Sudan I Research Articles

The effect of methyl yellow concentrations on the optical properties of polyvinyl chloride-methyl yellow film as a radiation dosimeter

A dosimetry system's ability to monitor absorbed doses is crucial for the quality assurance and control of products that have been exposed to radiation. Here, we propose a polyvinyl chloride (PVC)-methyl yellow (MY) film as a potential dosimeter for irradiation facilities. The PVC-MY film was prepared with a simple solvent-casting method at different MY concentrations from 0.3 to 1.2 mM. To evaluate the dosimeter's performance, the film was exposed to gamma-irradiation with irradiation doses of 0–25 kGy. The optical characteristics of the films examined using a UV–Vis spectrophotometer showed that the color of the films changed from yellow to red with increasing irradiation doses, and the color change sensitivity of the films increased with increasing MY concentrations. The absorption spectra of the irradiated PVC-MY films showed three maximum absorption peaks at 417, 522, and 547 nm. As irradiation doses increased, the film absorption at 417 nm decreased, while the film absorption at 522 and 547 nm increased. The film's stability studies suggest storage of the irradiated film in a cold-dark conditions is recommended to prevent damage and maintain response stability. The findings in this study emphasize the potential of the PVC-MY film as a dosimeter for irradiation facilities.

Multi-omics bioactivity profile-based chemical grouping and read-across: a case study with Daphnia magna and azo dyes

Grouping/read-across is widely used for predicting the toxicity of data-poor target substance(s) using data-rich source substance(s). While the chemical industry and the regulators recognise its benefits, registration dossiers are often rejected due to weak analogue/category justifications based largely on the structural similarity of source and target substances. Here we demonstrate how multi-omics measurements can improve confidence in grouping via a statistical assessment of the similarity of molecular effects. Six azo dyes provided a pool of potential source substances to predict long-term toxicity to aquatic invertebrates (Daphnia magna) for the dye Disperse Yellow 3 (DY3) as the target substance. First, we assessed the structural similarities of the dyes, generating a grouping hypothesis with DY3 and two Sudan dyes within one group. Daphnia magna were exposed acutely to equi-effective doses of all seven dyes (each at 3 doses and 3 time points), transcriptomics and metabolomics data were generated from 760 samples. Multi-omics bioactivity profile-based grouping uniquely revealed that Sudan 1 (S1) is the most suitable analogue for read-across to DY3. Mapping ToxPrint structural fingerprints of the dyes onto the bioactivity profile-based grouping indicated an aromatic alcohol moiety could be responsible for this bioactivity similarity. The long-term reproductive toxicity to aquatic invertebrates of DY3 was predicted from S1 (21-day NOEC, 40 µg/L). This prediction was confirmed experimentally by measuring the toxicity of DY3 in D. magna. While limitations of this ‘omics approach are identified, the study illustrates an effective statistical approach for building chemical groups.

Protolytic properties of methyl yellow both in water-ethanol medium and in hardened gelatin gel with the presence of sodium dodecylsulphate and tetrabutylammonium chloride

This paper presents the results of studying the acid-base properties of the indicator dye methyl yellow in water–ethanol solutions with a volume fraction of alcohol of 10 % and 50 %. The influence of the addition of NaCl salts and tetrabutylammonium chloride, as well as the anionic surfactant sodium dodecylsulfate (SDS) on the acidity constant of the indicator, was evaluated. Under the chosen conditions, ethanol additives have a more significant effect on the pKa value. For the first time, using the dynamic light scattering method, the particle sizes, polydispersity index, and ζ-potential of colloidal particles in pure aqueous and mixed water–ethanol solutions of methyl yellow (φalcohol from 0.2 % to 50 %) in the presence of NaCl and SDS were estimated. In solutions with φalcohol = 50 % colloidal particles were not found. It has been shown that the hardened gelatin gel of photographic film can be used as a convenient sorbent for methyl yellow. In the process of dye extraction into a gelatin film from water-alcohol solutions containing SDS and NaCl, the acid-base properties of the methyl yellow remained almost unchanged. The difference between the pKa values obtained for the indicator both in solution and in the film did not exceed the measurement error.

Combinatorial impact of Chelerythrine and DADS in the restoration of liver physiology during carcinogenic exposure in mice (Mus musculus)

Investigation of the efficacy of the combined drugs chelerythrine and DADS in restoring chemically induced hepatocellular carcinoma in Swiss albino mice. 4-6 week-old mice were considered for experimentation. The genotoxic carcinogen para-induced liver cancer--dimethyl-amino azobenzene along with nongenotoxic promoter carcinogen phenobarbital exposure. During the study, animals were co-treated with 100mg/kg body weight DADS and 5mg/kg body weight chelerythrine individually or in combination for 120 days. Bioparametric enzymatic assays of ALT, AST, ALKP, and GGT were performed. The estimation of TBARS, analysis of bone marrow chromosomal abnormalities, sperm head anomalies, and histopathological tissue structure in the co-treated group followed studies. An increase in enzymatic activities of plasma ALT, AST, ALKP, and GGT was observed after carcinogen exposure. Individual treatment of chelerythrine and DADS restored the activities mentioned above to some extent, although combined drugs successfully maintained the enzymatic activities in plasma. Changes in bone marrow chromosomal morphology and sperm head anomalies after carcinogen exposure were prevented in the individual and, most significantly, after combined drug therapy. Histopathological analysis of liver tissue of both male and female mice also demonstrated the preservation of tissue structures in the treated group, most significantly in the combined treatment, even after PB+P-DAB exposure. Chelerythrine and DADS individually protected liver tissue to a certain extent from the tumorigenic toxic effect of PB+P-DAB exposure. The combination of DADS and chelerythrine successfully guarded the tissue from any corrosive, carcinogenic impact and thus instigated further consideration as an effective alternative therapy against chemically induced hepatocarcinoma.

Lignin-based hydrophobic DESs extracts Sudan dyes from aqueous solution

As a synthetic pigment, Sudan red is commonly used as a food additive and is harmful to the human kidney and can even cause cancer. In this work, we developed a one-step strategy to synthesize lignin-based hydrophobic deep eutectic solvents (LHDES), which were fabricated via methyltrioctylammonium chloride (TAC) as hydrogen bond acceptor and alkali lignin as hydrogen bond donor. LHDES with different mass ratios were synthesized and the mechanism of formation was determined by different characterization techniques. The synthetic LHDES was used as the extraction solvent to establish a vortex-assisted dispersion-liquid microextraction method for the determination of Sudan red dyes. The practicality of LHDES was evaluated by applying it to the detection of Sudan Red I in real water samples (seawater, river water) and duck blood in foodstuffs, and the obtained extraction rate reached up to 98.62 %. The method is simple and effective for the determination of Sudan Red in food.

Nonreducing terminal chimeric isomaltomegalosaccharide and its integration with azoreductase for the remediation of soil-contaminated lipophilic azo dyes

Lipophilic azo dyes are practically water-insoluble, and their dissolution by organic solvents and surfactants is harmful to biological treatment with living cells and enzymes. This study aimed to evaluate the feasibility of a newly synthesized nonreducing terminal chimeric isomaltomegalosaccharide (N-IMS) as a nontoxic solubilizer of four simulated lipophilic azo dye wastes for enzymatic degradation. N-IMS bearing a helical α-(1 → 4)-glucosidic segment derived from a donor substrate α-cyclodextrin was produced by a coupling reaction of cyclodextrin glucanotransferase. Inclusion complexing by N-IMS overcame the solubility issue with equilibrium constants of 1786–242 M−1 (methyl yellow > ethyl red > methyl red > azo violet). Circular dichroism spectra revealed the axial alignment of the aromatic rings in the N-IMS cavity, while UV–visible absorption quenching revealed that the azo bond of methyl yellow was particularly induced. Desorption of the dyes from acidic and neutral soils was specific to aqueous organic over alkali extraction. The dissolution kinetics of the incorporated dyes followed a sigmoid pattern facilitating the subsequent decolorization process with azoreductase. It was demonstrated that after soil extraction, the solid dyes dissolved with N-IMS assistance and spontaneously digested by coupled azoreductase/glucose dehydrogenase (for a cofactor regeneration system) with the liberation of the corresponding aromatic amine.

Unveiling the binding details and esterase-like activity effect of methyl yellow on human serum albumin: spectroscopic and simulation study.

The food sector uses methyl yellow (MY) extensively as a colorant. The primary transporter in vivo that influences MY absorption, metabolism, distribution, and excretion is human serum albumin (HSA). Exploring the binding process and looking at how HSA and MY work physiologically at the molecular level is therefore very important. Experiments using steady-state fluorescence and fluorescence lifetimes proved that HSA and MY's quenching mechanisms were static. The HSA-MY complex's binding constant was estimated using thermodynamic parameters to be around 104 M-1. The hydrophobic forces were a major factor in the binding process, as evidenced by the negative ΔG, positive ΔH, and ΔS, which suggested that this contact was spontaneous. Site tests showed that MY linked to HSA's site I. Circular dichroism and three-dimensional fluorescence analysis revealed that the 1.33% α-helix content dropped and the amino acid microenvironment altered. While HSA's protein surface hydrophobicity decreased when engaging MY, the binding of MY to HSA reduced in the presence of urea. The stability of the system was assessed using molecular modeling. Additionally, HSA's esterase-like activity decreased when MY was present, and Ibf/Phz affected the inhibition mechanism of MY on HSA. These findings offer a distinctive perspective for comprehending the structure and functioning of HSA and evaluating the safety of MY.

Highly elastic halochromic fibers capable of reversible sensing of acidic/basic vapor for use in wearable textiles

Halochromic sensors, which allow users to visually recognize exposure to acid/base chemicals that are harmful to the human body, are routinely used in a wide range of industries, such as pharmaceuticals, biotechnology, cosmetics, and environmental/human monitoring systems. In this study, halochromic fibers that operate stably, even when exposed to rain or sweat and repeated stretching–releasing, were investigated. While the halochromic mesoporous silica was synthesized using tetraethylorthosilicate and cetyltrimethylammonium bromide, methyl yellow (MY) and bromothymol blue (BTB) as halochromic dyes were added so that MY and BTB were chemically or physically immobilized on the siloxane network structure of the halochromic mesoporous silica. Using the swelling and shrinking properties of the polymer, the halochromic mesoporous silica was embedded in a highly elastic spandex fiber composed of multiple strands. Because of the strong ionic and hydrogen bonding between the dye and the silica matrix, the dyes can be immobilized even in an aqueous solution without the leaching of the dyes. The stretchable halochromic fiber reversibly changed its color even after repeated exposure to acidic/basic conditions five times and could sense acid/base concentrations in the range of 0.5–10 wt %. In addition, because the halochromic mesoporous silica is tightly adhered between the stands of spandex fibers, stable color conversion properties were maintained even after stretching to 150% of the fibers and repeated 100 times. Because the halochromic fiber can be applied to lab coats, work clothes, and gloves, it is expected to be used as a wearable colorimetric sensor for daily life and industrial applications.

Investigation of heterojunction between α-Fe2O3/V2O5 and g-C3N4 ternary nanocomposites for upgraded photo-degradation performance of mixed pollutants: Efficient dual Z-scheme mechanism

In this present work, a g-C3N4 decorated dual Z-scheme α-Fe2O3 and V2O5 heterojunction of magnetically recoverable GFV (g-C3N4/α-Fe2O3/V2O5) composite was rationally synthesized using facile calcination and hydrothermal approach. The crystal structure, surface morphology, chemical composition and optical properties of the as-obtained composite photocatalysts (PCs) were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra high-resolution scanning electron microscopy (HR-SEM, high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) measurement, UV-Vis diffuse reflectance spectra (DRS) and photoluminescence (PL) analyses respectively. Benefiting from these structural and compositional features, the optimum GFV heterostructured PCs sample revealed that the superior photo-degradation performance of methyl yellow (MY) and methylene blue (MB) mixed dye under visible-light, while the degradation rates were 93.4% for MY and 87.5% for MB dye at 90 min, respectively. Moreover, the enhanced photo-degradation performance of GFV composite PCs displayed an extended visible-light fascination due to lower bandgap, reduced recombination rates, high charge separation and good charge transfer capacity with the efficient dual Z-scheme heterojunction. Meanwhile, high photo-degradation stability is continued after five successive reusability tests. A possible photo-degradation mechanism of dual Z-scheme charge transfer paths was also been proposed. This study is also capable of emerging visible-light active facile heterojunction photocatalysts for various organic pollutants removal with great efficiency.

Bifunctional monomer oligomers-based composite molecularly imprinted membranes for the electrochemical monitoring of Sudan I.

Herein, we developed a highly sensitive electrochemical sensor for the trace detection of Sudan I (SDI) dye based on composite molecularly imprinted membranes (MIMs). The pentenyl (lipoic acyl)-isoleucyl-chitosan oligosaccharide (P(L)ICO) and pentenyl-asparaginyl-chitosan oligosaccharide (PASCO) served as bifunctional monomer oligomers. After deposition of gold nanoparticles on a glassy carbon electrode (GCE) surface, a P(L)ICO layer successfully self-assembled on the surface. Subsequently, the primary MIM was polymerised on the electrode surface by using SDI as a template, PASCO as a functional monomer oligomer, and ethylene glycol dimethacrylate as a cross-linking agent. Electrochemical polymerisation was then conducted in an N,N'-methylenebisacrylamide solution. After eluting the SDI molecules from the composite MIMs, the fabricated SDI-MIM(PM)/Fn-Au/GCE demonstrated specific adsorption of SDI. Under optimal conditions, the constructed sensor exhibited a linear relationship between decreasing peak current and SDI concentration from 0.02 to 3.5 μM with a low detection limit of 4 nM (S/N = 3). As a proof of concept, SDI-MIM(PM)/Fn-Au/GCE was also applied to detect SDI in chili powder samples, with recoveries ranging from 96.8 to 106.6%.

Allergic contact dermatitis from dyes used in the temple of spectacles.

We observed an increasing number of patients who presented with facial or retro-auricular dermatitis after skin contact with plastic spectacles or plastic covered temples. To identify the allergens in plastic spectacles that may cause allergic contact dermatitis. All patients with suspected allergic contact dermatitis to eyewear were tested with Solvent Orange 60 (SO60), four additionally with Solvent Yellow 14 (SY14), and five with scrapings from their own spectacles. In one case, a chemical analysis of the spectacles was performed to uncover the causative allergen. Three patients were allergic to SO60, two patients to SY14, and two patients were allergic to both SO60 and SY14. Patients with suspected allergic contact dermatitis from spectacles should be tested with SO60 and SY14, and based on findings from previous reports, also with Solvent Red 179.

Nitrogen, phosphorus, sulfur tri-doped porous carbon derived from covalent polymer with versatile performances in supercapacitor, oxygen reduction reaction and electro-fenton degradation

Versatility in energy storage and electrocatalysis is highly desired in material design due to the capability in simultaneous solving the energy and environment associated issues. The heteroelement doped carbons are traditional energy storage and electrocatalysis materials, so it is significant to further explore their versatilities. Herein, N, P, S tri-doped porous carbon was designed for application in supercapacitors (SCs), oxygen reduction reaction (ORR) and electro-Fenton (EF) via controlled pyrolysis of a covalent triazine polymer precursor. Given the high N, P, S heteroelement contents containing special functionalities and the porous texture with high specific surface area, the tri-doped porous carbon demonstrates abundant electrochemically active sites and therefore considerable capacitive and electrocatalytic capabilities. The symmetric supercapacitor based on the tri-doped carbon material delivers high energy densities in acidic (11.6 Wh kg −1 ) and alkaline (11.3 Wh kg −1 ) electrolytes. Moreover, the tri-doped carbon material also demonstrates superior four electrons (4e − ) ORR catalytic activity in alkaline medium essential for fuel cell, and two electrons (2e − ) ORR catalytic activity toward hydrogen peroxide in acidic medium, which further enables high EF degradation efficiency (98.0% in 150 min) for mixed dyes. This work demonstrates the versatility of N, P, S tri-doped porous carbon in electrochemical energy storage and pollution treatment. • Biomass-derived carbon materials are synthesized via bifunctional-salt activation. • Bifunctional salts are used to regulate heteroatom doping sites and pore structures. • The catalyst with N, P doping site achieves two-electron governed ORR with low AE. • The EF degradation of methyl yellow is up to 98.4% after 60 min with good stability. • The catalyst proves excellent reusability in treating wastewater with mixed dyes.

Preparation of Polyamidoamine Dendrimer Modified Magnetic Nanoparticles and Its Application for Reliable Measurement of Sudan Red Contaminants in Natural Waters at Parts-Per-Billion Levels.

The health threat from Sudan red dyes has been the subject of much attention in recent years and is crucial to design and establish reliable measurement technologies. In the present study, a new magnetic nanomaterial, polyamidoamine dendrimer-modified magnetic nanoparticles (Gn-MNPs), was synthesized and characterized. The nanomaterials had good adsorption capacity for Sudan dyes from natural waters. G1.5-MNPs possessed excellent adsorption capacity and a linear adsorption relationship over the range from 0.02 to 300 μg L−1 of Sudan dyes with relative coefficients all larger than 0.996. The sensitivity of the proposed method was excellent with detection limits over the range from 1.8 to 5.5 ng L−1 and the precision was less than 3.0%. G1.5-MNPs showed a remarkable application potential for the enrichment of trace environment pollutants in aqueous samples and the developed method based on this nanomaterial could be a robust and reliable alternative tool for routine monitoring of such pollutants.

Photo-Electroswitchable Arylaminoazobenzenes.

Azobenzenes appended with a redox-active arylamino group (redox auxiliary, RA) are prepared and shown to undergo fast, complete, and catalytic Z→E azo isomerization upon electron loss from the RA unit of the azobenzene. The RA-azo structures can be reversibly (E→Z→E)n cycled by sequential photo- and electrostimulation. Due to the robust nature of the RA•+-azo radical cation chain carrying species, initiation of electron transfer (ET) catalysis occurs at low levels (1.0-0.04 mol %) of catalytic loading and is effective even at Z-RA-azo concentrations of 10-4-10-5 M, yielding TONs (turnover numbers) of 100-2300 under such dilute conditions. The RA-azo Z→E conversion is demonstrated using chemical oxidation (redox switching), electrochemical oxidation (electro switching), and photochemical oxidation (photoredox switching). The Z→E acceleration is shown to be at least 2 × 109-fold for RA-azo 5. DFT calculations on methyl yellow suggest that a N-centered radical cation of the RA group stabilizes the Z→E N-N twist transition state of the RA•+-azo, yielding a large reduction in the barrier for RA•+-azo compared to neutral RA-azo. The RA-azo structure class has nanomechanical features that can be toggled with photo- and electrostimulation, the latter offering a quick switch for complete Z→E conversion.

Two-dimensional g-C3N4 nanosheets supporting Co3O4-V2O5 nanocomposite for remarkable photodegradation of mixed organic dyes based on a dual Z-scheme photocatalytic system

A dual Z-scheme g-C3N4-Co3O4-V2O5 nanocomposite was synthesized through a simple wet impregnation technique. The phase purity and optical behavior of the synthesized samples were characterized by various analytical techniques. The morphology consequences indicated that Co3O4 nanorods and V2O5 nanoparticles were effectively embedded on the exterior of g-C3N4 nanosheets. The emission properties and energy band gap measurement of g-C3N4-Co3O4-V2O5 nanocomposite reveal suppression of e−-h+ recombination and the optical absorption are redshifted to the visible region. The photodegradation capability of the prepared samples was assessed against mixed organic dyes (methylene blue (MB) and methyl yellow (MY)) under visible light illumination. The g-C3N4-Co3O4-V2O5 nanocomposite established that the enhanced photocatalytic properties in the photodegradation of mixed dyes compared to bare and hybrid samples. The as-prepared g-C3N4-Co3O4-V2O5 nanocomposite shows the enhanced degradation efficiency for 93.8 and 93.2% over the MY and MB aqueous dyes under the visible light irradiation. Notably, the g-C3N4-Co3O4-V2O5 photocatalyst was recycled in four consecutive runs with no noticeable loss of catalytic performance. A synergistic dual Z-scheme g-C3N4-Co3O4-V2O5 photocatalyst could be constructed based on the energy band matching within g-C3N4, Co3O4 and V2O5 NPs.

N, P-dual doped carbonaceous catalysts derived from bifunctional-salt activation for effective electro-Fenton degradation on waterborne organic pollutions

To achieve the two-electron governed oxygen reduction reaction (ORR) is the major challenge for carbonaceous catalyst in the electro-Fenton (EF) degradation on the exhaustive stubborn pollutants from industrial wastewater. Herein, a bifunctional salts strategy utilizing EDTA-2K and NaH2PO2.H2O as heteroatom dopants and porogens is proposed to regulate the doping amounts of N, P heteroatoms as well as the content of active species (pyrrolic-N and P-C bonding motifs) to enhance 2e--ORR selectivity for EF degradation. It is found that the generated gaseous substances could serve as soft template to create micro-/meso-pores for the accommodation of highly oxidizing .OH radicals. In addition, thanks to the high N, P doping amounts (both are 2.9 at. %, respectively), large specific surface area (1388 m2 g-1) and appropriate pore sizes (1.5/3.8 nm), the optimized carbonaceous catalyst enables high EF degradation efficiencies up to 98.4 % (60 min) and 97.1 % (150 min), respectively for methyl yellow and mixed dyes with good stability and reusability. The current work paved a new concept to engineer the carbonaceous catalysts for the promoted catalytic activity and selectivity in the electro-degradation of organic pollution.

Rapid magnetic enrichment and sensitive detection of Sudan pollutants with nanoscale zero valent iron-based nanomaterials in combination with liquid chromatography-ultraviolet detector

In present work, we reported a new nanomaterial nano Fe0 decorated with SiO2 and dopamine by self-assembly method (Fe@SiO2@PDA). A sensitive method for determination of Sudan pollutants in aqueous samples was developed using Fe@SiO2@PDA as magnetic solid phase extraction adsorbents prior to high-performance liquid chromatography with variable wavelength detector. The possible parameters which would affect the enrichment have been optimized. The best parameters were as follows: elutent, 4.5 mL methanol; adsorbent dosage, 30 mg; adsorption time, 20 min; elution time, 18 min; sample pH 7; sample volume, 40 mL. The experimental results demonstrated that Fe@SiO2@PDA exhibited good adsorption properties to Sudan Red dyes. The established method provided excellent linear ranges over 0.01–50 μg L−1 and detection limits ranged from 2.0 to 5.1 ng L−1 for Sudan red I-IV. The developed method was also evaluated with real water samples and the results demonstrated that it was of applicative value owing to its merits including robustness, easy operation, fastness, cheapness and high enrichment efficiency, and had great prospect in environmental fields.

Detection and Estimation of Metanil Yellow & Congo Red: Carcinogenic Food Colourants, Present in Different Food Samples

Nowadays adulteration is a social disease which is applied on food to make food more attractive and to gain more profit from it. Along with different processed food products, Spices like Turmeric powder, red chilli powder, etc. provides good nutrition to us until they are treated with some foreign colours or organic colours to make them adulterated, which causes various detrimental effects in physiological system such as heart failure, liver damage, cancer and many more, if people consume them over a certain period of time. Metanil yellow, Sudan red dye, Congo red are such organic dyes which are used abundantly in different spices and processed food products. These dyes are toxic chemicals and could be carcinogenic as well. The presence of all these components can be detected with chemical experiments. This present research study is focused on the detection of adulterants present in sample on the basis of pH variation of adulterated food sample from the pure one and its estimation by variation of spectrophotometric absorbance with the concentration of the adulterant in the sample. After testing samples with different concentration of adulterants, it has been observed that pH of samples is gradually increasing with the increase in concentration of adulterants from 0 to 16.66 gm/100gm present in the sample.

Defective cuprous oxide as a selective surface‐enhanced Raman scattering sensor of dye adulteration in Chinese herbal medicines

AbstractChinese herbal medicine is an ancient part of humanity's heritage. However, the quality of commercial Chinese herbal remedies is currently compromised by illegal dyeing and adulteration. A rapid screening method of suspected dyeing compounds based on surface‐enhanced Raman scattering (SERS) has proven difficult to develop due to the extreme complexity of the extraction of traditional Chinese medicinal products, as well as the lack of selective signal enhancement for target adulterants on commercially available Ag or Au substrates. Defective Cu2O nanostructures provide specific anchoring sites for dye adulterants such as Sudan red dyes on the basis of coordination between hydroxyl/azo groups and exposed Cu sites. This coordination facilitates an effective analyte–substrate charge‐transfer, resulting in a prominent Raman signal enhancement for the analyte. Based on the mechanism of selective signal enhancement on Cu2O, this study shows that the adulterant Sudan red III in the extractions of various herbal medicines can be detected directly even at an extremely low concentration of 0.3 mg/kg. The findings suggest the advantages of semiconducting materials as promising SERS substrates for practical applications.

Spectroscopic Properties of Two 5'-(4-Dimethylamino)Azobenzene Conjugated G-Quadruplex Forming Oligonucleotides.

The synthesis of two 5′-end (4-dimethylamino)azobenzene conjugated G-quadruplex forming aptamers, the thrombin binding aptamer (TBA) and the HIV-1 integrase aptamer (T30695), was performed. Their structural behavior was investigated by means of UV, CD, fluorescence spectroscopy, and gel electrophoresis techniques in K+-containing buffers and water-ethanol blends. Particularly, we observed that the presence of the 5′-(4-dimethylamino)azobenzene moiety leads TBA to form multimers instead of the typical monomolecular chair-like G-quadruplex and almost hampers T30695 G-quadruplex monomers to dimerize. Fluorescence studies evidenced that both the conjugated G-quadruplexes possess unique fluorescence features when excited at wavelengths corresponding to the UV absorption of the conjugated moiety. Furthermore, a preliminary investigation of the trans-cis conversion of the dye incorporated at the 5′-end of TBA and T30695 showed that, unlike the free dye, in K+-containing water-ethanol-triethylamine blend the trans-to-cis conversion was almost undetectable by means of a standard UV spectrophotometer.