Quanterix director reports 99,400-share purchase

Quanterix Corp director William P. Donnelly, through trusts established by him and his spouse, reported two indirect open-market purchases of common stock.

Rhea-AI Filing Summary

Quanterix Corp director William P. Donnelly, through trusts established by him and his spouse, reported two indirect open-market purchases of common stock. On August 12, 2026, the trusts acquired 27,155 shares at a weighted average price of $2.75 per share, in multiple trades between $2.58 and $2.95. On August 13, 2026, they acquired an additional 72,245 shares at a weighted average price of $2.93 per share, in trades between $2.85 and $3.13. In total, the trusts purchased 99,400 shares of Quanterix common stock in these transactions.

Insider Trade Summary

Net Buyer: 99,400 shares

Net Buy 2 txns

Insider DONNELLY WILLIAM P

Role Director

Bought 99,400 shs ($286K)

Type	Security	Shares	Price	Value
Purchase	Common Stock F3, F2	72,245	$2.93	$212K
Purchase	Common Stock F1, F2	27,155	$2.75	$75K

Holdings After Transaction: Common Stock — 99,400 shares (Indirect, See Footnote)

Footnotes (3)

1. F1. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $2.58 to $2.95, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote.
2. F2. Owned jointly by trusts established by the reporting person and his spouse.
3. F3. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $2.85 to $3.13, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote.

Key Figures

Shares purchased 2026-08-12: 27,155 shares Price range 2026-08-12: $2.58 to $2.95 Shares purchased 2026-08-13: 72,245 shares +2 more

5 metrics

Shares purchased 2026-08-12 27,155 shares Indirect open-market purchase at weighted average price $2.75 per share

Price range 2026-08-12 $2.58 to $2.95 Range of prices for August 12, 2026 purchases

Shares purchased 2026-08-13 72,245 shares Indirect open-market purchase at weighted average price $2.93 per share

Price range 2026-08-13 $2.85 to $3.13 Range of prices for August 13, 2026 purchases

Total shares purchased 99,400 shares Combined indirect purchases across both reported days

Key Terms

weighted average price, indirect, open market or private transaction, trusts

4 terms

weighted average price financial

"The price reported in Column 4 is a weighted average price."

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

indirect financial

"Shares were reported as indirectly owned through jointly established trusts."

open market or private transaction financial

"Transaction code P indicates a purchase in open market or private transaction."

trusts financial

"Owned jointly by trusts established by the reporting person and his spouse."

A trust is a legal arrangement where one party (the trustee) holds and manages assets—like cash, stocks, property, or a pool of investments—on behalf of others (the beneficiaries). For investors it matters because trusts can package assets into a single, managed vehicle that may offer professional oversight, specific tax or estate benefits, and tradeable shares or units that change how you access, control, and receive income from those assets; think of it as a secure box managed for your financial benefit.

FAQ

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

What insider transactions did Quanterix (QTRX) disclose in this Form 4?

Quanterix disclosed that director William P. Donnelly, via jointly established trusts, indirectly purchased a total of 99,400 shares of common stock in open-market transactions on August 12 and 13, 2026.

How many Quanterix (QTRX) shares were bought on August 12, 2026?

On August 12, 2026, trusts associated with director William P. Donnelly purchased 27,155 shares of Quanterix common stock at a weighted average price of $2.75 per share, across trades ranging from $2.58 to $2.95.

What was the August 13, 2026 Quanterix (QTRX) insider purchase size and price?

On August 13, 2026, the same trusts acquired 72,245 shares of Quanterix common stock at a weighted average price of $2.93 per share, with individual trade prices ranging from $2.85 to $3.13.

Were the Quanterix (QTRX) insider purchases direct or indirect holdings?

The reported 99,400 shares of Quanterix common stock were held indirectly, owned jointly by trusts established by the reporting person, director William P. Donnelly, and his spouse, as noted in the filing footnotes.

Did Quanterix (QTRX) indicate these trades were under a Rule 10b5-1 plan?

The Form 4 indicates the Rule 10b5-1 trading plan checkbox was not selected, and the footnotes describe only weighted average pricing and trust ownership, without referencing any trading plan.

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

Form 4 Insider Transactions: What Each Field Means →

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Available on EDGAR 08/14/2026 - 04:05 PM Accepted by SEC EDGAR 08/14/2026 - 04:01 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

DONNELLY WILLIAM P

(Last) (First) (Middle)

C/O QUANTERIX CORPORATION

900 MIDDLESEX TURNPIKE

(Street)

BILLERICA MASSACHUSETTS 01821

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Quanterix Corp [ QTRX ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
08/12/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	08/12/2026		P		27,155	A	$2.75(1)	27,155	I	See footnote(2)
Common Stock	08/13/2026		P		72,245	A	$2.93(3)	99,400	I	See Footnote(2)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $2.58 to $2.95, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote.

2. Owned jointly by trusts established by the reporting person and his spouse.

3. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $2.85 to $3.13, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote.

Remarks:

	/s/ Meghan Shevlin, Attorney-in-Fact	08/14/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)