# How to Detect Disease Markers Using Colored Proteins > A 1981 method for measuring disease-related proteins in blood by attaching them to naturally colored proteins that can be detected with light. - **Patent:** US 4302536 - **Original title:** Colorimetric immunoassay process - **Owner:** Individual - **Granted:** 1981 - **Status:** Public domain (expired) - **Times cited:** 27 - **Field:** biotech, medical_diagnostics ## What it does This patent describes a way to find specific substances (antigens) in blood or cells by using a special 'tag.' The process involves creating a reagent by chemically bonding an antibody—which naturally seeks out a specific target—to a 'chromoprotein' like ferritin or cytochrome c. Because these chromoproteins have a natural color, they absorb specific wavelengths of light. When the tagged antibody binds to the target in a sample, the resulting mixture can be measured using a standard light-measuring device (colorimeter) to determine exactly how much of the target substance is present. ## What it does NOT cover - Does not cover methods using radioactive labels for detection - Does not cover fluorescent markers or labels that require excitation light - Does not cover detection methods that rely on enzymatic color changes rather than the inherent color of the protein - Does not cover the use of synthetic dyes or artificial chromophores ## The clever bit Instead of using an artificial dye, the inventor used naturally occurring proteins (like ferritin) that already possess a distinct color, effectively turning a biological molecule into a built-in sensor. ## Real-world examples 1. Diagnostic blood serum testing 2. Protein concentration analysis in clinical labs 3. Bacterial antibody detection ## Why it matters Before this method, detecting specific proteins often required complex, expensive, or radioactive techniques. By using naturally colored proteins that were already abundant in biological research, this patent provided a path toward simpler, direct colorimetric assays that could be performed with standard lab equipment. ## Frequently asked questions ### What does How to Detect Disease Markers Using Colored Proteins cover? A 1981 method for measuring disease-related proteins in blood by attaching them to naturally colored proteins that can be detected with light. ### Who owns patent US 4302536? Individual owns this patent, granted in 1981. ### When does this patent expire? This patent has expired and is now in the public domain — anyone can use the invention freely. ### What is patent US 4302536 cited by? This patent has been cited by 27 later patents that build on its ideas. ### What problem does this patent solve? Before this method, detecting specific proteins often required complex, expensive, or radioactive techniques. By using naturally colored proteins that were already abundant in biological research, this patent provided a path toward simpler, direct colorimetric assays that could be performed with standard lab equipment. ### What does this patent NOT cover? Does not cover methods using radioactive labels for detection **Full plain-English explainer:** https://patentbrief.org/patent/us/4302536/colorimetric-immunoassay-process **Original patent:** https://patents.google.com/patent/US4302536 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Two Special Antibodies Find Substances in Body Fluids](https://patentbrief.org/patent/us/4376110/psa-test-for-prostate-cancer) — This patent describes a "sandwich" method using two highly specific, man-made antibodies to detect and measure tiny amounts of specific substances, like disease markers, in a fluid sample. - [Making Hybrid Antibodies from Different Animals](https://patentbrief.org/patent/us/4816567/recombinant-antibody-production-in-cho-cells) — This patent describes how to create new, engineered antibodies by combining parts of antibodies from two different animal species, then growing them in a lab. - [How to Build Smaller, Synthetic Antibody-Like Molecules for Medicine](https://patentbrief.org/patent/us/5455030/immunotheraphy-using-single-chain-polypeptide-binding-molecules) — This patent describes a way to create small, single-chain proteins that mimic the binding power of full-sized antibodies to deliver medicine more effectively. - [Detecting Genetic Differences Using DNA Probes and Enzymes](https://patentbrief.org/patent/us/4683194/pcr-process) — This 1987 patent describes a method to find tiny differences in DNA sequences by using special DNA pieces (probes) and cutting enzymes, which can help diagnose genetic conditions like sickle cell anemia. - [Using Insect Cells to Create Antibodies for Human Diseases](https://patentbrief.org/patent/us/5397703/hepatitis-c-virus-genome-discovery) — A method for creating disease-fighting antibodies by using insect cells to display human proteins, which are then injected into animals to trigger an immune response.