Portolan Capital, George McCabe report 6.25% stake in Quanterix (QTRX)

Rhea-AI Filing Summary

Quanterix Corp Schedule 13G/A amendment shows Portolan Capital Management, LLC and George McCabe beneficially own 2,945,823 shares of Quanterix Common Stock, representing 6.25% of the class. The filing lists sole voting and dispositive power of 2,945,823 shares for each Reporting Person. The cover identifies CUSIP 74766Q101 and the principal business address for the Reporting Persons as 2 International Place, FL 26, Boston, MA 02110. The statement is signed by George McCabe on 05/15/2026.

Key Figures

Shares beneficially owned: 2,945,823 shares Percent of class: 6.25% CUSIP: 74766Q101 +3 more

6 metrics

Shares beneficially owned 2,945,823 shares Amount listed on cover page/Item 4(a)

Percent of class 6.25% Row 11 of the cover page/Item 4(b)

CUSIP 74766Q101 Cover page and Item 2(e)

Filing type Schedule 13G/A (Amendment No. 4) Header of the provided excerpt

Sole voting/dispositive power 2,945,823 shares Rows 5 and 7 of the cover page / Item 4(c)(i) and 4(c)(iii)

Signature date 05/15/2026 Executed signature blocks

Key Terms

Schedule 13G/A, beneficially owned, sole dispositive power, CUSIP

4 terms

Schedule 13G/A regulatory

"Header: "(Amendment No. 4 ) Quanterix Corp""

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.

beneficially owned financial

"Item 2: "beneficially owned (1) directly by Portolan Capital Management, LLC""

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 dispositive power financial

"Cover rows 7 and Item 4(c)(iii): "Sole Dispositive Power 2,945,823.00""

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.

CUSIP regulatory

"Item 2(e): "CUSIP No.: 74766Q101""

A CUSIP is a nine-character alphanumeric code that uniquely identifies a U.S. or Canadian financial security—such as a stock, bond, or fund share—like a Social Security number for an investment. It matters to investors because brokers, exchanges and record-keepers use the CUSIP to match trades, track ownership, settle transactions and pull accurate records, reducing errors and ensuring money and securities go to the right place.

See more from StockTitan in Google Search and AI answers. Adds StockTitan as a preferred source · opens Google

Add on Google Not now

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 4)

Quanterix Corp

(Name of Issuer)

Common Stock, $0.001 par value per share

(Title of Class of Securities)

74766Q101

(CUSIP Number)

03/31/2026

(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 2,945,823.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 2,945,823.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,945,823.00

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)

6.25 %

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 2,945,823.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 2,945,823.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,945,823.00

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)

6.25 %

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.
	Not Applicable
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:	05/15/2026

George McCabe

Signature:	George McCabe
Name/Title:	George McCabe
Date:	05/15/2026