Concentrations Of Other Molecules Research Articles

Modular protein-oligonucleotide signal exchange.

While many methods are available to measure the concentrations of proteins in solution, the development of a method to quantitatively report both increases and decreases in different protein concentrations in real-time using changes in the concentrations of other molecules, such as DNA outputs, has remained a challenge. Here, we present a biomolecular reaction process that reports the concentration of an input protein in situ as the concentration of an output DNA oligonucleotide strand. This method uses DNA oligonucleotide aptamers that bind either to a specific protein selectively or to a complementary DNA oligonucleotide reversibly using toehold-mediated DNA strand-displacement. It is possible to choose the sequence of output strand almost independent of the sensing protein. Using this strategy, we implemented four different exchange processes to report the concentrations of clinically relevant human α-thrombin and vascular endothelial growth factor using changes in concentrations of DNA oligonucleotide outputs. These exchange processes can operate in tandem such that the same or different output signals can indicate changes in concentration of distinct or identical input proteins. The simplicity of our approach suggests a pathway to build devices that can direct diverse output responses in response to changes in concentrations of specific proteins.

Zirconia-Based Electrochemical Oxygen Sensor for Accurately Determining Water Vapor Concentration

Zirconia-based electrochemical sensors for measuring the oxygen concentration in the automotive exhaust have been used on vehicles for nearly 40 years. The oxygen sensor is an electrochemical cell based on oxygen-ion conducting zirconia. The sensor consists of a single electrochemical cell which has one electrode exposed to a reference atmosphere (typically air) and the other electrode exposed to the measurement (exhaust) gas and operates as a simple Nernst cell. The open circuit voltage of this zirconia electrochemical cell changes with variations in the oxygen partial pressures existing adjacent to its two electrodes. The emf generated by this Nernst cell gives a measurement of the concentration of oxygen in the exhaust gas. This measurement can be used by the engine control unit to adjust the air-to-fuel ratio so as to maintain it close to stoichiometry, thereby minimizing the unwanted emissions. All gasoline (and some diesel) vehicles produced today utilize an oxygen sensor to control their emission systems. Although successfully used for stoichiometric A/F control for many years, Nernst-type oxygen sensors are not useful for applications away from stoichiometry because of their low sensitivity (i.e. weak logarithmic dependence of the emf on oxygen partial pressure). However, double-zirconia-cell sensors have been developed [1,2] which have much higher sensitivity and thus a wider range of operation and are therefore applicable to A/F measurement and control from very rich to very lean A/F mixtures. These sensors are based on oxygen pumping, which involves the transfer of oxygen from one side of a zirconia cell to the other by passing an electric current through the device. Since these sensors operate over a wide range, they are referred to as “wide-range oxygen” or “universal exhaust gas oxygen” (UEGO) sensors. Most gasoline vehicles, as well as diesel powertrains which operate lean, employ UEGO sensors to meet the emission requirements. A double-cell oxygen-pumping device (UEGO sensor) also can be used to measu­re the concentration of other oxygen-containing molecules in the exhaust gas, e.g. H2O, CO2, SO2, and NOx. In order to mea­sure the H2O concentration, a voltage is applied across the pump-cell that is greater than the dissociation potential for H2O. A measurement of the pumping current through the cell provides a measure of the oxygen generated from the decomposition of water and thus a measure of the H2O concentration in the gas. However, in the exhaust gas this measurement is confounded by the fact that molecular oxygen and other molecules also are dissociated. If the concentrations of these other molecules were constant, then the concentration of H2O could still be determined uniquely by subtracting the contribution of these other molecules. However, the concentrations of the different oxygen-containing molecules in the exhaust gas vary with engine operating conditions. This problem can be overcome by varying the voltage across the pump cell and measuring the pumping currents at various dissociation potentials. At a lower potential the concentration of oxygen can be measured. A second voltage larger than the dissociation potential of the measurement gas, H2O e.g., is applied to measure the concentration of oxygen plus water. The water concentration can be determined by subtracting the pumping current due to oxygen from the pumping current due to the combination. Other gases, CO2 e.g., can also be measured in a similar fashion. In principle, these measurements can be achieved without any modification to the existing sensor hardware. A simple modification to the electronic control circuitry is all that is required to perform this type of measurement. Figure 1 shows the sensitivity of a commercially available UEGO sensor for the dissociation of H2O as a function of dissociation potential. A typical operating value for the sensing voltage Vs for oxygen measurement is 450 mV. The plot below was generated from data measured in the lab at various water concentrations in a carrier gas of dry nitrogen. From the plot it is evident that water dissociation is occurring at potentials less than 800 mV. Additionally, the output begin to saturate at a potential approaching 1100 mV, suggesting that full dissociation of the water has been achieved. The pumping current of the sensor is linear as a function of water concentration for Vs = 1080 mV. The application of this technology to measure ambient humidity on-board a vehicle during fuel cut will be discussed. Figure 1

Pyridoxal 5'‐phosphate in cerebrospinal fluid; factors affecting concentration

Analysis of pyridoxal 5'-phosphate (PLP) concentration in 256 cerebrospinal fluid (CSF) samples from patients with neurological symptoms showed that the variance is greater than indicated by previous studies. The age-related lower reference limit has been revised to detect inborn errors of metabolism that lead to PLP depletion without a high false positive rate: < 30 days, 26 nmol/L; 30 days to 12 months, 14 nmol/L; 1-2 years, 11 nmol/L; > 3 years, 10 nmol/L. Inborn errors leading to PLP concentrations below these values include pyridoxine-dependent epilepsy due to antiquitin deficiency, and molybdenum cofactor deficiency that leads to the accumulation of sulfite, a nucleophile capable of reacting with PLP. Low PLP levels were also seen in a group of children with transiently elevated urinary excretion of sulfite and/or sulfocysteine, suggesting that there may be other situations in which sulfite accumulates and inactivates PLP. There was no evidence that seizures or the anticonvulsant drugs prescribed for patients in this study led to significant lowering of CSF PLP. A small proportion of patients receiving L-dopa therapy were found to have a CSF PLP concentration below the appropriate reference range. This may have implications for monitoring and treatment. A positive correlation was seen between the CSF PLP and 5-methyl-tetrahydrofolate (5-MTHF) and tetrahydrobiopterin (BH(4)) concentrations. All are susceptible to attack by nucleophiles and oxygen-derived free-radicals, and CSF has relatively low concentrations of other molecules that can react with these compounds. Further studies of CSF PLP levels in a wide range of neurological diseases might lead to improved understanding of pathogenesis and possibilities for treatment.

Sialochemistry: a diagnostic tool?

Saliva has proven to be a discriminating element in forensic arenas, an effective indicator of acute diseases of salivary glands, and a promising probe for drug monitoring. With the advent of sensitive immunochemical assays, the compositional profile of human salivary secretions has been expanded considerably. Thus, the establishment of a range of "normal values" for a variety of "intrinsic" and "extrinsic" salivary components represented the initial step to use saliva as a diagnostic tool of oral health status. Unfortunately, numerous cross-sectional studies have shown a wide individual variation in the salivary composition of healthy populations, thus precluding its use as a diagnostic chair-side test for the screening of the most common chronic oral diseases (e.g. caries and periodontal disease). A possible explanation may arise from the wide functional versatility of salivary molecules. For instance, it has been recognized recently that in addition to its digestive properties, salivary amylase may modulate bacterial colonization, whereas histatins are not only antifungal but also bactericidal. Thus, low levels of already known antimicrobial salivary molecules (e.g., secretory IgA, lactoferrin, and lysozyme) could be compensated with higher concentrations of other molecules with antimicrobial activity, such as amylase and histatins. Consequently, for caries and periodontal diseases, longitudinal sialochemical studies may yield more insight than cross-sectional studies.

On the existence of bound water in biological systems as probed by dielectric spectroscopy

Results of dielectric relaxation studies on binary aqueous solutions are summarized to look for indications of the presence of bound water. The solutes include simple inorganic and organic electrolytes, polyelectrolytes, small organic molecules and polymers. It is shown that even simple solutions exhibit a great variety of dielectric effects. It therefore appears to be impossible to unambiguously discuss dielectric spectra of complex biological tissues in which different polarization mechanisms overlap. The results for solutions taken as models for biological systems indicate two types of affected water which might be considered 'bound': dielectrically saturated water in strong electric fields and water in regions with a high concentration of other molecules. Characteristics of both states of water in mixtures are presented.