Enhanced Detection Efficiency Research Articles

Single Base Pair Mismatch Detection Using Cationic Conjugated Polymers through Fluorescence Resonance Energy Transfer

AbstractA simple method using water‐soluble conjugated polymers and a DNA intercalator has been proposed for single base pair mismatch detection with enhanced detection efficiency. Fluorescence resonance energy transfer (FRET) was used as an indicator for unwinding of dsDNA due to base pair mismatch at elevated temperatures. The optical amplification effect of the CPs helps to achieve enhanced detection efficiency.magnified image

Platform for enhanced detection efficiency in luminescence-based sensors

Luminescence-based biochip measurement platforms are employed in a wide range of biological applications, such as biomedical diagnostics. Based on an understanding of the anisotropic emission properties of luminescence emitters close to a dielectric interface, a simple strategy for producing a better than 25-fold enhancement of the detected luminescence is presented. This strategy is demonstrated for low cost polymer platforms compatible with mass-production.

Using passive converters to enhance detection efficiency of 100-MeV neutrons

The effect of passive iron converters was investigated at energies of 20–140MeV. An enhanced detection efficiency for neutron energies above 70MeV was found using iron converters of 2–3cm thickness. The experimental findings will be implemented in a high-efficiency large-area detector for neutrons in the energy range 100–200MeV at the National Superconducting Cyclotron Laboratory.

Particle size dependent response of aerosol counters

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions. The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.

Improving neutron detection efficiency by using passive converters

The effect of passive iron converters on the detection efficiency of neutrons in a plastic scintillator was investigated at energies of 20–140 MeV. An enhanced detection efficiency for neutron energies above 70 MeV was found using iron converters of 2–3 cm thickness. The experimental results are compared to a simulation.

Detection of large cluster ions by time-of-flight mass spectrometry with a conversion dynode

A linear time-of-flight mass spectrometer (TOF-MS) has been constructed to measure mass distribution of negatively-charged clusters formed in the hot filament diamond chemical vapor deposition (CVD) process and in the metal evaporation. A conversion dynode made of CsI was employed to enhance detection efficiency of the large clusters greater than 10 000 amu. An atomic peak from the tungsten evaporation was used for the mass calibration of the carbon clusters. The carbon clusters produced in the CVD diamond process was loosely bound so that they were easily fragmented during passage through accelerating electric fields. The mass distribution measured with the TOF-MS system showed much less abundance of large clusters than those measured previously with the energy analyzer and Wien filter.

Downsizing of Johansson spectrometer for X-ray fluorescence trace analysis with brilliant undulator source

The downsizing of a Johansson-type X-ray fluorescence (XRF) spectrometer has been examined as a way of enhancing detection efficiency with a tolerable loss of energy resolution. A compact spectrometer equipped with a Ge(2 2 0) analyzing crystal with a Rowland radius of 120 mm has been tested with a highly brilliant helical undulator source at BL40XU, SPring-8. The energy resolution obtained for cobalt Kα 1 (6930.32 eV) was 8.8 eV, which is 10–20 times better than that obtained using a Si(Li) detector, and effectively improved the signal-to-background ratio for XRF spectra. The combination of the present spectrometer and a third generation synchrotron source could provide new opportunities for trace analytical applications, which have been difficult so far by conventional synchrotron XRF experiments based on a Si(Li) detector system. The detection limit obtained for solid bulk samples has reached a level of several tens of ppb.

Procedure for shifting groundwater monitoring locations to enhance detection efficiency near landfills

A heuristic was devised for shifting contaminant detection wells near landfills. The heuristic establishes an initial configuration of monitoring wells and then shifts the wells iteratively until it reaches a specified release detection efficiency. Computer simulations of contaminant transport gauge the performance of the monitoring configurations. In configurations derived by the heuristic, all wells are located the same distance from a landfill, measured parallel to groundwater flow. This facilitates a uniform lag time for release detection. However, the distance between wells, measured perpendicular to groundwater flow, can vary to enhance overall detection efficiency. In practice, the heuristic can be used to identify effective monitoring configurations for detecting potential releases from landfills.

Observation of an indirect pathway in the femtosecond study of alkyl nitrite photodissociation in the S1 state

The present work has addressed the question of the dissociation time of four alkyl nitrites upon photoexcitation in the S1 state (methyl nitrite, n- , and t-butyl nitrites and i-amyl nitrite). The time resolved Laser Induced Fluorescence technique has been used in the femtosecond regime under bulk conditions. The photodissociation has been initiated at 351 nm by 150 fs pump pulses, and has been probed using a two-photon process at 467 nm by 200 fs pulses. The LIF signal has qualitatively the same shape for the four nitrites: it passes through a transient peak before reaching a plateau. The two-photon process that induces the detected fluorescence is nonresonant for detection of the dissociation product NO through the A←X transition. Conversely, the two-photon process is resonant or quasiresonant for detection of the excited nitrite molecule in the S1 level before it dissociates. This leads to an enhanced detection efficiency of the non-dissociated excited molecule versus that of the NO fragment. A simple kinetic model has been developed to account for this detection scheme. It shows that the transient peak is observable only if the lifetime of the excited molecule is comparable or larger than the temporal width of the lasers. In that case, the model allows the determination of an effective lifetime of the excited molecule from the measured LIF signal. Lifetimes have been found in the range of 125 fs for the four nitrites investigated. This has allowed us to answer a controversy on the dissociation mechanism of methyl nitrite and to confirm that an indirect pathway exists in the photodissociation of this molecule.

Free beta-chorionic gonadotropin: a cross-reactivity study of two immunometric assays used in prenatal maternal serum screening for Down's syndrome.

We have evaluated the cross-reactivity characteristics of two distinct immunometric assays for the measurement of free beta-human chorionic gonadotropin (free beta). These maternal serum assays have been used in the initial studies which evaluated free beta as a marker in the prenatal detection of Down's syndrome. It has been suggested that free beta assays are subject to substantial potential for cross-reactivity. To confirm that free beta was the analyte responsible for enhanced detection efficiency both non-competitive and competitive cross-reactivity evaluations were undertaken. These studies demonstrated acceptably small cross-reactivity to other glycoprotein hormones or their beta components. We conclude that properly designed free beta assays will provide specific analyte measurement and improved detection efficiency in Down's syndrome screening.

Enhanced detection of atmospheric-turbulence-distorted 1-μm coherent lidar returns using a two-dimensional heterodyne detector array

We have employed a two-dimensional multielement heterodyne detector array and demonstrated, for the first time to our knowledge, the enhanced detection efficiency of atmospheric-turbulence-distorted 1-microm coherent lidar returns. The heterodyne lidar signal intensity and statistical signal fluctuation were measured for both a 2 x 2 detector array and a single detector as a function of the atmospheric turbulence parameter C(n)(2). The detector array improved the lidar detection efficiency by a factor of approximately 4, and the statistical signal distribution changed from Rayleigh to Gaussian. This improvement is shown to be consistent with a firstorder analysis.

On the detection of large organic ions by secondary electron production

A particle detector based on the detection of secondary electrons ejected at the impact of the particle on the detector surface has been constructed. It has been utilized in plasma desorption time-of-flight mass spectrometry to achieve post-acceleration yielding enhanced detection efficiency and identification of metastable decay channels in the spectrometer. Threshold velocities for electron ejection at the impact of large ions on a surface have been determined. Further, the multiplicity of secondary electrons ejected on the impact of the detected ion on the surface has been determined by energy measurements of the ensemble of ejected electrons.