This invention allows ultra-low levels of virtually any biological analyte to be detected and quantified rapidly, simply and inexpensively with an electrochemical biosensor using a novel electrochemically detectable tag that replaces optical labels. The tag binds to an analyte directly, or indirectly using one or more ligands and particles, and consists of a quadruplex electrochemically detectable oligonucleotide rich in guanine, or a single-stranded electrochemically detectable oligonucleotide rich in guanine that self-assembles into a quadruplex electrochemically detectable oligonucleotide when exposed to cations that enable quadruplex self-assembly. Quadruplex electrochemically detectable oligonucleotide tags are exposed, adsorbed or hybridized at the surface of a biosensor working electrode. An electrochemical technique facilitates the quadruplex tags to produce 8-oxoguanine oxidation signals proportional to the analyte level in the samples. The resulting analyte levels measured from 8-oxoguanine oxidation signals are 1,000 times lower than analyte levels measured from guanine oxidation signals.

Provided herein is technology relating to detecting and identifying nucleic acids and particularly, but not exclusively, to compositions, methods, kits, and systems for detecting, identifying, and quantifying target nucleic acids with high confidence at single-molecule resolution.

Provided herein is technology relating to detecting and identifying nucleic acids and particularly, but not exclusively, to compositions, methods, kits, and systems for detecting, identifying, and quantifying target nucleic acids with high confidence at single-molecule resolution.

The disclosure provides compositions and methods for the quantification of a target nucleic acid sequence or sequences in a sample using next generation sequencing. The methods of the disclosure can be used to determine titer of one or more target organisms in a sample.

The disclosure provides compositions and methods for the quantification of a target nucleic acid sequence or sequences in a sample using next generation sequencing. The methods of the disclosure can be used to determine titer of one or more target organisms in a sample.

A fractional concentration of clinically-relevant DNA in a mixture of DNA from a biological sample is determined based on amounts of DNA fragments at multiple sizes. For example, the fractional concentration of fetal DNA in maternal plasma or tumor DNA in a patient's plasma can be determined. The size of DNA fragments in a sample is shown to be correlated with a proportion of fetal DNA and a proportion of tumor DNA, respectively. Calibration data points (e.g., as a calibration function) indicate a correspondence between values of a size parameter and the fractional concentration of the clinically-relevant DNA. For a given sample, a first value of a size parameter can be determined from the sizes of DNA fragments in a sample. A comparison of the first value to the calibration data points can provide the estimate of the fractional concentration of the clinically-relevant DNA.

A fractional concentration of clinically-relevant DNA in a mixture of DNA from a biological sample is determined based on amounts of DNA fragments at multiple sizes. For example, the fractional concentration of fetal DNA in maternal plasma or tumor DNA in a patient's plasma can be determined. The size of DNA fragments in a sample is shown to be correlated with a proportion of fetal DNA and a proportion of tumor DNA, respectively. Calibration data points (e.g., as a calibration function) indicate a correspondence between values of a size parameter and the fractional concentration of the clinically-relevant DNA. For a given sample, a first value of a size parameter can be determined from the sizes of DNA fragments in a sample. A comparison of the first value to the calibration data points can provide the estimate of the fractional concentration of the clinically-relevant DNA.

The present disclosure relates to compositions and methods of RNA analysis. In particular, the present disclosure provides a method of RNA analysis that includes obtaining a sample, applying one or more multi-partite probes to the sample, where each of the one or more multi-partite probes includes at least two sub-probes, annealing at least one of the applied one or more multi-partite probes to at least one target nucleic acid within the sample, and ligating the at least two sub-probes associated with the at least one annealed multi-partite probe to create a target nucleic acid proxy that can be detected.

The present disclosure relates to compositions and methods of RNA analysis. In particular, the present disclosure provides a method of RNA analysis that includes obtaining a sample, applying one or more multi-partite probes to the sample, where each of the one or more multi-partite probes includes at least two sub-probes, annealing at least one of the applied one or more multi-partite probes to at least one target nucleic acid within the sample, and ligating the at least two sub-probes associated with the at least one annealed multi-partite probe to create a target nucleic acid proxy that can be detected.

Methods for non-invasive assessment of genetic variations that make use of nucleic acid fragment length information, in particular length of fragments in circulating cell-free nucleic acids and compares the number of counts from fragments with different length.