Intensity Of Color Development Research Articles

Immunodipstick based gold nanosensor for vitamin B12 in fruit and energy drinks

The aim of the work is to develop a gold nanoparticle-based immunodipstick for the rapid detection of vitamin B12 in food samples. The membrane was coated with capturing reagents, that is, Bovine serum albumin–vitamin B12 conjugate and was dipped in different concentrations of vitamin B12 solution containing vitamin B12 IgY antibodies labeled with gold nanoparticles (GNPs). The intensity of color development was inversely proportional to the vitamin B12 concentration with maximum intensity at zero vitamin B12 concentration. The visible detection limit of vitamin B12 was determined to be 1 ng ml−1. GNPs of definite size were synthesized and conjugation efficiency of the GNP–protein conjugates was confirmed qualitatively and quantitatively through gel electrophoresis, flocculation assay, UV-visible, fluorescence spectroscopy, Fourier-transform infrared spectroscopy and transmission electron microscopy. The detection limit of this method is higher than the conventional method, enzyme-linked immunosorbent assay. The results of fruit drinks spiked with 1, 10 and 100 ng ml−1 of vitamin B12 and labeled drinks were in good agreement with those obtained by ELISA. The reproducibility and stability were checked. The simple and non-instrumental dipstick method may further be extended to the screening of other forms of vitamin B12 in food.

Selection of an optimum pH-indicator for developing lactic acid bacteria-based time–temperature integrators (TTI)

Among all time–temperature integrator (TTI) types, microbial-based TTIs prevail since their response is directly related to food spoilage. For the development of lactic acid bacteria-based TTIs, optimum pH-indicators were chosen as follows. Five kinds of potential pH-indicators and four species of lactic acid bacteria were used to create microbial-based TTIs. The qualifying standards for pH-indicator selection were defined as (1) the effect of microorganism inhibition, (2) the simplicity of mechanistic interpretation of the color development reaction, and (3) intensity of color development. In particular, the reaction of TTI color development could be enhanced from non zero-order to zero-order. Overall, the optimum pH-indicator for the microbial TTIs was bromocresol green, followed by bromocresol purple, bromophenol blue, chlorophenol red, and congo red, in descending rank order. In conclusion, the choice of pH-indicators was found to be selective to assure effective color development of TTI.

Gold nanoparticles based dipstick immunoassay for the rapid detection of dichlorodiphenyltrichloroethane: An organochlorine pesticide

Gold nanoparticles (GNPs) based dipstick competitive immunoassay was developed to detect organochlorine pesticide such as DDT at nanogram level (ppb). GNPs of definite size were synthesized and conjugated to anti-DDT antibodies (IgY), which served as the detecting reagent. DDA-BSA conjugate (antigen) was immobilized on to nitro cellulose (NC) membrane containing strip. GNPs conjugated anti-DDT antibodies were treated with different concentrations of free DDT ranging from 0.7 ng mL −1 to 1000 ng mL −1 to form an immunocomplex. This immunocomplex solution was further reacted with DDA-BSA conjugate immobilized NC membrane containing strips by dipping the strip in the immunocomplex solution. The free GNPs conjugated anti-DDT antibodies present in the immunocomplex solution were targeted for competitive binding with immobilized DDA-BSA on NC membrane containing strip. Depending on the concentration of free DDT in the sample the binding of GNPs conjugated anti-DDT antibodies to the immobilized DDA-BSA varied and was detected by the development of red color (due to gold nanoparticles) in the detection zone of NC membrane containing strips. The intensity of color development was inversely proportional to the DDT concentration with maximum intensity at zero DDT concentration. The lowest detection limit of DDT was determined to be 27 ng mL −1 with the optimized conditions. The dipstick technique based on GNPs is suitable for the detection of several toxins in food and environmental samples and can be applied for rapid on-site testing of pesticides.

Alterações morfológicas e acúmulo de compostos fenólicos em plantas de sorgo sob estresse de alumínio

Os efeitos do alumínio (Al+3) sobre a morfologia e o acúmulo de compostos fenólicos foram avaliados em duas cultivares de sorgo (Sorghum bicolor (L.) Moench) com tolerância diferencial ao Al+3. As plantas foram mantidas em solução nutritiva durante dez dias, na presença (185 mM) ou na ausência de Al+3. Os ápices radiculares foram coloridos com hematoxilina férrica, sendo a intensidade da coloração observada na presença do Al+3 muito próxima entre as cultivares, o que inviabiliza a aplicação desse teste, isoladamente, para discriminação entre o genótipo sensível e o tolerante ao Al+3. As análises da morfologia externa e interna dos ápices radiculares de plantas tratadas com Al+3 também foram muito similares entre as duas cultivares, não permitindo a utilização dessas características para seleção entre a cultivar sensível e a tolerante. O maior acúmulo de lignina e, principalmente, a menor produção de compostos fenólicos, observados na presença do Al+3 nas raízes das plantas da cultivar tolerante (BR006R), são parâmetros que possibilitam a discriminação das cultivares quanto à tolerância ao Al+3.

A modification of the Lowry method for detecting protein in media containing lignocellulosic substrates

Clostridium thermocellum culture media containing crude cellulosic substrates, prepared by the steam-explosion of wood or straw, were found to interfere strongly with the Lowry method of protein determination. Investigations into the mode of interferences demonstrated that either the intercept (blank value) and/or the slope (intensity of color development) were affected. The efficiencies of precipitation procedures using the trichloroacetic acid method and the deoxycholate-trichloroacetic acid method were compared.

Determination of Sodium Carboxymethyl Cellulose in Household Detergents by Anthrone-Naphthalenediol Method

Ordinarily, the household detergents contain about 1% of sodium carboxymethyl cellulose (CMC) to prevent redeposition of soil. For the determination of CMC itself, nitric acid-methanol method is usual. This method is not applicable for the determination of CMC in household detergents, as the components which are insoluble in 80% methanol solution are added to CMC.Anthrone or naphthalenediol method is used for the determination of CMC in household detergents. In the both methods, however, intensity of color development is influenced by the degree of substitution of hydrogen of hydroxy radicals by carboxymethyl radicals. If the degree of substitution isunknown, the content of CMC can not be found unless the degree of substitution is assumed. Furthermore, intensity of color development is influenced by ingredients of detergent.Authors noted that intensity of color development of these methods indicate reverse relationship with the degree of substitution, and found that combination of these two method is available to determine both the content and the degree of substitution. At the same time, the measuring conditions were investigated for. As a result, this method is useful for the determination of CMC in household detergents.

Chemical Stability of Indicators and Substrate-Indicators Used for the Detection of Phosphatase Activity

Summary The reagents 2, 6-dibromo-N-chloro- p -quinoneimine (BQC), N, 2, 6-trichloro- p -quinoneimine (CQC), phenolphthalein phosphate, and p -nitrophenyl phosphate, in powder form and as solutions, for use as indicators or substrate-indicators in phosphatase testing, were stored under a variety of conditions, to observe rates of deterioration. CQC reagent was remarkably superior to BQC in maintaining chemical stability over long periods of time. Storage conditions for maximum stability of the four reagents were determined. BQC and CQC powder may be stored at any temperature between −5 and 20° C. for as long as 1 yr. BQC solutions may be stored at −5° C. for not longer than 30 days. CQC solutions may be stored at 5° C. for as long as 258 days. Phenolphthalein phosphate powder may be stored at −5° C. as long as 1 yr., whereas solutions of this reagent may be stored at −5° C. as long as 258 days. Powdered p -nitrophenyl phosphate may be stored at −5° C. as long as 105 days, and solutions of this reagent may be stored at −5° C. as long as 81 days. The indicators CQC and BQC, in solution, are best kept in dark brown, well-stoppered glass containers, while the two substrate-indicators are best protected in clear glass, well-stoppered containers. CQC and BQC were compared relative to their solubilities and rate and intensity of color development in simple model systems and in actual milk phosphatase systems. In absolute methanol, absolute ethanol, and 95% ethanol, CQC was rapidly and completely soluble. BQC was readily soluble only in absolute methanol. The rate of blue color development was influenced greatly by the chemical system in which the indicators reacted with available phenol. The rate was similar for both BQC and CQC in the zinc sulfate-borate color development system associated with the Sanders and Sager method (8). In the trichloracetic acid-carbonate buffer color development system of the Cornell phosphatase method, both indicators reacted more rapidly with the available phenol. Maximum color development for each indicator was attained four times faster at 37° C. and twice as fast at 25° C. in the trichloracetic acid-carbonate system. The data show that maximum color can be developed in the Cornell method in 15min. at room temperature, rather than the earlier recommended 15min. at 37° C. In the trichloroacetic acid-carbonate system CQC developed slightly more blue color than BQC at high levels of free phenol, but at low levels no differences were observed. The chemical stability, solubility, and rate and intensity of color development indicate that CQC is more suitable for use as an indicator for phosphatase testing than is BQC. It should receive preference in the future.

An improved method for the Schultz cholesterol test.

The Schultz histochemical adaptation of the Burchard-Liebermann reaction is considered by most authors to be specific for cholesterol and its esters (2, 3). The latter are thought to respond positively to the test after being converted to 7-hydroxycholesterol or a compound very similar to it (4). There are three undesirable technical features associated with the Schultz test procedure when it is used as commonly described. First, there is frequently a precipitation of ferric ammonium sulfate on the tissue sections during incubation. Secondly, bubble formation often occurs after the coverslip is applied, many times regardless of the purity of the acetic-sulfuric acid mixture. Lastly, the intensity of color development is often quite variable from one area to another, especially when the amount of cholesterol present in the tissue is small. We have found these difficulties in the technique to be of considerable concern in our laboratory since ruminant adrenals, which we work with primarily, contain much less cholesterol than those of most other species.

VARIABLES WHICH AFFECT COLOR DEVELOPMENT IN A MODIFICATION OF ZIMMERMANN'S REACTION AND A SPECTROPHOTOMETRIC ANALYSIS OF COLORS DEVELOPED WITH KETOSTEROIDS12

DURING THE COURSE of the experiments recorded in the preceding paper(i) it became increasingly obvious that a number of variable factors influence the rate and intensity of color development in the assay of androgens3 by the mdinitrobensene reaction. These findings had been noted previously by other observers. When we began our observations in 1937, Zimmermann (2, 3) and Wu and Chou (4) had already published their data which were incomplete and not entirely in accord. Callow, Callow and Emmens (5) later reported a more comprehensive study of these variables. Their publication served to reemphasize the importance of the latter, but did not contain sufficiently detailed data on this phase of the problem. Using Wu and Chou's technic as a point of departure, Callow et al. attempted to find those conditions which give the maximum intensity of color per unit weight ofandrogen. Zimmermann had previously pointed out that an attempt