film modified electrode for simultaneous determination of Pb(II) and Cd(II) ions

Different aminonaphetalenesulphonic acid derivatives like 5-aminonaphthalene-1-sulphonic acid (5AN1SA), 2-aminonaphthalene-1-sulphonic acid (2AN1SA), 8-aminonaphthalene-2-sulphonic acid (8AN2SA) and 4-amino-3-hydroxynaphthalene-1-sulphonic acid (4A3HN1SA) were used to construct polymer/bismuth film modified electrode for simultaneous determination of Pb(II) and Cd(II) ions with the aim of developing a cheaper and sensitive electrode that could possibly replace Nafion. Among the different modified electrodes, poly (8AN2SA)/bismuth film modified electrodes showed the highest electrochemical response for both ions. These electrochemical results were also supported by density functional theory (DFT) calculations. Based on these experimental and theoretical results, poly (8AN2SA)/bismuth film glassy carbon modified electrode was further investigated to develop a simple and sensitive electrochemical method for the simultaneous determination of Pb(II) and Cd(II) ions. After optimizing the different experimental parameters, the proposed method gave a linear range of 1-40 μg/L with the detection limit of 0.38 and 0.08 μg/L for the simultaneous determination of Pb(II) and Cd(II) ions, respectively.

A bi-modal, cellulose-based sensor for fluorometric detection of Fe(III) and antimicrobial studies of its silver-loaded form

The study reports designing of a new, low-cost and environmentally friendly colorimetric and fluorometric sensor by using cellulose-based materials for detection and determination of Fe(III). To make powder cellulose (Cel) and filter paper (PCel) fluorescent, they were modified with hexamethylene diisocyanate (HMDI) and 4-sulfo-1,8-naphthalimide (Nap). Fluorescent Cel-Nap and PCel-Nap materials were used for spectroscopic detection of Fe(III). The working range of the designed sensor was determined as 1.0 × 10^-5-4.5 × 10^-5 M with a low limit of detection (LOD) (7.51 μM). Antimicrobial properties of cel-based compounds and Ag(I)-containing compounds were tested against five bacteria; Bacillus cereus, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and two fungi; Candida albicans and Candida tropicalis. The materials exhibited antimicrobial effects and their antifungal properties were more effective than their antibacterial properties.

On-site, rapid and visual method for nanomolar Hg2+ detection based on the thymine–Hg2+–thymine triggered “double” aggregation of Au nanoparticles enhancing the Tyndall effect

This work describes a new nanosensor for the simple, rapid, portable, colorimetric analysis of mercury(ii) (Hg²⁺) ions by combining the sensitive Tyndall effect (TE) of colloidal Au nanoparticles (AuNPs) with specific thymine–Hg²⁺–thymine (T–Hg²⁺–T) coordination chemistry for the first time. For the TE-inspired assay (TEA), in the presence of Hg²⁺ in a sample, the analyte can selectively mediate the hybridization of three types of flexible single-stranded DNAs (ssDNAs) to form stable rigid double-stranded DNAs (dsDNAs) via the T–Hg²⁺–T ligand interaction. Subsequent self-assembly of the dsDNAs with terminal thiol groups on the AuNPs' surfaces led to their “double” aggregation in addition to the lack of sufficient ssDNAs as the stabilizing molecules in a high-salt solution, resulting in a remarkably enhanced TE signal that positively relied on the Hg²⁺ level. The results demonstrated that such a TEA method enabled rapid naked-eye qualitative analysis of 625 nM Hg²⁺ within 10 min with an inexpensive laser pointer pen as an inexpensive handheld light source to generate the TE response. Making use of a smartphone for portable TE readout could further quantitatively detect the Hg²⁺ ions in a linear concentration range from 156 to 2500 nM with a limit of detection as low as 25 nM. Moreover, the developed equipment-free nanosensor was also used to analyze the Hg²⁺ ions in real samples including tap water, drinking water, and pond water, the obtained recoveries were within the range of 93.68 to 108.71%. To the best of our knowledge, this is the first report of using the AuNPs and functional nucleic acids to design a TE-based biosensor for the analysis of highly toxic heavy metal ions.

A new equipment-free colorimetric nanosensor was initially developed for quantitative point-of-need detection of nanomolar Hg²⁺ ions based on the enhancement in Tyndall effect of Au nanoparticles via their target-triggered “double” aggregation.

Chitosan/thiol functionalized metal-organic framework composite for the simultaneous determination of lead and cadmium ions in food samples

In this work, a facile solid phase extraction (SPE) method was developed for the analysis of trace Pb²⁺ and Cd²⁺ by using chitosan/thiol modified metal-organic frameworks (CS/MOF-SH) composite as adsorbent followed by graphite furnace atomic absorption spectrometer (GF-AAS) detection. The potential influencing factors, such as solution pH, adsorbent dosage, and extraction time, were fully estimated. Under the optimized extraction conditions, the detection limits of Pb²⁺ and Cd²⁺ were 0.033 µg L^-1 and 0.008 µg L^-1, respectively. Compared to other studies, CS/MOF-SH not only possessed superior adsorption performance, but also had the advantages of ease of handling and recyclability. Encouragingly, the developed method was of high accuracy and could monitor trace Pb²⁺ and Cd²⁺ in various certified reference materials (rice, wheat and tea) with complicated matrices, demonstrating its practical potential for regular monitoring of trace heavy metal ions in real food samples.

Preconcentration with Chlorella vulgaris combined with energy dispersive X-ray fluorescence spectrometry for rapid determination of Cd in water

Freshwater green algae Chlorella vulgaris was selected as an adsorbent, and a simple, rapid, economical and environmentally friendly method for the detection of heavy metal Cd in water samples based on preconcentration with C. vulgaris combined with energy dispersive X-ray fluorescence (EDXRF) spectrometry was proposed.  Chlorella vulgaris could directly and rapidly adsorb Cd²⁺ without any pretreatment, and the maximum adsorption efficiency could be obtained when the contact time was 1 min with an optimal pH of 10. The obtained Cd-enriched thin samples after preconcentration with C. vulgaris by suction filtration of reaction solution had very good uniformity, which could be directly measured by EDXRF spectrometry, and the net integral fluorescence intensity of Cd Kα characteristic peak had a very good linear relationship with the initial concentration of Cd in the range of 0.703-74.957 µg ml^-1 with a correlation coefficient of 0.9979. When the Cd thin samples with a Cd-enriched region of 15.1 mm in diameter were formed by the developed preconcentration method with suction filtration of 10 ml reaction solution, the detection limit of this method was 0.0654 µg ml^-1, which was lower than the maximum allowable discharge concentration of Cd in various industrial wastewaters. The proposed method was simple to operate, and could effectively remove the influence of matrix effect of water samples and effectively improve the sensitivity and stability of EDXRF spectrometry directly detecting heavy metals in water samples, which was successfully applied to detect Cd in real water samples with satisfactory results, and the recoveries ranged from 94.80% to 116.94%. Moreover, this method can be applied to the rapid detection and early warning of excessive Cd in discharged industrial wastewaters. This work will provide a methodological basis for the development of rapid and online monitoring technology and instrument of heavy metal pollutants in water.

Ammonium Pyrrolidine Dithiocarbamate-Modified CdTe/CdS Quantum Dots as a Turn-on Fluorescent Sensor for Detection of Trace Cadmium Ions

In this work, ammonium pyrrolidine dithiocarbamate (APDC) was used as a surface etchant to modify CdTe/CdS core-shell quantum dots (QDs). The APDC etchant combines with the cadmium ions (Cd²⁺) on the surface of the QDs, resulting in the formation of surface holes. The formation of these holes changes the QD surface structure, which leads to fluorescence quenching of the QDs. Newly added Cd²⁺ can selectively recognize and combine with these holes; thus, the fluorescence intensity of the QDs can be restored. The linear response of this turn-on fluorescent sensor was found to be 0-100 μg/L and 100-600 μg/L under the determined optimal conditions, and its limit of detection (LOD) for Cd²⁺ was 2.642 μg/L (23.5 nmol/L).

Thiolated poly(aspartic acid)-functionalized two-dimensional MoS2, chitosan and bismuth film as a sensor platform for cadmium ion detection

In this work, a sensitive electrochemical platform for determination of cadmium ions (Cd²⁺) is obtained using thiolated poly(aspartic acid) (TPA)-functionalized MoS₂ as a sensor platform by differential pulse anodic stripping voltammetry (DPASV). The performance of the TPA–MoS₂-modified sensor is systemically studied. It demonstrates that the TPA–MoS₂ nanocomposite modified sensor exhibits superior analytical performance for Cd²⁺ over a linear range from 0.5 μg L⁻¹ to 50 μg L⁻¹, with a detection limit of 0.17 μg L⁻¹. Chitosan is able to form a continuous coating film on the surface of the GC electrode. The good sensing performance of the TPA–MoS₂-modified sensor may be attributed to the following factors: the large surface area of MoS₂ (603 m² g⁻¹), and the abundant thiol groups of TPA. Thus, the TPA–MoS₂-modified sensor proves to be a reliable and environmentally friendly tool for the effective monitoring of Cd²⁺ existing in aquacultural environments.

In this work, a sensitive electrochemical platform for determination of cadmium ions (Cd²⁺) is obtained using thiolated poly(aspartic acid) (TPA)-functionalized MoS₂ as a sensor platform by differential pulse anodic stripping voltammetry (DPASV).