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.
Original patent title: “Colorimetric immunoassay process”
A 1981 method for measuring disease-related proteins in blood by attaching them to naturally colored proteins that can be detected with light. Granted to Individual in 1981 with 14 claims and 27 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent 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
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
Instead of using an artificial dye, the inventorinventorThe person who actually conceived the invention. Listed on the patent regardless of who owns it.Read more → used naturally occurring proteins (like ferritin) that already possess a distinct color, effectively turning a biological molecule into a built-in sensor.
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Diagnostic blood serum testing
Protein concentration analysis in clinical labs
Bacterial antibody detection
Why it matters
The bigger picture
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.
Filed
August 15, 1978
Granted
November 24, 1981
Market context
Who's building on this
Companies in this space
Modern diagnostic companies continue to refine immunoassay techniques, though the industry has largely shifted toward more sensitive fluorescent and chemiluminescent methods. The core principle of linking a detection molecule to an antibody remains the foundation of ELISA and other common lab tests.
Market impact
This patent helped standardize the use of direct colorimetric measurement in clinical assays. It provided a framework for quantifying proteins without needing the complex secondary reactions that were common in earlier, more cumbersome diagnostic protocols.
Claim 1 — Plain English
What this patent covers
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.
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.
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
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Early stage
Citation count
29/40
Moderately cited
Claim breadth
9/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$22K – $69K
Midpoint $43K · expired or expiring · industry ×1.6
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
14 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Longenecker, R. W. (1981). How to Detect Disease Markers Using Colored Proteins (U.S. Patent No. 4,302,536). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/4302536/colorimetric-immunoassay-process
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
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
Same assignee
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