Quanterix Corporation SEC Filing

Portolan Capital Management, LLC and its manager George McCabe report beneficial ownership of 3,633,622 shares of Quanterix Corp common stock, representing 9.36% of the class, as disclosed on a Schedule 13G (Amendment No. 3).

Accepted by SEC EDGAR 08/13/2025 - 04:10 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

Portolan Capital Management, LLC and its manager George McCabe report beneficial ownership of 3,633,622 shares of Quanterix Corp common stock, representing 9.36% of the class, as disclosed on a Schedule 13G (Amendment No. 3). The filing shows sole voting and sole dispositive power over these shares and indicates Portolan acts in its capacity as a registered investment adviser while Mr. McCabe is identified as the manager with indirect interest.

The statement includes a certification that the securities were not acquired to change or influence control of the issuer, consistent with a passive 13G filing. No shared voting or dispositive powers are reported and no other holders are identified in this filing.

Positive

• 3,633,622 shares disclosed, representing a 9.36% ownership stake in Quanterix
• Sole voting power and sole dispositive power reported for the full position
• Filed by a registered investment adviser (Portolan Capital Management, LLC), with manager identified (George McCabe)
• Schedule 13G filing and certification state the position is not intended to change control (passive intent)

Negative

• None.

Insights

Financial Analyst

TL;DR: A registered adviser reports a material, passive stake of 9.36% (3.63M shares) with sole control of voting and disposition.

Portolan's disclosed position is quantitatively significant for a single reporting person and could be relevant to ownership concentration metrics for Quanterix (QTRX). Because the filing is a Schedule 13G, it indicates passive intent per the form type, and the certification reiterates no intent to change control. For valuation or market-impact analysis, this ownership level is material but the filing contains no transaction details, timing, or plans to trade that would imply near-term market activity.

Corporate Governance Expert

TL;DR: The filing documents a single investor with sole voting and dispositive authority over a 9.36% stake, filed as a passive Schedule 13G.

The report explicitly names Portolan Capital (an investment adviser) and George McCabe (Manager) and shows no shared powers, which simplifies governance analysis: this holder can vote the disclosed shares but asserts no intent to influence control. From a governance perspective, disclosure improves transparency about shareholder concentration; however, the document does not indicate any changes to board composition or control arrangements.

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

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 3)

Quanterix Corp

(Name of Issuer)

Common Stock, $0.001 par value per share

(Title of Class of Securities)

74766Q101

(CUSIP Number)

06/30/2025

(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)

SCHEDULE 13G

CUSIP No. 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 3,633,622.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 3,633,622.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,633,622.00

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)

9.36 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

CUSIP No. 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 3,633,622.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 3,633,622.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,633,622.00

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)

9.36 %

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) 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) 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.
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. Various persons have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Common Stock of Quanterix Corp. No one person's interest in the Common Stock of Quanterix Corp. is more than five percent of the total outstanding Common Stock.
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:	08/13/2025

George McCabe

Signature:	George McCabe
Name/Title:	George McCabe
Date:	08/13/2025