Exhibit 4.1

Exhibit 4.1

INCORPORATED UNDER THE LAWS OF THE STATE OF MINNESOTA

SEE REVERSE SIDE

FOR CERTAIN DEFINITIONS

CUSIP 83568W 40 6

THIS CERTIFIES THAT

is the owner of

FULLY PAID AND NON-ASSESSABLE COMMON SHARES, $.01 PAR VALUE, OF

SONTRA MEDICAL CORPORATION

transferable on the books of the Corporation by the holder hereof in person or by Attorney upon surrender of this certificate properly endorsed. This certificate is not valid unless countersigned by the Transfer Agent and Registrar. IN WITNESS WHEREOF, the said Corporation has caused this certificate to be signed by facsimile signatures of its duly authorized officers.

Dated:

COUNTERSIGNED AND REGISTERED: WELLS FARGO BANK, N.A.

TRANSFER AGENT

AND REGISTRAR

AUTHORIZED SIGNATURE

ASSISTANT SECRETARY

PRESIDENT

AMERICAN FINANCIAL PRINTING INCORPORATED – MINNEAPOLIS

SONTRA MEDICAL CORPORATION

THE BOARD OF THIS CORPORATION HAS THE AUTHORITY TO CREATE AND DETERMINE THE RELATIVE RIGHTS AND PREFERENCES OF CLASSES OR SERIES OF SHARES OF CAPITAL STOCK OTHER THAN COMMON STOCK. THIS CORPORATION WILL FURNISH TO ANY SHAREHOLDER UPON WRITTEN REQUEST SENT TO ITS PRINCIPAL EXECUTIVE OFFICES, AND WITHOUT CHARGE, A FULL STATEMENT OF THE BOARD’S AUTHORITY TO CREATE AND DETERMINE THE RELATIVE RIGHTS AND PREFERENCES OF CLASSES OR SERIES OF SHARES OF CAPITAL STOCK AS WELL AS THE DESIGNATIONS, PREFERENCES, LIMITATIONS AND RELATIVE RIGHTS OF THE SHARES OF EACH CLASS OR SERIES THEN OUTSTANDING OR AUTHORIZED TO BE ISSUED.

The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:

TEN COM – as tenants in common TEN ENT – as tenants by entireties

JT TEN – as joint tenants with right of survivorship and not as tenants in common

UTMA – Custodian (Cust) (Minor) under Uniform Transfer to Minors

Act

(State)

Additional abbreviations may also be used though not in the above list.

For value received hereby sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER OF ASSIGNEE

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS INCLUDING POSTAL ZIP CODE OF ASSIGNEE

Shares of the capital stock represented by the within Certificate, and do hereby irrevocably constitute and appoint

Attorney

to transfer the said stock on the books of the within-named Corporation with full power of substitution in the premises.

Dated

NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY PARTICULAR WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATEVER.

SIGNATURE GUARANTEED

ALL GUARANTEES MUST BE MADE BY A FINANCIAL INSTITUTION (SUCH AS A BANK OR BROKER) WHICH IS A PARTICIPANT IN THE SECURITIES TRANSFER AGENTS MEDALLION PROGRAM (“STAMP”), THE NEW YORK STOCK EXCHANGE, INC. MEDALLION SIGNATURE PROGRAM (“MSP”), OR THE STOCK EXCHANGES MEDALLION PROGRAM (“SEMP”) AND MUST NOT BE DATED. GUARANTEES BY A NOTARY PUBLIC ARE NOT ACCEPTABLE.