<PAGE>

                                                                   EXHIBIT 10.10

[CONFIDENTIAL TREATMENT REQUESTED. CONFIDENTIAL PORTIONS OF THIS AGREEMENT HAVE
BEEN REDACTED AND HAVE BEEN SEPARATELY FILED WITH THE COMMISSION]


                   ASSIGNMENT OF PATENT RIGHTS AND TECHNOLOGY

          This Assignment is entered into this 1st day of August, 1991, by and
between the Board of Regents of The University of Texas System, an agency of the
State of Texas (hereinafter "Assignor" which term includes successors and
assigns), Dr. Adam Heller, an individual residing at 5317 Valburn Circle,
Austin, Texas 78731 (hereinafter "Heller"), and E. Heller and Company, a Texas
Corporation, having its principal place of business at 5317 Valburn Circle,
Austin, Texas 78731 (hereinafter "Assignee," which term includes successors and
assigns).

                              W I T N E S S E T H:

          WHEREAS, by virtue of two assignments one of which was executed by
Heller and Brian A. Gregg (coinventor) on August 28, 1989, and the second of
which was executed by Heller and Ruben Maidan (coinventor) on March 22, 1991,
which are attached hereto as Exhibit "A", Assignor is the owner of all right,
title, and interest in and to certain Patent Rights (as hereinafter defined)
"Enzyme Electrodes" and "Interferant Eliminating Biosensors"; and

          WHEREAS, Assignor is the owner of all right, title, and interest in
and to certain Technology (as hereinafter defined) and Know-How (as hereinafter
defined) relating to "Enzyme Electrodes", "Interferant Eliminating Biosensors",
and "Preactivated Interferant Eliminating Biosensors"; and

          WHEREAS, under the Rules and Regulations promulgated by the Assignor,
Heller has a partial interest in fifty percent (50%) of the royalties received
by Assignor from licensing or other disposition of the Patent Rights, the
Technology, and the Know-How, after costs of licensing and obtaining a patent or
other protection have first been recaptured by Assignor (hereinafter the "Heller
Interest") and Heller has assigned such interest to Assignee; and,


          WHEREAS, Heller desires to confirm the assignment of the Heller
Interest to Assignee; and,

          WHEREAS, Assignor and Heller entered into a letter agreement dated
August 1, 1991, attached hereto as Exhibit "B", and desire to confirm that
agreement; and,

          WHEREAS, Assignee desires to acquire all of Assignor's right, title,
and interest in, to, and under the Patent Rights, the Technology, and the
Know-How, and desires to confirm the assignment of the Heller Interest to
Assignee; and,

          WHEREAS, Assignor desires to assign, sell, and convey the entire
right, title, and interest of Assignor in the Patent Rights, the Technology, and
the Know-How to Assignee, its successors and assigns, in exchange for the
consideration hereinafter set forth; and,

          NOW, THEREFORE, in consideration of the covenants and agreements
herein contained and other good and valuable consideration, the sufficiency of
which is hereby acknowledged, the parties hereto agree as follows:




<PAGE>

                                   ARTICLE I

                                  DEFINITIONS

     1.1  Technology. The term "Technology" as used herein shall mean all
          ----------
inventions, patents, patent applications, and rights listed on Exhibits "C" and
"D".

     1.2  Patent Rights. The term "Patent Rights" as used herein shall mean all
          -------------
patent applications listed on Exhibit "C" or patents that issue thereon, and any
subject matter that may in the future be included in a continuation,
continuation-in-part, or divisional, to these patent applications, which is
disclosed in writing to Assignor and which names Heller as either sole or joint
inventor including an invention disclosure entitled "Preactivated Interferant
Eliminating Biosensors" attached hereto as Exhibit "D".

     1.3  Know-How. The term "Know-How" as used herein shall mean existing
          --------
technology not claimed in the Patent Rights, but nevertheless proprietary,
valuable trade secrets, inventions, processes, procedures, methods, product
codes, formulas, techniques, designs, drawings, technical and clinical data, and
other valuable and technical information relating to "Enzyme Electrodes",
"Interferant Eliminating Biosensors", and "Preactivated Interferant Eliminating
Biosensors".

     1.4  Licensed Products. The term "Licensed Products" as used herein shall
          -----------------
mean products covered by one or more claims of the Patent Rights or produced by
methods covered by one or more claims of such Patent Rights or utilizing or
incorporating Technology or Know-How.

     1.5  Licensed Processes. The term "Licensed Processes" as used herein shall
          ------------------
mean all methods and procedures covered by one or more claims of the Patent
Rights or utilizing or incorporating Technology or Know-How for the manufacture
or use of Licensed Products.

     1.6  Income. The term "Income" as used herein shall mean all income
          ------
received by Assignee from the sale, licensing, or other transfer of the Patent
Rights, the Technology, or the Know-How to third parties (excluding any
reimbursement to Assignee by a third party of the actual out-of-pocket legal
expenses and costs Assignee has incurred for filing, prosecution and maintenance
of any issued patent and/or patent application covered under Patent Rights,
documentation of which shall be provided in Assignee's semi-annual written
reports).


                                  ARTICLE II

                                  ASSIGNMENT

     2.1 Assignment by Assignor. Assignor hereby assigns, sells, and conveys to
         ----------------------
Assignee, its successors and assigns, the entire right, title, and interest
throughout the world in and to the Patent Rights and the Technology, subject
only to: (a) any rights of the United States Government which may exist now or
in the future due to a research funding agreement to which the United States
Government may be a party; and (b) the conditions of this Agreement.

                                      -2-
<PAGE>

     2.2  Assignment by Heller. Heller hereby confirms the assignment, sale, and
          --------------------
conveyance to Assignee, its successors and assigns, of the entire right, title,
and interest throughout the world in and to the Heller Interest.

                                  ARTICLE III

                                 CONSIDERATION

     3.1  License to Third Party. Assignor, Heller, and Assignee agree that, in
          ----------------------
the event the Patent Rights, the Technology, and/or the Know-How are sold,
licensed, or otherwise disposed of for value to a third party or parties,
Assignor shall receive twenty percent (20%) of all consideration derived from
such sale, license, or other disposition, subject to retention by Assignee of
its first thirty thousand dollars ($30,000) in gross income or other
consideration. Accordingly, Assignee agrees to pay to Assignor twenty percent
(20%) of all consideration received from a third party or third parties beyond
the first thirty thousand dollars ($30,000) in gross income or other
consideration. In the event that Assignee engages in litigation and/or
settlement negotiations to protect Patent Rights, twenty percent (20%) of any
recovery by Assignee shall be paid to Assignor, provided, however, that Assignee
shall be entitled to deduct reasonable attorneys' fees and court costs incurred
in such litigation and/or settlement negotiations. Such payment to Assignor
shall be made within thirty (30) days following the expiration of the calendar
quarter in which Assignee receives a payment. All payments shall be made to The
University of Texas at Austin at: The University of Texas at Austin, Office of
the Executive Vice President and Provost, Main Building 201, Austin, Texas
78712-1111, Attention: Patricia C. Ohlendorf.

     3.2  Manufacture and Sale of Licensed Products by Assignee. Should Assignee
          -----------------------------------------------------
elect to itself manufacture, sell, or otherwise dispose of for value Licensed
Products or Licensed Processes, Assignor and Assignee agree to negotiate the
compensation Assignee shall pay to Assignor. Assignee further agrees that the
compensation due Assignor shall be an amount representing the equivalent of what
Assignor reasonably believes it would have received as royalty, licensing fees,
and other compensation ("Compensation") had Assignor licensed or otherwise
disposed of for value the Technology, Patent Rights and Know How (hereafter
"Technology", for the purposes of this Paragraph 3.2) to a party other than
Assignee ("Third Party"). This equivalent amount shall be negotiated in good
faith by the parties, taking into account, but not limited to, the following:
(a) Compensation Assignee must pay to a Third Party for the use of comparable
Technology; (b) Compensation Assignee receives for its own license or other
disposal for value of the Technology to a Third Party; (c) The nature and scope
of the license or other disposal for value of the Technology by Assignor to a
Third Party, as exclusive or nonexclusive, restricted or nonrestricted in terms
of territory or with respect to whom the Licensed Products and/or Licensed
Processes may be sold; (d) Assignor's policies and procedures regarding the
licensing or other disposal for value of its intellectual property; (e) The
effect of the Technology in promoting the sales of other products of the Third
Party; (f) The duration of Technology related patents and term of any license;
(g) The established or projected profitability of the Licensed Products and
Licensed Processes; (h) The utility and advantages of the Licensed Products and
Licensed Processes over old modes or existing products or processes, if any,
that can be used for achieving similar results; (i) The portion of the profit or
the selling price of Licensed Products and Licensed Processes that may be
customary in the particular business or in comparable businesses which market
the Technology, if any, or similar Technology; (j) The portion of the profit
from the sale or other disposal for value of Licensed Products and Licensed
Processes that should be credited to the Technology as




                                      -3-
<PAGE>

distinguished from non-Technology related elements, such as business risks by
the Third Party and/or significant features or improvements to the Technology
added by the Third Party; and (k) The Compensation due Assignor had the
Technology been licensed pursuant to Paragraph 3.1. Any negotiating dispute
shall be subject to mediation as described in Article XI hereto. Payment by
Assignee to Assignor shall be made as described in Paragraph 3.1 above.


     3.3  Assignment Fee. Assignee shall pay to Assignor a fee of thirty
          --------------
thousand dollars ($30,000) by September 1, 1991.

                                   ARTICLE IV

                           BOOKS, RECORDS, AND REPORTS

     4.1  Books. Assignee shall maintain true and complete books of account
          -----
containing an accurate record of all data necessary for the proper computation
of income, royalty and other payments, and the calculation thereof, as well as
attorneys' fees and court costs. Assignor or its authorized representative shall
have the right to examine such books, under appropriate terms of confidentiality
with Assignee, at all reasonable times, upon ten (10) days prior written notice
for the sole purpose of verifying the accuracy of reports rendered by Assignee.
Such examination shall be made during normal business hours at Assignee's
principal place of business or such other location as Assignor and Assignee may
agree.

     4.2  Payments and Reports. Assignee shall submit to Assignor semi-annual
          --------------------
written reports covering that fiscal period of Assignee and accurately
identifying income and expenses in sufficient form and detail as to enable
Assignor to determine the income, royalties, or other payments due. Such reports
shall be due thirty (30) days following each semi-annual period. A report shall
be submitted, even if no income has been received or no royalties or other
payments are due during the fiscal quarters of that period, in accord with the
terms of Paragraph 3.1 herein. Reports shall be mailed to The University of
Texas at Austin at the address in Paragraph 3.1 herein.

     4.3  Commercialization Report. Assignee shall submit to Assignor, at the
          ------------------------
address listed in paragraph 3.1 herein, a written report by September 1 of each
year which details Assignee's commercialization efforts during the preceding
year with regard to Patent Rights, Technology, and Know-How.

                                   ARTICLE V

                                CONFIDENTIALITY

     5.1  Duty of Confidence. Assignor and Assignee each agree that all
          ------------------
information contained in documents marked "confidential" which are forwarded to
one by the other shall be received in strict confidence, used only for the
purposes of this Agreement, and not disclosed by the recipient party (except as
required by law or court order), its agents or employees without the prior
written consent of the other party, unless such information (a) was in the
public domain at the time of disclosure, (b) later became part of the public
domain through no act or omission of the recipient party, its employees, agents,
successors or assigns, (c) was lawfully disclosed to the recipient party




                                      -4-
<PAGE>

by a third party having the right to disclose it, (d) was already known by the
recipient party at the time of disclosure, (e) was independently developed, (f)
is required to be submitted to a government agency pursuant to any preexisting
obligation, or (g) must be disclosed under the Texas Open Records Act.

     5.2  Degree of Care. Each party's obligation of confidentiality hereunder
          --------------
shall be fulfilled by using at least the same degree of care with the other
party's confidential information as it uses to protect its own confidential
information. This obligation shall exist while this Agreement is in force.

                                  ARTICLE VI

                       CONSIDERATION RECEIVED BY HELLER

     6.1  Sufficiency of Consideration. Heller acknowledges that he has received
          ----------------------------
sufficient consideration for assigning his rights in the Patent Rights, the
Technology, and the Know-How hereunder from Assignee and no further
consideration shall be received by Heller from either Assignor or Assignee in
connection with this Assignment. Heller expressly waives his right to receive
any royalties or other benefits under the Rules and Regulations of the Board of
Regents of The University of Texas System relating to intellectual property
rights in the Patent Rights, the Technology, and the Know-How and acknowledges
that any such royalties or other benefits that would be due to Heller but for
this Agreement shall be and remain the property of The University of Texas at
Austin. Specifically: (a) as stated in Exhibit B hereto, Subsection (1), the
fifty percent of the investors' share of the $30,000 paid to The University of
Texas at Austin remaining after the deduction of an amount covering patent
expenses thus far paid by The University in regards to Patent Rights, shall be
shared with Heller's coinventors in the proportion each would receive were
Heller still included among the inventors who share in The University's income;
and (b) as stated in Exhibit B hereto, Subsection (7), the fifty percent of the
investors' share of any income paid to The University of Texas at Austin under
this Assignment shall be shared with Heller's coinventors in the proportion each
would receive were Heller still included among the inventors who share in The
University's income.


                                  ARTICLE VII

                             RESERVATION BY ASSIGNOR

     7.1  Reservation. Assignee and Heller acknowledge and agree to the
          -----------
reservation by Assignor for all components of The University of Texas System of
a *** nonexclusive license to use Patent Rights, Technology, and Know-How in
educational and research activities.

                                 ARTICLE VIII

                                REPRESENTATIONS

     8.1  Representation. The parties hereto represent and warrant that they
          --------------
have the right and authority to enter into this Assignment and that they have
not executed or entered into any other agreements inconsistent with the terms
and provisions hereof.

*** Confidential treatment requested

                                      -5-
<PAGE>

     8.2  Documents. Heller and Assignor covenant that Heller, Assignor, and
          ---------
their heirs, legal representatives, assigns, administrators, and executors,
will, at the expense of Assignee, its successors and assigns, execute all papers
and perform such other acts as may be reasonably necessary to give Assignee, its
successors and assigns, the full benefit of this Assignment.

                                  ARTICLE IX

                            USE OF NAME OR FACILITIES

     9.1  Name. Assignee shall not use the name of Assignor or The University of
          ----
Texas at Austin in any promotional material.

     9.2  Facilities. Heller acknowledges and agrees that any direct
          ----------
commercialization efforts with respect to Patent Rights, Technology, or Know-How
are his or Assignee's private endeavor and shall not be carried out using
facilities or other resources of Assignor or The University of Texas at Austin.
Assignee shall not use the facilities or other resources of Assignor or The
University of Texas at Austin.

                                   ARTICLE X

                                    BREACH

     10.1 Default. In the event that Assignee shall default in any of its
          -------
material obligations under this Assignment (including but not limited to the
payment of compensation to Assignor), Assignor may require the reconveyance of
the assigned intellectual property should Assignor give Assignee written notice
of default, and such default is not cured within ninety (90) days of Assignee's
receipt of such notice. Assignee further agrees to notify Assignor of any such
cure in writing sent to the address listed in Paragraph 3.1 herein, and shall
describe such cure to Assignor's satisfaction. Assignor's right to require
reconveyance hereunder shall not preclude Assignor from seeking or obtaining any
other remedy to which it may be entitled, at any time.


                                  ARTICLE XI

                                   MEDIATION

     11.1 Dispute Resolution. Any dispute arising under or related to this
          ------------------
Assignment which involves a question of fact may be submitted by either party
for mediation, if the parties are unable to resolve the dispute within a
reasonable time after written notice is sent by one party to the other of the
existence of such dispute. The institution of any mediation proceeding shall not
relieve Assignee of its compensation obligations described in Article III
herein, during the pendency of such proceeding.

                                      -6-
<PAGE>

                                  ARTICLE XII

                                 GOVERNING LAW

     12.1 Construction and Enforcement. This Assignment shall be construed and
          ----------------------------
enforced in accordance with the laws of the United States of America and of the
State of Texas.

                                 ARTICLE XIII

                            DISCLAIMER OF WARRANTY

     13.1 Specific Disclaimer. Assignor makes no representations other than
          -------------------
those expressly stated in this Assignment, and specifically, Assignor MAKES NO
EXPRESS OR IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE, OR THAT THE TECHNOLOGY OR PATENT RIGHTS OR KNOW HOW WILL NOT INFRINGE
ANY PATENT OR OTHER PROPRIETARY RIGHT.


                                  ARTICLE XIV

                                INDEMNIFICATION

     14.1 Hold Harmless. Assignee shall hold harmless and indemnify Assignor,
          -------------
the University of Texas System, and The University of Texas at Austin, its
officers, employees and agents from and against any claims, demands, or causes
of action whatsoever, including without limitation those arising on account of
any injury or death of persons or damage to property caused by, or arising out
of, or resulting from, the exercise or practice of the Assignment granted
hereunder by Assignee or its officers, employees, agents or representatives.

                                  ARTICLE XV

                                  DISPOSITION

     15.1 Assignee may not assign or otherwise dispose of (except by license)
the Patent Rights and Technology without the prior written consent of Assignor.

                                      -7-
<PAGE>

         EXECUTED by the duly authorized representatives of the parties on the
date indicated below the signatures of the parties hereto.

ASSIGNOR:                                          HELLER
--------                                           ------
BOARD OF REGENTS OF THE
UNIVERSITY OF TEXAS SYSTEM


By: /s/ Hans Mark                              By: /s/ Adam Heller
    ------------------------------------           -----------------------------
Hans Mark                                           Adam Heller
Chancellor

Date:  May 15, 1992                            Date: ILLEGIBLE
      ----------------------------------             ---------------------------


APPROVED AS TO CONTENT:                        ASSIGNEE:
                                               --------
                                               E. HELLER AND COMPANY

By: /s/ G. J. Fonken                           By: /s/ Ephraim Heller
    ------------------------------------           -----------------------------
G. J. Fonken                                   (Print) Ephraim Heller
                                                       -------------------------
Executive Vice President and Provost           Title Illegible
                                               ---------------------------------
The University of Texas at Austin

Date:                                          Date:  ILLEGIBLE
      ----------------------------------             ---------------------------


APPROVED AS TO FORM:


By: /s/ Dudley R. Dobie, Jr.
    ------------------------------------
Dudley R. Dobie, Jr.
Office of General Counsel

Date: 5/11/92
      ----------------------------------
<PAGE>

THE STATE OF TEXAS

COUNTY OF TRAVIS

          BEFORE ME, the undersigned Notary Public, on this day personally
appeared Hans Mark, Chancellor for The University of Texas System, an agency of
the State of Texas, known to me to be the person whose name is subscribed to the
foregoing instrument, and acknowledged to me that he executed the same for the
purposes and consideration therein expressed.

         GIVEN UNDER MY HAND AND SEAL OF OFFICE this 15th day of May.


                                 /s/ Becky F. Boyer
                                 -----------------------------------------------
                                 Notary Public, State of Texas

(SEAL)                           My Commission Expires: 9/19/92
                                                        ------------------------

                                 /s/ Becky F. Boyer
                                     -------------------------------------------
                                 Typed or Printed Name of Notary
<PAGE>

THE STATE OF TEXAS

COUNTY OF TRAVIS

          BEFORE ME, the undersigned Notary Public, on this day personally
appeared Adam Heller of 5317 Valburn Circle, Austin, Texas, known to me to be
the person whose name is subscribed to the foregoing instrument, and
acknowledged to me that he executed the same for the purposes and consideration
therein expressed.

          GIVEN UNDER MY HAND AND SEAL OF OFFICE this 17th day of April, 1992.


                                    /s/ Norma R. Horn
                                    --------------------------------------------
                                    Notary Public, State of Texas

(SEAL)                              My Commission Expires: 4/5/95
                                                           ---------------------

                                    /s/ Norma R. Horn
                                        ----------------------------------------
                                    Typed or Printed Name of Notary
<PAGE>

THE STATE OF TEXAS

COUNTY OF TRAVIS

         BEFORE ME, the undersigned Notary Public, on this day personally
appeared Ephraim Heller of E. Heller and Company, 5317 Valburn Circle, Austin,
Texas 78731, known to me to be the person whose name is subscribed to the
foregoing instrument, and acknowledged to me that he executed the same for the
purposes and consideration therein expressed.

         GIVEN UNDER MY HAND AND SEAL OF OFFICE this 17th day of April, 1992.


                                      /s/ Norma R. Horn
                                      ------------------------------------------
                                      Notary Public, State of Texas

(SEAL)                                My Commission Expires: 4/5/95
                                                             -------------------

                                      /s/ Norma R. Horn
                                      ------------------------------------------
                                      Typed or Printed Name of Notary
<PAGE>

                                    EXHIBIT A

                                                              FILE NO. UTSB: 413
                                                                          PATENT

                               A S S I G N M E N T
                               -------------------

         FOR GOOD AND VALUABLE CONSIDERATION, the receipt, sufficiency and
adequacy of which are hereby acknowledged, the undersigned, does hereby:

         SELL, ASSIGN AND TRANSFER to Board of Regents, The University of Texas
System (the "Assignee"), having a place of business at 201 West 7th Street,
Austin, Texas, 78701, the entire right, title and interest for the United States
and all foreign countries in and to any and all improvements which are disclosed
in the application for United States Letters Patent, Serial No. 389,226, which
                                                     ------------------
has been filed on August 2, 1989 and is entitled ENZYME ELECTRODES, such
                                                 ------ ----------
application and all divisional, continuing, substitute, renewal, reissue and all
other applications for patent which have been or shall be filed in the United
States and all foreign countries on any of such improvements; all original and
reissued patents which have been or shall be issued in the United States and all
foreign countries on such improvements; and specifically including the right to
file foreign applications under the provisions of any convention or treaty and
claim priority based on such application in the United States;

         AUTHORIZE AND REQUEST the issuing authority to issue any and all United
States and foreign patents granted on such improvements to the Assignee;

         WARRANT AND COVENANT that no assignment, grant, mortgage, license or
other agreement affecting the rights and property herein conveyed has been or
will be made to others by the undersigned, and that the full right to convey the
same as herein expressed is possessed by the undersigned;

         COVENANT, when requested and at the expense of the Assignee, to carry
out in good faith the intent and purpose of this assignment, the undersigned
will execute all divisional, continuing, substitute, renewal, reissue, and all
other patent applications on any and all such improvements; execute all rightful
oaths, declarations, assignments, powers of attorney and other papers;
communicate to the Assignee all facts known to the undersigned relating to such
improvements and the history thereof; and generally do everything possible which
the Assignee shall consider desirable for vesting title to such improvements in
the Assignee, and for securing, maintaining and enforcing proper patent
protection for such improvements;
<PAGE>

         TO BE BINDING on the heirs, assigns, representatives and successors of
the undersigned and extend to the successors, assigns and nominees of the
Assignee.

(Signature) /s/ Brian A. Gregg                Date August 28, 1989
            ---------------------------            -----------------------------
      Name: Brian A. Gregg

(Signature) /s/ Adam Heller                   Date August 28, 89
            ---------------------------            -----------------------------
      Name: Adam Heller

(Signature)                                   Date  Recorded Patent & Transfer
                                                    Office 9/28/89
            ___________________________            -----------------------------
      Name:

(Signature)                                   Date  /s/ ILLEGIBLE, Commissioner
                                                    of Patents
            ___________________________            -----------------------------
      Name:



STATE OF TEXAS                              )
                                            )     ss.
COUNTY OF TRAVIS                            )

         BEFORE ME, the undersigned authority, on this 28th day of August,
1989, personally appeared Brian A. Gregg and Adam Heller known to me to be the
persons whose names subscribed to the foregoing instrument and acknowledged to
me that they executed the same of their own free will for the purposes and
consideration therein expressed.

                                             /s/ Norma R. Horn
                                             -----------------------------------
                                             Notary or Consular Officer

[SEAL]

                             ARNOLD, WHITE & DURKEE

P. O. Box 4433                           2001 Jefferson Davis Highway, Suite 40,
Houston, Texas  77210                    Arlington, Virginia 22202

                                      -2-
<PAGE>

                               EXHIBIT A

                                                                       UTSB: 465
                                                                          PATENT

                              A S S I G N M E N T
                              - - - - - - - - - -

    FOR GOOD AND VALUABLE CONSIDERATION, the receipt, efficiency and adequacy
of which are hereby acknowledged, the undersigned, do hereby:
    SELL, ASSIGN AND TRANSFER to Board of Regents, The University of Texas
System (the "Assignee"), having a place of business at 201 West 7th Street,
Austin, Texas, 78701, the entire right, title and interest for the United States
and all foreign countries in and to any and all improvements which are disclosed
in the application for United States Letters Patent, Serial No. 07/664,054,
which has been filed on March 4, 1991, and is entitled INTERFERANT ELIMINATING
BIOSENSORS, such application and all divisional, continuing, substitute,
renewal, reissue and all other applications for patent which have been or shall
be filed in the United States and all foreign countries on any of such
improvements; all original and reissued patents which have been or shall be
issued in the United States and all foreign countries on such improvements; and
specifically including the right to file foreign applications under the
provisions of any convention or treaty and claim priority based on such
application in the United States;
    AUTHORIZE AND REQUEST the issuing authority to issue any and all United
States and foreign patents granted on such improvements to the Assignee;
    WARRANT AND COVENANT that no assignment, grant, mortgage, license or other
agreement affecting the rights and property herein conveyed has been or will be
made to others by the undersigned, and that the full right to convey the same as
herein expressed is possessed by the undersigned;
    COVENANT, when requested and at the expense of the Assignee, to carry out in
good faith the intent and purpose of this assignment, the undersigned will
execute all divisional, continuing, substitute, renewal, reissue, and all other
patent applications on any and all such improvements; execute all rightful
oaths, declarations, assignments, powers of attorney and other papers;
communicate to the Assignee all facts known to the undersigned relating to such
improvements and the history thereof; and generally do everything possible which
the Assignee shall consider desirable for vesting title to such improvements in
the Assignee, and for securing, maintaining an enforcing proper patent
protection for such improvements;
    TO BE BINDING on the heirs, assigns, representatives and successors of the
undersigned and extend to the successors, assigns and nominees of the Assignee.

(Signature)  /s/ Adam Heller                 Date  March 22, 1991
           ________________________________       ____________________________
      Name:      Adam Heller


(Signature)  /s/ Ruben Maidan                Date  March 22, 1991
           ________________________________       ____________________________
      Name:      Ruben Maidan

STATE OF TEXAS     )
                   ) ss.
COUNTY OF TRAVIS   )
          _________

    BEFORE ME, the undersigned authority, on this 22nd day of March, 1991,
personally appeared ADAM HELLER and RUBEN MAIDAN, known to me to be the persons
whose names are subscribed to the foregoing instrument and acknowledged to me
that they executed the same of their own free will for the purposes and
consideration therein expressed.

                                              /s/ Constance J. Hannan
                                              ________________________________
                                              Notary of Consular Officer
                                              Constance J. Hannan
                                              My commission expires 4/11/93

[SEAL]

                            ARNOLD, WHITE & DURKEE

  P.O. Box 4433                         2001 Jefferson Davis Hwy., Ste. 401
  Houston, Texas  77210                 Arlington, Virginia  22202
<PAGE>

                                   EXHIBIT B

August 1, 1991

Dr. Adam Heller
Department of Chemical Engineering
CPE 4.450

Re:      UTSB:413 - "Enzyme Electrodes"
         UTSB:465 - "Interferant Eliminating Biosensors"

Dear Dr. Heller:

         I write to followup our previous communications regarding your request
that The University exclusively license or release to you the inventions
entitled UTSB:413 and UTSB:465, which you co-invented. I am setting out below
conditions under which The University will release and/or assign to you, as
appropriate, its intellectual property rights in the subject matter presently
described in patent applications UTSB:413 and UTSB:465, and any subject matter
that may in the future be included in a continuation, continuation-in-part, or
divisional, to these patent applications. These conditions are consistent with
similar arrangements into which The University has entered:

         (1)      You (or your company) will pay The University a nonrefundable
                  fee of Thirty Thousand Dollars ($30,000) by September 1, 1991.
                  These funds shall be used by The University to pay patent
                  expenses that we have thus far incurred on these cases. In the
                  unlikely event that funds remain after deduction of those
                  expenses, we shall share with your coinventors the proportion
                  of the fifty percent (50%) inventors' share that each would
                  receive were you still included among the inventors who share
                  in The University's income;

         (2)      Effective August 1, 1991, you (or your company) shall assume
                  all financial and decision making responsibility for
                  maintenance and prosecution of these patent applications and
                  any patents that issue, including foreign counterparts. The
                  University shall inform Arnold, White & Durkee of this shift
                  in responsibility. Should you wish to have the cases
                  transferred from Arnold, White & Durkee to your own attorney,
                  The University will cooperate in this transfer subject to
                  reimbursement of any associated expenses above $300.00;

         (3)      You (and your company) agree to, and acknowledge, reservation
                  by The University of Texas System for itself and its component
                  institutions of a royalty-free, nonexclusive license to use
                  the inventions in educational and research activities;

         (4)      Any direct commercialization efforts regarding these
                  inventions will be your (or your company's) private endeavor
                  and cannot be carried out using University facilities or other
                  resources;

         (5)      In the event the inventions are commercialized, twenty percent
                  (20%) of any royalties or other income that you (or your
                  company) receive from such commercialization shall be paid to
                  The University as royalty after the total gross income
                  received by you (or your company) reaches Thirty Thousand
                  Dollars ($30,000);




<PAGE>

Dr. Adam Heller
August 1, 1991
Page 2


         (6)      You will inform this office in writing by September 1st of
                  each year of any commercialization efforts made regarding the
                  inventions during the previous year. At the time any royalty
                  payments shall become due to The University, they shall be
                  paid on a quarterly basis; and

         (7)      You acknowledge that you shall not receive any portion of the
                  inventors' share of income which The University may receive
                  from commercialization of these inventions. Your coinventors
                  will receive from The University the proportion of the
                  inventors' share that they would have received were you still
                  going to receive a portion of such funds.

         It is our intent to include in this release/assignment the disclosure
that you recently made of an invention entitled "Preactivated Interferant
Eliminating Biosensors." However, any future inventions, other than those that
can be filed as continuations or continuations-in-part on the existing
applications, cannot be included in this release/assignment. All such future
inventions are subject to individual disclosure and review in accordance with
our usual procedures. At such time we will give fair consideration to any
request by you that an invention be released to you.

         After careful consideration, I have decided that these terms are
considered final by The University. If you agree to them, please sign in the
space indicated below on both copies and return one to me. We shall then
consider the terms effective and operational although formal assignment
documents for the two pending patent applications will need to be prepared and
executed. We will ask The University of Texas System to prepare these documents
upon receipt of an executed copy of this letter.

                                                Sincerely yours,

                                                /s/ G.J. Fonken
                                                G.J. Fonken
GJF:cm

cc:      Associate Vice President Patricia C. Ohlendorf
         Dean Herbert H. Woodson
         Associate Dean Dale E. Klein
         Professor Thomas Edgar
         Mr. Dudley R. Dobie, Jr.
         Ms. Paulette Braeutigam
         Dr. Brian A. Gregg
         Dr. Ruben Maiden

/s/ Adam Heller
----------------------------------------------
Dr. Adam Heller

Date August 4, 1991
     -----------------------------------------

                                      -2-

<PAGE>

                                   EXHIBIT C

                 U.S. Serial
                 Filing No.
UT File No.        (Date)           Title                     Inventor(s)
-----------      -----------        -----                     -----------

UTSB:413           389,226          Enzyme Electrodes         Brian A. Gregg
                   (3-2-89)                                   Adam Heller

UTSB:465           664,054          Interferant Eliminating
                                       Biosensors             Adam Heller
                   (3-4-91)                                   Ruben Maidan

<PAGE>

                                    EXHIBIT D

                              INVENTION DISCLOSURE
                        The University of Texas at Austin


                                 I. Descriptive



1. Title of invention ***.
                      ---
2. Brief description. Is the Invention a new process, composition of matter, a
   device, or one or more products? A new use for or an improvement to an
   existing product or process?

***
---

Use additional sheets to elaborate or attach descriptive materials.

3. From the description, pick out and expand on novel and unusual features. How
   does the invention differ from present technology? What problems does it
   solve or what advantages does it possess?

***
---


*** Confidential treatment requested
<PAGE>

                                      ***


                                      -2-


*** Confidential treatment requested
<PAGE>

4.   If not indicated previously, what are possible uses for the invention? In
     addition to immediate applications, are there other uses that might be
     realized in the future?

***
--------------------------------------------------------------------------------
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________

5.   Does the invention possess disadvantages or limitations? Can they be
     overcome? How?

________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________


6.   Enclose sketches, drawings, photographs, and other materials that help
     illustrate the description. (Rough artwork, flow sheets, Polaroid
     photographs, and penciled graphs are satisfactory as long as they tell a
     clear and understandable story. Enclosed.

                           II.  Other Pertinent Data

1.   Are there publications--theses, reports, preprints, reprints, etc.--
     pertaining to the invention? Please list with publication dates, and attach
     copies insofar as possible. Include manuscripts for publication (submitted
     or not), news releases, feature articles, and items from internal
     publications.

     a.   ***
          ----------------------------------------------------------------------
     b.
          ______________________________________________________________________
     c.
          ______________________________________________________________________
     d.
          ______________________________________________________________________

2.   Are laboratory records and data available? Give reference numbers and
     physical location, but do not enclose.
                               ---

***
--------------------------------------------------------------------------------
________________________________________________________________________________

3.   Are related patents or other publications known to the inventor? Please
     list.

***
-------------------------------------------------------------------------------
_______________________________________________________________________________
_______________________________________________________________________________

                                      -3-


*** Confidential treatment requested
<PAGE>

4.   Date, place, and circumstances of first public disclosure.

***
-------------------------------------------------------------------------------
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________

5.   Was the work that led to the invention sponsored? If yes, attach copy of
     contact or agreement if possible, and fill in the appropriate blanks below.

     a.   Title of government agency         ***             Conract No.
                                    ---------------------                   ____
     b.   Name of industrial company
                                    ____________________________________________
     c.   Name of university sponsor
                                    ____________________________________________
     d.   Other sponsor(s) ***
                           ------------------------------------------

6.   Any commercial interest shown at this stage?  Name companies and specific
     persons if possible.

***
--------------------------------------------------------------------------------
________________________________________________________________________________
________________________________________________________________________________

     a.   Do you know of other qualified firms?  Please list.
                                                             -------------------

***
--------------------------------------------------------------------------------
________________________________________________________________________________

7.   Name(s) and title(s) of inventor(s)

     a.   ***
          ----------------------------------------------------------------------

     b.   ***
          ----------------------------------------------------------------------

     c.
          ______________________________________________________________________

(Contract for more data       ***                  Telephone        ***
                        -------------------------               --------------
                              (name)

                                      -4-

*** Confidential treatement requested
<PAGE>

8.   Mailing address for inventor(s) ***
                                     ----------------------------------

***
--------------------------------------------------------------------------------
(street and number)               (city and state)               (zip code)

9.   Signature(s) of inventor(s) and date

     a.   /s/ ***                      ***                     (date) ***
          ----------------------------------------------------        ---------

     b.   /s/ ***                      ***                     (date) ***
          ----------------------------------------------------        ---------

     c.                                                        (date)
          ____________________________________________________        ---------

     Use the space below and additional sheets to elaborate on answers to
questions and to provide any other helpful data.

*** Confidential treatment requested

                                      -5-


<PAGE>

6.   ***


***



***

*** Confidential treatment requested

                                      -6-