Study on the interaction of nucleic acids with silver nanoparticles—Al(III) by resonance light scattering technique and its analytical application

It is found that Al(III) can further enhance the intensity of resonance light scattering (RLS) of the silver nanoparticles (AgNPs) and nucleic acids system. Based on this, a novel method of determination of nucleic acids is proposed in this paper. Under optimum conditions, there are linear relationships between the enhancing extent of RLS and the concentration of nucleic acids in the range of 1.0 × 10⁻⁹-1.0 × 10⁻⁷ g mL⁻¹, 1.0 × 10⁻⁷-2.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 1.0 × 10⁻⁹-7.0 × 10⁻⁸ g mL⁻¹ for calf thymus DNA (ctDNA) and 1.0 × 10⁻⁹-1.0 × 10⁻⁷ g mL⁻¹ for yeast RNA (yRNA). The detection limits (S/N = 3) of fsDNA, ctDNA and yRNA are 4.1 × 10⁻¹⁰ g mL⁻¹, 4.0 × 10⁻¹⁰ g mL⁻¹ and 4.5 × 10⁻¹⁰ g mL⁻¹, respectively. The studies indicate that the RLS enhancement effect should be ascribed to the formation of AgNPs-Al(III)-DNA aggregations through electrostatic attraction and adsorption bridging action of Al(III). And the sensitivity and stability of the AgNPs-fsDNA system could be enhanced by Al(III).     

Determination of itopride hydrochloride by high-performance liquid chromatography with Ru(bpy)3 electrogenerated chemiluminescence detection

In this work, a stable electrogenerated chemiluminescence (ECL) detector was developed. The detector was prepared by packing cation-exchanged resin particles in a glass tube, followed by inserting Pt wires (working electrode) in this tube and sealing. The leakage of Ru(bpy)₃²⁺ can be compensated by adding a small amount of Ru(bpy)₃²⁺ into solution phase. Coupled with high-performance liquid chromatography separation, the detector has been used for determination of itopride hydrochloride in human serum. Under the optimal conditions, the ECL intensity has a linear relationship with the concentration of itopride hydrochloride in the range of 1.0 × 10⁻⁸ g mL⁻¹ to 1.0 × 10⁻⁶ g mL⁻¹ and the detection limit was 3 × 10⁻⁹ g mL⁻¹ (S/N = 3). The as-prepared ECL detector displayed good sensitivity and stability.     

Fluorescence enhancement of CdTe/CdS quantum dots by coupling of glyphosate and its application for sensitive detection of copper ion

A novel fluorescent probe for Cu²⁺ determination based on the fluorescence quenching of glyphosate (Glyp)-functionalized quantum dots (QDs) was firstly reported. Glyp had been used to modify the surface of QDs to form Glyp-functionalized QDs following the capping of thioglycolic acid on the core–shell CdTe/CdS QDs. Under the optimal conditions, the response was linearly proportional to the concentration of Cu²⁺ between 2.4 × 10⁻² μg mL⁻¹ and 28 μg mL⁻¹, with a detection limit of 1.3 × 10⁻³ μg mL⁻¹ (3δ). The Glyp-functionalized QDs fluorescent probe offers good sensitivity and selectivity for detecting Cu²⁺. The fluorescent probe was successfully used for the determination of Cu²⁺ in environmental samples. The mechanism of reaction was also discussed.     

Synchronous fluorescence determination of DNA based on the interaction between methylene blue and DNA

The fluorescence intensity of methylene blue (MB) quenched by DNA in the pH range of 6.5-8.0 was studied with synchronous fluorescence technology. A novel method for detecting single-stranded and double-stranded DNA was developed. The decreased fluorescence intensity at 664 nm is in proportion to the concentration of DNA in the range of 0.28-11.0 μmol L⁻¹ for ctDNA, 0.14-8.25 μmol L⁻¹ for thermally denatured ctDNA and 0.28-8.25 μmol L⁻¹ for hsDNA. The detection limits (S/N = 3) are 0.11, 0.04 and 0.04 μmol L⁻¹, respectively. The method is rapid, selective, and the reagents are lower toxic. It has been used for the determination of DNA in synthetic samples with good satisfaction. In addition, the interaction modes between MB and ctDNA and the mechanism of the fluorescence quenching were also discussed in detail. The experimental results from absorption spectra and fluorescence polarization indicate that the possible interaction modes between MB and DNA are the electrostatic binding and the intercalation binding.     

Determination of indole-3-acetic acid and indole-3-butyric acid in mung bean sprouts using high performance liquid chromatography with immobilized Ru(bpy)3-KMnO4 chemiluminescence detection

A novel method for determination of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) in an extract from mung bean sprouts using high performance liquid chromatography (HPLC) with chemiluminescence (CL) detection is described. The method is based on the CL reaction of auxin (indole-3-acetic acid and indole-3-butyric acid) with acidic potassium permanganate (KMnO₄) and tris(2,2′-bipyridyl)ruthenium(II), which was immobilized on the cationic ion-exchange resin. The chromatographic separation was performed on a Nucleosil RP-C18 column (i.d.: 250 mm × 4.6 mm, particle size: 5 μm, pore size: 100) with an isocratic mobile phase consisting of methanol-water-acetic acid (45:55:1, v/v/v). At a flow rate of 1.0 mL min⁻¹, the total run time was 20 min. Under the optimal conditions, the linear ranges were 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ g mL⁻¹ and 5.0 × 10⁻⁷ to 1.0 × 10⁻⁵ g mL⁻¹ for IAA and IBA, respectively. The detection limits were 2.0 × 10⁻⁸ g mL⁻¹ and 2.0 × 10⁻⁷ g mL⁻¹ for IAA and IBA, respectively. The relative standard deviation (RSD) of intra-day were 3.1% and 2.3% (n = 11) for 2 × 10⁻⁶ g mL⁻¹ IAA and 2 × 10⁻⁶ g mL⁻¹ IBA; The relative standard deviations of inter-day precision were 6.9% and 4.9% for 2 × 10⁻⁶ g mL⁻¹ IAA and 2 × 10⁻⁶ g mL⁻¹ IBA. The proposed method had been successfully applied to the determination of auxin in mung bean sprouts.     

Protein determination using methylene blue in a synchronous fluorescence technique

A new method for detecting protein by synchronous fluorescence enhancement was developed, based on the combination of near infrared (NIR) fluorescence and the dedimerization phenomenon of methylene blue (MB). Under analytical conditions, there are linear relationships between the enhancing extent of synchronous fluorescence of MB-sodium dodecyl benzene sulfonate (SDBS)-protein at 667 nm and the concentration of protein in the range of 8.0 × 10⁻⁸-4.0 × 10⁻⁵ g mL⁻¹ for bovine serum albumin (BSA), 1.0 × 10⁻⁷-3.5 × 10⁻⁵ g mL⁻¹ for egg albumin (EA). The detection limits (S/N = 3) of BSA and EA are 8.9 ng mL⁻¹ and 10.0 ng mL⁻¹, respectively. The fluorescence enhancement mechanism is discussed in detail. Results from multiple techniques indicate that the fluorescence enhancement of the system originates from the hydrophobic microenvironment provided by BSA and SDBS, and the formation of an MB-SDBS-BSA complex, as well as the deaggregation of some MB dimer.     

Study on the interaction between oxolinic acid aggregates and protein and its analytical application

It was found that oxolinic acid (OA) at high concentration can self-assemble into nano- to micro- meter scale OA aggregates in Tris-HCl (pH 7.48) buffer solution. The nanoparticles of OA were adopted as fluorescence probes in the quantitative analysis of proteins. Under optimum conditions, the fluorescence quenching extent of nanometer scale OA aggregates was in proportion to the concentration of albumins in the range of 3.0 × 10⁻⁸ to 3.0 × 10⁻⁵ g mL⁻¹ for bovine serum albumin (BSA) and 8.0 × 10⁻⁸ to 8.0 × 10⁻⁶ g mL⁻¹ for human serum albumin (HSA). The detection limits (S/N = 3) were 3.4 × 10⁻⁹ g mL⁻¹ for BSA, and 2.6 × 10⁻⁸ g mL⁻¹ for HSA, respectively. Samples were satisfactorily determined. The interaction mechanism of the system was studied using fluorescence, UV-vis, resonance light scattering (RLS) and transmission electron microscope (TEM) technology, etc., indicating that the nonluminescent complex was formed between serum albumin molecular and OA, to disaggregate the self-association of OA, which resulted in the dominated static fluorescence quenching in the system.     

A highly sensitive coupling technique for the determination of trace quercetin based on solid substrate room temperature phosphorimetry and poly (vinyl alcohol) complex imprinting

Al³⁺ could react with quercetin (Q) to form [AlQ]³⁺ complex which could be used as a template for the preparation of poly (vinyl alcohol)–[AlQ]³⁺ complex imprinting (PVA-C-I). The [AlQ]³⁺ not only had good matching ability and selectivity with the cavity of PVA-C-I, but also could react with the fluorescein isothiocyanate anion (FITC⁻) on the outside of cavity by electrostatic interaction to form ion-association complex [AlQ]³⁺·[(FITC)⁻]₃. The ion-association complex could emit strong and stable room temperature phosphorescence (RTP) on polyamide membrane (PAM) and the ΔI_p of the system had linear relationship with the content of Q, showing the highly selective identification of PVA-C-I to Q. Thus, a new coupling technique for the determination of trace Q based on solid substrate room temperature phosphorimetry and poly (vinyl alcohol) complex imprinting (PVA-C-I-SSRTP) was established. The linear range and limit of detection (LOD) of this method were 0.010–2.0 (×10⁻¹² g mL⁻¹) and 2.0 × 10⁻¹⁴ g mL⁻¹, respectively, showing wide linear range and high sensitivity of PVA-C-I-SSRTP. This method was used to determine the content of Q in waste water, and the results are consistent with those by spectrofluorimetry. Meanwhile, the mechanism for the determination of Q using PVA-C-I-SSRTP was also discussed.     

Synthesis and investigation on the interaction with calf thymus deoxyribonucleic acid of a novel fluorescent probe 7-oxobenzo[b][1,10]phenanthroline-12(7H)-sulfonic acid

In this paper, the synthetic route of a potential antitumor reagent, benzo[b][1,10] phenanthrolin-7(12H)-one (BPO), was improved. A sulfonic group was introduced to BPO to form a new compound, 7-oxobenzo[b][1,10]phenan-throline-12(7H)-sulfonic acid (OPSA), in order to enhance its water-solubility. The molecular structure of OPSA has been confirmed by IR, UV, MS, ¹H NMR and elements analysis. It was proved in our experiments that DNA could quench the fluorescence of OPSA and the maximum quenched intensity appeared at 408 nm (λ_ex = 284 nm). The quenched fluorescence intensity was proportional to the concentration of DNA. Based on this phenomenon, OPSA had been used as the fluorescent probe for detection of calf thymus DNA (ct-DNA) and the corresponding linear response range was from 1.0 to 150.0 μg mL⁻¹ and the limit of detection (LOD) was 3.8 ng mL⁻¹. Its interaction with ct-DNA was investigated by fluorescence, absorption and viscosity measurements. When binding to ct-DNA, OPSA showed obvious fluorescence quenching and the quenched intensity was stable with the presence and absence of NaCl. The absorption spectra of OPSA had no evidence of increasing or decreasing when ct-DNA was added. The viscosity of OPSA and ct-DNA mixture showed no obvious change comparing with the viscosity of ct-DNA along. The results suggested that the interaction between OPSA and ct-DNA was groove binding in nature. Scatchard plots constructed from fluorescence titration data gave a binding constant of 8.9 × 10⁵ L mol⁻¹ and a binding site size of 0.35 base pairs per bound drug molecule.     

Electrospun nanofiber based colorimetric probe for rapid detection of Fe in water

An imidazole derivative, 2-(2′-pyridyl)imidazole (PIMH), was developed as a colorimetric probe for the qualitative analysis of Fe²⁺ in aqueous solution. PIMH was then used to post-functionalize poly(vinylbenzyl chloride) (PVBC) nanofibers after electrospinning so as to afford a solid state colorimetric probe. Upon treatment with Fe²⁺ the probe displayed a distinctive color change both in liquid and solid platforms. The linear dynamic range for the colorimetric determination of Fe²⁺ was 0.0988–3.5 μg mL⁻¹. The ligand showed a high chromogenic selectivity for Fe²⁺ over other cations with a detection limit of 0.102 μg mL⁻¹ in solution (lower than the WHO drinking water guideline limit of 2 mg L⁻¹), and 2 μg mL⁻¹ in the solid state. The concentration of Fe²⁺ in a certified reference material (Iron, Ferrous, 1072) was found to be 2.39 ± 0.01 mg L⁻¹, which was comparable with the certified value of 2.44 ± 0.12 mg L⁻¹. Application of the probe to real samples spiked with Fe²⁺ achieved recoveries of over 97% confirming accuracy of the method and its potential for on-site monitoring.     

Fluorescence enhancement effect for the determination of proteins with morin-Al3+ -cetyltrimethylammonium bromide

It is found that the fluorescence intensity of morin-Al³⁺ complex can be greatly enhanced by proteins in the presence of cetyltrimethylammonium bromide (CTAB). It is considered that protein and CTAB provide a hydrophobic environment with low polarity and large viscosity, resulting in the fluorescence enhancement of morin-Al³⁺ complex. The experiments indicate that under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins (such as bovine serum albumin (BSA), human serum albumin (HSA) and egg albumin (EA)) in the wide range, and their detection limits (S/N = 3) are 2.6 × 10⁻⁹, 1.4 × 10⁻⁸ and 1.6 × 10⁻⁸ g ml⁻¹, respectively. This method has satisfactorily been used for the determination of protein in actual sample. In comparison with most of fluorimetric methods reported, this method is quick and simple, and has high sensitivity, wide linear range and good stability.     

An ultrasensitive post chemiluminescence reaction of ammonium in NBS-dichlorofluorescein system and its application

A strong post chemiluminescence (PCL) phenomenon was observed when ammonium was injected into the reaction mixture after the finish of CL reaction of N-bromosuccinimide (NBS) and dichlorofluorescein. Based on this, a sensitive flow injection PCL method was established for the determination of ammonium. The possible CL mechanism of the reaction was proposed based on a series of experiments. The PCL intensity responded linearly to the concentration of ammonium in the range 3.0 × 10⁻¹¹-1.0 × 10⁻⁷ g mL⁻¹ with a detection limit of 1 × 10⁻¹¹ g mL⁻¹. The relative standard deviation (R.S.D.) was 1.4% for 1.0 × 10⁻⁹ g mL⁻¹ ammonium (n = 11). This method had been applied to the determination of ammonium in samples of mineral water, tap water and river water.     

Investigation on enhanced chemiluminescence reaction systems with bis(hydrogenperiodato) argentate(III) complex anion for fluoroquinolones synthetic antibiotics

A novel chemiluminescence (CL) reaction system with bis(hydrogenperiodato) argentate(III) complex anion (Ag(III) complex, [Ag(HIO₆)₂]⁵⁻), for the first time, is developed for the determination of lomefloxacin (LMFX), enrofloxacin (ENLX) and pefloxacin (PFLX). The possible CL emission mechanism was discussed by comparing the fluorescence emission with CL spectra. The CL conditions of [Ag(HIO₆)₂]⁵⁻-H₂SO₄-LMFX/ENLX/PFLX systems were investigated and optimized. Under the optimized experimental conditions, the CL intensity is proportional to the concentration of the drugs in the range 0.2994-36.80 × 10⁻⁷ g mL⁻¹ for LMFX, 4.00-30.0 × 10⁻⁷ g mL⁻¹ for ENLX and 1.54-27.64 × 10⁻⁷ g mL⁻¹ for PFLX. The limit of detection (s/n = 3) was 9.1 × 10⁻⁹ g mL⁻¹ for LMFX, 3.1 × 10⁻⁹ g mL⁻¹ for ENLX and 4.4 × 10⁻⁹ g mL⁻¹ for PFLX. The recovery of LMFX, ENLX and PELX from the spiked pharmaceutical preparations was in the range of 92.3-105% with the RSDs of 0.5-2.7%. For urine, serum and milk samples the recoveries of the three drugs were in the range of 85.1-107% for LMFX with the RSDs of 2.3-3.4%. 80.2-112% for ENLX with the RSDs of 1.4-2.8%, and 87.8-114% for PFLX with the RSDs of 1.6-2.7%. The proposed method was applied successfully to the determination of these compounds in real samples.     

Electrochemical studies of the interaction of Basic Brown G with DNA and determination of DNA

A new method of electrochemical probe has been proposed for the determination of Herring Sperm DNA (DNA) based on its interaction with Basic Brown G (BBG). The electrochemical behavior of interaction of BBG with DNA was investigated on Hg electrode. In 0.1 mol L⁻¹ NH₃-NH₄Cl buffer solution (pH 8.0), BBG can be reduced on Hg electrode with a well-defined voltammetric peak at −0.67 V (versus SCE). In the presence of DNA, the reduction peak current of BBG decreases and the peak potential shifts to a more positive potential without the appearance of new peak. The study shows that a new BBG-DNA complex is formed by linear sweep voltammetry (LSV) and spectrophotometry. The decrease of the second order derivative of reductive peak current (Δi^″p) of BBG is proportional to the concentration of DNA in the range of 0.10-36 μg mL⁻¹. Limit of detection of DNA is 0.04 μg mL⁻¹. DNA of Hepatitis B Virus in serum samples was determined satisfactorily. Additionally, the binding mechanism was preliminarily discussed. The mode of interaction between BBG and DNA was found to be intercalation binding.     

Flow injection chemiluminescence determination of naproxen based on KMnO4-Na2SO3 reaction in neutral aqueous medium

A simple, rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of naproxen. It was found that strong CL signal was generated when naproxen was mixed with KMnO₄ and Na₂SO₃ in neutral aqueous medium. Under the optimum experimental conditions, the CL intensity was linearly related to the concentration of naproxen from 4.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g mL⁻¹ (r = 0.9993). The detection limit was 2 × 10⁻⁹ g mL⁻¹ naproxen, the relative standard deviation for 1.0 × 10⁻⁷ g mL⁻¹ naproxen solution was 1.5% (n = 11) and the sampling frequency was 120 h⁻¹. The method was applied to the determination of naproxen in pharmaceutical preparation with satisfactory results. The mechanism of CL reaction was discussed briefly.     

Flow-injection chemiluminescence assay for ultra-trace determination of DNA using rhodamine B-Ce(IV)-DNA ternary system in sulfuric acid media

A novel flow-injection chemiluminescence method for the determination of DNA at ultra-trace level has been established. In 0.8 M sulfuric acid media, the chemiluminescence of the rhodamine B-cerium (IV) or Ce(IV) system is enhanced by DNA, activated previously by imidazole-HCl buffer solution (pH 7.0). The enhanced intensity of chemiluminescence is in proportion to log DNA concentration 1.0×10⁻⁸ to 0.1 μg ml⁻¹ for herring sperm DNA and 2.0×10⁻⁶ to 0.2 μg ml⁻¹ for calf thymus DNA with 3σ detection limits of 8.3×10⁻⁹ μg ml⁻¹ for herring sperm DNA and 3.5×10⁻⁷ μg ml⁻¹ for calf thymus DNA, respectively. The relative standard deviation for 1.0×10⁻⁴ μg ml⁻¹ herring sperm DNA was 0.99% and 2.0×10⁻³ μg ml⁻¹ for calf thymus DNA was 1.1% (n=11). Using the optimized system, DNA contents in six synthetic samples has been determined with recoveries of 99.5-109.0%. The possible mechanism has also been studied in this paper.     

Flow-injection post chemiluminescence determination of atropine sulfate

A new post chemiluminescence (PCL) reaction was observed when atropine sulfate was injected into the reaction mixture after the finish of CL reaction of Ce(IV) and sodium sulfite. The possible mechanism for the PCL reaction was discussed via the investigation of the CL kinetic characteristics, the CL spectra, the UV absorption spectra and the fluorescence spectra of some related substances. The flow injection PCL method for the determination of atropine sulfate was established. The relative standard deviation (R.S.D.) was 2.8% (n = 11, c = 5.0 × 10⁻⁶ g mL⁻¹). The PCL intensity responded linearly to the concentration of atropine sulfate in the range 1.0 × 10⁻⁶ to 5.0 × 10⁻⁵ g mL⁻¹ with a linear correlation of 0.9947. The detection limit was 4 × 10⁻⁷ g mL⁻¹ atropine sulfate. The method had been applied to the determination of atropine sulfate in the tablets and the results were consistent with the method of Chinese pharmacopoeia.     

Flow injection chemiluminescence determination of nitrofurazone in pharmaceutical preparations and biological fluids based on oxidation by singlet oxygen generated in N-bromosuccinimide-hydrogen peroxide reaction

A simple flow injection chemiluminescence (FI-CL) method was proposed for the determination of nitrofurazone. Strong CL signal was generated during the reaction of nitrofurazone with H₂O₂ and N-bromosuccinimide (NBS) in alkaline condition. The CL signal was proportional to the nitrofurazone concentration in the range 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ g mL⁻¹. The detection limit was 2 × 10⁻⁸ g mL⁻¹ nitrofurazone and the relative standard deviation was less than 4% (6.0 × 10⁻⁶ g mL⁻¹ nitrofurazone, n = 11). The proposed method was successfully applied to the determination of nitrofurazone in compound furacillin nasal drops, human plasma and urine samples. The CL reaction mechanism was also discussed briefly. Singlet oxygen generated in the reaction between H₂O₂ and NBS was suggested to be participated in the CL reaction.     

A new rhodamine-based dual chemosensor for Al and Cu

A new rhodamine B derivative bearing a hydrazone group has been designed and prepared. The synthesized colorimetric and fluorescent molecular chemosensor can be used as a dual probe, selectively detecting Al³⁺ and Cu²⁺ in acetonitrile solution by monitoring changes in the absorption and fluorescence spectral patterns. The results show that Al³⁺ ions can induce a greater fluorescence enhancement, while the addition of Cu²⁺ ions induces a strong UV–vis absorption enhancement with weak fluorescence. The limits of detection of Cu²⁺ and Al³⁺ were estimated to be 2.9 × 10⁻⁷ M and 8.3 × 10⁻⁹ M, respectively.     

Direct electrogenerated chemiluminescence detection in high-performance liquid chromatography for determination of ofloxacin

Ofloxacin (OFLX) exhibited strong electrogenerated chemiluminescence (ECL) in NaNO₃ solution with a dual-electrode system when constant current was exerted. Based on this observation, a sensitive direct ECL method coupled with high-performance liquid chromatography (HPLC) separation was developed for determination of OFLX in human serum. Factors affected the ECL emission were investigated. Under the optimal conditions, the ECL intensity has a linear relationship with the concentration of OFLX in the range of 1.0 × 10⁻⁸ to 4.0 × 10⁻⁶ g mL⁻¹ and the detection limit was 4 × 10⁻⁹ g mL⁻¹ (S/N = 3). The proposed method was sensitive, simple and convenient to operate.