Fujirebio v. Quanterix: Patent Dispute Over Tau Assay Diagnostics Dismissed With Prejudice
Fujirebio Diagnostics, Inc. brought a patent infringement action against Quanterix Corporation in Delaware, asserting US11275092B2 against Quanterix's Simoa® Tau Kits and Fujirebio's own Lumipulse pTau 217 plasma assays. The case closed after 317 days with all claims dismissed with prejudice and declaratory judgment counterclaims dismissed without prejudice.
Tau Assay Patent Dispute Ends in Stipulated Dismissal With Prejudice
Fujirebio Diagnostics, Inc. filed this infringement action on 28 May 2025 in the Delaware District Court before Judge Gregory B. Williams, asserting US11275092B2 — a patent directed to tau protein detection plasma assay technology — against Quanterix Corporation. The accused products include Quanterix's Simoa® Tau Kits, Fujirebio's Lumipulse G pTau 217 Plasma Assay, and the Lumipulse G pTau 217/ß-Amyloid 1-42 Plasma Ratio Assay.
The recorded basis of termination is Dismissed with Prejudice. The docket order reflects a stipulation under Fed. R. Civ. P. 41(a)(2) and (c), by which all claims asserted by Quanterix were dismissed with prejudice and all declaratory judgment counterclaims asserted by Fujirebio Diagnostics, Inc. and Fujirebio Europe N.V. were dismissed without prejudice, with each party to bear its own costs, expenses, and attorneys' fees. The order was entered by the court as stipulated.
The case resolved in approximately 317 days — a relatively swift conclusion for a Delaware patent infringement action. The asymmetric treatment of claims (plaintiff claims dismissed with prejudice; DJ counterclaims dismissed without prejudice) is notable and visible in the public record. The specific commercial or licensing terms, if any, underlying the parties' agreement to stipulate are not disclosed in the available record.
See Complete Case & Patent Analysis →Filing to Dismissed with Prejudice in 317 days
317 days from filing to dismissal — below average for Delaware patent cases.
US11275092B2 — tau protein detection plasma assay technology
Any company developing, manufacturing, or commercialising tau or phospho-tau plasma assay products — particularly pTau 217 or pTau/Aß ratio assays — should assess freedom to operate against US11275092B2. This case confirms that Fujirebio Diagnostics is prepared to enforce this patent in US federal court, and the dismissal with prejudice leaves the patent's validity and scope unresolved. Diagnostics firms entering or expanding in the Alzheimer's blood biomarker market face meaningful FTO risk.
Official order — verbatim text
The stipulation dismisses all of Quanterix's asserted claims with prejudice and Fujirebio's declaratory judgment counterclaims without prejudice, with each party bearing its own costs. This asymmetric structure means the infringement claims are finally resolved against re-filing, while the DJ counterclaims remain available for future proceedings. No merits determination on the patent's validity or infringement was made by the court.
Dismissed with prejudice: what the stipulated resolution means for both parties
Rule 41 stipulated dismissal with prejudice — what it means
A dismissal with prejudice under Fed. R. Civ. P. 41(a)(2) is a final adjudication on the merits — the dismissed claims cannot be re-filed. Here, the parties jointly stipulated to the dismissal, and the court entered it as ordered. The asymmetric structure — plaintiff's claims dismissed with prejudice, defendant's DJ counterclaims dismissed without prejudice — is exactly as stated in the docket order.
Stipulated — court-enteredFujirebio's infringement claims permanently extinguished
With the infringement claims dismissed with prejudice, Fujirebio Diagnostics cannot reassert the same claims under US11275092B2 against Quanterix based on the same accused products in this action. The patent itself remains in force; the dismissal affects only the asserted claims in this case. The specific terms underlying the parties' agreement to reach this resolution are not disclosed in the available record.
Claims barred — patent intactQuanterix's DJ counterclaims dismissed without prejudice
Quanterix's declaratory judgment counterclaims were dismissed without prejudice, meaning they were not adjudicated on the merits and could, in principle, be refiled in appropriate circumstances. Quanterix avoids a merits ruling on its DJ claims. Each party bears its own costs, expenses, and attorneys' fees — no cost award was made against either side.
DJ claims preserved — own costsTau assay IP landscape remains commercially sensitive post-dismissal
The dismissal leaves US11275092B2 unchallenged on the merits in this proceeding. Companies developing or commercialising tau and phospho-tau plasma assays — particularly those directed at Alzheimer's blood-based diagnostics — should monitor Fujirebio's enforcement posture and Quanterix's Simoa platform IP position. The absence of a merits ruling means the validity and scope of US11275092B2 remain open questions in the sector.
Patent validity undecidedFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Fujirebio Diagnostics, Inc. | Company | /Search in Eureka ↗ |
| Defendant | Quanterix Corporation | Company | /Search in Eureka ↗ |
| Plaintiff counsel | Anthony J. Fitzpatrick | Attorney | Counsel for Fujirebio Diagnostics, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Christopher S. Kroon | Attorney | Counsel for Fujirebio Diagnostics, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Monte Terrell Squire | Attorney | Counsel for Fujirebio Diagnostics, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Poornarchita Dwarakanath | Attorney | Counsel for Fujirebio Diagnostics, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Thomas J. Kowalski | Attorney | Counsel for Fujirebio Diagnostics, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Duane Morris, LLP | Law Firm | Representing Fujirebio Diagnostics, Inc.Search in Eureka ↗ |
| Defendant counsel | Cameron Paul Clark | Attorney | Counsel for Quanterix CorporationSearch in Eureka ↗ |
| Defendant counsel | Elizabeth M. Flanagan | Attorney | Counsel for Quanterix CorporationSearch in Eureka ↗ |
| Defendant counsel | Jeremy A. Tigan | Attorney | Counsel for Quanterix CorporationSearch in Eureka ↗ |
| Defendant counsel | Matthew R. Clauss | Attorney | Counsel for Quanterix CorporationSearch in Eureka ↗ |
| Defendant counsel | Orion Armon | Attorney | Counsel for Quanterix CorporationSearch in Eureka ↗ |
| Defendant law firm | Cooley LLP | Law Firm | Representing Quanterix CorporationSearch in Eureka ↗ |
| Defendant law firm | Morris, Nichols, Arsht & Tunnell LLP | Law Firm | Representing Quanterix CorporationSearch in Eureka ↗ |
| Presiding judge | Judge Gregory B. Williams | Judge | Delaware District CourtSearch in Eureka ↗ |
R&D signals in the tau plasma assay and neurodegenerative diagnostics space
Forward-looking patent and R&D intelligence derived from Fujirebio v. Quanterix — mapping the IP landscape around tau assay technology and blood-based Alzheimer's diagnostics.
Fujirebio's tau and pTau assay patent filing activity
US11275092B2 represents one node in Fujirebio's broader IP position in tau and phospho-tau detection. Tracking Fujirebio's continuation filings, family members, and prosecution activity in the US16/522237 patent family can reveal where the company is building enforcement coverage — and which product categories may face future assertion risk.
Fujirebio patent portfolioFiling trends in blood-based pTau 217 and Alzheimer's biomarker assays
The pTau 217 plasma assay market is experiencing rapid patent activity as diagnostics companies race to commercialise blood-based Alzheimer's screening. Monitoring filing trends in immunoassay platforms for tau, pTau 217, and amyloid-beta ratios can identify where IP density is highest and where white space for novel approaches exists.
pTau 217 assay IP trendsQuanterix Simoa platform patent position in ultra-sensitive biomarker detection
Quanterix's Simoa® single-molecule array technology underpins its Tau Kit product line. Understanding the depth of Quanterix's own patent filings around ultra-sensitive immunoassay detection — and how these interact with Fujirebio's asserted patents — is critical for any organisation assessing competitive IP risk in the neurodegenerative diagnostics market.
Quanterix Simoa IP landscapeAdjacent R&D opportunities beyond pTau 217 in neurodegeneration biomarkers
The contested IP around pTau 217 and tau plasma assays suggests adjacent white-space opportunities in complementary neurodegeneration biomarkers — such as neurofilament light chain (NfL), GFAP, and novel amyloid-beta ratio panels — where patent density may be lower. Mapping these adjacencies can guide R&D investment toward differentiated and less encumbered diagnostic approaches.
Neurodiagnostic biomarker white spaceSimilar patent cases: tau assay and biomarker diagnostics litigation in Delaware
Explore related patent infringement cases involving tau protein and phospho-tau plasma assay technology filed in Delaware District Court and comparable US jurisdictions.
What this case signals for the tau diagnostics IP landscape
A swift stipulated dismissal in a Delaware tau assay patent case leaves key validity and infringement questions unresolved — with sector-wide implications.
US11275092B2 emerges from this litigation without a merits ruling
The with-prejudice dismissal of Fujirebio's claims extinguishes this action but leaves the patent's validity and claim scope judicially untested. Competitors and licensees in the tau plasma assay space should treat US11275092B2 as an active enforcement risk and conduct FTO analysis accordingly.
Asymmetric dismissal terms warrant close reading by Quanterix's IP team
Quanterix's declaratory judgment counterclaims were dismissed without prejudice — preserving the right to challenge US11275092B2 in a future proceeding if needed. This structural asymmetry, visible in the public record, is a meaningful data point for understanding each party's post-litigation IP posture.
Fujirebio v Quanterix — key questions answered
The case was dismissed with prejudice on 10 April 2026, approximately 317 days after filing. All infringement claims asserted by Quanterix were dismissed with prejudice pursuant to a joint stipulation under Fed. R. Civ. P. 41(a)(2) and (c). Declaratory judgment counterclaims by Fujirebio Diagnostics and Fujirebio Europe N.V. were dismissed without prejudice. Each party bears its own costs.
The asserted patent is US11275092B2 (application no. US16/522237), which is directed to tau protein plasma assay detection technology. It was asserted against Quanterix's Simoa® Tau Kits and Fujirebio's Lumipulse G pTau 217 Plasma Assay and pTau 217/ß-Amyloid 1-42 Plasma Ratio Assay products in the context of blood-based Alzheimer's and neurodegeneration diagnostics.
Dismissal with prejudice is a final resolution — the dismissed infringement claims cannot be re-filed in a new action. In this case, the dismissal was stipulated by the parties and entered by the court. The asymmetric structure (plaintiff claims dismissed with prejudice; defendant DJ counterclaims dismissed without prejudice) means Fujirebio's infringement claims are permanently barred, while Quanterix's DJ counterclaims were not adjudicated on the merits.
No. The case was resolved by a joint stipulation of dismissal without any trial or substantive merits ruling. The validity, enforceability, and claim scope of US11275092B2 were not adjudicated by the court. The patent remains in force and its claim scope remains an open question for the tau diagnostics sector.
Fujirebio Diagnostics was represented by Duane Morris LLP, with attorneys including Anthony J. Fitzpatrick, Christopher S. Kroon, Monte Terrell Squire, Poornarchita Dwarakanath, and Thomas J. Kowalski. Quanterix Corporation was represented by Cooley LLP and Morris, Nichols, Arsht & Tunnell LLP, with attorneys including Cameron Paul Clark, Elizabeth M. Flanagan, Jeremy A. Tigan, Matthew R. Clauss, and Orion Armon.
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