UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No.     )*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

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 control number.

Schedule 13D

This statement relates to the Common Stock, $0.001 par value (the “Common Stock”) of Icagen, Inc. (the “Issuer”) having its principal executive office at 4222 Emperor Boulevard, Suite 350, Durham, NC 27703.

This statement is being filed by New Leaf Ventures II, L.P. (“NLV II”), New Leaf Venture Associates II, L.P. (“NLV Associates”) and New Leaf Venture Management II, L.L.C. (“NLV Management” and together with NLV II and NLV Associates, the “Reporting Entities”) and Philippe O. Chambon (“Chambon”), James Niedel (“Niedel”), Vijay Lathi (“Lathi”), Ronald Hunt (“Hunt”), Srinivas Akkaraju (“Akkaraju”) and Jeani Delagardelle (“Delagardelle” and together with Chambon, Niedel, Lathi, Hunt and Akkaraju, the “Managing Directors”). The Reporting Entities and the Managing Directors collectively are referred to as the “Reporting Persons”.

The address of the principal business office of NLV II, NLV Associates, NLV Management, Chambon, Niedel and Hunt is New Leaf Venture Partners, Times Square Tower, 7 Times Square, Suite 3502, New York, NY 10036. The address of the principal business office of Lathi, Akkaraju and Delagardelle is New Leaf Venture Partners, 2500 Sand Hill Road, Suite 203, Menlo Park, CA 94025.

The principal business of NLV II is to make, hold and dispose of equity and equity-related investments, principally in healthcare, medical device and life sciences companies. The principal business of NLV Associates is to act as the sole general partner of NLV II. The principal business of NLV Management is to act as the sole general partner of NLV Associates. The principal business of each of the Managing Directors is to manage the Reporting Entities and a number of affiliated partnerships with similar businesses.

During the five years prior to the date hereof, none of the Reporting Persons has been convicted in a criminal proceeding or has been a party to a civil proceeding ending in a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

Each of NLV II and NLV Associates is a limited partnership organized under the laws of the State of Delaware. NLV Management is a limited liability company organized under the laws of the State of Delaware. Each Managing Director other than Philippe O. Chambon is a citizen of the United States. Philippe O. Chambon is a citizen of France.

Not applicable.

On July 20, 2011, the Issuer issued a press release describing a proposed acquisition of the Issuer by Pfizer, Inc. (“Pfizer”) pursuant to which Pfizer and/or one or more of its affiliates would acquire all outstanding shares of Common Stock not held by it in a tender offer for a per share consideration of $6.00 (the “Proposed Transaction”). Upon an analysis of the terms of the Proposed Transaction, the Reporting Persons concluded that the Proposed Transaction undervalues the Issuer and is not in the best interests of all stockholders.

On July 28, 2011, the Reporting Persons and Merlin Nexus III, L.P. (“Merlin”) jointly delivered a letter (the “Joint Letter”) to the Issuer’s Board of Directors and issued a press release (the “Press Release”). The Joint Letter states the Proposed Transaction undervalues the Issuer and states the belief that the Proposed Transaction is not in the best interests of all stockholders. The Joint Letter further states that each of the Reporting Persons and Merlin would not tender their shares in the Proposed Transaction on the current terms, and are considering other options, including reaching out to additional stockholders of the Issuer to share their concerns. The Reporting Persons disclaim beneficial ownership of all shares held by Merlin and its affiliates.

Merlin BioMed Private Equity Advisors, LLC has filed a Schedule 13D reporting events on July 28, 2011, on behalf of itself, Merlin and Dominique Sémon (collectively, “Merlin BioMed”), in which Merlin BioMed discloses beneficial ownership of 10.0% of shares of Common Stock of the Issuer. The Reporting Persons disclaim all group membership with Merlin or any other persons for purposes of this Schedule 13D.

The references to the Joint Letter and the Press Release in this Schedule 13D are qualified in their entirety by reference to the Joint Letter and the Press Release, copies of which are filed with this Schedule 13D as Exhibit 1 and Exhibit 2, respectively, and incorporated herein by reference as if set forth in their entirety.

The Reporting Persons acquired their shares of Common Stock in the ordinary course of their business. Although the Reporting Persons do not believe that providing their views or engaging in communications as described above would constitute activities that have the purpose or effect of changing or influencing control of the Issuer, the Reporting Persons are filing this Schedule 13D in order to remove any possible impediment to providing such views or engaging in such communications.

Each of the Reporting Persons intends to review its investment on a regular basis and, as a result thereof, may at any time or from time to time determine, either alone or as part of a group, (a) to acquire additional securities of the Issuer, through open market purchases, privately negotiated transactions or otherwise, (b) to dispose of all or a portion of the securities of the Issuer owned by it in the open market, in privately negotiated transactions or otherwise, or (c) to take any other available course of action, which could involve one or more of the types of transactions or have one or more of the results described in the next paragraph of this Item 4. Any such acquisition or disposition or other transaction would be made in compliance with all applicable laws and regulations. Notwithstanding anything contained herein, each of the Reporting Persons specifically reserves the right to change its intention with respect to any or all of such matters. In reaching any decision as to its course of action (as well as to the specific elements thereof), each of the Reporting Persons currently expects that it would take into consideration a variety of factors, including, but not limited to, the following: the Issuer’s business and prospects; other developments concerning the Issuer and its businesses generally; other business opportunities available to the Reporting Persons; changes in law and government regulations; general economic conditions; and money and stock market conditions, including the market price of the securities of the Issuer.

Other than as set forth in this Statement, the Reporting Persons have no present plans or proposals which relate to or would result in:

(a) The acquisition by any person of additional securities of the Issuer, or the disposition of securities of the Issuer;

(b) An extraordinary corporate transaction, such as a merger, reorganization or liquidation, involving the Issuer or any of its subsidiaries;

(c) A sale or transfer of a material amount of assets of the Issuer or of any of its subsidiaries;

(d) Any change in the present board of directors or management of the Issuer, including any plans or proposals to change the number or term of directors or to fill any existing vacancies on the board;

(e) Any material change in the present capitalization or dividend policy of the Issuer;

(f) Any other material change in the Issuer’s business or corporate structure;

(g) Changes in the Issuer’s charter, bylaws or instruments corresponding thereto or other actions which may impede the acquisition of control of the Issuer by any person;

(h) A class of securities of the Issuer being delisted from a national securities exchange or ceasing to be authorized to be quoted in an inter-dealer quotation system of a registered national securities association;

(i) A class of equity securities of the Issuer becoming eligible for termination of registration pursuant to Section 12(g)(4) of the Act; or

(j) Any action similar to any of those enumerated above.

Each of the Reporting Persons may be deemed to own beneficially 2.67% of the Issuer’s Common Stock, which percentage is calculated based upon 7,499,008 shares reported to be outstanding as of April 30, 2011. Each of the Reporting Persons, except NLV II, disclaims beneficial ownership of the NLV II Shares.

None.

Exhibit 1 – Letter dated July 28, 2011 to the Board of Directors of the Issuer.

Exhibit 2 – Press Release, issued July 28, 2011.

Exhibit 99.1 – Agreement regarding filing of joint Schedule 13D.

Exhibit 99.2 – Powers of Attorney regarding Schedule 13D filings.

SIGNATURE

After reasonable inquiry and to the best of its knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Date:    July 29, 2011

Exhibit 1

July 28, 2011

Board of Directors

c/o Charles A. Sanders, M.D., Chairman of the Board

Icagen, Inc.

4222 Emperor Blvd, Suite 350

Durham, NC 27703

Dear Members of the Board of Directors:

As a follow-up to the recently announced acquisition of Icagen, Inc. (“Icagen”), we are writing this letter to express our concerns about the planned acquisition by Pfizer Inc (“Pfizer”) at a price of $56 million or $6.00 per share. We believe the purchase price dramatically undervalues Icagen’s assets, and is not in the best interests of all stockholders.

To date, we have had access only to Icagen’s publicly available information. Based solely on that information, it appears to us that Icagen has made significant progress in advancing both its own proprietary program ICA-105665, which is expected to soon enter into a phase II clinical trial for epilepsy, and the Pfizer partnership targeting the sodium ion channels for the treatment of pain. In December 2010, Icagen and Pfizer initiated the first phase I study of compound PF-05089771 in healthy volunteers. PF-05089771 is a selective and potent Nav1.7 targeting compound developed by Icagen and the first of three compounds expected to enter the clinic over the next 12 months.

Pursuant to the Collaborative Research and License Agreement entered into with Pfizer in August 2007, each of these compounds has the potential to earn up to $359 million in milestones along with future percentage royalties with rates in the high-single to low double digits. At the time of the deal, Pfizer found the sodium ion channel targets attractive enough to pay what was then considered to be double the median size of an early-stage deal since 2003 of $175.4 million.¹ As late as January 2010, Pfizer continued to express its interest in the program, calling Nav1.7 an “Exciting New Pain Target” in a public presentation despite the compound being almost 12 months away from entering the clinic.² We believe that Nav1.7 is a uniquely interesting target in the multi-billion dollar market for pain therapies based on the inability of families from Northern Pakistan who hold mutations in the SCN9A gene (which encodes the Nav1.7 ion channel) to feel pain. As quoted from a 2006 paper published in Nature, “The complete inability to sense pain in an otherwise healthy individual is a very rare phenotype.”³

Data found on the NIH website,⁴ indicates that in late December 2010, Pfizer initiated a phase I single ascending dose study that was expected to be completed in March 2011. While the early data have not been presented, the facts that the trial continues to escalate to higher doses, that Pfizer initiated a

second phase I multiple ascending dose trial⁵ and that Pfizer has entered into a definitive agreement to acquire Icagen all suggest that the data thus far remain very positive.

As institutional stockholders of Icagen, we have spent considerable time analyzing the company’s programs and their future potential. While we believe that an acquisition by Pfizer makes sense, we strongly believe that for the other Icagen stockholders a higher valuation is warranted for the available assets. New therapeutics that have the ability to provide pain relief without gastrointestinal safety concerns offer significant opportunities to large pharmaceutical companies. Past pharmaceutical products to treat pain have demonstrated the ability to quickly ramp and maintain worldwide sales of greater than $2 billion annually. We have used much more conservative sales estimates for each compound and have used significant adjustments for risk to discount the potential future value of those cash flows. As a result of our analysis based on the available data, we believe the fair enterprise value of Icagen, excluding the value of its own internal phase II program in epilepsy, should be in the range of $100 to $165 million. In contrast, under the current terms of the merger agreement, Pfizer is seeking to purchase Icagen for $56 million or $6.00 per share. Further, the true cost to Pfizer to acquire Icagen is significantly less, potentially as little as $22 million. This is based on our estimates of $14 million of cash on Icagen’s balance sheet, $4 million in committed R&D reimbursements by Pfizer through the end of 2011, and potential payments of $16 million over the next 12 months for the achievement of regulatory and clinical milestones for the three compounds in development.

For the reasons discussed above, we strongly disagree with the Board’s approval of the merger agreement and the sale of the company to Pfizer at the current price. We would like the opportunity to discuss with the Board the reasons for the transaction at this time, why it believes this is the best price reasonably available, and whether the unreported phase I clinical data from the PF-05089771 program should be made public as it may be material to the stockholders of the company. We believe that the Board should have sought a greater valuation for Icagen and at the present time we do not intend to tender our shares under the current acquisition terms. We continue to explore our options, including potentially contacting other stockholders to share our concerns.

Sincerely,

Exhibit 2

Icagen Stockholders Contest Proposed Acquisition Price by Pfizer in Letter to Board

New York, NY, July 28, 2011 – Merlin Nexus and New Leaf Venture Partners (NLV Partners), stockholders in Icagen, Inc. (Nasdaq: ICGN), disclosed today a letter submitted to the Icagen Board contesting the Company’s planned acquisition by Pfizer Inc (NYSE: PFE). According to a July 20, 2011 press announcement, Pfizer plans to purchase the 8.3 million shares of Icagen stock it already does not own at a price of $6.00 per share, resulting in an aggregate transaction value of approximately $56 million. Merlin Nexus and NLV Partners “believe the purchase price dramatically undervalues Icagen’s assets and is not in the best interests of all stockholders.”

The letter to the Icagen Board noted that “Icagen has made significant progress in advancing both its own proprietary program ICA-105665, which is expected to soon enter into a phase II clinical trial for epilepsy, and the Pfizer partnership targeting the sodium ion channels for the treatment of pain.” The pain program is currently focused on PF-05089771, “a selective and potent Nav1.7 targeting compound developed by Icagen and the first of three compounds expected to enter the clinic over the next 12 months.”

The letter continued, “We believe that Nav1.7 is a uniquely interesting target in the multi-billion dollar market for pain therapies based on the inability of families from Northern Pakistan who hold mutations in the SCN9A gene (which encodes the Nav1.7 ion channel) to feel pain. As quoted from a 2006 paper published in Nature,¹ ‘The complete inability to sense pain in an otherwise healthy individual is a very rare phenotype.’

“Data found on the NIH website² indicate that in late December 2010, Pfizer initiated a phase I single ascending dose study of PF-05089771 that was expected to be completed in March 2011. While the early data have not been presented, the facts that the trial continues to escalate to higher doses, that Pfizer initiated a second phase I multiple ascending dose trial³ and that Pfizer has entered into a definitive agreement to acquire Icagen all suggest that the data thus far remain very positive.”

The letter concluded, “We believe that the Board should have sought a greater valuation for Icagen and at the present time, we do not intend to tender our shares under the current acquisition terms. We continue to explore our options, including potentially contacting other stockholders to share our concerns.”

About Merlin Nexus

Merlin Nexus, based in New York, is an investment management company focused on crossover private equity investing in the life sciences industry. Merlin Nexus invests globally in private and public healthcare companies and manages several crossover private equity funds with capital commitments totaling $200 million. Our investor base consists of financial institutions, funds of funds, family offices and high net worth individuals.

About NLV Partners

New Leaf Venture Partners is a leader in healthcare technology venture investing. Our investment professionals bring a unique blend of technological, clinical, and operational experience to our investments. We work closely with our entrepreneurs to help build successful portfolio companies. We focus primarily on later-stage biopharmaceutical products, early-stage medical devices, and laboratory infrastructure technologies.

New Leaf currently manages $1.1 billion in assets. This includes our newest fund, New Leaf Ventures II, L.P., which closed with commitments of $450 million in October 2007, New Leaf Ventures I, L.P. and the healthcare technology portfolio of the Sprout Group, one of the oldest U.S. venture capital fund groups. For more information please visit http://www.nlvpartners.com

Contacts:

Burns McClellan on behalf of NLV Partners

Justin Jackson, 212-213-0006

jjackson@burnsmc.com

Exhibit 99.1

AGREEMENT

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13D need be filed with respect to the ownership by each of the undersigned of shares of stock of Icagen, Inc.

EXECUTED this 29th day of July, 2011.

Exhibit 99.2

POWER OF ATTORNEY

KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints CRAIG L. SLUTZKIN as his true and lawful attorney-in-fact and agent for him and in his name, place and stead, in any and all capacities, to sign any and all documents relating to any and all Securities and Exchange Commission filings which may be required, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, thereby ratifying and confirming all that said attorney-in-fact may lawfully do or cause to be done by virtue hereof.

This power shall continue in effect until terminated in writing.

Dated: October 5, 2005

POWER OF ATTORNEY

KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints CRAIG L. SLUTZKIN as his/her true and lawful attorney-in-fact and agent for him/her and in his/her name, place and stead, in any and all capacities, to sign any and all documents relating to any and all Securities and Exchange Commission filings which may be required, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he/she might or could do in person, thereby ratifying and confirming all that said attorney-in-fact may lawfully do or cause to be done by virtue hereof.

This power shall continue in effect until terminated in writing.

Dated: September 29, 2006

POWER OF ATTORNEY

KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints CRAIG L. SLUTZKIN as his true and lawful attorney-in-fact and agent for him and in his name, place and stead, in any and all capacities, to sign any and all documents relating to any and all Securities and Exchange Commission filings which may be required, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, thereby ratifying and confirming all that said attorney-in-fact may lawfully do or cause to be done by virtue hereof.

This power shall continue in effect until terminated in writing.

Dated: February 2, 2009