Posts Tagged ‘concentrations’

New Technology for Turn-On Fluorescence Detection of Cyanide in Water

New Technology for Turn-On Fluorescence Detection of Cyanide in Water

New Technology for Turn-On Fluorescence Detection of Cyanide in Water

A molecular probe was prepared that selectively responds to cyanide in aqueous solutions by fluorescence enhancement. Using the peptide ?-turn as a structural template, we designed a series of diphenylacetylene derivatives in which the ?-conjugated backbone was functionalized with an aldehyde group to render the molecule nonfluorescent. The N-H···O hydrogen bond across the 2,2?-functionalized diphenylacetylene turn motif activates the carbonyl group toward nucleophilic attack, and chemical transformation of this internal quencher site by reaction with CN- elicits a rapid (k = 72 M-1 s-1) enhancement in the emission at ?max = 375 nm. Tethering of an ammonium group to the hydrogen bond donor fragment significantly increased both the response kinetics and the intensity of the fluorescence signal. In addition to providing electrostatic attraction toward the CN- ion, this positively charged R-NH3+ fragment can engage in a secondary hydrogen bond to facilitate the formation of the cyanohydrin adduct responsible for the signaling event. The structurally optimized molecular probe 3 responds exclusively to ?M-level cyanide in neutral aqueous solutions, with no interference from other common anions including F- and AcO-.

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54645kcn New Technology for Turn On Fluorescence Detection of Cyanide in WaterScientists from Indiana University Bloomington are reporting in J. Am. Chem. Soc. the development of a fluorescent molecular probe that can detect minuscule concentrations of cyanide in water at normal pH levels. This research can conceivably be extended into a commercialization stage to develop a simple and cheap cyanide detector:

“This is the first system that works in water at normal pH levels and can be modified at will to enhance its reactivity,” said IU Bloomington chemist Dongwhan Lee, who led the research. “We are now looking at how to make the detector more sensitive.”

Graduate student Junyong Jo is the report’s first author.

One of the reasons the detector is not ready for market, Lee says, is that its optical properties need to be improved to emit light at longer wavelengths with less interference from background signals, especially those of biological origin. Since pond or river water is likely to contain living organisms and other organic matter, Lee says the detector system must be perfected.

Another unique aspect of the detector molecule is its modular structure.

“This is an essentially three-component chemical device with an activator, a receptor, and a reporter module,” Lee said. “These three components we can change at will in the future, either to make the detector more sensitive, or have it detect an entirely different toxin by sending out signals as different colors of light. Because of the structure’s modularity, a change in one of the three components doesn’t really affect the others.”

Lee and Jo were inspired by life itself — the natural properties of proteins — when they began designing their sensor molecule. The design of this novel system takes advantage of the structure-organizing “beta turn” motif commonly found in protein structures. The detector is essentially inert, except in the presence of cyanide, with which it preferentially reacts. The addition of cyanide induces a subtle but important structural change in the detector that turns it into a pigment that absorbs ultraviolet light (currently 270 nm) and convert it to light emission at around 375 nm, a purplish color at the very edge of human beings’ normal vision range.

Cyanide is a negatively charged ion composed of one carbon and one nitrogen atom. Among its many chemical targets inside cells is the oxidative phosphorylation system, which is a crucial producer of energy. Cyanide disrupts the system, making it impossible for cells to maintain even the most basic processes, which is one reason cyanide is considered a poison.

Source : http://pubs.acs.org/doi/abs/10.1021/ja907056m

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Nano Scale Mass Spectrometer Developed

Nano Scale Mass Spectrometer Developed

Nano Scale Mass Spectrometer Developed

PASADENA, Calif.-Using devices millionths of a meter in size, physicists at the California Institute of Technology (Caltech) have developed a technique to determine the mass of a single molecule, in real time.

The mass of molecules is traditionally measured using mass spectrometry, in which samples consisting of tens of thousands of molecules are ionized, to produce charged versions of the molecules, or ions. Those ions are then directed into an electric field, where their motion, which is choreographed by both their mass and their charge, allows the determination of their so-called mass-to-charge ratio. From this, their mass can ultimately be ascertained.

The new technique, developed over 10 years of effort by Michael L. Roukes, a professor of physics, applied physics, and bioengineering at the Caltech and codirector of Caltech’s Kavli Nanoscience Institute, and his colleagues, simplifies and miniaturizes the process through the use of very tiny nanoelectromechanical system (NEMS) resonators. The bridge-like resonators, which are 2 micrometers long and 100 nanometers wide, vibrate at a high frequency and effectively serve as the “scale” of the mass spectrometer.

“The frequency at which the resonator vibrates is directly proportional to its mass,” explains research physicist Askshay Naik, the first author of a paper about the work that appears in the latest issue of the journal Nature Nanotechnology. Changes in the vibration frequency, then, correspond to changes in mass.

“When a protein lands on the resonator, it causes a decrease in the frequency at which the resonator vibrates and the frequency shift is proportional to the mass of the protein,” Naik says.

As described in the paper, the researchers used the instrument to test a sample of the protein bovine serum albumin (BSA), which is known to have a mass of 66 kilodaltons (kDa; a dalton is a unit of mass used to describe atomic and molecular masses, with one dalton approximately equal to the mass of one hydrogen atom).

The BSA protein ions are produced in vapor form using an electrospray ionization (ESI) system.The ions are then sprayed on to the NEMS resonator, which vibrates at a frequency of 450 megahertz. “The flux of proteins reaching the NEMS is such that only one to two protein lands on the resonator in a minute,” Naik says.

When the BSA protein molecule is dropped onto the resonator, the resonator’s vibration frequency decreases by as much as 1.2 kiloHertz-a small, but readily detectable, change. In contrast, the beta-amylase protein molecule, which has a mass of about 200 kDa, or three times that of BSA, causes a maximum frequency shift of about 3.6 kHz.

Because the location where the protein lands on the resonator also affects the frequency shift-falling onto the center of the resonator causes a larger change than landing on the end or toward the sides, for example-”we can’t tell the mass with a single measurement, but needed about 500 frequency jumps in the published work,” Naik says. In future, the researchers will decouple measurements of the mass and the landing position of the molecules being sampled. This technique, which they have already prototyped, will soon enable mass spectra for complicated mixtures to be built up, molecule-by molecule.

Eventually, Roukes and colleagues hope to create arrays of perhaps hundreds of thousands of the NEMS mass spectrometers, working in parallel, which could determine the masses of hundreds of thousands of molecules “in an instant,” Naik says.

As Roukes points out, “the next generation of instrumentation for the life sciences-especially those for systems biology, which allows us to reverse-engineer biological systems-must enable proteomic analysis with very high throughput. The potential power of our approach is that it is based on semiconductor microelectronics fabrication, which has allowed creation of perhaps mankind’s most complex technology.”

The paper, “Towards single-molecule nanomechanical mass spectrometry,” appears in the July 4 issue of Nature Nanotechnology. The other authors of the paper are graduate student Mehmet S. Hanay and staff scientist Philip Feng, from Caltech, and Wayne K. Hiebert of the National Research Council of Canada. The work was supported by the National Institutes of Health and, indirectly, by the Defense Advanced Research Projects Agency and the Space and Naval Warfare Systems Command.

Caltech physicists have created a mass spectrometer capable of measuring individual molecules in real time. Current mass spectrometers require specific concentrations of molecules that are larger in size, and today’s devices take up considerably more room than the 2 micrometers long by 100 nanometers wide resonators in the new spectrometer.

The bridge-like resonators, which are 2 micrometers long and 100 nanometers wide, vibrate at a high frequency and effectively serve as the “scale” of the mass spectrometer.

“The frequency at which the resonator vibrates is directly proportional to its mass,” explains research physicist Askshay Naik, the first author of a paper about the work that appears in the latest issue of the journal Nature Nanotechnology. Changes in the vibration frequency, then, correspond to changes in mass.

“When a protein lands on the resonator, it causes a decrease in the frequency at which the resonator vibrates and the frequency shift is proportional to the mass of the protein,” Naik says.

As described in the paper, the researchers used the instrument to test a sample of the protein bovine serum albumin (BSA), which is known to have a mass of 66 kilodaltons (kDa; a dalton is a unit of mass used to describe atomic and molecular masses, with one dalton approximately equal to the mass of one hydrogen atom).

The BSA protein ions are produced in vapor form using an electrospray ionization (ESI) system.The ions are then sprayed on to the NEMS resonator, which vibrates at a frequency of 450 megahertz. “The flux of proteins reaching the NEMS is such that only one to two protein lands on the resonator in a minute,” Naik says.

When the BSA protein molecule is dropped onto the resonator, the resonator’s vibration frequency decreases by as much as 1.2 kiloHertz-a small, but readily detectable, change. In contrast, the beta-amylase protein molecule, which has a mass of about 200 kDa, or three times that of BSA, causes a maximum frequency shift of about 3.6 kHz.

Because the location where the protein lands on the resonator also affects the frequency shift-falling onto the center of the resonator causes a larger change than landing on the end or toward the sides, for example-”we can’t tell the mass with a single measurement, but needed about 500 frequency jumps in the published work,” Naik says. In future, the researchers will decouple measurements of the mass and the landing position of the molecules being sampled. This technique, which they have already prototyped, will soon enable mass spectra for complicated mixtures to be built up, molecule-by molecule.

source : http://www.caltech.edu/article/13277

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Cheap and Simple Microfluidic Lab-on-a-Chip Detects Analytes

Cheap and Simple Microfluidic Lab-on-a-Chip Detects Analytes

Cheap and Simple Microfluidic Lab-on-a-Chip Detects Analytes

When someone develops liver cancer, the disease introduces a very subtle difference to their bloodstream, increasing the concentration of a particular molecule by just 10 parts per billion.

That small shift is difficult to detect without sophisticated lab equipment – but perhaps not for long. A new “lab on a chip” designed by Brigham Young University professor Adam Woolley and his students reveals the presence of ultra-low concentrations of a target molecule.

As the BYU researchers report in the journal Analytical Chemistry, their experiments detected as little as a single nanogram – one billionth of a gram – of the target molecule from a drop of liquid. And instead of sending the sample to a lab for chemical analysis, the chip allows them to measure with such precision using their own eyes.

“The nice thing about the system that we have developed is that this could be done anywhere,” Woolley said. “Somebody could put the sample in, look at it, and have the result they need.”

The trick is to line a tiny pipe with receptors that catch a specific molecule and allow others to pass by. When a drop of liquid is placed on the clear chip, capillary action draws the fluid through the channel, flowing up to one centimeter per second. As more of the target molecules are snagged by the receptors, the space constricts and eventually stops the flow.

How far the sample flows is a direct indication of the concentration of the target molecule (higher concentration = shorter distance, lower concentration = longer distance).

“The accuracy gained with this system should make it competitive with more expensive and complicated immunoassay systems,” said Chuck Henry, a chemist at Colorado State University who was not affiliated with the project.

Woolley and his students hope their prototype will work as a blueprint for making inexpensive diagnostic tests for a variety of diseases and genetic disorders.

“There are a lot of molecules associated with diseases where concentrations around a nanogram per milliliter or less in blood are the difference between a disease state versus a healthy state,” Woolley said.

Four students worked on the project, led by graduate student Debolina Chatterjee of New Delhi, India. She and fellow grad student Danielle Mansfield mentored two undergraduates on the project, Neil Anderson and Sudeep Subedi.

The experience helped Anderson gain admission into law school at Cornell, where he is studying patent law. Subedi is completing a degree in clinical laboratory science and plans to eventually return to his homeland of Nepal and help establish better medical infrastructure.

Simplified analysis systems that offer the performance of benchtop instruments but the convenience of portability are highly desirable. We have developed novel, miniature devices that feature visual inspection readout of a target’s concentration from a 1 ?L volume of solution introduced into a microfluidic channel. Microchannels are constructed within an elastomeric material, and channel surfaces are coated with receptors to the target. When a solution is flowed into the channel, the target cross-links multiple receptors on the surface, resulting in constriction of the first few millimeters of the channel and stopping of flow. Quantitation is performed by measuring the distance traveled by the target solution in the channel before flow stops. A key advantage of our approach is that quantitation is accomplished by simple visual inspection of the channel, without the need for complex detection instrumentation. We have tested these devices using the model system of biotin as a receptor and streptavidin as the target. We have also characterized three factors that influence flow distance: solution viscosity, device thickness, and channel height. We found that solution capillary flow distance scales with the negative logarithm of target concentration and have detected streptavidin concentrations as low as 1 ng/mL. Finally, we have identified and evaluated a plausible mechanism wherein time-dependent channel constriction in the first few millimeters leads to concentration-dependent flow distances. Their simplicity coupled with performance makes these “flow valve” systems especially attractive for a host of analysis applications.

Brigham Young University researchers have developed a simple new way of detecting tiny concentrations (down to a nanogram – one billionth of a gram) of a given chemical without the use of any complicate and expensive equipment.

They created narrow channels within glass slides that are lined with receptors for the chemical to be quantified. When a sample drop is placed at one end of a channel, it is drawn in by capillary action. As the target molecules are captured by the receptors, the channel gradually becomes constricted. The distance that the liquid manages to travel is inversely proportional to the quantity of the target molecule in the sample.

From the study abstract:

We have tested these devices using the model system of biotin as a receptor and streptavidin as the target. We have also characterized three factors that influence flow distance: solution viscosity, device thickness, and channel height. We found that solution capillary flow distance scales with the negative logarithm of target concentration and have detected streptavidin concentrations as low as 1 ng/mL. Finally, we have identified and evaluated a plausible mechanism wherein time-dependent channel constriction in the first few millimeters leads to concentration-dependent flow distances.

Source : http://news.byu.edu/archive12-oct-microfluidic.aspx

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