Portolan reports 4.02% stake in Quanterix Corp

Quanterix Corp reported an updated ownership statement from Portolan Capital Management, LLC and its manager George McCabe.

Rhea-AI Filing Summary

Quanterix Corp reported an updated ownership statement from Portolan Capital Management, LLC and its manager George McCabe. The reporting group beneficially owns 1,899,308 shares of Quanterix common stock, representing 4.02% of the outstanding class as of the stated date.

Portolan Capital Management, LLC holds these shares directly in its capacity as investment manager for various clients, and George McCabe is deemed to own them indirectly as Manager of Portolan. The reporting persons have sole voting and dispositive power over all 1,899,308 shares and no shared voting or dispositive power, and they characterize their position as ownership of 5 percent or less of the class.

Key Figures

Shares beneficially owned: 1,899,308 shares Percent of class: 4.02% Sole voting power: 1,899,308 shares +3 more

6 metrics

Shares beneficially owned 1,899,308 shares Common stock beneficially owned by each reporting person

Percent of class 4.02% Percentage of Quanterix common stock owned by the reporting persons

Sole voting power 1,899,308 shares Shares over which the reporting persons have sole power to vote

Shared voting power 0 shares Shares over which the reporting persons share voting power

Sole dispositive power 1,899,308 shares Shares over which the reporting persons have sole power to dispose

Shared dispositive power 0 shares Shares over which the reporting persons share dispositive power

Key Terms

beneficially owned, sole voting power, sole dispositive power, Schedule 13G/A, +1 more

5 terms

beneficially owned financial

"shares Common Stock of the Issuer beneficially owned (1) directly by Portolan"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

sole voting power financial

"5 | Sole Voting Power 1,899,308.00 6 | Shared Voting Power 0.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

sole dispositive power financial

"7 | Sole Dispositive Power 1,899,308.00 8 | Shared Dispositive Power 0.00"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

Schedule 13G/A regulatory

"form_type": "SCHEDULE 13G/A""

A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.

registered investment adviser financial

"Portolan Capital Management, LLC, a registered investment adviser, in its capacity"

A registered investment adviser (RIA) is a firm or individual legally registered with regulators to give personalized investment advice and manage clients' money, with a duty to put clients’ interests ahead of their own. Think of an RIA as a licensed financial guide who must disclose fees, conflicts and how they are paid; that transparency and legal duty matter to investors because it reduces the risk of hidden costs or biased recommendations.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What ownership stake in Quanterix Corp (QTRX) does Portolan Capital report?

Portolan Capital Management, LLC and George McCabe report beneficial ownership of 1,899,308 shares of Quanterix Corp common stock, representing 4.02% of the outstanding class, with sole voting and dispositive power over all reported shares.

Who are the reporting persons in the Quanterix Corp (QTRX) Schedule 13G/A?

The reporting persons are Portolan Capital Management, LLC, a registered investment adviser, and George McCabe, its Manager, who is deemed to own the shares indirectly through his role at Portolan.

Does Portolan Capital have sole or shared voting power over QTRX shares?

Portolan Capital and George McCabe report sole voting power over 1,899,308 shares of Quanterix Corp common stock and no shared voting power, indicating exclusive authority to vote those shares.

What percentage of Quanterix Corp (QTRX) does Portolan Capital say it owns?

The reporting group states that its beneficial ownership of Quanterix Corp common stock is 4.02% of the class, and it identifies this as ownership of 5 percent or less of the outstanding shares.

How does George McCabe hold his interest in Quanterix Corp (QTRX)?

George McCabe’s interest is reported as indirect beneficial ownership of 1,899,308 shares through his role as Manager of Portolan Capital Management, LLC, which holds the shares for various advisory clients.

Where are the reporting persons for the Quanterix Corp (QTRX) stake based?

The principal business office of both reporting persons is 2 International Place, FL 26, Boston, MA 02110. Portolan Capital Management, LLC is organized in Delaware, and George McCabe is a citizen of the United States.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 08/14/2026 - 03:10 PM EDT Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 5)

Quanterix Corp

(Name of Issuer)

Common Stock, $0.001 par value per share

(Title of Class of Securities)

74766Q101

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 74766Q101

1

Names of Reporting Persons

Portolan Capital Management, LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 1,899,308.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,899,308.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,899,308.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

4.02 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

CUSIP Number(s): 74766Q101

1

Names of Reporting Persons

George McCabe

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 1,899,308.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,899,308.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,899,308.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

4.02 %

12

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Quanterix Corp
(b)	Address of issuer's principal executive offices: 900 Middlesex Turnpike, Billerica, MA 01821
Item 2.
(a)	Name of person filing: This statement is being filed with respect to the shares Common Stock of the Issuer beneficially owned (1) directly by Portolan Capital Management, LLC, a registered investment adviser, in its capacity as investment manager for various clients, and (2) indirectly by George McCabe, the Manager of Portolan Capital Management, LLC. Portolan Capital Management, LLC and Mr. McCabe are sometimes individually referred to herein as a "Reporting Person" and collectively as the "Reporting Persons."
(b)	Address or principal business office or, if none, residence: The address of the principal business office of each of the Reporting Persons is 2 International Place, FL 26, Boston, MA 02110
(c)	Citizenship: Portolan Capital Management, LLC - DE Mr. McCabe - USA
(d)	Title of class of securities: Common Stock, $0.001 par value per share
(e)	CUSIP No.: 74766Q101
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated by reference herein.
(b)	Percent of class: The information required by Item 4(b) is set forth in Row 11 of the cover page for each of the Reporting Persons and is incorporated by reference herein.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated by reference herein.
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated by reference herein.
	(iv) Shared power to dispose or to direct the disposition of: 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Ownership of 5 percent or less of a class
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Portolan Capital Management, LLC

Signature:	George McCabe
Name/Title:	George McCabe/Manager
Date:	08/14/2026

George McCabe

Signature:	George McCabe
Name/Title:	George McCabe
Date:	08/14/2026