Colorimetric Approach Research Articles

Colorimetric Assays for Acetylcholinesterase Activity and Inhibitor Screening Based on the Disassembly−Assembly of a Water-Soluble Polythiophene Derivative

A complex between an anionic polythiophene derivative (PT-COO(-)) and a cationic surfactant, myristoylcholine, has been prepared and applied to be colorimetric probe for acetylcholinesterase (AChE) assays. The complex formation process, AChE activity assay and inhibitor screening has been studied by absorption spectroscopy. It was confirmed that the introduction of myristoylcholine into PT-COO(-) phosphate buffer solution resulted in the disassembly of PT-COO(-) aggregates, and further addition of AChE into the above solution led to the reassembly of PT-COO(-) due to the catalyzed hydrolysis of myristoylcholine and the collapse of the complex. The colorimetric assay for AChE can be readily realized with the concentration of AChE as low as 0.2 U/mL. The results also demonstrate that the colorimetric approach can be applied for screening inhibitors of AChE.

Flexible Colorimetric Detection of Mercuric Ion by Simply Mixing Nanoparticles and Oligopeptides

8 ] has been made over the past few decades. Such optical sensors are normally based on the simple measurement of the UV/Vis spectrum, fl uorescence spectrum, or colorimetry. Colorimetric detec-tion, which is visually and simply read out by the naked eye, is particularly attractive for point-of-use applications. What has limited such a colorimetric approach based on organic chromophoric probes is the narrow selectivity, solubility, and detection range. Recently, colorimetric detection based on Au nanopar-ticles (NPs) has drawn much attention,

A gold nanorod based colorimetric probe for the rapid and selective detection of Cu2+ ions

A gold nanorod (AuNR) based colorimetric probe was reported for the rapid and selective detection of Cu(2+) ions. The probe was fabricated by functionalizing cysteine (Cys) onto AuNR (Cys-AuNR) with an aspect ratio of 2.3. The strong coordination of Cu(2+) with cysteine resulted in a stable Cys-Cu-Cys complex, and induced the aggregation of the colloidal nanorods along with a rapid colour change from blue-green to dark gray. Potential factors affecting the performance of the probe for the detection of Cu(2+) were carefully optimized, including the pH value of the buffer media, the concentration of cysteine, and the kinetics for the coordination of Cu(2+) with Cys-AuNR. Under optimal conditions, the developed colorimetric method gave a linear range of 1-100 μM for Cu(2+), and a detection limit (3s) of 0.34 μM. Moreover, the developed method exhibited excellent selectivity for Cu(2+), and quantitative spike-recoveries from 90% to 107% in environmental water samples. The proposed colorimetric approach can in principle be used to detect other metal ions by functionalizing various specific ligands onto the AuNR that can selectively bind the other target metal ions.

Robust Spectral Implementation of High-Fidelity Printer Characterization for Cross-Media High-Dynamic-Range Imaging Applications

This research introduces a multi-spectral type of High-Fidelity (Hi-Fi) colorant color separation algorithm for printing/printer system using more than four inks (colorants). This Hi-Fi colorant separation algorithm, derived for six-colorant CMYKOG printer systems, finds the best colorant combination to reproduce spectra of every color, concerned in high-dynamicrange of original images for an accurate color-matching or – reproduction application. This work revised and extended a previous research, which carried out a seven-ink of CMYKRGB FM printing characterization of presses, only used in the conventional Graphic Arts. An Epson 9900 inkjet printer, having the capability of a six-colorant set, CMYKOG, was spectrally characterized for High-Fidelity (Hi-Fi) multi-color printer simulation. The superset of CMYKOG was divided into three subsets, including two five-colorant groupings of CMYKO and CMYKG, and one four-colorant grouping of CMYK. The spectral printer characterization applied a polynomial regression approach with singular value decomposition method (SVD). The mean ΔE*00 values were 0.98∼1.17 and 1.06∼1.33 found in the forward and the reverse processes respectively. Also 0.0008 ∼ 0.0011 and 0.0009 ∼ 0.0024 of the mean RMSE values were obtained for the forward and the reverse spectral transform respectively. It implies the spectral reflectance of every color in test datasets was satisfactorily reconstructed. Moreover, to robustly perform a feasible approach of spctral color management for Hi-Fi printer simulation in cross-media color reproduction system, a GUI-based of HDR (High-Dynamic-Range) image-fusion module were also be introduced to produce original HDR complex color images. It integrated algorithms of: 1) a multi-raw-processed-image fusion process based on both luminance and gray-balancing strategies; 2) a multiple-conversing-points type of gamut-mapping; 3) Adaptive Multi-illuminants white-balancing; 4) the CIECAM02 color appearance modeling; 5) a Gaussian pyramid type of image enhancement; and 6) a logarithmic HDR tone mapping; and finally an ideal simulated CIEXYZ type of spectra sensing model which adopts interim AdobeRGB connection reference space, combined with CIE 1931 2° standard observer. Consequently, a robust spectral type of cross-media color reproduction system, based on a colorimetric approach of HDR and Hi-Fi (High-Fidelity) was implemented in the study.

Substantiation in Enterococcus faecalis of dose-dependent resistance and cross-resistance to pore-forming antimicrobial peptides by use of a polydiacetylene-based colorimetric assay.

A better understanding of the antimicrobial peptide (AMP) resistance mechanisms of bacteria will facilitate the design of effective and potent AMPs. Therefore, to understand resistance mechanisms and for in vitro assessment, variants of Enterococcus faecalis that are resistant to different doses of the fungal AMP alamethicin (Alm(r)) were selected and characterized. The resistance developed was dose dependent, as both doses of alamethicin and degrees of resistance were colinear. The formation of bacterial cell aggregates observed in resistant cells may be the prime mechanism of resistance because overall, a smaller cell surface in aggregated cells is exposed to AMPs. Increased rigidity of the membranes of Alm(r) variants, because of their altered fatty acids, was correlated with limited membrane penetration by alamethicin. Thus, resistance developed against alamethicin was an adaptation of the bacterial cells through changes in their morphological features and physiological activity and the composition of membrane phospholipids. The Alm(r) variants showed cross-resistance to pediocin, which indicated that resistance developed against both AMPs may share a mechanism, i.e., an alteration in the cell membrane. High percentages of colorimetric response by both AMPs against polydiacetylene/lipid biomimetic membranes of Alm(r) variants confirmed that altered phospholipid and fatty acid compositions were responsible for acquisition of resistance. So far, this is the only report of quantification of resistance and cross-resistance using an in vitro colorimetric approach. Our results imply that a single AMP or AMP analog may be effective against bacterial strains having a common mechanism of resistance. Therefore, an understanding of resistance would contribute to the development of a single efficient, potent AMP against resistant strains that share a mechanism of resistance.

Label-free colorimetric estimation of proteins using nanoparticles of silver

Abstract Metallic nanoparticles have received considerable attention in bioassays and diagnostics due to their unique surface plasmon resonance (SPR) properties. Gold nanoparticles have been employed for the development of SPR-based colorimetric bioassays. In the present report we have described a sensitive colorimetric approach for estimation of proteins, within a detection limit of 10∼80 μg/mL, using unmodified silver nanoparticles. Besides the common advantages of colorimetric assay such as simplicity, high sensitivity, and low cost, our method has a label-free design and provides an important and attractive alternative to classical sensing probes and systems. The present work will contribute to the development of nanotechnology-based diagnostic tools.

A new microtitre plate screening method for evaluating the viability of aerobic respiring bacteria in high surface biofilms

It is difficult to determine the effects of bactericidal compounds against bacteria in a biofilm because classical procedures for determining cell viability require several working days, multiple complicated steps and are frequently only applicable to cells in suspension. We attempt to develop a compact, inexpensive and versatile system to measure directly the extent of biofilm formation from water systems and to determine the viability of respiring bacteria in high surface biofilms. It has been reported that the reduction of tetrazolium sodium salts, such as XTT (sodium 3,3'-[1-[(phenylamino)carbonyl]-3,4-tetrazolium]Bis(4-methoxy)-6-nitro)benzene sulfonic acid hydrate), during active bacterial metabolism can be incorporated into a colorimetric method for quantifying cell viability. XTT is reduced to a soluble formazan compound during bacterial aerobic metabolism such that the amount of formazan generated is proportional to the bacterial biomass. We show here, for the first time, that this colorimetric approach can be used to determine the metabolic activity of adherent aerobic bacteria in a biofilm as a measure of cell viability. This technique has been used to estimate viability and proliferation of bacteria in suspension, but this is the first application to microbial communities in a real undisturbed biofilm. This simple new system can be used to evaluate the complex biofilm community without separating the bacteria from their support. Thus, the results obtained by this practice may be more representative of the circumstances in a natural system, opening the possibility to multiple potential applications.

Colorimetric Sensing of Adenosine Based on Aptamer Binding Inducing Gold Nanoparticle Aggregation

AbstractA simple and rapid colorimetric approach for the determination of adenosine has been developed via target inducing aptamer structure switching, thus leading to Au colloidal solution aggregation. In the absence of the analytes, the aptamer/gold nanoparticle (Au NP) solution remained well dispersed under a given high ionic strength condition in that the random‐coil aptamer was readily wrapped on the surface of the Au NPs, which resulted in the enhancement of the repulsive force between the nanoparticles due to the high negative charge density of DNA molecules. While in the presence of adenosine, target‐aptamer complexes were formed and the conformation of the aptamer was changed to a folded structure which disfavored its adsorption on the Au NP surface, thus leading to the reduction of the negative charge density on each Au NP and then the reduced degree of electrostatic repulsion between Au nanoparticles. As a result, the aggregation of the Au colloidal solution occurred. The changes of the absorption spectrum could be easily monitored by a UV‐Vis spectrophotometer. A linear correlation exists between the ratio of the absorbance of the system at 522 to 700 nm (A522 nm/A700 nm) and the concentration of adenosine between 100 nmol·L−1 and 10 µmol·L−1, with a detection limit of 51.5 nmol·L−1.

Cellular Toxicity of Nanogenomedicine in MCF-7 Cell Line: MTT assay

Cytotoxicity of the futuristic nanogenomedicine (e.g., short interfering RNA and antisense) may hamper its clinical development. Of these, the gene-based medicine and/or its carrier may elicit cellular toxicity. For assessment of such cytotoxicity, a common methodology is largely dependent upon utilization of the 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay which has been widely used as a colorimetric approach based on the activity of mitochondrial dehydrogenase enzymes in cells. In this current investigation, MCF-7 cells were inoculated in 96-well plate and at 50% confluency they were treated with different nanopolyplexes and subjected to MTT assay after 24 hours. Water soluble yellow MTT is metabolized by the metabolically active cells to the water insoluble purple formazan, which is further dissolved in dimethylsulfoxide and Sornson s buffer pH 10.5. The resultant product can be quantified by spectrophotometry using a plate reader at 570 nm.

Cellular Toxicity of Nanogenomedicine in MCF-7 Cell Line: MTT assay

Cytotoxicity of the futuristic nanogenomedicine (e.g., short interfering RNA and antisense) may hamper its clinical development. Of these, the gene-based medicine and/or its carrier may elicit cellular toxicity. For assessment of such cytotoxicity, a common methodology is largely dependent upon utilization of the 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay which has been widely used as a colorimetric approach based on the activity of mitochondrial dehydrogenase enzymes in cells. In this current investigation, MCF-7 cells were inoculated in 96-well plate and at 50% confluency they were treated with different nanopolyplexes and subjected to MTT assay after 24 hours. Water soluble yellow MTT is metabolized by the metabolically active cells to the water insoluble purple formazan, which is further dissolved in dimethylsulfoxide and Sornson s buffer pH 10.5. The resultant product can be quantified by spectrophotometry using a plate reader at 570 nm.

A Hybrid Electrochemical−Colorimetric Sensing Platform for Detection of Explosives

A highly selective, sensitive, and low-cost hybrid sensing platform is developed based on extraordinary properties of explosives in an ionic liquid and an integrated electrochemical and colorimetric approach.

Colorimetric recognition of DNA intercalators with unmodified gold nanoparticles

A colorimetric approach to recognize the binding mode between DNA and molecules was developed, which was based upon the electrostatic interaction between DNA and gold colloids.

Agricultural Ammonia Monitoring Technology

We report on development of ammonia monitoring technology for confine animal feeding operations (CAFOs). The atmosphere within a CAFO is typically hot with high humidity and often considerable concentrations of ammonia. High levels of particulates are often also present. These conditions present a challenge to conventional ammonia monitoring technologies. Here, we discuss our recent progress on development of a fast, sensitive and robust colorimetric approach for ammonia in this challenging environment.

An Ionic‐Liquid Based Probe for the Sequential Preconcentration from Headspace and Direct Voltammetric Detection of Phenols in Wastewaters

AbstractA conveniently assembled probe is here proposed for the electrochemical detection of the phenol index (total volatile phenols) in wastewaters, which exploits some advantageous properties of ionic liquids (ILs), such as their negligible vapor pressure, good electrical conductivity and ability to dissolve a wide range of organic and inorganic compounds. It consists of three Pt wires piercing through a Teflon rod, whose exposed end is coated with an adhesive film of ionic liquid which assured the necessary ionic conductivity between the electrodes while displaying concomitantly good solvent properties. The electrode assembly was exposed to the headspace in equilibrium with wastewater samples for controlled times, until a convenient preconcentration of volatile phenols was achieved. At the end of this step, voltammetric detection was directly performed in situ. The performance of this device was assayed in both phenol synthetic samples and in real wastewaters, after that the preconcentration step was optimized with regard to the effect of pH of the sample, preconcentration time, sample and probe temperature and nature of IL. Voltammetric responses characterized by good repeatability (±4%) were recorded, whose height and area depended linearly on the phenol concentration over a wide range (ca. 3 orders of magnitude). The detection limit, estimated for a signal‐to‐noise ratio of 3 (2 μM at 20 °C and 0.2 μM at 80 °C), was lower than the limit set by the European Community for phenols in wastewaters (ca. 5 μM). The results found in real samples were in acceptable agreement with those obtained by the 4‐aminoantipyrine colorimetric approach which is recommended as the standard method.

Direct examination of the dietary preference of the copepodcalanus helgolandicus using the colorimetric approach

The food selectivity of tethered females of the copepodCalanus helgolandicus was examined by using the colorimetric approach. First, feeding behavior of the copepod did not show any differences between the red-color stained with neutral red and non-stained diets using the diatomCoscinodiscus curvatulus. Then, the copepods were fed a mixtures of two diets, the diatomC. curvatulus, stained with neutral red, and the dinoflagellateGymnodinium sanguineum for 14~60 minutes of feeding duration. The foregut colors of females were examined using a stereo-microscope and a video monitor. The foreguts of animals fed with a high density of diatoms in mixed diets showed a dark red color, whereas those fed with a high density of dinoflagellate in mixed diets were a dark yellow. The results suggest that this species of copepod may not selectively feed either one of the diets used for this study. Their feeding activity may be more likely related to the density of available prey in their environment. Therefore, this quick and easy colorimetric approach could provide very useful information, like the pre-screening procedure before designing and conducting the time-consuming and complex feeding experiments to understand the feeding ecology of copepods.

Screening the Sequence Selectivity of DNA-Binding Molecules Using a Gold Nanoparticle-Based Colorimetric Approach

We have developed a novel competition assay that uses a gold nanoparticle (Au NP)-based, high-throughput colorimetric approach to screen the sequence selectivity of DNA-binding molecules. This assay hinges on the observation that the melting behavior of DNA-functionalized Au NP aggregates is sensitive to the concentration of the DNA-binding molecule in solution. When short, oligomeric hairpin DNA sequences were added to a reaction solution consisting of DNA-functionalized Au NP aggregates and DNA-binding molecules, these molecules may either bind to the Au NP aggregate interconnects or the hairpin stems based on their relative affinity for each. This relative affinity can be measured as a change in the melting temperature (Tm) of the DNA-modified Au NP aggregates in solution. As a proof of concept, we evaluated the selectivity of 4',6-diamidino-2-phenylindone (an AT-specific binder), ethidium bromide (a nonspecific binder), and chromomycin A (a GC-specific binder) for six sequences of hairpin DNA having different numbers of AT pairs in a five-base pair variable stem region. Our assay accurately and easily confirmed the known trends in selectivity for the DNA binders in question without the use of complicated instrumentation. This novel assay will be useful in assessing large libraries of potential drug candidates that work by binding DNA to form a drug/DNA complex.

A Colorimetric Sensor Array for Organics in Water

Molecular recognition of organic compounds in aqueous solutions is inherently challenging due to the potential interference from the very high concentration of water. Here we present a simple colorimetric sensor array that probes a wide range of chemical properties. By printing hydrophobic dyes on a hydrophobic membrane, sensor arrays are easily prepared that provide substantial chemical selectivity for the identification and quantification of various organics (both single compounds and complex mixtures) dissolved in water. It is possible to differentiate easily even among closely related organic compounds. Upon immersion in aqueous solutions, digital imaging of the dye array before and after exposure to an analyte provide a color change profile that is a fingerprint for the organic components of the solution. Facile identification of a wide variety of aqueous organic solutions is possible over a concentration range of 0.1 M to 1 muM. Complex mixtures present no inherent difficulty; for example, a series of commercial soft drinks were easily distinguished using the colorimetric sensor array approach.

Colorimetric Approach to High-Throughput Mutation Analysis

High-throughput genomic mutation screening for primary tumors has characteristically been expensive, labor-intensive, and inadequate to detect low levels of mutation in a background of wild-type signal. We present a new, combined PCR and colorimetric approach that is inexpensive, simple, and can detect the presence of 1% mutation in a background of wild-type. We compared manual dideoxy sequencing of p53 for eight lung cancer samples to a novel assay combining a primer extension step and an enzymatic colorimetric step in a 96-well plate with covalently attached oligonucleotide sequences. For every sample, we were able to detect the presence or absence of the specific mutation with a statistically significant difference between the sample optical density (OD) and the background OD, with a sensitivity and specificity of 100%. This assay is straightforward, accurate, inexpensive, and allows for rapid, high-throughput analysis of samples, making it ideal for genomic mutation or polymorphism screening studies in both clinical and research settings.

A Colorimetric Approach to Anion Sensing: A Selective Chemosensor of Fluoride Ions, in which Color is Generated by Anion‐Enhanced π Delocalization

Ein farbloser neutraler Rezeptor ohne charakteristische chromogene Substituenten erkennt selektiv Fluorid-Ionen (siehe Schema). Der Rezeptor trägt zwei äquivalente Molekülarme, die jeweils mit einer Thioharnstoff-Gruppe ausgerüstet sind. Die gelbe Farbe des Rezeptor-Anion-Komplexes stammt von einer ausgeprägten π-Elektronen-Delokalisierung, induziert durch die starken Wasserstoffbrücken zwischen den F−-Ionen und den inneren NH-Gruppen der Thioharnstoff-Einheiten.

A colorimetric approach to anion sensing: a selective chemosensor of fluoride ions, in which color is generated by anion-enhanced pi delocalization.

A colorless neutral receptor with no particular chromogenic substituents selectively recognizes fluoride ions with a concomitant development of a yellow color (see scheme). The receptor contains two equivalent arms, each equipped with a thiourea fragment. Color originates from the extended π delocalization induced by the strong hydrogen-bonding interaction of the F− ion with the internal NH groups of thiourea moieties. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2004/z53148_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.