Compositions useful for the detection of single molecules in a sample are provided. In some aspects, the disclosure provides a nucleotide connected to a nucleic acid comprising a FRET label comprising at least three luminescent molecules. In some embodiments, the nucleic acids described herein comprise one or more structural features that provide enhanced fluorescence intensity. In some aspects, methods of sequencing using the labeled nucleotides of the disclosure are provided.

Aspects of the application provide methods of identifying and sequencing proteins, polypeptides, and amino acids, and compositions useful for the same. In some aspects, the application provides methods of obtaining data during a degradation process of a polypeptide, and outputting a sequence representative of the polypeptide. In some aspects, the application provides amino acid recognition molecules comprising a shielding element that enhances photostability in polypeptide sequencing reactions.

The present description provides methods, assays and reagents useful for sequencing proteins. Sequencing proteins in a broad sense involves observing the plausible identity and order of amino acids, which is useful for sequencing single polypeptide molecules or multiple molecules of a single polypeptide. In one aspect, the methods are useful for sequencing multiple polypeptides. The methods and reagents described herein can be useful for high resolution interrogation of the proteome and enabling ultrasensitive diagnostics critical for early detection of diseases.

A detection method for a quaternary ammonium compound having a -carboxyl group includes: mixing a sample including the quaternary ammonium compound having the -carboxyl group, a fluorescent compound having a fluorophore and a polar aprotic solvent to form a reaction solution. A S.sub.N2 nucleophilic substitution reaction is performed between the fluorophore of the fluorescent compound and the -carboxyl group of the quaternary ammonium compound to obtain a derivation solution including a derivative which is a quaternary ammonium compound with the -carboxyl group substituted with the fluorophore of the fluorescent compound. An extractant and a cosolvent are added to the derivation solution to form a water-in-oil emulsion which disperses in the derivation solution, followed by extracting the derivative from the derivation solution by the extractant to obtain an analytic solution, wherein a polarity of the extractant is higher than a polarity of the polar aprotic solvent. The derivative in the analytic solution is detected; and therefore, the quaternary ammonium compound having the -carboxyl group in the sample can be easily detected by reverse-phase liquid chromatography, fluorescence spectrometry or mass spectrometry.

Aspects of the application provide methods of identifying and sequencing proteins, polypeptides, and amino acids, and compositions useful for the same. In some aspects, the application provides methods of obtaining data during a degradation process of a polypeptide, and outputting a sequence representative of the polypeptide. In some aspects, the application provides amino acid recognition molecules comprising a shielding element that enhances photostability in polypeptide sequencing reactions.

Aspects of the application provide methods of identifying and sequencing proteins, polypeptides, and amino acids, and compositions useful for the same. In some aspects, the application provides methods of obtaining data during a degradation process of a polypeptide, and outputting a sequence representative of the polypeptide. In some aspects, the application provides amino acid recognition molecules comprising a shielding element that enhances photostability in polypeptide sequencing reactions.

Aspects of the application provide methods of identifying and sequencing proteins, polypeptides, and amino acids, and compositions useful for the same. In some aspects, the application provides methods of obtaining data during a degradation process of a polypeptide, and outputting a sequence representative of the polypeptide. In some aspects, the application provides amino acid recognition molecules comprising a shielding element that enhances photostability in polypeptide sequencing reactions.

Aspects of the application provide methods of identifying and sequencing proteins, polypeptides, and amino acids, and compositions useful for the same. In some aspects, the application provides methods of obtaining data during a degradation process of a polypeptide, and outputting a sequence representative of the polypeptide. In some aspects, the application provides amino acid recognition molecules comprising a shielding element that enhances photostability in polypeptide sequencing reactions.

Aspects of the application provide methods of identifying and sequencing proteins, polypeptides, and amino acids, and compositions useful for the same. In some aspects, the application provides methods of obtaining data during a degradation process of a polypeptide, and outputting a sequence representative of the polypeptide. In some aspects, the application provides amino acid recognition molecules comprising a shielding element that enhances photostability in polypeptide sequencing reactions.

Aspects of the application provide methods of identifying and sequencing proteins, polypeptides, and amino acids, and compositions useful for the same. In some aspects, the application provides methods of obtaining data during a degradation process of a polypeptide, and outputting a sequence representative of the polypeptide. In some aspects, the application provides amino acid recognition molecules comprising a shielding element that enhances photostability in polypeptide sequencing reactions.