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Dengue surveillance trusts only on reverse transcription-polymerase chain reaction (RT-PCR) type methodologies for confirmation of dengue virus serotypes; however, its real time application is restricted due to the expensive, complicated, and time-consuming process. In search of a new sensing system, here, we have reported a two-way-detection method for Dengue virus (DENV) serotype identification along with DNA quantification by using a new class of nanocomposite of gold nanoparticles (AuNP) and nitrogen, sulfur codoped graphene quantum dots (N,S-GQDs). The N,S-GQDs@AuNP has been used for serotype detection via a simple fluorescence technique using four dye-combined probe DNAs which is further validated by confocal microscopy. The quantification of the DNA has been measured by the differential pulse voltammetric (DPV) technique using methyelene blue as a redox indicator. Results obtained in this study, clearly demonstrate that the N,S-GQDs@AuNP can efficiently detect the four serotypes of DENV individually in the concentration range of 10

Herein we describe The Purple Flask, a novel color-changing redox reaction that uses ascorbic acid as an electron donor, atmospheric oxygen as an electron acceptor, a copper–iron mixture as a redox catalyst, and the purple phenothiazine dye thionine as redox indicator. This formulation has several advantages over other versions of the classic “blue bottle” reaction for classroom demonstrations: (i) It uses noncaustic chemicals and proceeds at mildly acidic pH 4.2. (ii) The purple color generated by the oxidation reaction is intense, but fades rapidly. (iii) The reduction reaction rate is very temperature sensitive, which enables exploration of the impact of temperature on reaction kinetics. The Purple Flask is a vivid classroom demonstration that quickly captures student attention and can be used to illustrate the principles of redox chemistry in settings ranging from middle school through high school advanced placement chemistry and introductory college chemistry.

Sensing of intracellular NAD(P)H is important for numerous applications ranging from diagnostic assays to drug discovery. Up to now, investigation of NAD(P)H-dependent pathways in live cells has been restrained by the lack of efficient tools. Toward this goal, we developed a small molecule indicator, which allows both colorimetric and fluorescent NAD(P)H detection in biological samples. The design is based on a cyanine dye scaffold and utilizes a novel two-acceptor “turn-on” mechanism. Consequently, this indicator features unprecedented sensitivity and rapid response toward NAD(P)H at low micromolar levels under physiological conditions. First, we demonstrated the value of this reagent in a diagnostic assay of glucose, through the enzyme-coupling reaction of NAD(P)+-dependent glucose dehydrogenase (GDH). Second, we showed the utility of our indicator for NAD(P)H imaging in live cells. We confirmed its ability to reflect different NAD(P)H levels using the human colon cancer cell line deficient on mitochond...

A simple and ultrasensitive microRNA (miRNA) electrochemical biosensor employing multiwalled carbon nanotube (MWCNT)-polyamidoamine (PAMAM) dendrimer and methylene blue (MB) redox indicator is reported in this work. The assay utilizes a glass carbon (GC) electrode modified with MWCNT-PAMAM, on which the oligonucleotide capture probes are immobilized. The electrochemical detection of miRNAs is completed by measuring the reduction signal change of MB before and after the probe hybridization with target miRNA (miRNA24 is used as a model case). The MWCNT-PAMAM/GC electrode shows greatly enhanced signal to MB reduction in contrast to bare GC electrode. The functionalization of MWCNT with PAMAM maintains the electrochemical property of MWCNT to MB reduction but minimizes the undesired adsorption of MB on the MWCNT surface. The effect of experimental variables on the miRNA detection is investigated and optimized. A detection limit of 0.5 fM and a linear peak current density-concentration relationship up to 100 nM are obtained following 60 min hybridization. The proposed assay is successfully used to detect miRNA24 in total RNA sample extracted from HeLa cells.

Using supported ionic-liquid membrane (SILM)-inspired methodologies, we have synthesized, characterized, and developed a humidity sensor by coating a liquid composite material onto a hygroscopic, porous substrate. Similar to pH paper, the sensor responds to the environment's relative humidity and changes color accordingly. The humidity indicator is prepared by casting a few microliters of low-toxicity reagents on a nontoxic substrate. The sensing material is a newly synthesized liquid composite that comprises a hygroscopic medium for environmental humidity capture and a color indicator that translates the humidity level into a distinct color change. Sodium borohydride was used to form a liquid composite medium, and DenimBlu30 dye was used as a redox indicator. The liquid composite medium provides a hygroscopic response to the relative humidity, and DenimBlu30 translates the chemical changes into a visual change from yellow to blue. The borate-redox dye-based humidity sensor was prepared, and then Fourier transform infrared spectroscopy, differential scanning calorimetry, and image analysis methods were used to characterize the chemical composition, optimize synthesis, and gain insight into the sensor reactivity. Test results indicated that this new sensing material can detect relative humidity in the range of 5-100% in an irreversible manner with good reproducibility and high accuracy. The sensor is a low-cost, highly sensitive, easy-to-use humidity indicator. More importantly, it can be easily packaged with products to monitor humidity levels in pharmaceutical and food packaging.

An automated electrochemical microtiter plate assay for the quantification of free radical scavengers (antioxidants) in food samples is described. Dietary antioxidant capacity measurements were achieved using the radical compound 2,2-diphenyl-1-picrylhydrazyl (DPPH·) as an amperometric redox indicator, with a pencil lead working electrode, in conjunction with a Pt counter-electrode and Ag/AgCl reference electrode, moving sequentially through the 24 vials of a standard 6 × 4 microtiter plate. Programmed analyses were performed successfully with synthetic antioxidants of known concentrations and with tea infusions, fruit juices, and vegetable extracts. The novel methodology is simple and convenient as, unlike common DPPH· antioxidant electroanalysis, it avoids the time-consuming cleaning of electrochemical cells between measurements. Microtiter plate-based robotic electrochemical antioxidant assaying is thus a good option for handling large sample collections and may be applicable in the production of food and herbal remedies.

We report photocatalytic studies employing colloids of pure hematite (α-Fe2O3) and hematite loaded with 1 and 5 wt % platinum, respectively. The kinetics of the dechlorination of the redox indicator 2,6-dichloroindophenol (DCIP) have been studied in aqueous colloidal suspensions of hematite at pH 7. At the same time, α-Fe2O3 carries out the photooxidation of water. The formation of hydroxyl radicals and of H2O2 has been investigated employing coumarin and p-hydroxyphenylacetic acid as reagents, respectively. With an increased amount of platinum on the colloidal surface, an enhanced photonic efficiency of the dye reduction is observed.

Two redox indicators, thionine and phenosafranine, were successfully immobilized on an affinity chromatography gel and were shown to retain their redox activity. The formal potentials (versus the standard hydrogen electrode) near pH 7 were determined to be 52 mV for immobilized thionine and −286 mV for immobilized phenosafranine. It was demonstrated that the immobilized indicators can be packed in a flow cell and monitored spectrophotometrically to determine their speciation. The absorption spectra and electrochemical behavior of the indicators were only slightly affected by immobilization on the gel. For both indicators, immobilization caused the formal potential to decrease (15−20 mV) and the absorption spectrum to shift to higher wavelengths (20−40 nm) with respect to the free (unbound) indicators. These immobilized redox indicators couple with some redox-active species [Cr(VI), O2, and Fe(II)] that are important in environmental samples.

Surface-attached peptide nucleic acids (PNA) are shown to retain their unique and efficient hybridization properties, reported in solution studies. PNA recognition layers thus offer significant advantages for sequence-specific DNA biosensors, compared to their DNA counterparts. These advantages include significantly higher sensitivity and specificity (including greater discrimination against single-base mismatches), faster hybridization at room and elevated temperatures, minimal dependence on ionic strength, and use of shorter (10−15-mer) probes. Such unique properties and advantages are illustrated in connection with electrochemical detection of the hybridization event using the Co(phen)33+ redox indicator and a carbon paste electrode transducer. The new capabilities and opportunities afforded by the use of PNA surface probes are discussed.

An undergraduate toxicity experiment is described using the redox indicator resazurin as an indicator of dehydrogenase activity. Two types of bacteria are utilized, the Gram positive Streptococcus cremoris and a Gram negative bacterium, Escherichia coli, to demonstrate the potentially different toxicological responses to the same chemical. The resazurin reduction is followed spectrophometrically and appears to follow zero order kinetics, with absorbance versus time plots giving correlation coefficients of 0.99 or better. Working in pairs, students are easily able to carry out 10 kinetic runs in a three hour laboratory session. Percent inhibition by a chemical is determined by comparison with controls. Toxicity data are presented for a series of chlorobenzenes and the Hg2+ ion for two bacteria.

Apparent oxidation-reduction potentials at pH 7.0 and 25 degrees C were determined using the H2-hydrogenase system with ferredoxins from the following sources: Clostridium pasteurianum, -403 mV; C tartarovorum, -424 mV; C. acidi-urici, -434 mV; Peptococcus aerogenes, -427 mV; Chromatium D, -482 mV (pH 8.0); B. polymyxa, Fd I, -377 mV, and Fd II, -422 mV; and spinach, -428 mV. The pH dependence of these values was variable, ranging from -2 to -24 mV/pH unit increase for different ferredoxins. Over the range of buffer concentrations between 0.05 and 0.2 M, the potentials did not vary significantly. The number of electrons transferred during reduction (as determined by integrations of EPR spectra and by dithionite titration) is 2 for the first five proteins, while potentiometric data for all the cases fit a Nernst equation for which n = 1. The E degrees' value for the redox indicator methylviologen at pH 7.4 was found to be -460 mV, according to both the H2-hydrogenase system and cyclic voltammetry, significantly different from the value previously reported at higher pH's. Additionally, the presence of C. pasteuranum ferredoxin appears to shift the E degrees value of methylviologen to even more negative values. An analysis of sources of error inherent with potential determinations with H2 and hydrogenase is presented. The electronic and EPR spectra of P. aerogenes ferredoxin, for which the x-ray structure has been published, are given here. It appears that the determination of potentials of ferredoxin and other low-potential porteins with the H2-hydrogenase system affords certain experimental advantages over alternative methods currently employed with these and similar substances.

The redox potentials for both electron transfers for the enzyme lactate oxidase have been measured at pH 7.0 in 0.01 M imidazole buffer at 25 degrees C. Methylviologen is the electrochemically generated reducing agent capable of transferring both electrons to the enzyme in this spectroelectrochemical experiment. The E0' values are as follows: for EFlox + e- = EFl-., E0'1 = -0.067 +/- 0.006 V; for EFl-. + e- + H+ = EFlredH-, E0'2 = -0.231 +/- 0.004 V. All potentials are reported vs. the standard hydrogen electrode (SHE). Both electron transfers are reversible. Consistent with the 164-mV potential separation, 95% of the enzyme anion radical is thermodynamically stabilized at half-reduction in all experiments.