Droplet digital polymerase chain reaction (ddPCR) is
a new technology that was recently commercialized to enable the precise
quantification of target nucleic acids in a sample. ddPCR measures
absolute quantities by counting nucleic acid molecules encapsulated
in discrete, volumetrically defined, water-in-oil droplet partitions.
This novel ddPCR format offers a simple workflow capable of generating
highly stable partitioning of DNA molecules. In this study, we assessed
key performance parameters of the ddPCR system. A linear ddPCR response
to DNA concentration was obtained from 0.16% through to 99.6% saturation
in a 20,000 droplet assay corresponding to more than 4 orders of magnitude
of target DNA copy number per ddPCR. Analysis of simplex and duplex
assays targeting two distinct loci in the Lambda DNA genome using
the ddPCR platform agreed, within their expanded uncertainties, with
values obtained using a lower density microfluidic chamber based digital
PCR (cdPCR). A relative expanded uncertainty under 5% was achieved
for copy number concentration using ddPCR. This level of uncertainty
is much lower than values typically observed for quantification of
specific DNA target sequences using currently commercially available
real-time and digital cdPCR technologies.
We demonstrate that thin films consisting of cross-linked nanoparticle aggregates function as highly sensitive strain gauges. The sensors exploit the exponential dependence of the interparticle tunnel resistance on the particle separation. Their sensitivity (gauge factor) is two orders of magnitude higher than that of conventional metal foil gauges and rivals that of state-of-the-art semiconductor gauges. We describe the strain gauge behavior in a tunneling model that predicts the dependence of the gauge factor on several parameters, in particular, the nanoparticle size, the interparticle separation gap, and the conductance of the linker molecules.
Digital polymerase chain reaction (PCR) is a promising technique for estimating target DNA copy number. PCR solution is distributed throughout numerous partitions, and following amplification, target DNA copy number is estimated based on the proportion of partitions containing amplified DNA. Here, we identify approaches for obtaining reliable digital PCR data. Single molecule amplification efficiency was significantly improved following fragmentation of total DNA and bias in copy number estimates reduced by analysis of short intact target DNA fragments. Random and independent distribution of target DNA molecules throughout partitions, which is critical to accurate digital PCR measurement, was demonstrated by spatial distribution analysis. The estimated relative uncertainty for target DNA concentration was under 6% when analyzing five digital panels comprising 765 partitions each, provided the panels contained an average of 212 to 3,365 template molecules. Partition volume was a major component of this uncertainty estimate. These findings can be applied to other digital PCR studies to improve confidence in such measurements.
Experimental efforts to characterize and develop an understanding of non Fermi liquid (NFL) behavior at low temperature in f-electron materials are reviewed for
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