Colorimetric and visual read-out determination of cyanuric acid exploiting the interaction between melamine and silver nanoparticles

We present two colorimetric procedures for the determination of cyanuric acid, using silver nanoparticle-based (AgNPs) probes. The first is making use of melamine-modified AgNPs which bind to cyanuric acid through hydrogen bonding to form a large conjugate network that enhances the aggregation of AgNPs to produce an absorbance peak at 640 nm and a green coloration. In the second assay, melamine is directly added to the sample in order to form a stable complex with cyanuric acid. AgNPs are then added, resulting in the formation of an absorbance peaking at 525 nm and a color change from green (blank sample) to purple or orange-red as a function of cyanuric acid concentration. Matrix effects, that originate from the interaction of alkaline earth metals with the charged surface of the AgNPs, are mitigated through a matrix-matched calibration. In this manner, spectral transitions can be selectively attributed to the concentration of cyanuric acid, which can be even visually quantified at low mg L^?1 levels with minimum sample pre-treatment and without sophisticated instrumentation.

Colorimetric and visual determination of total nereistoxin-related insecticides by exploiting a nereistoxin-driven aggregation of gold nanoparticles

Microchimica Acta - We describe a method for the visual and colorimetric determination of total nereistoxin-related insecticide residues. It is based on the nereistoxin-induced aggregation of gold...     

Highly sensitive voltammetric determination of arsenite by exploiting arsenite-induced conformational change of ssDNA and the electrochemical indicator Methylene Blue

Microchimica Acta - The authors describe a voltammetric method for the determination of arsenite [As(III)] based on an As(III)-specific binding probe DNA (SBP DNA; a single-stranded DNA) and the...     

Colorimetric determination of thrombin by exploiting a triple enzyme-mimetic activity and dual-aptamer strategy

The article describes a colorimetric assay for the determination of thrombin. It is based on the application of a triple enzyme-mimetic activity and a dual aptamer binding strategy. The triple signal amplification relies on oxidation of the chromogenic enzyme substrate 3,3,5,5-tetramethylbenzidine (TMB) that is catalyzed by composites consisting of graphene oxide (GO), gold/platinum nanoparticles (AuPtNP), and aptamer (Apt15), a G-quadruplex/hemin conjugate. The dual-aptamer target binding strategy is based on the fact that thrombin has two active sites to be recognized by its aptamers (Apt15 and Apt29). Magnetic beads (MBs) were modified with Apt29 (Apt29-MB) and then are bound by the GO-AuPtNP-Apt15/G-quadruplex/hemin composites. In the presence of thrombin, Apt29-MB and the GO-AuPtNP-Apt15/G-quadruplex/hemin composites form a sandwich-like superstructure. Thus, the absorbance increases due to the formation of TMB oxide produced by catalysis of the composites. Under optimized conditions, the absorbance at 450 nm increases linearly in the 0.30 to 100 nM thrombin concentration range, and the limit of detection is 0.15 nM. The method is simple, rapid, and does not require complicated instrumentation. Bovine serum albumin, human serum albumin and other proteins were found not to interfere.

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Graphical abstract Schematic presentation of the photometric thrombin assay based on a triple enzyme-mimetic activity of combined nanomaterials (consisting of GO, AuPtNPs and the G-quadruplex/hemin DNAzyme) and two aptamers TMB: 3,3,5,5-tetramethylbenzidine, TMB_ox: 3,3,5,5-tetramethylbenzidine oxide, AuPtNP: gold/platinum nanoparticles).

     

Colorimetric determination of cysteine by exploiting its inhibitory action on the peroxidase-like activity of Au@Pt core-shell nanohybrids

The authors report that the peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine. This finding has led to  a highly sensitive colorimetric assay for cysteine that is based on the nanohybrid-catalyzed oxidation of TMB by H₂O₂ to form a blue product. The method has a detection limit of 5.0 nM and a linear range from 10 nM to 20 μM. The assay is highly selective over other amino acids. It was successfully applied to the determination of cysteine in an injection containing a mixture of amino acids.

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Graphical abstract The peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine, enabling the determination of cysteine.

     

Colorimetric and visual determination of dicyandiamide using gallic acid-capped gold nanoparticles

Microchimica Acta - A new method is presented for the visual detection of dicyandiamide (DCD). Gold nanoparticles (AuNPs) capped with gallic acid (GA) were synthesized in a single step at room...     

单扫描极谱法快速测定牛奶中的三聚氰胺

三聚氰胺在KOH-Na2SO3体系中有一灵敏的氧化峰,峰电位为-0.34 V(vs.SCE),二阶导数峰峰电流与三聚氰胺浓度在1.0×10-2-10.0 mg/L范围内呈良好的线性关系(r=0.9992)。实验发现,将含有150 g/L NaCl的牛奶溶液在100℃中放置10 min,能够有效地避免胶体蛋白的干扰,从而将极谱法成功用于牛奶中三聚氰胺的检测。当牛奶中三聚氰胺含量在0.4~10.0 mg/L时,其浓度与峰电流成线性关系,检测限可达0.1 mg/L,回收率在78.2%~92.5%之间,整个检测时间不超过20 min。     

Atropisomers and near-atropisomers: achieving stereoselectivity by exploiting the conformational preferences of aromatic amides

The conformational preferences of aromatic amides are remarkably easy to control with a high degree of selectivity. This article reviews the consequences of this unusual form of stereocontrol, which enables for example the asymmetric synthesis of atropisomers and the ability to achieve remote stereocontrol by conformational relay.     

Colorimetric and visual determination of DNase I activity using gold nanoparticles as an indicator

Patients with prostate cancer and systemic lupus erythematosus exhibit reduced DNase I activity, and patients with myocardial infarction exhibit increased DNase I activity. So the assay of DNase I is of high importance. A colorimetric assay is described here for the determination of the activity of DNase. It is based on strand scission of dsDNA as catalyzed by DNase I. The products of digestion (nucleoside monophosphates) can better stabilize citrate capped AuNPs than dsDNA. In the absence of DNase I, the AuNPs aggregate in presence of NaCl and then display a blue color. In the presence of the analyte (DNase I), AuNPs do not aggregate but rather remain dispersed and display a red color. These findings were exploited to design a DNase I activity assay that is based on the measurement of ratio of absorbances at 520 nm (red) to 650 nm (blue). The detection limit for DNase I activity is found to be 7.1 U?L^?1. In our perception, this assay has a large potential with respect to diagnoses of DNase I activity-related diseases and in drug screening.

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Graphical Abstract A method is described for the determination of the activity of DNase I. It is based on the capability of nucleoside monophosphates (dNMPs; formed by DNase-catalyzed scission of dsDNA) to stabilize red gold NPs against NaCl-induced aggregation. AuNPs stabilized with dsDNA, in contrast, readily aggregate in presence of NaCl to form blue clusters.

     

Colorimetric determination of molybdenum by the reaction with thiocyanate

Summary A new method for the photometric determination of micro quantities of molybdenum through the thiocyanate method has been developed. The reduction of Mo VI to Mo V is achieved by photochemical reaction at 2 N acidity without the addition of an extraneous reducing agent. The coloured complex is stable for about 36 hrs. in 2.0N acid concentration. The method is accurate to about ±1.0% and Beer's Law is obeyed within the limits of 0 to 100 g.

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Zusammenfassung Ein Verfahren zur photometrischen Bestimmung von Mikromengen MolybdÄn mit der Thiocyanatmethode wird beschrieben. Die Reduktion von Mo^VI zu Mo^V wird durch photochemische Reaktion in 2 n saurem Medium ohne Zusatz eines weiteren Reduktionsmittels erreicht. In diesem SÄuremedium ist der Farbkomplex etwa 36 Std lang stabil. Die erhaltenen Werte sind auf ±1,0% genau und das Beersche Gesetz wird von 0–100 g befolgt.

     

Colorimetric determination of manganese

The colour developed, when freshly formed manganese dioxide dissolves in alkaline tellurate solution is found to be suitable for the colorimetric determination of manganese. The colour obeys Beer's law within the concentration range 1.886.10^-4 - 7.54.10^-4M. The colour is developed by oxidizing Mn(II) (in presence of 2.5M alkali) with the equivalent amount of H₂O₂ in the presence of 4 moles of telluric acid per mole Mn(II).     

Colorimetric determination of sinalbin

Summary Sinalbin (Sinapinp-hydroxybenzylglucosinolate) is present in white mustard seed(sinapis alba) and on enzymatic hydrolysis liberates a sharp, hot, pungent and flavoury compound,p-hydroxybenzyl isothiocyanate (p-HBI). A new sensitive colorimetric method has been developed in which thep-HBI is reacted with sodium hydroxide to givep-hydroxybenzyl alcohol and sodium thiocyanate. The thiocyanate is converted into cyanogen bromide by reacting it with bromine. The cyanogen bromide is then treated with pyridine—benzidine reagent to give a red colour which has an absorption maximum at 518 nm. The red complex solution obeys Beer's law over the concentration range 0.1–0.5 g of SCN per ml of the solution. One mole of sinalbin gives rise to one mole of thiocyanate ion. Recovery is 90%.

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Zusammenfassung Sinalbin (Sinapin-p-hydroxybenzylglucosinolat) ist ein Inhaltsstoff des Samens von weißem Senf (Sinapis alba) und bildet bei enzymatischer Hydrolyse eine scharf schmeckende, würzig riechende Verbindung, p-Hydroxybenzyl-isothiocyanat (p-HBI). Ein neues kolorimetrisches Verfahren wurde entwickelt, das auf der Reaktion von p-HBI mit Natronlauge beruht, wobei p-Hydroxybenzylalkohol und NaCNS entstehen. Dieses wird mit Brom zu Bromcyan umgesetzt, das seinerseits mit Pyridin-Benzidin eine Rotfärbung mit dem Absorptionsmaximum bei 518 nm gibt. Die Lösung dieser roten Komplexverbindung folgt dem Beer'schen Gesetz von 0,1–0,5 g SCN^–/ml. Ein Mol Sinalbin entspricht einem Grammion Thiocyanat. Die Ausbeute beträgt etwa 90%.

     

Colorimetric determination of magnesium

From a critical study of the colorimetric determination of magnesium with titan yellow we concluded that: a. titan yellow must be present in excess; b. a mixture of glycerol and starch solution is satisfactory as protecting colloid; c. the influence of calcium becomes constant with concentrations 10 mg Ca⁺² per 100 ml; d. aluminium, iron, phosphate, ammonium and silica interfere; e. alkali-ions interfere when present in large quantities.The method is rapid and the accuracy is satisfactory and can be recommended for the determination of Mg⁺² in water and in silicates.     

Colorimetric determination of anionic detergents

Many types of anionic detergents can be determined colorimetrically by the action of the detergent on a protein-bromcresol purple complex. The amount of free dye liberated from the complex is proportional to the amount of detergent added between certain limits.     

Colorimetric determination of organic compounds by formation of hydroxamic acids

Carboxylic acids, their chlorides, anhydrides, esters, lactones, amides, lactams and imides react with hydroxylamine to give hydroxamic acids which are then treated with iron(III). Other compounds or groups of compounds can also be determined after a prior conversion into hydroxylamine-reactive derivatives. The calorimetric applications of these reactions are reviewed. The effect of various factors is discussed. A selective procedure for determination of acid chlorides and anhydrides and an improved procedure for determination of carboxylic esters and lactones are presented.