Rapid on-chip postcolumn labeling and high-resolution separations of DNA

When performing genetic analysis on microfluidic systems, labeling the sample DNA for detection is a critical preparation step. Labeling procedures often involve fluorescently tagged primers and PCRs, which lengthen experimental run times and introduce higher levels of complexity, increasing the overall cost per analysis. Alternatively, on-chip labeling techniques based on intercalating dyes permit rapid labeling of DNA fragments. However, as noted in the literature, the stochastic nature of dye-DNA complex formation hinders the native electrophoretic migration of DNA fragments, degrading the separation resolution. In this study, we present a novel method of controllably labeling DNA fragments at the end of the electrophoretic separation channel in a glass microfluidic chip. Permitting the DNA to separate and labeling just before detection, achieves the rapid labeling associated with intercalators while maintaining the high resolution of native DNA separations. Our analyses are completed in minutes, rather than the hours typical of sample prelabeling. We demonstrate an electrophoretic microchip-based intercalator labeling technique that achieves higher resolution performance than reported in the literature to date.     

Active to sterile neutrino mixing limits from neutral-current interactions in MINOS

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07×10(20) protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754 ± 28(stat) ± 37(syst) for oscillations among three active flavors. The fraction f(s) of disappearing ν(μ) that may transition to ν(s) is found to be less than 22% at the 90% C.L.     

Measurement of the neutrino mass splitting and flavor mixing by MINOS

Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of 7.25×10(20) protons on target. A fit to neutrino oscillations yields values of |Δm(2)|=(2.32(-0.08)(+0.12))×10(-3) eV(2) for the atmospheric mass splitting and sin(2)(2θ)>0.90 (90% C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively.     

Direct comparison of methods for extracting the rate from first order data with background

Many methods involving a lag or retardation can linearize A exp(?kt) + Z data, allowing k to be obtained from the slope. A classification scheme is found in which the efficiencies are related to the classes of methods. The methods yielding k with the smallest standard deviations (σ_k) are compared quantitatively. The resulting error factors for k and the lags are tabulated for each of the four methods compared, for use by the experimenter. This is done for various ranges, backgrounds, and kinds of random noise. Effects on k and σ_k due to correlation, incorrect weighting, choice of lag, and the distribution of the plotted data are detailed. Effects at high noise levels are discussed for the (usually) best direct method, due to Guggenheim. These include the onset and extent of bias in k and failure of the method to yield any k.     

A microfluidic study of mechanisms in the electrophoresis of supercoiled DNA

In this work, microfluidic chips were used to study the electrophoresis of supercoiled DNA (SC DNA) in agarose. This system allowed us to study the electrophoretic and trapping behaviours of SC DNA of various lengths, at various fields and separation distances. Near a critical electric field the DNA is trapped such that the concentration falls exponentially with distance. The trapping of such circular DNA has been explained in terms of the 'lobster trap' or 'impalement' model where shorter fibres become trapping sites at higher fields, leading to an ongoing (and gradual) increase in trapping with increasing field. By contrast, the present study suggests that under some circumstances the traps have a barrier such that only when the DNA has sufficient energy (at high enough fields) can it become trapped, leading to a sudden transition in behaviours at the critical field. We propose an 'activated impalement' mechanism of trapping in which only at sufficiently high fields is the SC DNA impaled and trapped for long times. The critical electric field appears to be inversely proportional to the length of the DNA molecule, suggesting that the force required to impale the SC DNA is constant.