Determination of primary and secondary oxidation products in vegetable oils with gold nanoparticle based fluorometric turn-on nanosensor: A new total oxidation value

Oxidation of fats and oils gives rise to lipid hydroperoxides as primary oxidation products (POPs) and carbonyl compounds as secondary oxidation products (SOPs). Here, we report the sensitive detection of POPs and SOPs (oxidation products) involving direct and indirect redox reactions with iodide ions, respectively, using the fluorophore probe (fluorescein-5-isothiocyanate-gold nanoparticles; FITC-AuNPs). Iodide released the fluorescent FITC from FITC-AuNPs in the turn-on mode. In case of SOPs, an indirect iodide determination was made through the use of chloramine-T as carbonyl reagent. To various vegetable oil samples, deep frying process (at 160 °C, simulating frying conditions) and soft oil oxidation (at 100 °C, simulating cooking conditions) were carried out for a period of time (1, 5 and 10 days). Total content of POPs varied between 4.00 and 5.70 g TBHP (t-butylhydroperoxide)/kg oil, and the amount of SOPs was found as 1.12-4.11 g t-2-nonenal/kg oil in non-oxidized oil samples. The proposed method was validated against FOX and p-anisidine value (p-AV) assays. Sensory analyses (taste, color, smell and appearance) results of non-oxidized and deep-fried oil samples were consistent with those of the proposed FITC-AuNP nanosensor. Finally, a new total oxidation (TOD) value (expressed as iodide equivalent meq/kg oil) was proposed to determine the overall oxidation state and quality of the oils. Our proposed TOD value is not only mathematically precise with respect to its units (i.e. POPs and SOPs are added up in the same equivalent units to obtain TOD) but also is in better accordance with the results of sensory analysis.

Ultrasensitive iodide detection in biofluids based on hot electron-induced reduction of p-Nitrothiophenol on Au@Ag core-shell nanoparticles

Surveillance of iodine intake is important because either inadequate or excessive amount of iodine may lead to thyroid malfunctions. Herein, we report a method for fast iodide quantification based on a plasmonic hot electron-driven chemical reaction, which occurs on Au@Ag core-shell nanoparticles (NPs) coated with p-nitrothiophenol (PNTP) molecules. Upon resonant light illumination, hot electron-hole pairs are generated in the NPs. The hot holes capture iodide ions (I^-) and form AgI which decomposes under light; while the hot electrons are shifted to the electron orbital (LUMO) of PNTP and trigger its reduction to p-aminothiophenol (PATP). By measuring characteristic surface-enhanced Raman spectroscopic (SERS) peaks of PNTP and PATP, the concentration of I^- in water can be quantitatively determined, with a linear response in the 0.5-20 μM range and a detection limit of 0.30 μM. The Au@Ag nanosensor was then applied for I^- detection in various biofluids including urine, serum and saliva, exhibiting superior detection sensitivity and high selectivity. This sensing assay requires a small sample volume of ∼10 μL and completes the entire detection process in ∼2 min, and therefore holds significant potential for application in point-of-care settings.

Hydrolytically Stable Zr-Based Metal-Organic Framework as a Highly Sensitive and Selective Luminescent Sensor of Radionuclides

Effective detections of radionuclides including uranium and its predominant fission products, for example, iodine, are highly desired owing to their radiotoxicity and potential threat to human health. However, traditional analytical techniques of radionuclides are instrument-demanding, and chemosensors targeted for sensitization of radionuclides remain limited. In this regard, we report a sensitive and selective sensor of UO₂²⁺ and I^- based on the unique quenching behavior of a luminescent Zr-based metal-organic framework, Zr₆O₄(OH)₄(OH)₆(H₂O)₆(TCPE)_1.5·(H₂O)₂₄(C₃H₇NO)₉ (Zr-TCPE). Immobilization of the luminescent tetrakis(4-carboxyphenyl)ethylene (TCPE^4-) linkers by Zr₆ nodes enhances the photoluminescence quantum yield of Zr-TCPE, which facilitates the effective sensing of radionuclides in a "turn-off" manner. Moreover, Zr-TCPE can sensitively and selectively recognize UO₂²⁺ and I^- ions with the lowest limits of detection of 0.67 and 0.87 μg/kg, respectively, of which the former one is much lower than the permissible value (30 μg/L) defined by the U.S. EPA. In addition, Zr-TCPE features excellent hydrolytic stability and can withstand pH conditions ranging from 3 to 11. To facilitate real-world applications, we have further fabricated polyvinylidene fluoride-integrating Zr-TCPE as luminescence-based sensor membranes for on-site sensing of UO₂²⁺ and I^-.

Phenylalanine gold nanoclusters as sensing platform for π-π interfering molecules: a case study of iodide

The photo-physical properties of metal nano clusters are sensitive to their surrounding medium. Fluorescence enhancement, quenching, and changes in the emitted photon properties are usual events in the sensing applications using these nano materials. Combining this sensitivity with unique properties of self-assembled structures opens new opportunities for sensing applications. Here, we synthesized gold nanoclusters by utilizing phenylalanine amino acid as both capping and reducing molecule. Phenylalanine is able to self-assemble to rod-shaped nano structure in which the π-π interaction between the aromatic rings is a major stabilizing force. Any substance as iodide anion or molecule that is able to weaken this interaction influence the fluorescence of metal nano-clusters. Since the building blocks of the self-assembled structure are made through the reaction of gold ions and phenylalanine, the oxidized products and their effect of sensing features are explored.

Biointeraction of Erythrocyte Ghost Membranes with Gold Nanoparticles Fluorescents

The application of new technologies for treatments against different diseases is increasingly innovative and effective. In the case of nanomedicine, the combination of nanoparticles with biological membranes consists of a “camouflage” technique, which improves biological interaction and minimizes the secondary effects caused by these remedies. In this work, gold nanoparticles synthesized by chemical reduction (Turkevich ≈13 nm) were conjugated with fluorescein isothiocyanate to amplify their optical properties. Fluorescent nanoparticles were deposited onto the surface of hemoglobin-free erythrocytes. Ghost erythrocytes were obtained from red blood cells by density gradient separation in a hypotonic medium and characterized with fluorescence, optical, and electron microscopy; the average size of erythrocyte ghosts was 9 µm. Results show that the functional groups of sodium citrate (COO-) and fluorophore (-N=C=S) adhere by electrostatic attraction to the surface of the hemoglobin-free erythrocyte membrane, forming the membrane–particle–fluorophore. These interactions can contribute to imaging applications, by increasing the sensitivity of measurement caused by surface plasmon resonance and fluorescence, in the context of biological membranes.

Enhancement of the Peroxidase-Like Activity of Iodine-Capped Gold Nanoparticles for the Colorimetric Detection of Biothiols

A colorimetric assay was developed for the detection of biothiols, based on the peroxidase-like activity of iodine-capped gold nanoparticles (AuNPs). These AuNPs show a synergetic effect in the form of peroxidase-mimicking activity at the interface of AuNPs, while free AuNPs and iodine alone have weak catalytic properties. Thus, iodine-capped AuNPs possess good intrinsic enzymatic activity and trigger the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), leading to a change in color from colorless to yellow. When added to solution, biothiols, such as cysteine, strongly bind to the interface of AuNPs via gold-thiol bonds, inhibiting the catalytic activity of AuNPs, resulting in a decrease in oxidized TMB. Using this strategy, cysteine could be linearly determined, at a wide range of concentrations (0.5 to 20 μM), with a detection limit of 0.5 μM using UV-Vis spectroscopy. This method was applied for the detection of cysteine in diluted human urine.

Blue luminescent graphene quantum dot conjugated cysteamine functionalized-gold nanoparticles (GQD-AuNPs) for sensing hazardous dye Erythrosine B

Erythrosine B (ErB) is a xanthenes approved dye that widely used in various fields such as foods, drugs and cosmetics. This work intended to analyze the interaction of this dye on synthesized graphene quantum dot conjugated cysteamine functionalized gold nanoparticles. Pyrolysis of citric acid was applied to graphene quantum dots (GQDs) synthesis. These are zero dimensional materials promising considerable applications because of their extraordinary physicochemical properties. In this work, to improve its applications conjugates of GQDs and gold nanoparticles (GQD-AuNPs) are synthesized and characterized with FESEM, TEM, EDX and FTIR techniques. Interaction of ErB with synthesized conjugates was investigated using fluorescence technique and the results demonstrate that ErB can quench fluorescence of GQD-AuNPs conjugates, considerably. At last, we used of this good interaction for construction sensor for detection of ErB in the concentration range of 1.2 nM to 50 nM and the obtained LOD was 0.03 nM (S/N = 3) with correlation coefficient of (99%).

Label-free iodide detection using functionalized carbon nanodots as fluorescent probes

A label-free fluorescent nanoprobe for iodide ion (I^-) detection was developed based on the direct fluorescence quenching of spermine-functionalized carbon dots (SC-dots), whether in complex biological fluids or living cells. The positively charged SC-dots were fabricated via one-step microwave synthesis and exhibited excellent optical properties. Due to the strong quenching ability of I^-, SC-dots were utilized for I^- detection with high sensitivity and excellent selectivity, which offered a relatively low detection limit of 0.18 μM. This strategy was also successfully applied for I^- detections in human serum and HeLa cells. The detection process is facile, highly sensitive and selective, providing a new insight into the potential applications of SC-dots for anion nanoprobe designs in clinical diagnosis and other biologically related areas. Graphical abstract.

Nanostructured hybrid surface enhancement Raman scattering substrate for the rapid determination of sulfapyridine in milk samples

The fabrication of surface-enhanced Raman spectroscopy (SERS) substrates, which can offer the advantages of strong Raman signal enhancement with good reproducibility, is still a challenge for practical applications. In this work, a simple and reproducible SERS substrate combining the properties of multi-walled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs), is proposed for the determination and quantification of sulfapyridine in milk samples with a concentration range of 10-100 ng mL^-1. The Raman signals of sulfapyridine is enhanced at factor of 4394. The procedure presented is capable of detecting and quantifying small quantities of sulfapyridine without implying any preconcentration step, just using an affordable and portable Raman spectrometer. The precision, in terms of repeatability and inter and intermediate precision, was lower than 8% in all cases.

Copper nanoclusters as fluorescence-quenching probes for the quantitative analysis of total iodine

Tannic acid-coated copper nanoclusters (CuNCs@TA) were synthesized and used quantitatively to analyze iodine in kelp. Compared with other methods for iodine detection, the proposed method showed excellent performance. The iodine-induced linear decrease in the fluorescence intensity of CuNCs@TA allowed the quantitative detection of iodine in the range 20-100 μM, and the limit of detection for iodine was 18 nM. The probe can be used for the determination of iodine in real samples with reliable and accurate results. Modified Stern-Volmer equation and thermodynamic calculation studies were used to discuss the quenching mechanism.

Pyridoxal conjugated gold nanoparticles for distinct colorimetric detection of chromium(iii) and iodide ions in biological and environmental fluids

We developed pyridoxal conjugated gold nanoparticles (CAPy-AuNPs) for the selective colorimetric detection of Cr³⁺ and iodide ions in an aqueous medium.

Gold-Nanoparticle-Immobilized Desalting Columns for Highly Efficient and Specific Removal of Radioactive Iodine in Aqueous Media

There has been worldwide attention on the efficient removal of radioactive iodine, because it is commonly released in nuclear plant accidents. Increasing concerns on environmental problems due to the radioactive iodine are leading us to develop stable and sustainable technology for remediation of radioelement contaminants. In this work, we report a highly efficient chromatographic method for specific and rapid capture of radioactive iodine. The gold nanoparticles immobilized dextran gel columns showed excellent removal capabilities of radioactive iodine in various conditions. These results suggested that our platform technology can be a promising method for the desalination of radioactive iodines in water.

Interaction of glucose-derived carbon quantum dots with silver and gold nanoparticles and its application for the fluorescence detection of 6-thioguanine

The interaction of glucose-derived carbon quantum dots (CQDs) with silver (Ag) and gold (Au) nanoparticles (NPs) was explored by fluorescence spectroscopy. Both metal NPs cause an efficient quenching of CQD fluorescence, which is likely due to the energy transfer process between CQDs as donors and metal NPs as acceptors. The Stern-Volmer plots were evaluated and corresponding quenching constants were found to be 1.9 × 10¹⁰ and 2.2 × 10⁸ M^-1 for AgNPs and AuNPs, respectively. The analytical applicability of these systems was demonstrated for turn-on fluorescence detection of the anti-cancer drug, 6-thioguanine. Because the CQD-AgNP system had much higher sensitivity than the CQD-AuNP system, we used it as a selective fluorescence probe in a turn-on assay of 6-thioguanine. Under optimum conditions, the calibration graph was linear from 0.03 to 1.0 μM with a detection limit of 0.01 μM. The developed method was applied to the analysis of human plasma samples with satisfactory results.

In vivo mapping and assay of matrix metalloproteases for liver tumor diagnosis

A fluorescent probe constructed by simultaneous modification of FITC-grafted peptide and thiolated mPEG on the surface of gold nanoparticles forin vivomapping and assay of matrix metalloproteases.

Spectroscopic and electron microscopic analysis of bi-ligand functionalized glycopolymer/FITC–gold nanoparticles

We report a strategy to quantify the relative binding affinity of glycopolymers on FITC-AuNP by release of the FITC via self-assembly process and which was improved by introducing a PEG segment to the glycopolymer of similar functionalities.

Synthesis of “amphiphilic” carbon dots and their application for the analysis of iodine species (I2, I− and IO3−) in highly saline water

In this work, “amphiphilic” carbon dots (A-CDs) with a strong green fluorescence were synthesized by a simple and green method at room temperature, and the synthesized A-CDs could be used for the analysis of iodine species (I₂, I⁻ and IO₃⁻) in highly saline water.

Ultrasensitive turn-on fluorescent detection of trace thiocyanate based on fluorescence resonance energy transfer

Thiocyanate (SCN(-)) is a small anion byproduct of cyanide metabolism. Several methods have been reported to measure SCN(-) above the micromolar level. However, SCN(-) is derived from many sources such as cigarettes, waste water, food and even car exhaust and its effect is cumulative, which makes it necessary to develop methods for the detection of trace SCN(-). In this paper, a simple and ultrasensitive turn-on fluorescence assay of trace SCN(-) is established based on the fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and fluorescein. The detection limit is 0.09 nM, to the best of our knowledge, which has been the lowest detection LOD ever without the aid of costly instrumentation. The fluorescence of fluorescein is significantly quenched when it is attached to the surface of AuNPs. Upon the addition of SCN(-), the fluorescence is turned on due to the competition action between SCN(-) and fluorescein towards the surface of AuNPs. Under an optimum pH, AuNPs size and concentration, incubation time, the fluorescence enhancement efficiency [(IF-I0)/I0] displays a linear relationship with the concentration of SCN(-) in the range of 1.0 nM to 40.0 nM. The fluorescein-AuNP sensor shows absolutely high selectivity toward SCN(-) than other 16 anions. The common metal ions, amino acids and sugars have no obvious interference effects. The accuracy and precision were evaluated based on the recovery experiments. The cost effective sensing system is successfully applied for the determination of SCN(-) in milk products and saliva samples.

A surface enhanced Raman scattering probe for highly selective and ultra sensitive detection of iodide in water and salt samples

Iodine is a biophilic and essential trace element for all life and especially for vertebrates, which require it to produce indispensable thyroid hormones in their thyroid glands. As a result, the adequate measurement of iodine in water and food samples is crucial to lead a healthy life. Motivated by its importance, this is the first time in the literature that the highly selective and ultra sensitive (30 ppt limit) surface enhanced Raman scattering (SERS)-based detection of iodide ions (I(-)) from environmental and food samples has been reported. The desired sensitivity and selectivity has been achieved by measuring the change in the SERS intensity originating from Rh6G-adsorbed 30 nm gold nanoparticles (GNPs) upon the addition of I(-). The strong chemical affinity offered by I(-) towards the gold surface results in extra negative charge being deposited on it. As a result, the GNP surface attracts a greater number of positively charged Rh6G molecules and induces a marked increase in the number of hot spots through aggregation, providing a significant enhancement of the Raman signal intensity. The oxidation of I(-) to molecular iodine (I(2)) by hydrogen peroxide (H(2)O(2)) is employed for the successful screening of the bromide ion (Br(-)) which shows substantial interference at higher concentrations.

Ultra-small gold nanoparticles synthesized in aqueous solution and their application in fluorometric collagen estimation using bi-ligand functionalization

Ultra-small hydrosol LBH-AuNPs were synthesized, and their application in the FRET based estimation of collagen investigated using bi-ligand functionalised LBH-AuNPs.

Au25(SG)18 as a fluorescent iodide sensor

The recently emerging gold nanoclusters (GNC) are of major importance for both basic science studies and practical applications. Based on its surface-induced fluorescence properties, we investigated the potential use of Au(25)(SG)(18) (GSH: glutathione) as a fluorescent iodide sensor. The current detection limit of 400 nM, which can possibly be further enhanced by optimizing the conditions, and excellent selectivity among 12 types of anion (F(-), Cl(-), Br(-), I(-), NO(3)(-), ClO(4)(-), HCO(3)(-), IO(3)(-), SO(4)(2-), SO(3)(2-), CH(3)COO(-) and C(6)H(5)O(7)(3-)) make Au(25)(SG)(18) a good candidate for iodide sensing. Furthermore, our work has revealed the particular sensing mechanism, which was found to be affinity-induced ratiometric and enhanced fluorescence (abbreviated to AIREF), which has rarely been reported previously and may provide an alternative strategy for devising nanoparticle-based sensors.

Exploiting the light–metal interaction for biomolecular sensing and imaging

The ability of metal surfaces and nanostructures to localize and enhance optical fields is the primary reason for their application in biosensing and imaging. Local field enhancement boosts the signal-to-noise ratio in measurements and provides the possibility of imaging with resolutions significantly better than the diffraction limit. In fluorescence imaging, local field enhancement leads to improved brightness of molecular emission and to higher detection sensitivity and better discrimination. We review the principles of plasmonic fluorescence enhancement and discuss applications ranging from biosensing to bioimaging.

Selective detection of iodide and cyanide anions using gold-nanoparticle-based fluorescent probes

We developed two simple, rapid, and cost-effective fluorescent nanosensors, both featuring bovine serum albumin labeled with fluorescein isothiocyanate (FITC))-capped gold nanoparticles (FITC-BSA-Au NPs), for the selective sensing of cyanide (CN(-)) and iodine (I(-)) ions in high-salinity solutions and edible salt samples. During the preparation of FITC-BSA-Au NP probes, when AuNPs were introduced to the mixture containing FITC and BSA, the unconjugated FITC and FITC-labeled BSA (FITC-BSA) adsorbed to the particles' surfaces. These probes operated on a basic principle that I(-) and CN(-) deposited on the surfaces of the Au NPs or the etching of Au NPs induced the release of FITC molecules or FITC-BSA into the solution, and thus restored the florescence of FITC. We employed FITC-BSA to protect the Au NPs from significant aggregation in high-salinity solutions. In the presence of masking agents such as S(2)O(8)(2-)/Pb(2+), FITC-BSA-Au NPs facilitated the selective detection of CN(-) (by at least 150-fold in comparison with other anions). We also demonstrated that the FITC-BSA-Au NPs in the presence of H(2)O(2) could selectively detect I(-) down to 50 nM. Taking advantages of their high stability and selectivity, we employed our FITC-BSA-Au NP-based probes for the detection of CN(-) and I(-) in water samples (pond water, tap water, and seawater) and detection of I(-) in edible salt samples, respectively. This simple, rapid, and cost-effective sensing system appears to demonstrate immense practical potential for the detection of anions in real samples.

Supramolecular complexation for environmental control

Supramolecular complexes offer a new and efficient way for the monitoring and removal of many substances emanating from technical processes, fertilization, plant and animal protection, or e.g. chemotherapy. Such pollutants range from toxic or radioactive metal ions and anions to chemical side products, herbicides, pesticides to drugs including steroids, and include degradation products from natural sources. The applications involve usually fast and reversible complex formation, due to prevailing non-covalent interactions. This is of importance for sensing as well as for separation techniques, where the often expensive host compounds can then be reused almost indefinitely. Immobilization of host compounds, e.g. on exchange resins or on membranes, and their implementation in smart new materials hold particular promise. The review illustrates how the design of suitable host compounds in combination with modern sensing and separation methods can contribute to solve some of the biggest problems facing chemistry, which arise from the everyday increasing pollution of the environment.

Gold nanoparticles for the colorimetric and fluorescent detection of ions and small organic molecules

In recent years, gold nanoparticles (AuNPs) have drawn considerable research attention in the fields of catalysis, drug delivery, imaging, diagnostics, therapy and biosensors due to their unique optical and electronic properties. In this review, we summarized recent advances in the development of AuNP-based colorimetric and fluorescent assays for ions including cations (such as Hg(2+), Cu(2+), Pb(2+), As(3+), Ca(2+), Al(3+), etc) and anions (such as NO(2)(-), CN(-), PF(6)(-), F(-), I(-), oxoanions), and small organic molecules (such as cysteine, homocysteine, trinitrotoluene, melamine and cocaine, ATP, glucose, dopamine and so forth). Many of these species adversely affect human health and the environment. Moreover, we paid particular attention to AuNP-based colorimetric and fluorescent assays in practical applications.