Ernst & Young LLP

Westpark Corporate Center

8484 Westpark Drive

McLean, VA 22102

Tel: +1 703 747 0000

Fax: +1 703 747 0100

ey.com

December 31, 2014

Securities and Exchange Commission

100 F Street, N.E.

Washington, DC 20549

Ladies and Gentlemen:

We have read the section titled “Experts” included within the Registration Statement on Form S‑1, Amendment No. 1, dated December 31, 2014, of OpGen, Inc. and are in agreement with the statements contained in the paragraphs on page 107 therein. We have no basis to agree or disagree with other statements of the registrant contained therein.

/s/ Ernst & Young LLP