Detection of Fe(III)EDTA by using photoluminescent carbon dot with the aid of F- ion

Food Additives and Evolved Methods of Detection: A Review

Food additives are essential constituents of food products in the modern world. The necessity of food processing went up rapidly as to meet requirements including, imparting desirable properties like preservation, enhancement and regulation of color and taste. The methods of identification and analysis of such substances are crucial. With the advancement of technology, a variety of techniques are emerging for this purpose which have many advantages over the existing conventional ways. This review is on different kinds of additives used in the food industry and few prominent methods for their determination ranging from conventional chromatographic techniques to the recently evolved nano-sensor techniques.

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.

"Switch-Off-On" Detection of Fe3+ and F- Ions Based on Fluorescence Silicon Nanoparticles and Their Application to Food Samples

An approach to the detection of F⁻ ions in food samples was developed based on a “switch-off-on” fluorescence probe of silicon nanoparticles (SiNPs). The fluorescence of the synthetic SiNPs was gradually quenched in the presence of Fe³⁺ ion and slightly recovered with the addition of F⁻ ion owing to the formation of a stable and colorless ferric fluoride. The fluorescence recovery exhibited a good linear relationship (R² = 0.9992) as the concentration of F⁻ ion increased from 0 to 100 μmol·L⁻¹. The detection limit of the established method of F⁻ ion was 0.05 μmol·L⁻¹. The recovery experiments confirmed the accuracy and reliability of the proposed method. The ultraviolet–visible spectra, fluorescence decays, and zeta potentials evidenced the fluorescence quenching mechanism involving the electron transfer between the SiNPs and Fe³⁺ ion, while the fluorescence recovery resulted from the formation of ferric fluoride. Finally, SiNPs were successfully applied to detect F⁻ ions in tap water, Antarctic krill, and Antarctic krill powder.

Dual-excitation and dual-emission carbon dots for Fe3+ detection, temperature sensing, and lysosome targeting

Dual-excitation and dual-emission carbon dots (CDs) have been prepared by simple one-step hydrothermal treatment of p-phenylenediamine and 5-aminosalicylic acid. The as-prepared CDs emit bright green fluorescence under excitation at 320-400 nm and bright orange fluorescence under excitation at 490-560 nm. Interestingly, the CDs can be employed as a dual-excitation and dual-emission fluorescent probe for Fe³⁺ detection in aqueous solution and living cells. Furthermore, the obtained CDs can function as a promising dual-excitation and dual-emission temperature sensor. Additionally, the CDs can be utilized for lysosomal targeting.

Simple and Sensitive Multi-components Detection Using Synthetic Nitrogen-doped Carbon Dots Based on Soluble Starch

Although carbon dots (CDs) as fluorescent sensors have been widely exploited, multi-component detection using CDs without tedious surface modification is always a challenging task. Here, two kinds of nitrogen-doped CDs (NCD-m and NCD-o) based on soluble starch (SS) as carbon source were prepared through one-pot hydrothermal process using m-phenylenediamine and o-phenylenediamine as nitrogenous dopant respectively. Through fluorescence "on-off" mechanism of CDs, NCD-m and NCD-o could be used as a fluorescence sensor for detection of Fe ³⁺ and Ag ⁺ with LOD of 0.25 and 0.51 μM, respectively. Additionally, NCD-m could be used for indirect detection of ascorbic acid (AA) with LOD of 5.02 μM. Moreover, fluorescence intensity of NCD-m also exhibited the sensitivity to pH change from 2 to 13. More importantly, Both NCD-m and NCD-o had potential application for analysis of complicated real samples such as tap water, Vitamin C tablets and orange juice. Ultimately, the small size of NCD-m could contribute to reinforcing intracellular endocytosis, which allowed them to be used for bacteria imaging. Obviously, these easily obtainable nitrogen-doped CDs were able to be used for multi-components detection. Strategy for synthesis of nitrogen-doped carbon dots (NCDs) and a schematic for fabrication of as-prepared NCDs for detection of Fe ³⁺, Ag ⁺ and ascorbic acid (AA).

Continuous response fluorescence sensor for three small molecules based on nitrogen-doped carbon quantum dots from prunus lannesiana and their logic gate operation

In this study, an environmentally friendly and water-soluble nitrogen-doped carbon quantum dots (N-CQDs) with quantum yield (QY) of 8.59% were prepared by one-step hydrothermal synthesis without any chemical reagent using the leaves of prunus lannesiana as precursors. The properties and quality of N-CQDs were investigated by Ultraviolet-visible absorption spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential, high-resolution transmission electron microscopy and fluorescence spectroscopy. The fluorescence of the prepared N-CQDs can be quenched by Fe³⁺ through the synergistic effect of the formation of non-fluorescent complex and internal filtration effect (IFE) between Fe³⁺ and N-CQDs. And the quenched fluorescence can be "turned on" after adding ascorbic acid (AA) because Fe³⁺ can be released from the surface of N-CQDs through the redox reaction between AA and Fe³⁺. While the restored fluorescence can be "turned off" again by hydrogen peroxide (H₂O₂) due to the re-oxidation of Fe²⁺ to Fe³⁺. So, the three inputs "logic gate" is achieved and the "on-off-on-off" continuous response fluorescence sensor is formed, which can be applied for the continuous detection of Fe³⁺, AA and H₂O₂ with the linear range of 40-260 μM, 10-200 μM and 40-140 μM, respectively. Finally, the sensor was successfully applied to determine Fe³⁺, AA and H₂O₂ in real samples with the satisfactory recoveries (95.35%-104.10%) and repeatability (relative standard deviation (RSD) ≤ 1.68%). The continuous response fluorescence sensor prepared by simple green synthesis route has the characteristics of fast response, acceptable sensitivity and good selectivity.

Determination of melamine in milk based on β-cyclodextrin modified carbon nanoparticles via host-guest recognition

Illegal addition of melamine (MEL) to milk has caused serious food safety accident. It is urgent to develop a highly sensitive method for detecting MEL in milk. β-Cyclodextrin with inner hydrophobic and outer hydrophilic cavities have been widely used in smart sensors design. In this study, an "ON-OFF-ON" sensor for MEL detection was constructed based on β-cyclodextrin modified carbon nanoparticles (β-CD-CNPs). The sensor is switched "OFF" when Fe³⁺ interacts with β-CD-CNPs and switched "ON" when MEL replaces Fe³⁺. Fluorescence recovery of β-CD-CNPs exhibits good linear correlations with MEL concentration ranging from 10.00 ng/mL ~ 180.00 ng/mL and 180.00 ~ 1000.00 ng/mL, the detection limit is 6.82 ng/mL. The sensor was applied to analysis melamine in milk samples with recovery between 94.80% ~ 102.05%, and RSD bellow 12.61%. The results show that this method can meet the requirements of real sample analysis.

Economical, green and rapid synthesis of CDs-Cu2O/CuO nanotube from the biomass waste reed as sensitive sensing platform for the electrochemical detection of hydrazine

Reeds live widely in swamp and wetland and have an important ecological balance functions in environmental protection. However, the use of reeds is not effectively. The carbon dots (CDs) have been developed as the family of 0D nanocarbon materials and have all the advantages of the carbon family. In this work, we prepared CDs via hydrothermal method using reed. It is surprising that the reed-derived CDs are an effective reducing agent. A highly catalytically active composite material CDs-Cu₂O/CuO was synthesized using economical, green, one-step ultrasonic method and used for the detection of hydrazine. The electrochemical detection of hydrazine was investigated by cyclic voltammetry. The result shows that the CDs-Cu₂O/CuO exhibited good electrocatalytic activity for the oxidation of hydrazine. The fabricated sensor presented a wide linear range from 0.99 μM to 5903 μM and a detection limit of 0.024 μM. In addition, the CDs-Cu₂O/CuO exhibited good sensitivity, stability and repeatability. Therefore, the CDs-Cu₂O/CuO provides a new idea for the utilization of reed and low-cost electrocatalytic nanocomposite.

Green and facile synthesis of water-soluble carbon dots from ethanolic shallot extract for chromium ion sensing in milk, fruit juices, and wastewater samples

Self-functionalized carbon dots (CDs) were prepared from ethanolic shallot extract to obtain a total phenolic precursor.

Reed-derived fluorescent carbon dots as highly selective probes for detecting Fe3+ and excellent cell-imaging agents

A kind of highly selective and sensitive fluorescent probe for detecting Fe3+, carbon dots (CDs), was prepared with renewable reed naturally containing C, N, O, and S elements as a green and eco-friendly carbon source by a simple hydrothermal process. The fluorescence of CDs without purification and surface modification can be quenched by Fe3+ in a wide concentration range of 0 to 362 μmol L-1 (concentration of Fe3+), with detection limits as low as 0.014 μmol L-1 in 0-50 μmol L-1. Characterizations, such as TEM, XPS, Raman and FTIR, confirmed that the static quenching mechanism involved the generation of non-luminescent complexes between Fe3+ and functional groups (carboxyl group, sulfur-oxyl group and hydroxyl group) on the surface of CDs and with the aggregation of CDs. More importantly, CDs had good biocompatibility and nontoxicity according to an MTT cell-viability assay, and cells labeled with CDs emitted blue, green and red color fluorescence. Thus, the static quenching mechanism was confirmed. So, this reed-derived natural CD solution can be utilized in detecting Fe3+, culture cells, and cell imaging.

Light and ferric ion responsive fluorochromic hydrogels with high strength and self-healing ability

Here, light and ferric ion (Fe³⁺) responsive fluorochromic hydrogels with high strength and self-healing ability were designed and synthesized.