No abstract

A nanopore-based device provides single-molecule detection and analytical capabilities that are achieved by electrophoretically driving molecules in solution through a nano-scale pore. The nanopore provides a highly confined space within which single nucleic acid polymers can be analyzed at high throughput by one of a variety of means, and the perfect processivity that can be enforced in a narrow pore ensures that the native order of the nucleobases in a polynucleotide is reflected in the sequence of signals that is detected. Kilobase length polymers (single-stranded genomic DNA or RNA) or small molecules (e.g., nucleosides) can be identified and characterized without amplification or labeling, a unique analytical capability that makes inexpensive, rapid DNA sequencing a possibility. Further research and development to overcome current challenges to nanopore identification of each successive nucleotide in a DNA strand offers the prospect of `third generation' instruments that will sequence a diploid mammalian genome for ~$1,000 in ~24 h.

We present a novel method for integrating two single-molecule measurement modalities, namely, total internal reflection microscopy and electrical detection of biomolecules using nanopores. Demonstrated here is the electrical measurement of nanopore based biosensing performed simultaneously and in-sync with optical detection of analytes. This method makes it possible, for the first time, to visualize DNA and DNA-protein complexes translocating through a nanopore with high temporal resolution ͑1000 frames/s͒ and good signal to background. This paper describes a detailed experimental design of custom optics and data acquisition hardware to achieve simultaneous high resolution electrical and optical measurements on labeled biomolecules as they traverse through a ϳ4 nm synthetic pore. In conclusion, we discuss new directions and measurements, which this technique opens up.

In this study, the authors use new reference models for 23 human centromeres and find that at all cell cycle phases centromeric CENP-A chromatin complexes are octameric nucleosomes with two molecules of CENP-A. This finding refutes previous models that have suggested that hemisomes may briefly transition to octameric nucleosomes.

Background:Measurements of the ionic current flowing through nanometer-scale pores (nanopores) have been used to analyze single DNA and RNA molecules, with the ultimate goal of achieving ultrafast DNA sequencing. However, attempts at purely electronic measurements have not achieved the signal contrast required for single nucleotide differentiation. In this report we propose a novel method of optical detection of DNA sequence translocating through a nanopore. Methods: Each base of the target DNA sequence is 1st mapped onto a 2-unit code, 2 10-bp nucleotide sequence, by biochemical conversion into Designed DNA Polymers. These 2-unit codes are then hybridized to complementary, fluorescently labeled, and self-quenching molecular beacons. As the molecular beacons are sequentially unzipped during translocation through a <2-nm-wide nanopore, their fluorescent tags are unquenched and are detected by a custom-built dual-color total internal reflection fluorescence (TIRF) microscope. The 2-color optical signal is then correlated to the target DNA sequence. Results: A dual-color TIRFM microscope with singlemolecule resolution was constructed, and controlled fabrication of 1-dimensional and 2-dimensional arrays of solid-state nanopores was performed. A nanofluidic cell assembly was constructed for TIRF-based optical detection of voltage-driven DNA translocation through a nanopore. Conclusions: We present a novel nanopore-based DNA sequencing technique that uses an optical readout of DNA translocating unzipping through a nanopore. Our technique offers better single nucleotide differentiation in sequence readout, as well as the possibility of largescale parallelism using nanopore arrays.