SEC Form DEFA14A filed by Quanterix Corporation

www.investorvote.com/QTRX Step 1: Go to www.investorvote.com/QTRX. Step 2: Click on the icon on the right to view meeting materials. Step 3: Return to the investorvote.com window and follow the instructions on the screen to log in. Online Go to www.investorvote.com/QTRX or scan the QR code — login details are located in the shaded bar below. The Sample Company 2024 Stockholder Meeting Notice 03ZGYC + + Important Notice Regarding the Availability of Proxy Materials for the Quanterix Corporation Stockholder Meeting to be held on June 3, 2024. Under Securities and Exchange Commission rules, you are receiving this notice that the proxy materials for the annual stockholders’ meeting are available on the Internet. Follow the instructions below to view the materials and vote online or request a copy. The items to be voted on at the annual meeting are on the reverse side. Your vote is important! This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The 2024 proxy statement and our 2023 annual report to stockholders are available for viewing, printing and downloading at: Obtaining a Copy of the Proxy Materials – If you want to receive a copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. Please make your request as instructed on the reverse side on or before May 22, 2024 to facilitate timely delivery. 2NOT Easy Online Access — View your proxy materials and vote. When you go online, you can also help the environment by consenting to receive electronic delivery of future materials. Step 4: Make your selections as instructed on each screen for your delivery preferences. Step 5: Vote your shares. Votes submitted electronically must be received by 1:00 am, Eastern Time, on June 3, 2024. MMMMMMMMMMMM MMMMMMMMM MR A SAMPLE DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4 ADD 5 ADD 6 ENDORSEMENT_LINE______________ SACKPACK_____________ 1234 5678 9012 345 C 1234567890 COY MMMMMMM 000001

Here’s how to order a copy of the proxy materials and select delivery preferences: Current and future delivery requests can be submitted using the options below. If you request an email copy, you will receive an email with a link to the current meeting materials. PLEASE NOTE: You must use the number in the shaded bar on the reverse side when requesting a copy of the proxy materials. — Internet – Go to www.investorvote.com/QTRX. — Phone – Call us free of charge at 1-866-641-4276. — Email – Send an email to [email protected] with “Proxy Materials Quanterix Corporation” in the subject line. Include your full name and address, plus the number located in the shaded bar on the reverse side, and state that you want a paper copy of the meeting materials. To facilitate timely delivery, requests for a paper copy of proxy materials must be received by May 22, 2024. Quanterix Corporation’s Annual Meeting of Stockholders will be held on June 3, 2024, at 10:00 a.m. Eastern Time, at 900 Middlesex Turnpike, Building 1, Billerica, MA 01821. Proposals to be voted on at the meeting are listed below along with the Board of Directors’ recommendations. The Board of Directors recommends a vote FOR all nominees and FOR Proposals 2 and 3. 1. Election of Directors: 01 - Karen A. Flynn 02 - Martin D. Madaus, Ph.D. 2. To approve, by a non-binding advisory vote, the compensation of our named executive officers, as disclosed in the proxy statement. 3. Ratification of the appointment of Ernst & Young LLP as the independent registered public accounting firm for the fiscal year ending December 31, 2024. PLEASE NOTE – YOU CANNOT VOTE BY RETURNING THIS NOTICE. To vote your shares you must go online or request a paper copy of the proxy materials to receive a proxy card. If you wish to attend and vote at the meeting, please bring this notice with you. 2024 Stockholder Meeting Notice