<Page>

                              AMENDED AND RESTATED

                          1997 STOCK INCENTIVE PLAN OF

                                  NANOGEN, INC.

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                                TABLE OF CONTENTS
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ARTICLE 1.        INTRODUCTION........................................................1

ARTICLE 2.        ADMINISTRATION......................................................1
     2.1          Committee Composition...............................................1
     2.2          Committee Responsibilities..........................................2

ARTICLE 3.        SHARES AVAILABLE FOR GRANTS.........................................2
     3.1          Basic Limitation....................................................2
     3.2          Additional Shares...................................................2
     3.3          Dividend Equivalents................................................2

ARTICLE 4.        ELIGIBILITY.........................................................2
     4.1          General Rules.......................................................2
     4.2          Outside Directors...................................................2
     4.3          Incentive Stock Options.............................................2

ARTICLE 5.        OPTIONS.............................................................3
     5.1          Stock Option Agreement..............................................3
     5.2          Number of Shares....................................................3
     5.3          Exercise Price......................................................3
     5.4          Exercisability and Term.............................................3
     5.5          Effect of Change in Control.........................................3
     5.6          Modification or Assumption of Options...............................3
     5.7          Other Requirements Prior to Company's Initial Public Offering.......4

ARTICLE 6.        PAYMENT FOR OPTION SHARES...........................................4
     6.1          General Rule........................................................4
     6.2          Surrender of Stock..................................................4
     6.3          Exercise/Sale.......................................................4
     6.4          Exercise/Pledge.....................................................4
     6.5          Promissory Note.....................................................4
     6.6          Other Forms of Payment..............................................4

ARTICLE 7.        STOCK APPRECIATION RIGHTS...........................................4
     7.1          SAR Agreement.......................................................4
     7.2          Number of Shares....................................................5
     7.3          Exercise Price......................................................5
     7.4          Exercisability and Term.............................................5
     7.5          Effect of Change in Control.........................................5
     7.6          Exercise of SARs....................................................5
     7.7          Modification or Assumption of SARs..................................5

ARTICLE 8.        RESTRICTED SHARES AND STOCK UNITS...................................5
     8.1          Time, Amount and Form of Awards.....................................5
     8.2          Payment for Awards..................................................5
     8.3          Vesting Conditions..................................................6
     8.4          Form and Time of Settlement of Stock Units..........................6
     8.5          Death of Recipient..................................................6
     8.6          Creditors' Rights...................................................6

ARTICLE 9.        VOTING AND DIVIDEND RIGHTS..........................................6

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     9.1          Restricted Shares...................................................6
     9.2          Stock Units.........................................................6

ARTICLE 10.       PROTECTION AGAINST DILUTION.........................................7
     10.1         Adjustments.........................................................7
     10.2         Reorganizations.....................................................7

ARTICLE 11.       AWARDS UNDER OTHER PLANS............................................7

ARTICLE 12.       PAYMENT OF DIRECTOR'S FEES IN SECURITIES............................7
     12.1         Effective Date......................................................7
     12.2         Elections to Receive NSOs, Restricted Shares or Stock Units.........7
     12.3         Number and Terms of NSOs, Restricted Shares or Stock Units..........7

ARTICLE 13.       LIMITATION ON RIGHTS................................................8
     13.1         Retention Rights....................................................8
     13.2         Stockholders' Rights................................................8
     13.3         Regulatory Requirements.............................................8

ARTICLE 14.       LIMITATION ON PAYMENTS..............................................8
     14.1         Gross-Up Payment....................................................8
     14.2         Determination by Accountant.........................................8
     14.3         Underpayments and Overpayments......................................9
     14.4         Related Corporations................................................9

ARTICLE 15.       WITHHOLDING TAXES...................................................9
     15.1         General.............................................................9
     15.2         Share Withholding...................................................9

ARTICLE 16.       ASSIGNMENT OR TRANSFER OF AWARDS....................................9
     16.1         General.............................................................9
     16.2         Trusts..............................................................9

ARTICLE 17.       FUTURE OF THE PLAN.................................................10
     17.1         Term of the Plan...................................................10
     17.2         Amendment or Termination...........................................10

ARTICLE 18.       DEFINITIONS........................................................10

ARTICLE 19.       EXECUTION..........................................................13
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                                      -ii-
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                              AMENDED AND RESTATED

                          1997 STOCK INCENTIVE PLAN OF

                                  NANOGEN, INC.


      ARTICLE 1. INTRODUCTION

      The Plan was adopted by the Board effective as of August 1, 1997, and was
approved by the Company's stockholders as of August 1, 1997. The Plan is
effective as of August 1, 1997. However, Articles 7, 8 and 9 shall not apply
prior to the Company's initial public offering on April 14, 1998. The Plan was
subsequently (a) amended and restated on June 30, 1999 to increase the number of
shares available for issuance under the Plan in Section 3.1; (b) amended on
April 14, 2000 for options issued on and after that date, to increase the period
during which such options may be exercised after the death or disability of a
Plan Participant to twelve months in Section 5.4; (c) amended and restated on
June 6, 2000 to increase the number of shares available for issuance under the
Plan in Section 3.1 to 4,508,760; and (d) amended and restated on June 13, 2001
to increase the number of shares available for issuance under the Plan in
Section 3.1 to its current number.

      The purpose of the Plan is to promote the long-term success of the Company
and the creation of stockholder value by (a) encouraging Key Employees to focus
on critical long-range objectives, (b) encouraging the attraction and retention
of Key Employees with exceptional qualifications and (c) linking Key Employees
directly to stockholder interests through increased stock ownership. The Plan
seeks to achieve this purpose by providing for Awards in the form of Restricted
Shares, Stock Units, Options (which may constitute incentive stock options or
nonstatutory stock options) or stock appreciation rights.

      The Plan shall be governed by, and construed in accordance with, the laws
of the State of California.

      ARTICLE 2. ADMINISTRATION

      2.1 Committee Composition. The Plan shall be administered by the
Committee. Except as provided below, the Committee shall consist exclusively of
directors of the Company, who shall be appointed by the Board. In addition, the
composition of the Committee shall satisfy:

            (a) Such requirements, if any, as the Securities and Exchange
      Commission may establish for administrators acting under plans intended to
      qualify for exemption under Rule 16b-3 (or its successor) under the
      Exchange Act; and

            (b) Such requirements as the Internal Revenue Service may establish
      for outside directors acting under plans intended to qualify for exemption
      under section 162(m)(4)(C) of the Code.

The Board may act on its own behalf with respect to Outside Directors and may
also appoint one or more separate committees composed of one or more officers of
the Company who need not be directors of the Company and who need not satisfy
the foregoing requirements, who may administer the Plan with respect to Key
Employees who are not "covered employees" under section 162(m)(3) of the Code
and who are not required to report pursuant to Section 16(a) of the Exchange
Act.

                                       -1-
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      2.2 Committee Responsibilities. The Committee shall (a) select the Key
Employees who are to receive Awards under the Plan, (b) determine the type,
number, vesting requirements and other features and conditions of such Awards,
(c) interpret the Plan and (d) make all other decisions relating to the
operation of the Plan. The Committee may adopt such rules or guidelines as it
deems appropriate to implement the Plan. The Committee's determinations under
the Plan shall be final and binding on all persons.

      ARTICLE 3. SHARES AVAILABLE FOR GRANTS

      3.1 Basic Limitation. Common Shares issued pursuant to the Plan may be
authorized but unissued shares or treasury shares. The aggregate number of
Common Shares available for Restricted Shares, Stock Units, Options and SARs
awarded under the Plan shall not exceed 6,008,760. Of the Common Shares
available hereunder, no more than 25% in aggregate shall be available with
respect to Outside Directors. The limitation of this Section 3.1 shall be
subject to adjustment pursuant to Article 10. The number of Common Shares
available under this Plan shall be increased by unexercised or forfeited Common
Shares under the Company's 1993 and 1995 Stock Plans.

      3.2 Additional Shares. If Stock Units, Options or SARs are forfeited or if
Options or SARs terminate for any other reason before being exercised, then the
corresponding Common Shares shall again become available for Awards under the
Plan. If Restricted Shares are forfeited before any dividends have been paid
with respect to such Shares, then such Shares shall again become available for
Awards under the Plan. If Stock Units are settled, then only the number of
Common Shares (if any) actually issued in settlement of such Stock Units shall
reduce the number available under Section 3.1 and the balance shall again become
available for Awards under the Plan. If SARs are exercised, then only the number
of Common Shares (if any) actually issued in settlement of such SARs shall
reduce the number available under Section 3.1 and the balance shall again become
available for Awards under the Plan.

      3.3 Dividend Equivalents. Any dividend equivalents distributed under the
Plan shall not be applied against the number of Restricted Shares, Stock Units,
Options or SARs available for Awards, whether or not such dividend equivalents
are converted into Stock Units.

      ARTICLE 4. ELIGIBILITY

      4.1 General Rules. Only Key Employees (including, without limitation,
independent contractors who are not members of the Board) shall be eligible for
designation as Participants by the Committee.

      4.2 Outside Directors. The Committee may provide that the NSOs that
otherwise would be granted to an Outside Director under this Plan shall instead
be granted to an affiliate of such Outside Director. Such affiliate shall then
be deemed to be an Outside Director for purposes of the Plan, provided that the
service-related vesting and termination provisions pertaining to the NSOs shall
be applied with regard to the service of the Outside Director.

      4.3 Incentive Stock Options. Only Key Employees who are common-law
employees of the Company, a Parent or a Subsidiary shall be eligible for the
grant of ISOs. In addition, a Key Employee who owns more than 10% of the total
combined voting power of all classes of outstanding stock of the Company or any
of its Parents or Subsidiaries shall not be eligible for the grant of an ISO
unless the requirements set forth in section 422(c)(6) of the Code are
satisfied.

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      ARTICLE 5. OPTIONS

      5.1 Stock Option Agreement. Each grant of an Option under the Plan shall
be evidenced by a Stock Option Agreement between the Optionee and the Company.
Such Option shall be subject to all applicable terms of the Plan and may be
subject to any other terms that are not inconsistent with the Plan. The Stock
Option Agreement shall specify whether the Option is an ISO or an NSO. The
provisions of the various Stock Option Agreements entered into under the Plan
need not be identical. Options shall be granted in consideration of services
rendered to the Company or a Subsidiary. A Stock Option Agreement may provide
that a new Option will be granted automatically to the Optionee when he or she
exercises a prior Option and pays the Exercise Price in the form described in
Section 6.2.

      5.2 Number of Shares. Each Stock Option Agreement shall specify the number
of Common Shares subject to the Option and shall provide for the adjustment of
such number in accordance with Article 10. Options granted to any Optionee in a
single calendar year shall in no event cover more than 750,000 Common Shares,
subject to adjustment in accordance with Article 10.

      5.3 Exercise Price. Each Stock Option Agreement shall specify the Exercise
Price; provided that the Exercise Price under an ISO shall in no event be less
than 100% of the Fair Market Value of a Common Share on the date of grant and
the Exercise Price under an NSO shall in no event be less than the par value of
the Common Shares subject to such NSO. In the case of an NSO, a Stock Option
Agreement may specify an Exercise Price that varies in accordance with a
predetermined formula while the NSO is outstanding, provided that prior to the
Company's initial public offering, the NSO Exercise Price shall be at least 85%
(110% for 10% shareholders) of the Fair Market Value of a Common Share of Stock
on the date of grant.

      5.4 Exercisability and Term. Each Stock Option Agreement shall specify the
date when all or any installment of the Option is to become exercisable,
provided that prior to the Company's initial public offering, Options shall
become exercisable pursuant to a schedule providing for at least 20% vesting per
year over a five-year period (or, in the case of performance options, to the
extent permitted under applicable regulations of the California Department of
Corporations). The Stock Option Agreement shall also specify the term of the
Option; provided that the term of an ISO shall in no event exceed 10 years from
the date of grant. A Stock Option Agreement may provide for accelerated
exercisability in the event of the Optionee's death, disability or retirement or
other events and may provide for expiration prior to the end of its term in the
event of the termination of the Optionee's service.

      Options may be awarded in combination with SARs, and such an Award may
provide that the Options will not be exercisable unless the related SARs are
forfeited. NSOs may also be awarded in combination with Restricted Shares or
Stock Units, and such an Award may provide that the NSOs will not be exercisable
unless the related Restricted Shares or Stock Units are forfeited.

      Options must be exercised within 90 days of the termination of employment
(twelve months for termination on account of death or disability).

      5.5 Effect of Change in Control. The Committee may determine, at the time
of granting an Option or thereafter, that such Option shall become fully
exercisable as to all Common Shares subject to such Option in the event that a
Change in Control occurs with respect to the Company.

      5.6 Modification or Assumption of Options. Within the limitations of the
Plan, the Committee may modify, extend or assume outstanding options or may
accept the cancellation of outstanding options (whether granted by the Company
or by another issuer) in return for the grant of new options for the same or a
different number of shares and at the same or a different exercise price. The
foregoing

                                       -3-
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notwithstanding, no modification of an Option shall, without the consent of the
Optionee, alter or impair his or her rights or obligations under such Option.

      5.7 Other Requirements Prior to Company's Initial Public Offering. Prior
to the Company's initial public offering, Optionees shall receive Company
financial statements at least annually.

      ARTICLE 6. PAYMENT FOR OPTION SHARES

      6.1 General Rule. The entire Exercise Price of Common Shares issued upon
exercise of Options shall be payable in cash at the time when such Common Shares
are purchased, except as follows:

            (a) In the case of an ISO granted under the Plan, payment shall be
      made only pursuant to the express provisions of the applicable Stock
      Option Agreement. The Stock Option Agreement may specify that payment may
      be made in any form(s) described in this Article 6.

            (b) In the case of an NSO, the Committee may at any time accept
      payment in any form(s) described in this Article 6.

      6.2 Surrender of Stock. To the extent that this Section 6.2 is applicable,
payment for all or any part of the Exercise Price may be made with Common Shares
which have already been owned by the Optionee for more than six months. Such
Common Shares shall be valued at their Fair Market Value on the date when the
new Common Shares are purchased under the Plan.

      6.3 Exercise/Sale. To the extent that this Section 6.3 is applicable,
payment may be made by the delivery (on a form prescribed by the Company) of an
irrevocable direction to a securities broker approved by the Company to sell
Common Shares and to deliver all or part of the sales proceeds to the Company in
payment of all or part of the Exercise Price and any withholding taxes.

      6.4 Exercise/Pledge. To the extent that this Section 6.4 is applicable,
payment may be made by the delivery (on a form prescribed by the Company) of an
irrevocable direction to pledge Common Shares to a securities broker or lender
approved by the Company, as security for a loan, and to deliver all or part of
the loan proceeds to the Company in payment of all or part of the Exercise Price
and any withholding taxes.

      6.5 Promissory Note. To the extent that this Section 6.5 is applicable,
payment may be made with a full-recourse promissory note; provided that the par
value of the Common Shares shall be paid in cash.

      6.6 Other Forms of Payment. To the extent that this Section 6.6 is
applicable, payment may be made in any other form that is consistent with
applicable laws, regulations and rules.

      ARTICLE 7. STOCK APPRECIATION RIGHTS

      7.1 SAR Agreement. Each grant of an SAR under the Plan shall be evidenced
by an SAR Agreement between the Optionee and the Company. Such SAR shall be
subject to all applicable terms of the Plan and may be subject to any other
terms that are not inconsistent with the Plan. The provisions of the various SAR
Agreements entered into under the Plan need not be identical. SARs may be
granted in consideration of a reduction in the Optionee's other compensation.

                                       -4-
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      7.2 Number of Shares. Each SAR Agreement shall specify the number of
Common Shares to which the SAR pertains and shall provide for the adjustment of
such number in accordance with Article 10. SARs granted to any Optionee in a
single calendar year shall in no event pertain to more than 300,000 Common
Shares, subject to adjustment in accordance with Article 10.

      7.3 Exercise Price. Each SAR Agreement shall specify the Exercise Price.
An SAR Agreement may specify an Exercise Price that varies in accordance with a
predetermined formula while the SAR is outstanding.

      7.4 Exercisability and Term. Each SAR Agreement shall specify the date
when all or any installment of the SAR is to become exercisable. The SAR
Agreement shall also specify the term of the SAR. An SAR Agreement may provide
for accelerated exercisability in the event of the Optionee's death, disability
or retirement or other events and may provide for expiration prior to the end of
its term in the event of the termination of the Optionee's service. SARs may
also be awarded in combination with Options, Restricted Shares or Stock Units,
and such an Award may provide that the SARs will not be exercisable unless the
related Options, Restricted Shares or Stock Units are forfeited. An SAR may be
included in an ISO only at the time of grant but may be included in an NSO at
the time of grant or thereafter. An SAR granted under the Plan may provide that
it will be exercisable only in the event of a Change in Control.

      7.5 Effect of Change in Control. The Committee may determine, at the time
of granting an SAR or thereafter, that such SAR shall become fully exercisable
as to all Common Shares subject to such SAR in the event that a Change in
Control occurs with respect to the Company.

      7.6 Exercise of SARs. The exercise of an SAR shall be subject to the
restrictions imposed by Rule 16b-3 (or its successor) under the Exchange Act, if
applicable. If, on the date when an SAR expires, the Exercise Price under such
SAR is less than the Fair Market Value on such date but any portion of such SAR
has not been exercised or surrendered, then such SAR shall automatically be
deemed to be exercised as of such date with respect to such portion. Upon
exercise of an SAR, the Optionee (or any person having the right to exercise the
SAR after his or her death) shall receive from the Company (a) Common Shares,
(b) cash or (c) a combination of Common Shares and cash, as the Committee shall
determine. The amount of cash and/or the Fair Market Value of Common Shares
received upon exercise of SARs shall, in the aggregate, be equal to the amount
by which the Fair Market Value (on the date of surrender) of the Common Shares
subject to the SARs exceeds the Exercise Price.

      7.7 Modification or Assumption of SARs. Within the limitations of the
Plan, the Committee may modify, extend or assume outstanding SARs or may accept
the cancellation of outstanding SARs (whether granted by the Company or by
another issuer) in return for the grant of new SARs for the same or a different
number of shares and at the same or a different exercise price. The foregoing
notwithstanding, no modification of an SAR shall, without the consent of the
Optionee, alter or impair his or her rights or obligations under such SAR.

      ARTICLE 8. RESTRICTED SHARES AND STOCK UNITS

      8.1 Time, Amount and Form of Awards. Awards under the Plan may be granted
in the form of Restricted Shares, in the form of Stock Units, or in any
combination of both. Restricted Shares or Stock Units may also be awarded in
combination with NSOs or SARs, and such an Award may provide that the Restricted
Shares or Stock Units will be forfeited in the event that the related NSOs or
SARs are exercised.

      8.2 Payment for Awards. To the extent that an Award is granted in the form
of newly issued Restricted Shares, the Award recipient, as a condition to the
grant of such Award, shall be required to

                                       -5-
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pay the Company in cash an amount equal to the par value of such Restricted
Shares. To the extent that an Award is granted in the form of Restricted Shares
from the Company's treasury or in the form of Stock Units, no cash consideration
shall be required of the Award recipients.

      8.3 Vesting Conditions. Each Award of Restricted Shares or Stock Units
shall become vested, in full or in installments, upon satisfaction of the
conditions specified in the Stock Award Agreement. A Stock Award Agreement may
provide for accelerated vesting in the event of the Participant's death,
disability or retirement or other events. The Committee may determine, at the
time of making an Award or thereafter, that such Award shall become fully vested
in the event that a Change in Control occurs with respect to the Company.

      8.4 Form and Time of Settlement of Stock Units. Settlement of vested Stock
Units may be made in the form of (a) cash, (b) Common Shares or (c) any
combination of both, as determined by the Committee. The actual number of Stock
Units eligible for settlement may be larger or smaller than the number included
in the original Award, based on predetermined performance factors. Methods of
converting Stock Units into cash may include (without limitation) a method based
on the average Fair Market Value of Common Shares over a series of trading days.
Vested Stock Units may be settled in a lump sum or in installments. The
distribution may occur or commence when all vesting conditions applicable to the
Stock Units have been satisfied or have lapsed, or it may be deferred to any
later date. The amount of a deferred distribution may be increased by an
interest factor or by dividend equivalents. Until an Award of Stock Units is
settled, the number of such Stock Units shall be subject to adjustment pursuant
to Article 10.

      8.5 Death of Recipient. Any Stock Units Award that becomes payable after
the recipient's death shall be distributed to the recipient's beneficiary or
beneficiaries. Each recipient of a Stock Units Award under the Plan shall
designate one or more beneficiaries for this purpose by filing the prescribed
form with the Company. A beneficiary designation may be changed by filing the
prescribed form with the Company at any time before the Award recipient's death.
If no beneficiary was designated or if no designated beneficiary survives the
Award recipient, then any Stock Units Award that becomes payable after the
recipient's death shall be distributed to the recipient's estate.

      8.6 Creditors' Rights. A holder of Stock Units shall have no rights other
than those of a general creditor of the Company. Stock Units represent an
unfunded and unsecured obligation of the Company, subject to the terms and
conditions of the applicable Stock Award Agreement.

      ARTICLE 9. VOTING AND DIVIDEND RIGHTS

      9.1 Restricted Shares. The holders of Restricted Shares awarded under the
Plan shall have the same voting, dividend and other rights as the Company's
other stockholders. A Stock Award Agreement, however, may require that the
holders of Restricted Shares invest any cash dividends received in additional
Restricted Shares. Such additional Restricted Shares shall be subject to the
same conditions and restrictions as the Award with respect to which the
dividends were paid. Such additional Restricted Shares shall not reduce the
number of Common Shares available under Article 3.

      9.2 Stock Units. The holders of Stock Units shall have no voting rights.
Prior to settlement or forfeiture, any Stock Unit awarded under the Plan may, at
the Committee's discretion, carry with it a right to dividend equivalents. Such
right entitles the holder to be credited with an amount equal to all cash
dividends paid on one Common Share while the Stock Unit is outstanding. Dividend
equivalents may be converted into additional Stock Units. Settlement of dividend
equivalents may be made in the form of cash, in the form of Common Shares, or in
a combination of both. Prior to distribution, any dividend equivalents which are
not paid shall be subject to the same conditions and restrictions as the Stock
Units to which they attach.

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      ARTICLE 10. PROTECTION AGAINST DILUTION

      10.1 Adjustments. In the event of a subdivision of the outstanding Common
Shares, a declaration of a dividend payable in Common Shares, a declaration of a
dividend payable in a form other than Common Shares in an amount that has a
material effect on the price of Common Shares, a combination or consolidation of
the outstanding Common Shares (by reclassification or otherwise) into a lesser
number of Common Shares, a recapitalization, a spinoff or a similar occurrence,
the Committee shall make such adjustments as it, in its sole discretion, deems
appropriate in one or more of (a) the number of Options, SARs, Restricted Shares
and Stock Units available for future Awards under Article 3, (b) the limitations
set forth in Sections 5.2 and 7.2, (c) the number of NSOs to be granted to
Outside Directors under Section 4.2, (d) the number of Stock Units included in
any prior Award which has not yet been settled, (e) the number of Common Shares
covered by each outstanding Option and SAR or (f) the Exercise Price under each
outstanding Option and SAR. Except as provided in this Article 10, a Participant
shall have no rights by reason of any issue by the Company of stock of any class
or securities convertible into stock of any class, any subdivision or
consolidation of shares of stock of any class, the payment of any stock dividend
or any other increase or decrease in the number of shares of stock of any class.

      10.2 Reorganizations. In the event that the Company is a party to a merger
or other reorganization, outstanding Options, SARs, Restricted Shares and Stock
Units shall be subject to the agreement of merger or reorganization. Such
agreement may provide, without limitation, for the assumption of outstanding
Awards by the surviving corporation or its parent, for their continuation by the
Company (if the Company is a surviving corporation), for accelerated vesting and
accelerated expiration (provided the Company has previously had its initial
public offering), or for settlement in cash.

      ARTICLE 11. AWARDS UNDER OTHER PLANS

      The Company may grant awards under other plans or programs. Such awards
may be settled in the form of Common Shares issued under this Plan. Such Common
Shares shall be treated for all purposes under the Plan like Common Shares
issued in settlement of Stock Units and shall, when issued, reduce the number of
Common Shares available under Article 3.

      ARTICLE 12. PAYMENT OF DIRECTOR'S FEES IN SECURITIES

      12.1 Effective Date. No provision of this Article 12 shall be effective
unless and until the Board has determined to implement such provision.

      12.2 Elections to Receive NSOs, Restricted Shares or Stock Units. An
Outside Director may elect to receive his or her annual retainer payments and
meeting fees from the Company in the form of cash, NSOs, Restricted Shares,
Stock Units, or a combination thereof, as determined by the Board. Such NSOs,
Restricted Shares and Stock Units shall be issued under the Plan. An election
under this Article 12 shall be filed with the Company on the prescribed form.

      12.3 Number and Terms of NSOs, Restricted Shares or Stock Units. The
number of NSOs, Restricted Shares or Stock Units to be granted to Outside
Directors in lieu of annual retainers and meeting fees that would otherwise be
paid in cash shall be calculated in a manner determined by the Board. The terms
of such NSOs, Restricted Shares or Stock Units shall also be determined by the
Board.

                                       -7-
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      ARTICLE 13. LIMITATION ON RIGHTS

      13.1 Retention Rights. Neither the Plan nor any Award granted under the
Plan shall be deemed to give any individual a right to remain an employee,
consultant or director of the Company, a Parent or a Subsidiary. The Company and
its Parents and Subsidiaries reserve the right to terminate the service of any
employee, consultant or director at any time, with or without cause, subject to
applicable laws, the Company's certificate of incorporation and by-laws and a
written employment agreement (if any).

      13.2 Stockholders' Rights. A Participant shall have no dividend rights,
voting rights or other rights as a stockholder with respect to any Common Shares
covered by his or her Award prior to the issuance of a stock certificate for
such Common Shares. No adjustment shall be made for cash dividends or other
rights for which the record date is prior to the date when such certificate is
issued, except as expressly provided in Articles 8, 9 and 10.

      13.3 Regulatory Requirements. Any other provision of the Plan
notwithstanding, the obligation of the Company to issue Common Shares under the
Plan shall be subject to all applicable laws, rules and regulations and such
approval by any regulatory body as may be required. The Company reserves the
right to restrict, in whole or in part, the delivery of Common Shares pursuant
to any Award prior to the satisfaction of all legal requirements relating to the
issuance of such Common Shares, to their registration, qualification or listing
or to an exemption from registration, qualification or listing.

      ARTICLE 14. LIMITATION ON PAYMENTS

      14.1 Gross-Up Payment. In the event that it is determined that any payment
or transfer by the Company under the Plan to or for the benefit of (the
"Payment") would be subject to the excise tax imposed by section 4999 of the
Code or any interest or penalties with respect to such excise tax (such excise
tax, together with any such interest or penalties, are collectively referred to
as the "Excise Tax"), then the Participant shall be entitled to receive an
additional payment (a "Gross-Up Payment") in an amount that shall fund the
payment by the Participant of any Excise Tax on the Payment as well as all
income taxes imposed on the Gross-Up Payment, any Excise Tax imposed on the
Gross-Up Payment and any interest or penalties imposed with respect to taxes on
the Gross-Up Payment or any Excise Tax.

      14.2 Determination by Accountant. All mathematical determinations and all
determinations of whether any of the Payments are "parachute payments" (within
the meaning of section 280G of the Code) including all determinations of whether
a Gross-Up Payment is required, of the amount of such Gross-Up Payment and of
amounts determined under Section 14.3 shall be made by the independent auditors
most recently selected by the Board (the "Auditors"), which shall provide its
determination (the "Determination"), together with detailed supporting
calculations regarding the amount of any Gross-Up Payment and any other relevant
matters, both to the Company and to the Participant within seven business days
of the Participant's termination date, if applicable, or such earlier time as is
requested by the Company or by the Participant (if the Participant reasonably
believes that any of the Total Payments may be subject to the Excise Tax). If
the Accounting Firm determines that no Excise Tax is payable by the Participant,
it shall furnish the Participant with a written statement that the Auditors have
concluded that no Excise Tax is payable (including the reasons therefor) and
that the Participant has substantial authority not to report any Excise Tax on
the Participant's federal income tax return. If a Gross-Up Payment is determined
to be payable, it shall be paid to the Participant within five business days
after the Determination is delivered to the Company or the Participant. Any
determination by the Auditors shall be binding upon the Company and the
Participant, absent manifest error.

                                       -8-
<Page>

      14.3 Underpayments and Overpayments. As a result of uncertainty in the
application of section 4999 of the Code at the time of the initial determination
by the Auditors hereunder, it is possible that Gross-Up Payments not made by the
Company should have been made ("Underpayments") or that Gross-Up Payments will
have been made by the Company which should not have been made ("Overpayments").
In either event, the Auditors shall determine the amount of the Underpayment or
Overpayment that has occurred. In the case of an Underpayment, the amount of
such Underpayment shall promptly be paid by the Company to or for the benefit of
the Employee. In the case of an Overpayment, the Employee shall, at the
direction and expense of the Company, take such steps as are reasonably
necessary (including the filing of returns and claims for refund), follow
reasonable instructions from, and procedures established by, the Company and
otherwise reasonably cooperate with the Company to correct such Overpayment;
PROVIDED, HOWEVER, that (i) the Employee shall in no event be obligated to
return to the Company an amount greater than the net after-tax portion of the
Overpayment that the Employee has retained or has recovered as a refund from the
applicable taxing authorities and (ii) this provision shall be interpreted in a
manner consistent with the intent of this Article 14, which is to make the
Employee whole, on an after-tax basis, for the application of the Excise Tax, it
being understood that the correction of an Overpayment may result in the
Employee's repaying to the Company an amount which is less than the Overpayment.

      14.4 Related Corporations. For purposes of this Article 14, the term
"Company" shall include affiliated corporations to the extent determined by the
Auditors in accordance with section 280G(d)(5) of the Code.

      ARTICLE 15. WITHHOLDING TAXES

      15.1 General. To the extent required by applicable federal, state, local
or foreign law, a Participant or his or her successor shall make arrangements
satisfactory to the Company for the satisfaction of any withholding tax
obligations that arise in connection with the Plan. The Company shall not be
required to issue any Common Shares or make any cash payment under the Plan
until such obligations are satisfied.

      15.2 Share Withholding. The Committee may permit a Participant to satisfy
all or part of his or her withholding or income tax obligations by having the
Company withhold all or a portion of any Common Shares that otherwise would be
issued to him or her or by surrendering all or a portion of any Common Shares
that he or she previously acquired. Such Common Shares shall be valued at their
Fair Market Value on the date when taxes otherwise would be withheld in cash.
Any payment of taxes by assigning Common Shares to the Company may be subject to
restrictions, including any restrictions required by rules of the Securities and
Exchange Commission.

      ARTICLE 16. ASSIGNMENT OR TRANSFER OF AWARDS

      16.1 General. An Award granted under the Plan shall not be anticipated,
assigned, attached, garnished, optioned, transferred or made subject to any
creditor's process, whether voluntarily, involuntarily or by operation of law,
except as approved by the Committee. Notwithstanding the foregoing, ISOs and,
prior to the Company's initial public offering, NSOs may not be transferable.
However, this Article 16 shall not preclude a Participant from designating a
beneficiary who will receive any outstanding Awards in the event of the
Participant's death, nor shall it preclude a transfer of Awards by will or by
the laws of descent and distribution.

      16.2 Trusts. Neither this Article 16 nor any other provision of the Plan
shall preclude a Participant from transferring or assigning Restricted Shares to
(a) the trustee of a trust that is revocable by such Participant alone, both at
the time of the transfer or assignment and at all times thereafter prior to such
Participant's death, or (b) the trustee of any other trust to the extent
approved in advance by the

                                       -9-
<Page>

Committee in writing. A transfer or assignment of Restricted Shares from such
trustee to any person other than such Participant shall be permitted only to the
extent approved in advance by the Committee in writing, and Restricted Shares
held by such trustee shall be subject to all of the conditions and restrictions
set forth in the Plan and in the applicable Stock Award Agreement, as if such
trustee were a party to such Agreement.

      ARTICLE 17. FUTURE OF THE PLAN

      17.1 Term of the Plan. The Plan, as set forth herein, was adopted as of
August 1, 1997, and became effective August 1, 1997, except that Articles 7, 8
and 9 shall not be effective prior to the date of the Company's initial public
offering on April 14, 1998. The Plan shall remain in effect until it is
terminated under Section 17.2, except that no ISOs shall be granted after July
31, 2007.

      17.2 Amendment or Termination. The Board may, at any time and for any
reason, amend or terminate the Plan. An amendment of the Plan shall be subject
to the approval of the Company's stockholders only to the extent required by
applicable laws, regulations or rules. No Awards shall be granted under the Plan
after the termination thereof. The termination of the Plan, or any amendment
thereof, shall not affect any Award previously granted under the Plan.

      ARTICLE 18. DEFINITIONS

      18.1 "Award" means any award of an Option, an SAR, a Restricted Share or a
Stock Unit under the Plan.

      18.2 "Board" means the Company's Board of Directors, as constituted from
time to time.

      18.3 "Change in Control" shall mean the occurrence of any of the following
events:

           (a) The consummation of a merger or consolidation of the Company with
      or into another entity or any other corporate reorganization, if more than
      50% of the combined voting power of the continuing or surviving entity's
      securities outstanding immediately after such merger, consolidation or
      other reorganization is owned by persons who were not stockholders of the
      Company immediately prior to such merger, consolidation or other
      reorganization;

           (b) A change in the composition of the Board, as a result of which
      fewer than one-half of the incumbent directors are directors who either:

               (A) Had been directors of the Company 24 months prior to such
           change; or

               (B) Were elected, or nominated for election, to the Board with
           the affirmative votes of at least a majority of the directors who had
           been directors of the Company 24 months prior to such change and who
           were still in office at the time of the election or nomination; or

           (c) Any "person" (as such term is used in sections 13(d) and 14(d) of
      the Exchange Act) by the acquisition or aggregation of securities is or
      becomes the beneficial owner, directly or indirectly, of securities of the
      Company representing 50% or more of the combined voting power of the
      Company's then outstanding securities ordinarily (and apart from rights
      accruing under special circumstances) having the right to vote at
      elections of directors (the "Base Capital Stock"); except that any change
      in the relative beneficial ownership of the Company's securities by any
      person resulting solely from a reduction in the aggregate number of
      outstanding shares of Base Capital Stock, and any decrease thereafter in
      such person's ownership of securities,

                                      -10-
<Page>

      shall be disregarded until such person increases in any manner, directly
      or indirectly, such person's beneficial ownership of any securities
      of the Company. Thus, for example, any person who owns less than 50%
      of the Company's outstanding shares, shall cause a Change in Control to
      occur as of any subsequent date if such person then acquires an
      additional interest in the Company which, when added to the person's
      previous holdings, causes the person to hold more than 50% of the
      Company's outstanding shares.

The term "Change in Control" shall not include the Company's initial public
offering or a transaction, the sole purpose of which is to change the state of
the Company's incorporation.

      18.4 "Code" means the Internal Revenue Code of 1986, as amended.

      18.5 "Committee" means a committee of the Board, as described in Article
2.

      18.6 "Common Share" means one share of the common stock of the Company.

      18.7 "Company" means Nanogen, Inc., a Delaware corporation.

      18.8 "Exchange Act" means the Securities Exchange Act of 1934, as amended.

      18.9 "Exercise Price," in the case of an Option, means the amount for
which one Common Share may be purchased upon exercise of such Option, as
specified in the applicable Stock Option Agreement. "Exercise Price," in the
case of an SAR, means an amount, as specified in the applicable SAR Agreement,
which is subtracted from the Fair Market Value of one Common Share in
determining the amount payable upon exercise of such SAR.

      18.10 "Fair Market Value" means the market price of Common Shares,
determined by the Committee as follows:

           (a) If the Common Shares were traded over-the-counter on the date in
question but was not traded on the Nasdaq Stock Market or the Nasdaq National
Market, then the Fair Market Value shall be equal to the mean between the last
reported representative bid and asked prices quoted for such date by the
principal automated inter-dealer quotation system on which the Common Shares are
quoted or, if the Common Shares are not quoted on any such system, by the "Pink
Sheets" published by the National Quotation Bureau, Inc.;

           (b) If the Common Shares were traded over-the-counter on the date in
question and were traded on the Nasdaq Stock Market or the Nasdaq National
Market, then the Fair Market Value shall be equal to the last-transaction price
quoted for such date by the Nasdaq Stock Market or the Nasdaq National Market;

           (c) If the Common Shares were traded on a stock exchange on the date
in question, then the Fair Market Value shall be equal to the closing price
reported by the applicable composite transactions report for such date; and

           (d) If none of the foregoing provisions is applicable, then the Fair
Market Value shall be determined by the Committee in good faith on such basis as
it deems appropriate.

Whenever possible, the determination of Fair Market Value by the Committee shall
be based on the prices reported in the Western Edition of THE WALL STREET
JOURNAL. Such determination shall be conclusive and binding on all persons.

      18.11 "ISO" means an incentive stock option described in section 422(b) of
the Code.

                                      -11-
<Page>

      18.12 "Key Employee" means (a) a common-law employee of the Company, a
Parent or a Subsidiary, (b) an Outside Director and (c) a consultant or adviser
who provides services to the Company, a Parent or a Subsidiary as an independent
contractor. Service as an Outside Director or as an independent contractor shall
be considered employment for all purposes of the Plan, except as provided in
Sections 4.2 and 4.3.

      18.13 "NSO" means a stock option not described in sections 422 or 423 of
the Code.

      18.14 "Option" means an ISO or NSO granted under the Plan and entitling
the holder to purchase one Common Share.

      18.15 "Optionee" means an individual or estate who holds an Option or SAR.

      18.16 "Outside Director" shall mean a member of the Board who is not a
common-law employee of the Company, a Parent or a Subsidiary.

      18.17 "Parent" means any corporation (other than the Company) in an
unbroken chain of corporations ending with the Company, if each of the
corporations other than the Company owns stock possessing 50% or more of the
total combined voting power of all classes of stock in one of the other
corporations in such chain. A corporation that attains the status of a Parent on
a date after the adoption of the Plan shall be considered a Parent commencing as
of such date.

      18.18 "Participant" means an individual or estate who holds an Award.

      18.19 "Plan" means this 1997 Stock Incentive Plan of Nanogen, Inc., as
amended from time to time.

      18.20 "Restricted Share" means a Common Share awarded under the Plan.

      18.21 "SAR" means a stock appreciation right granted under the Plan.

      18.22 "SAR Agreement" means the agreement between the Company and an
Optionee which contains the terms, conditions and restrictions pertaining to his
or her SAR.

      18.23 "Stock Award Agreement" means the agreement between the Company and
the recipient of a Restricted Share or Stock Unit which contains the terms,
conditions and restrictions pertaining to such Restricted Share or Stock Unit.

      18.24 "Stock Option Agreement" means the agreement between the Company and
an Optionee which contains the terms, conditions and restrictions pertaining to
his or her Option.

      18.25 "Stock Unit" means a bookkeeping entry representing the equivalent
of one Common Share, as awarded under the Plan.

      18.26 "Subsidiary" means any corporation (other than the Company) in an
unbroken chain of corporations beginning with the Company, if each of the
corporations other than the last corporation in the unbroken chain owns stock
possessing 50% or more of the total combined voting power of all classes of
stock in one of the other corporations in such chain. A corporation that attains
the status of a Subsidiary on a date after the adoption of the Plan shall be
considered a Subsidiary commencing as of such date.

                                      -12-
<Page>

      ARTICLE 19. EXECUTION

      To record the adoption of the Plan by the Board, the Company has caused
its duly authorized officer to affix the corporate name and seal hereto.


                                          NANOGEN, INC.



                                          By:  /s/ Vera P. Pardee
                                               ----------------------------
                                               Vera P. Pardee, Esq.
                                               Vice President, General
                                               Counsel and Secretary

                                      -13-