Fluorescent dyes are widely used as tracers for localization of biological structures by fluorescence microscopy, for quantification of analytes by fluorescence immunoassay, for flow cytometric analysis of cells, for measurement of physiological state of cells and other applications (Kanaoka, Angew. Chem. Intl. Ed. Engl. 16:137 (1977); Hemmila, Clin. Chem. 31: 359 (1985)). Among the advantages of fluorescent agent over other types of absorption dyes include the detectability of emission at a wavelength distinct from the excitation, the orders of magnitude greater detectability of fluorescence emission over light absorption, the generally low level of fluorescence background in most biological samples and the measurable intrinsic spectral properties of fluorescence polarization (Jolley et al., Clin. Chem. 27: 1190 (1981)), lifetime (U.S. Pat. No. 4,374,120) and excited state energy transfer (U.S. Pat. Nos. 3,996,345; and 4,542,104).
Fluorescent agents are now widely used to determine physiological functions in patients during routine checkups or diagnostic procedures, to monitor the exposure of workers and others to potentially harmful chemicals such as toxic or carcinogenic pesticides or inorganic materials in the atmosphere, soil, or drinking water, in determining the effectiveness of pharmaceuticals on disease states or conditions, in screening new compounds for biological activity as either promoters or inhibitors of particular enzymes, in monitoring gene and transgene expression, and in performing immunological and other laboratory assays such as enzyme-linked immunosorbent assays (ELISAs) and Western blots.
Optical methods of detection, such as fluorescence emission, UV absorptivity, and colorimetry are convenient and highly effective for detecting, monitoring, and measuring fluorescent agents, since methods such as these can generate either qualitative or quantitative information and detection can be achieved either by direct visual observation or by instrumentation.
For many applications that utilize fluorescent dyes as tracers, it is necessary to chemically react the dye with a biologically active ligand such as a cell, tissue, protein, antibody, enzyme, drug, hormone, nucleotide, nucleic acid, polysaccharide, lipid or other biomolecule to make a fluorescent ligand analog or to react the dye with natural or synthetic polymers. With these synthetic probes, the biomolecule frequently confers a specificity for a biochemical interaction that is under investigation and the fluorescent dye provides the method for detection and/or quantification of the interaction. Thus, useful dyes are based on a versatile fluorescent nucleus that allows the preparation of reactive derivatives of several different types that exhibit reactivity toward a variety of chemically reactive sites.
There is a recognized need for suitable fluorophores, particularly reactive fluorophores, for applications in multi-color, multiplexed applications, such as microscopy, flow cytometry, immunoassays, and nucleic acid sequencing. Presently there exists a need for a dye that is excited by a violet 405 nm laser, which is not excited by the 488 nm argon laser, with a long Stokes shift allowing for use of multiple lasers.
The existing, violet laser excitable dyes, about 405 nm, generally have a weak absorptivity (extinction coefficients of less than 20,000 cm−1 M−1 at their absorbance maxima), relatively low quantum yields, and/or or not particularly well solubilized in aqueous environments. Such properties are less than ideal for a fluorophore of interest for biological applications. Cascade Yellow is a common violet laser excitable dye, however this dye is relatively dim when conjugated to a carrier molecule or solid support and has a tendency to aggregate in an aqueous solution.
For example, the wide emission band-widths of many art-recognized dyes result in significant residual fluorescence background from the violet excited dyes at wavelengths typically used for detection of fluorescein emission (typically 515 to 525 nm). Moreover, fluorescence of many of the art-recognized dyes is frequently quenched in aqueous solution, resulting in low quantum yields. The lower quantum yield decreases the detection sensitivity or requires use of disproportionately larger quantities of the less fluorescent dye.
In view of the above, a fluorophore having a reactive group attached to the fluorescent nucleus of the fluorophore, which is water soluble, and highly fluorescent within a narrow wavelength range would be a highly desirable addition to the art-recognized array of reactive fluorophores. The present invention provides such fluorescent agents, conjugates incorporating the agents and methods of using the agents and their conjugates.