Blue Color Change Research Articles

A label-free hairpin aptamer probe for colorimetric detection of adenosine triphosphate based on the anti-aggregation of gold nanoparticles.

A facile and rapid colorimetric approach was described for selective and sensitive determination of adenosine triphosphate (ATP) based on a hairpin aptamer probe and the anti-aggregation of AuNPs. Poly(diallyldimethylammonium chloride) (PDDA) can induce the aggregation of AuNPs due to the electrostatic interaction causing a red to blue color change. Upon the addition of ATP, aptamer-based hairpin probe is opened and releases flexible ssDNA ends. The released flexible ssDNA ends can interact with PDDA and prevent PDDA-induced AuNPs aggregation. Thus, a visible color change from blue to red and a decrease in the absorption ratio (A610/A520) are observed. Under the optimal conditions, the hairpin aptamer-based colorimetric assay exhibits high sensibility and selectivity for the detection of ATP with a detection limit of 1.7nM. Moreover, this assay is successfully used in the rapid determination of ATP in spiked human serum samples with good recoveries in the range of 102.88 to 104.07%.

Cu@Au(Ag)/Pt nanocomposite as peroxidase mimic and application of Cu@Au/Pt in colorimetric detection of glucose and l-cysteine.

Nanomaterial-based artificial peroxidase has attracted extensive interests due to their distinct advantages over natural counterpart. Cu@Au/Pt and Cu@Ag/Pt nanocomposite with rambutan-like structure were prepared and discovered to function like peroxidase, which was illustrated by catalyzing the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) accompanied with a blue color change. Steady-state investigation indicates that the catalytic kinetics of Cu@Au/Pt and Cu@Ag/Pt all followed typical Michaelis–Menten behaviors and Cu@Au/Pt showed a strong affinity for H2O2, while Cu@Ag/Pt showed strong affinity for TMB. The color change and absorbance intensity strongly depend on the concentration of H2O2, thus the direct determination of H2O2 and indirect detection of glucose were demonstrated using Cu@Au/Pt with a detection limit of 1.5 μM and 6 μM, respectively. What is more important, the method was applied for detection of glucose in 50% fetal bovine serum with a detection limit of 80 μM, which is much lower than the lowest glucose content in blood for diabetes (7 mM). Moreover, the Cu@Au/Pt nanocomposite were also successfully applied for sensing l-cysteine because of the inhibition effect. Considering the good peroxidase-like activity and novel structure, Cu@Au(Ag)/Pt is expected to have a wide range of applications in bioassays and biocatalysis.

Pengolahan Citra Digital untuk Menentukan Kadar Asam Askorbat pada Buah dengan Metode Titrasi Iodimetri

Measurement of ascorbic acid in fruits can be implemented by various methods. The method often used to measure ascorbic acid levels is the iodometric titration method. In this research applying digital image processing with color segmentation to measure levels of ascorbic acid using iodimetry titration method, because end point indicator of titration is a change of blue color in the titration solvent. From the research, digital image processing is capable to detect the blue color changes in the titration solvent. Measurement of ascorbic acid level in lime fruit by implementing digital image processing with color space transformation to HSV showed that the average ascorbic acid content was 0.037% and an average error value of 17.54%.

Metastable α-AgVO3 microrods as peroxidase mimetics for colorimetric determination of H2O2.

Single phase metastable α-AgVO3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion were synthesized by direct coprecipitation at room temperature. They are shown to be viable peroxidase mimics that catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of H2O2. Kinetic analysis indicated typical Michaelis-Menten catalytic behavior. The findings were used to design a colorimetric assay for H2O2, best measured at 652nm. The method has a linear response in the 60 to 200 μM H2O2 concentration range, with a 2μM detection limit. Benefitting from the chemical stability of the microrods, the method is well reproducible. It also is easily performed and highly specific. Graphic abstract Single phase metastable α-AgVO3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion can efficiently catalyze the oxidation reaction of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue color change.

Protective effects of biodegradable collagen implants on thinned sclera after strabismus surgery: a paired-eye study

To determine the efficacy of a biodegradable Ologen (Aeon Astron Europe BV, Leiden, The Netherlands) collagen matrix in reducing the blue color change due to exposed thinned sclera after strabismus surgery. Fourteen patients with intermittent exotropia undergoing symmetric bilateral lateral rectus recession surgery were included in this prospective, randomized, paired-eye controlled study. In each patient, Ologen was implanted at the original rectus insertion site in one randomly selected eye; the other eye underwent conventional surgery. Ologen was inserted under the conjunctiva without suturing, covering the muscle insertion site. Conjunctival color change was analyzed using computer-based image analysis immediately and 1week, 1month, and 3months postoperatively. Slit-lamp photographs of each eye were evaluated using contrast limited adaptive histogram equalization (CLAHE), Canny edge, and the RGB (red-green-blue) model. Secondary outcomes were conjunctival and sclera thickness 3months postoperatively determined by anterior segment optical coherence tomography. Immediately and 1week postoperatively all color models showed no significant differences between Ologen-implanted and control eyes. Three months postoperatively, Ologen-implanted eyes exhibited significantly lower CLAHE (P=0.041) and RGB model blue color (P=0.008) values than control eyes. Canny edge (P=0.061) and RGB model red color (P=0.152) values did not differ between eyes. Conjunctival stroma and episcleral complex thickness was greater in Ologen-implanted eyes than in controls (P=0.001). Blue color change was significantly less noticeable in Ologen-implanted eyes than in controls. Thus, Ologen implantation helps prevent visible blue sclera at the original rectus insertion site after lateral rectus recession.

Ultra-sensitive fluorescent and colorimetric detection of UO22+ based on dual enzyme-free amplification strategies

A novel fluorescent and colorimetric strategy with enzyme-free dual amplification was developed for ultra-sensitively detection of uranyl in river waters samples. The enzyme-strand recycling and hairpin catalytic assembly (HCA) reaction were used as dual enzyme-free amplification strategies. Three hairpins labeled with fluorophore can absorb on the surface of gold nanoparticles (AuNPs) to prevent them from aggregation in salt solution and quench the fluorescent signal simultaneously. In the presence of UO22+, the HCA reaction between hairpins was induced to form rigid DNA triangles, resulting in the aggregation of AuNPs with a red to blue color change and a “turn-on” fluorescent signal. The limit of detection was as low as 0.1pM. Importantly, this strategy provided colorimetric and fluorescent dual signals for lower false-positives and higher anti-interference ability. It was successfully used for detection of uranyl in real waters samples.

An Affordable Microsphere-Based Device for Visual Assessment of Water Quality.

This work developed a prototype of an affordable, long-term water quality detection device that provides a visual readout upon detecting bacterial contamination. This device prototype consists of: (1) enzyme-releasing microspheres that lyse bacteria present in a sample, (2) microspheres that release probes that bind the DNA of the lysed bacteria, and (3) a detector region consisting of gold nanoparticles. The probes bind bacterial DNA, forming complexes. These complexes induce aggregation of the gold nanoparticles located in the detector region. The nanoparticle aggregation process causes a red to blue color change, providing a visual indicator of contamination being detected. Our group fabricated and characterized microspheres made of poly (ε-caprolactone) that released lysozyme (an enzyme that degrades bacterial cell walls) and hairpin DNA probes that bind to regions of the Escherichia coli genome over a 28-day time course. The released lysozyme retained its ability to lyse bacteria. We then showed that combining these components with gold nanoparticles followed by exposure to an E. coli-contaminated water sample (concentrations tested—106 and 108 cells/mL) resulted in a dramatic red to blue color change. Overall, this device represents a novel low-cost system for long term detection of bacteria in a water supply and other applications.

Visual and quantitative detection of glucose based on the intrinsic peroxidase-like activity of CoSe2/rGO nanohybrids

Glucose concentration in human body is a significant indicative for diabetes screening, so it is very significant to develop rapid and sensitive methods for glucose detection. Herein, CoSe2/reduced graphene oxide (CoSe2/rGO) nanohybrids were synthesized via a simple and convenient hydrothermal method, and also their morphologies and compositions were systematically characterized. The CoSe2/rGO nanohybrids were found to possess an intrinsic peroxidase-like activity and can effectively catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) accompanied with a blue color change. The catalytic activity of CoSe2/rGO nanohybrids is matched with the typical Michaelis–Menten kinetics and highly dependent on reaction time, pH, incubation temperature, and H2O2 concentration. The peroxidase-like CoSe2/rGO nanohybrids were successfully applied for the detection of H2O2 and glucose with the detection limit as low as 0.23μM and 0.553μM, respectively. Furthermore, some other carbohydrates, such as lactose, sucrose, galactose and fructose have no interferences with the detection of glucose. The detection platforms for glucose developed in the present work not only confirmed that the CoSe2/rGO nanohybrids possess intrinsic peroxidase-like activity but also showed great potential applications in varieties of simple, robust, and easy-to-make analytical approaches in the future.

Montmorillonite-loaded ceria nanocomposites with superior peroxidase-like activity for rapid colorimetric detection of H2O2

An efficient novel colorimetric sensor for H2O2 based on peroxidase-like CeO2-montmorillonite (MMT) nanocomposites that were successfully prepared by a facile one-pot approach, was realized. In comparison with other nanomaterials as peroxidase mimics, the catalytic reaction by the well-dispersed CeO2-MMT nanocomposites was in accordance with typical Michaelis–Menten kinetics, which exhibited a higher affinity to 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2, bringing about a superior peroxidase-like activity (a distinct blue color change was observed rapidly within 30s, by the naked eye.) than that of pure CeO2 nanoparticles, MMT and their hybrid materials, respectively. Under the optimized conditions, CeO2-MMT nanocomposites were used to establish a colorimetric biosensor for the detection of H2O2 in a relative wide range of 9×10−6M to 5×10−4M with a lower detection limit of 7.8×10−6M. The sensor was successfully applied in H2O2 detection in milk samples.

A Simple Paper-Based Colorimetric Device for Rapid Mercury(II) Assay.

Contamination of the environment by mercury(II) ions (Hg2+) poses a serious threat to human health and ecosystems. Up to now, many reported Hg2+ sensors require complex procedures, long measurement times and sophisticated instrumentation. We have developed a simple, rapid, low cost and naked-eye quantitative method for Hg2+ environmental analysis using a paper-based colorimetric device (PCD). The sample solution to which platinum nanoparticles (PtNPs) have been added is dispensed to the detection zone on the PCD, where the 3,3,5,5-tetramethylbenzidine (TMB) substrate has been pre-loaded. The PtNPs effect a rapid oxidization of TMB, inducing blue colorization on the PCD. However, Hg2+ in the solution rapidly interact with the PtNPs, suppressing the oxidation capacity and hence causing a decrease in blue intensity, which can be observed directly by the naked eye. Moreover, Hg2+ at concentrations as low as 0.01 uM, can be successfully monitored using a fiber optic device, which gives a digital readout proportional to the intensity of the blue color change. This paper-based colorimetric device (PCD) shows great potential for field measurement of Hg2+.

Observación del efecto reductor de N-Acetilcisteína en el metabolismo de levaduras

The research focuses on the design of experimental teaching using readily available materials and simple methods to implement. It arises as an example for learning, using baker's yeast Saccharomyces cerevisiae, because it has many of the metabolic pathways existing in mammalian cells. In this paper it was developed an essay that allow students to observe macroscopically the capacity of N- Acetyl cysteine (NAC) to stimulate the reducing power of yeast using indicator Methylene Blue (MB) color change.

Establishment of a loop-mediated isothermal amplification (LAMP) assay for the detection of phytoplasma-associated cassava witches’ broom disease

Cassava (Manihot esculenta Crantz) is one of the most important food crops in the tropics; however, bacterial phytopathogens pose a serious threat to its farming. Cassava Witches’ Broom Disease (CWB) is caused by the infection of phytoplasma and is manifested as reduction in tuber yield and starch content at harvest of 10 and 30 %, respectively. Although polymerase-chain reaction provides the gold standard in diagnostics, this method requires significant investments in infrastructure and training. Here, we developed a loop-mediated isothermal amplification (LAMP) assay that allows specific detection of phytoplasma from field-collected samples. Three primer sets were designed, of which two detected phytoplasma DNA sequence encoding 16S rRNA (16S rDNA), the other detected cassava actin. Following a 1 h LAMP reaction at 63 °C, a positive reaction can be visualized by agarose gel electrophoresis, hydroxynaphthol blue color change, or the presence of a precipitate. In a pilot field study, the assay was able to rapidly distinguish between healthy and CWB-infected cassava. With further development, a LAMP for routine on-site screening of cassava crops can be envisioned.

Synthesis and intrinsic enzyme-like activity of β-MnOOH nanoplates

Single phase β-MnOOH with high crystallinity was successfully synthesized by a method combining controlled hydrothermal synthesis and subsequently air oxidation. The results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy showed that the as-prepared β-MnOOH had a thin hexagonal layered structure, uniform particle size distribution, and good dispersion. The presence of hydrazine and suitable hydrothermal temperature (140 °C) are of the two key factors to synthesize pure phase β-MnOOH. The synthesized β-MnOOH nanoplates could catalyze the oxidation reaction of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine in the absence of H2O2 to produce a blue color change, indicating an intrinsic enzyme-like activity. Furthermore, as an inorganic enzyme mimic, β-MnOOH also showed high stability, which facilitates its potential applications as enzyme mimics in biosensor, biotechnology, and biomedicine.

A FRET-based ratiometric fluorescent probe for visualizing H2S in lysosomes

Hydrogen sulfide (H2S) is an endogenously produced gaseous signaling molecule with multiple biological functions. In order to detect the biological H2S, here a new FRET-based ratiomatric fluorescent probe was designed and synthesized for visualization of H2S in lysosomes. The probe displays good solubility, a marked yellow to blue emission color change in response of H2S and high H2S selectivity. Moreover, the probe could be used to detect of H2S in lysosomes with good biocompatibility.

A simple, high-throughput, colourimetric, field applicable loop-mediated isothermal amplification (HtLAMP) assay for malaria elimination.

BackgroundTo detect all malaria infections in elimination settings sensitive, high throughput and field deployable diagnostic tools are required. Loop-mediated isothermal amplification (LAMP) represents a possible field-applicable molecular diagnostic tool. However, current LAMP platforms are limited by their capacity for high throughput.MethodsA high-throughput LAMP (HtLAMP) platform amplifying mitochondrial targets using a 96-well microtitre plate platform, processing 85 samples and 11 controls, using hydroxynaphtholblue as a colourimetric indicator was optimized for the detection of malaria parasites. Objective confirmation of visually detectable colour change results was made using a spectrophotometer. A dilution series of laboratory-cultured 3D7 Plasmodium falciparum parasites was used to determine the limit of detection of the HtLAMP assay, using P. falciparum (HtLAMP-Pf) and Plasmodium genus (HtLAMP-Pg) primers, on whole blood and filter paper, and using different DNA extraction protocols. The diagnostic accuracy of HtLAMP was validated using clinical samples from Papua New Guinea, Malaysia, Ghana and The Gambia and its field applicability was evaluated in Kota Marudu district hospital, Sabah, Malaysia.ResultsThe HtLAMP assay proved to be a simple method generating a visually-detectable blue and purple colour change that could be objectively confirmed in a spectrophotometer at a wavelength of 600 nm. When compared with PCR, overall HtLAMP-Pg had a sensitivity of 98 % (n = 260/266, 95 % CI 95–99) and specificity 83 % (n = 15/18, 95 % CI 59–96). HtLAMP-Pf had a sensitivity of 97 % (n = 124/128, 95 % CI 92–99) and specificity of 96 % (n = 151/157, 95 % CI 92–99). A validation study in a regional hospital laboratory demonstrated ease of performance and interpretation of the HtLAMP assay. HtLAMP-Pf performed in this field setting had a sensitivity of 100 % (n = 17/17, 95 % CI 80–100) and specificity of 95 % (n = 123/128, 95 % CI 90–98) compared with multiplex PCR. HtLAMP-Pf also performed well on filter paper samples from asymptomatic Ghanaian children with a sensitivity of 88 % (n = 23/25, 95 % CI 69–97).ConclusionThis colourimetric HtLAMP assay holds much promise as a field applicable molecular diagnostic tool for the purpose of malaria elimination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0848-3) contains supplementary material, which is available to authorized users.

As a new peroxidase mimetics: The synthesis of selenium doped graphitic carbon nitride nanosheets and applications on colorimetric detection of H2O2 and xanthine

Selenium has been successfully doped into graphite phase carbon nitride (g-C3N4) by a simple thermal condensation method through calcinating the mixture of dicyandiamide, cyanuric acid and selenium dioxide. The morphology and composition of thus-prepared selenium doped graphite phase carbon nitride (Se-g-C3N4) nanosheets were characterized by transmission electron microscopy (TEM), high resolution TEM, X-ray diffraction (XRD), fourier transform infrared (FT-IR) spectra and X-ray photoelectron spectroscopy (XPS). Characterization results revealed that the resultant products have typical ultrathin lamellar structure with the uniform lateral diameter of 20nm. The amount of Se dopant is ca. 2.1at% based on the XPS result. For the first time, ultrathin Se-g-C3N4 nanosheets have been demonstrated to possess an intrinsic peroxidase activity by following the Michaelis–Menten kinetics and even have higher affinity to peroxidase substrates TMB and H2O2 in comparison to that of HRP. Se-g-C3N4 nanosheets is conducive to mediating electron transfer and thus to enhancing the catalytic oxidation of the substrate TMB in the presence of H2O2 to produce a blue color change in aqueous solution. More importantly, a sensitive and selective method for xanthine detection was developed using xanthine oxidase and the as-prepared Se-g-C3N4 nanosheets. On the basis of the high catalytic activity of Se-g-C3N4 nanosheets, a rapid, sensitive, and convenient approach was developed for colorimetric detection of xanthine with detection limit 1.6×10−8molL−1. Taking the advantages of this, the novel Se-g-C3N4 nanosheets represent a promising candidate as an enzyme mimic and may find a wide range of new applications in diagnostics and biotechnology fields.

Synthesis of α-MnSe crystal as a robust peroxidase mimic

α-MnSe crystals as green and cost-efficient peroxidase mimics were successfully synthesized via a facial hydrothermal route in a glycerol/water solution system. They were first found to catalyze the reaction of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to induce a blue color change, indicating an intrinsic peroxidase-like activity. The steady-state kinetic analysis showed that α-MnSe crystals had higher affinity for TMB and lower affinity for H2O2 compared with horseradish peroxidase. The crystal structure, morphology, and catalytic activity could be tailored by adjusting the starting raw materials. The usage of sodium dodecyl sulfate and glycerol could decrease the particle size of α-MnSe crystals to enhance the peroxidase-like activity. Furthermore, benefiting from the chemical and crystal stability, α-MnSe crystals have two potential advantages: long-term stability and ease of recovery, and thus have potential applications as a peroxidase mimic in chemical/bio detection.

Abstract 19342: Bilateral Phlegmasia Cerulea Dolens: More Than Meets the IVC

A 40 year-old woman presented with edema, discoloration and severe pain of the lower extremities. Four weeks prior, she noted chest pain with pain and swelling of the right arm and both legs. Imaging demonstrated sub-segmental pulmonary embolism (PE) with bilateral deep venous thrombi (DVT) of the legs and thrombus of the right brachial vein. She was treated with warfarin however despite anticoagulation, had progressive dyspnea. Repeat imaging demonstrated new PE and progression of bilateral DVT. Anticoagulation was transitioned to argatroban, and an IVC [[Unable to Display Character: fi]]lter was placed. Subsequently, she had worsened edema and discoloration of the lower extremities, weakness, and severe pain. On physical examination, the lower extremities were cold and deeply violaceous with 2/5 strength at the bilateral hips and 0/5 strength below. Pulses were absent. Ultrasound examination demonstrated complete thrombosis of the lower extremity venous system to the level of the IVC. The clinical triad of limb swelling, ischemic pain, and blue color change suggested bilateral phlegmasia cerulea dolens (PCD). She was referred emergently for catheter based thrombolysis, however despite restoration of venous patency, she had progressive lower limb ischemia. She underwent bilateral above-the-knee amputation on hospital day 4. Given her profound thrombotic state, she underwent evaluation for inherited and acquired thrombophilia. To evaluate for malignancy, whole-body PET/CT was performed demonstrating FDG avidity of the gallbladder, multiple liver lesions, and adenopathy at the porta hepatis concerning for metastatic gallbladder carcinoma. Fine-needle biopsy of a liver lesion demonstrated poorly differentiated adenocarcinoma. Given poor prognosis, the patient elected not to pursue further therapy and passed away at home. This patient presented with bilateral PCD as a [[Unable to Display Character: fi]]rst manifestation of metastatic gallbladder carcinoma. PCD is a rare cause of limb ischemia characterized by the clinical triad of limb swelling, ischemic pain, and blue color change. Early attention to restoring venous patency is critical to avoid life and limb loss, and thrombophilia evaluation including evaluation for malignancy should be included in the diagnostic evaluation.

A simple isothermal DNA amplification method to screen black flies for Onchocerca volvulus infection.

Onchocerciasis is a debilitating neglected tropical disease caused by infection with the filarial parasite Onchocerca volvulus. Adult worms live in subcutaneous tissues and produce large numbers of microfilariae that migrate to the skin and eyes. The disease is spread by black flies of the genus Simulium following ingestion of microfilariae that develop into infective stage larvae in the insect. Currently, transmission is monitored by capture and dissection of black flies and microscopic examination of parasites, or using the polymerase chain reaction to determine the presence of parasite DNA in pools of black flies. In this study we identified a new DNA biomarker, encoding O. volvulus glutathione S-transferase 1a (OvGST1a), to detect O. volvulus infection in vector black flies. We developed an OvGST1a-based loop-mediated isothermal amplification (LAMP) assay where amplification of specific target DNA is detectable using turbidity or by a hydroxy naphthol blue color change. The results indicated that the assay is sensitive and rapid, capable of detecting DNA equivalent to less than one microfilaria within 60 minutes. The test is highly specific for the human parasite, as no cross-reaction was detected using DNA from the closely related and sympatric cattle parasite Onchocerca ochengi. The test has the potential to be developed further as a field tool for use in the surveillance of transmission before and after implementation of mass drug administration programs for onchocerciasis.

Ratiometric sensing of fluoride and acetate anions based on a BODIPY-azaindole platform and its application to living cell imaging

A new BODIPY-azaindole based fluorescent sensor 1 was designed and synthesized as a new colorimetric and ratiometric fluorescent chemosensor for fluoride. The binding and sensing abilities of sensor 1 towards various anions were studied by absorption, emission and (1)H NMR titration spectroscopies. The spectral responses of 1 to fluoride in acetonitrile-water were studied: an approximately 69 nm red shift in absorption and ratiometric fluorescent response was observed. The striking light yellow to deep brown color change in ambient light and green to blue emission color change are thought to be due to the deprotonation of the indole moiety of the azaindole fluorophore. From the changes in the absorption, fluorescence, and (1)H NMR titration spectra, proton-transfer mechanisms were deduced. Density function theory and time-dependent density function theory calculations were conducted to rationalize the optical response of the sensor. Results were supported by confocal fluorescence imaging and MTT assay of live cells.