34 research outputs found
Unzipping Kinetics of Double-Stranded DNA in a Nanopore
We studied the unzipping kinetics of single molecules of double-stranded DNA
by pulling one of their two strands through a narrow protein pore. PCR analysis
yielded the first direct proof of DNA unzipping in such a system. The time to
unzip each molecule was inferred from the ionic current signature of DNA
traversal. The distribution of times to unzip under various experimental
conditions fit a simple kinetic model. Using this model, we estimated the
enthalpy barriers to unzipping and the effective charge of a nucleotide in the
pore, which was considerably smaller than previously assumed.Comment: 10 pages, 5 figures, Accepted: Physics Review Letter
Fast DNA translocation through a solid-state nanopore
We report translocation experiments on double-strand DNA through a silicon
oxide nanopore. Samples containing DNA fragments with seven different lengths
between 2000 to 96000 basepairs have been electrophoretically driven through a
10 nm pore. We find a power-law scaling of the translocation time versus
length, with an exponent of 1.26 0.07. This behavior is qualitatively
different from the linear behavior observed in similar experiments performed
with protein pores. We address the observed nonlinear scaling in a theoretical
model that describes experiments where hydrodynamic drag on the section of the
polymer outside the pore is the dominant force counteracting the driving. We
show that this is the case in our experiments and derive a power-law scaling
with an exponent of 1.18, in excellent agreement with our data.Comment: 5 pages, 2 figures. Submitted to PR
Microfluidic Chip for Molecular Amplification of Influenza A RNA in Human Respiratory Specimens
A rapid, low cost, accurate point-of-care (POC) device to detect influenza virus is needed for effective treatment and control of both seasonal and pandemic strains. We developed a single-use microfluidic chip that integrates solid phase extraction (SPE) and molecular amplification via a reverse transcription polymerase chain reaction (RT-PCR) to amplify influenza virus type A RNA. We demonstrated the ability of the chip to amplify influenza A RNA in human nasopharyngeal aspirate (NPA) and nasopharyngeal swab (NPS) specimens collected at two clinical sites from 2008–2010. The microfluidic test was dramatically more sensitive than two currently used rapid immunoassays and had high specificity that was essentially equivalent to the rapid assays and direct fluorescent antigen (DFA) testing. We report 96% (CI 89%,99%) sensitivity and 100% (CI 95%,100%) specificity compared to conventional (bench top) RT-PCR based on the testing of n = 146 specimens (positive predictive value = 100%(CI 94%,100%) and negative predictive value = 96%(CI 88%,98%)). These results compare well with DFA performed on samples taken during the same time period (98% (CI 91%,100%) sensitivity and 96%(CI 86%,99%) specificity compared to our gold standard testing). Rapid immunoassay tests on samples taken during the enrollment period were less reliable (49%(CI 38%,61%) sensitivity and 98%(CI 98%,100%) specificity). The microfluidic test extracted and amplified influenza A RNA directly from clinical specimens with viral loads down to 103 copies/ml in 3 h or less. The new test represents a major improvement over viral culture in terms of turn around time, over rapid immunoassay tests in terms of sensitivity, and over bench top RT-PCR and DFA in terms of ease of use and portability
A wearable optical device for continuous monitoring during neoadjuvant chemotherapy infusions
We present a new continuous-wave (CW) wearable diffuse optical device aimed at investigating the hemodynamic response of locally advanced breast cancer patients during a patient’s first neoadjuvant chemotherapy infusion. The system consists of a flexible substrate that supports an array of surface-mount LED and photodiode pairs (i.e. optodes). Probe performance was evaluated using solid tissue-simulating phantoms. Measurements revealed high SNR (65dB), low source-detector crosstalk (-59 dB), high measurement precision (0.17%), and good thermal stability (0.2% Vrms/°C). A cuff occlusion experiment was performed on the forearm of a healthy volunteer to demonstrate the ability to track rapid hemodynamic changes
Wearable near-infrared optical probe for continuous monitoring during breast cancer neoadjuvant chemotherapy infusions
We present a new continuous-wave wearable diffuse optical probe aimed at investigating the hemodynamic response of locally advanced breast cancer patients during neoadjuvant chemotherapy infusions. The system consists of a flexible printed circuit board that supports an array of six dual wavelength surface-mount LED and photodiode pairs. The probe is encased in a soft silicone housing that conforms to natural breast shape. Probe performance was evaluated using tissue-simulating phantoms and in vivo normal volunteer measurements. High SNR (71 dB), low source-detector crosstalk (−60  dB), high measurement precision (0.17%), and good thermal stability (0.22% Vrms/°C) were achieved in phantom studies. A cuff occlusion experiment was performed on the forearm of a healthy volunteer to demonstrate the ability to track rapid hemodynamic changes. Proof-of-principle normal volunteer measurements were taken to demonstrate the ability to collect continuous in vivo breast measurements. This wearable probe is a first of its kind tool to explore prognostic hemodynamic changes during chemotherapy in breast cancer patients
Discrimination of Single Base Substitutions in a DNA Strand Immobilized in a Biological Nanopore
A novel device for collecting and dispensing fingerstick blood for point of care testing
Effect of an Electrolyte Cation on Detecting DNA Damage with the Latch Constriction of α‑Hemolysin
The
effect of an electrolyte cation on the unzipping of furan-containing
double-stranded DNA in an α-hemolysin (αHL) nanopore is
described. The current through an open αHL channel increases
in proportion to the ion mobility. However, the ionic current measured
during residence of a DNA duplex inside of the protein pore shows
a more complex dependence on the choice of cation, indicating that
the current measured during DNA residence in the pore is modulated
by the specific interactions of the cations with the DNA and/or αHL.
The residence time (stability) of the DNA duplex inside of the pore
prior to unzipping is also highly dependent on the cation, in striking
contrast to the small variation in duplex stability (as measured by
the melting temperature) in bulk electrolyte solution. A missing base
in DNA can be detected in the latch region of αHL with optimal
current resolution in RbCl, while optimal time resolution is possible
in LiCl