The assignee for this patent application is
Reporters obtained the following quote from the background information supplied by the inventors: "In the development of immunoassay systems, many performance requirements need be met. Assays need be sensitive enough to detect analyte at very low levels in the subpicogram nanogram range. Total assay time needs to be 15 minutes or less in order to provide timely results for patient management in point of care situations, or to meet throughput requirements for batch analyzers. In some cases, analyte panels where multiple assays are simultaneously performed with the same sample are advantageous in order to minimize the turnaround time for results and test costs.
"Many immunoassays employ fluorescent labels because such labels offer many practical advantages. Compared to enzymes, fluorescent labels are much more stable and do not require an additional substrate reagent. For multianalyte panels, fluorescent labels enable the use of discrete binding zones within a common reaction chamber since each binding zone can be sequentially subjected to fluorescence excitation and emission measurements without interference from adjacent binding zones. Assays utilizing fluorescent labels, however, are less sensitive than enzyme based assays primarily due to the enzyme's ability to catalytically convert substrate to accumulate a great amount of product molecules over time.
"Arylsulfonate cyanine fluorescent dyes are described in Mujumdar et al. (1993) Bioconjugate Chemistry, 4:105-111; Southwick et al. (1990) Cytometry, 11:418-430; and U.S. Pat. No. 5,268,486. Cy5 is described in each of the references and is commercially available from
"Despite these excellent properties, arylsulfonate cyanine fluorescent dyes suffer from certain limitations. In particular, these dyes have a relatively narrow Stokes shift which results in significant overlap between the excitation and emission spectra of the dye. The overlap of excitation and emission spectra, in turn, can cause self-quenching of the fluorescence when the dye molecules are located close to each other when excited. Such self-quenching limits the number of arylsulfonate dye molecules which can be conjugated to a single antibody molecule for use in immunoassays. In the case of Cy5, an exemplary arylsulfonate cyanine fluorescent dye, the Stokes shift is 17 nm (which is the difference between an excitation wavelength of 650 nm and an emission wavelength of 667 nm). Optimal fluorescent yield is obtained when from two to four Cy5 molecules are conjugated to a single antibody molecule. The fluorescent signal output drops rapidly when more than four dye molecules are conjugated to a single antibody molecule. The inability to conjugate more than four dye molecules to individual antibody molecules significantly limits the sensitivity of immunoassays using Cy5-labelled antibodies and other binding substances.
"There is a need for an improved optical detection system and an improved method for detecting analytes with high sensitivity by fluorescent immunoassay. The system and method should be easy to handle by the users and provide high specific signal and minimal background noise."
In addition to obtaining background information on this patent application, NewsRx editors also obtained the inventor's summary information for this patent application: "The present invention is directed to a fluorescent detection system for measuring a fluorescent signal on a probe tip. The system comprises: (a) a probe having an aspect ratio of length to width at least 5 to 1, the probe having a distal end and a proximal end, the proximal end having a sensing surface bound with a fluorescent label; (b) a light source for emitting excitation light directly to the probe's sensing surface; © a collecting lens pointed toward the sensing surface; and (d) an optical detector for detecting the emission fluorescent light; where the collecting lens collects and directs the emission fluorescent light to the optical detector.
"The present invention is also directed to methods for detecting analytes by a fluorescent immunoassay. In one embodiment (three-step binding), the method comprises the steps of: (a) obtaining a probe having a first antibody immobilized on the tip of the probe, wherein the diameter of the tip surface is .ltoreq.5 mm; (b) dipping the probe tip into a sample vessel containing a sample solution having an analyte, moving the probe tip up and down and flowing the sample solution laterally in the sample vessel; © dipping the probe tip into a reagent vessel containing a reagent solution comprising a second antibody molecules conjugated with a first member of a binding pair, moving the probe tip up and down and flowing the reagent solution laterally in the reagent vessel; (d) dipping the probe tip into a washing vessel containing a wash solution; (e) dipping the probe tip into an amplification vessel containing an amplification solution comprising a polymer having a molecular weight of at least about 1 million Dalton and conjugated with at least 5 molecules of second member of the binding pair and at least 25 fluorescent labels, moving the probe tip up and down and flowing the amplification solution laterally in the amplification vessel to form an immunocomplex among the analyte, the first antibody, the second antibody, and the first and the second members of the binding pair on the probe tip; (f) dipping the probe tip into a second washing vessel containing a second wash solution; and (g) detecting the immunocomplex formed by detecting the fluorescent signal on the probe tip; wherein the first antibody and the second antibody are antibodies against the analyte.
"The methods of the present invention achieves high sensitivity because the unique combination of (i) using a probe having a small sensing surface area for binding analyte molecules, (ii) moving the probe tip up and down and flowing the reaction solution laterally in a reaction vessel, and (iii) using a high molecular weigh polymer conjugated with multiple binding molecules and multiple fluorescent labels.
"The present invention is further directed to a fluorescent labeling composition comprising: (a) a crosslinked FICOLL.RTM. (copolymers of sucrose and epichlorohydrin) having a molecular weight of at least 1 million Daltons, (b) at least 5 binding molecules, and © at least 25 fluorescent dye molecules, wherein the binding molecules and the fluorescent dye molecules are attached to the cross-linked FICOLL.RTM..
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 illustrates a first embodiment of the optical detection system.
"FIG. 2 illustrates a second embodiment of the optical detection system.
"FIG. 3 illustrates a third embodiment of the optical detection system.
"FIG. 4 illustrates a forth embodiment of the optical detection system.
"FIG. 5 illustrates a fifth embodiment of the optical detection system.
"FIG. 6 illustrates a sixth embodiment of the optical detection system.
"FIG. 7 illustrates the two-step binding method for detecting an analyte.
"FIG. 8 illustrates an optical detecting system where the light source and the detector are both mounted at the side opposite to the sensing surface of the probe.
"FIG. 9 illustrates another view of the optical detecting system where the probe is immersed into an analyte solution.
"FIG. 10 illustrates a flow chart of preparing crosslinked FICOLL.RTM. 400.
"FIG. 11 illustrates a flow chart of preparing Cy 5-antibody-crosslinked FICOLL.RTM. 400.
"FIG. 12 illustrates the elution pattern of SPDP-labeled crosslinked FICOLL.RTM. 400 by Sepharose 4B CL chromatography.
"FIG. 13 illustrates an immunoassay format for detecting protein A. Ab: antibody, Ag: antigen (protein A), Sa: streptavidin, B: biotin, F: fluorescent label."
For more information, see this patent application: ZUK, Robert F. Crosslinked Polysaccharide. Filed
Keywords for this news article include: Antibodies, Immunology, Sulfur Acids, Arylsulfonates, Blood Proteins, Immunoglobulins, Sulfur Compounds, Organic Chemicals, Arylsulfonic Acids,
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