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                                                                   EXHIBIT 10.23

THIS INSTRUMENT CONTAINS A CONFESSION OF JUDGMENT PROVISION THAT CONSTITUTES A
WAIVER OF IMPORTANT RIGHTS YOU MAY HAVE AS A DEBTOR AND ALLOWS THIS CREDITOR TO
OBTAIN A JUDGMENT AGAINST YOU WITHOUT ANY FURTHER NOTICE.

THIS INSTRUMENT AMENDS AND RESTATES THAT CERTAIN PROMISSORY NOTE EXECUTED BY THE
DEBTOR ON DECEMBER 6, 1999 IN THE ORIGINAL PRINCIPAL AMOUNT OF $250,000.00.

                      AMENDED AND RESTATED PROMISSORY NOTE

$190,905.00                                                  Richmond, Virginia
                                                         Date: December 13, 2001

         FOR VALUE RECEIVED, the undersigned, CELL ROBOTICS INTERNATIONAL, INC.,
a Colorado corporation ("Maker"), promises to pay to HUMAGEN FERTILITY
DIAGNOSTICS, INC., a Virginia corporation, or order, or assigns ("Noteholder"),
the sum of ONE HUNDRED NINETY THOUSAND, NINE HUNDRED, FIVE and 00/100 DOLLARS
($190,905.00), with interest thereon, commencing as of May 6, 2000 and
continuing until fully paid, at the rate of six percent (6.0%) per annum. All
payments of interest and principal shall be made to Noteholder at 2400 Hunter's
Way, Charlottesville, Virginia 22911, or at such other place as Noteholder may
designate in writing. The principal and all accrued interest shall be due and
payable in monthly installments of FIFTY THOUSAND and NO/100 DOLLARS
($50,000.00), commencing on January 31, 2002, and continuing on the last day of
each and every calendar month thereafter for a period of three consecutive
months. The remaining principal amount then outstanding hereunder and all then
accrued interest shall be due and payable on April 30, 2002.

         All payments shall be first applied to any late payment due, then
interest accrued or due, and then to the principal sum.

         The Maker shall have the privilege of prepayment of principal or
interest in whole or in part at any time without premium or penalty. Any
prepayment shall be first applied to any late payment then due, then to interest
accrued or due, and then to the principal sum.

         In the event of default on any installment due hereunder for a period
of five (5) days, Noteholder shall be entitled to receive, in addition to the
installment then due, a late charge in the amount of five percent (5%) of such
monthly installment then due. Should the undersigned fail to pay any installment
of this Promissory Note when due and within five (5) days after receipt of
written notice from the Noteholder with regard to such nonpayment, or upon
application of the appointment of a Receiver for the Maker, or upon the filing
of a petition in bankruptcy by or against the Maker, any such event shall
constitute a default hereunder and the entire unpaid amount hereof shall become
due and payable forthwith at the election of Noteholder and without further
notice. Failure to exercise this option upon any default or defaults shall not
constitute or be construed as a waiver of the right to exercise the said option
in the event of any subsequent default.

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         The Maker hereby waives presentment, demand, protest and notice of
dishonor and protest, and hereby agrees that extension or extensions of the time
of payment of this Promissory Note or any installment or part hereof may be made
before, at or after maturity by agreement with any one or more of the parties
hereto without notice to and without releasing the liability of any other party
to this Promissory Note, and they do likewise waive the benefit of all homestead
exemptions as to this debt and any right which they may have to require the
Noteholder to proceed against any person, and agree to pay all the expenses
incurred in collecting the same, including reasonable attorney's fees in case
this Promissory Note shall not be paid at maturity or when declared due and
payable as provided herein.

         The undersigned hereby appoints David Shane Smith as its attorney in
fact to appear in the Office of the Clerk of the Circuit Court of Richmond,
Virginia, to confess judgment upon this Note against it in favor of Humagen
Fertility Diagnostics, Inc. for the lesser of $190,905.00, or for the amount
then due hereunder, plus interest at 6.0% per annum and costs, including
reasonable attorneys' fees as determined hereinabove, and for which the Maker
authorizes the aforesaid attorney in fact, at any time after default hereof, to
confess judgment. The Maker waives presentment, demand, protest and notice.

         IMPORTANT NOTICE: THIS INSTRUMENT CONTAINS A CONFESSION OF JUDGMENT
PROVISION WHICH CONSTITUTES A WAIVER OF IMPORTANT RIGHTS YOU MAY HAVE AS A
DEBTOR AND ALLOWS THE CREDITOR TO OBTAIN A JUDGMENT AGAINST YOU WITHOUT ANY
FURTHER NOTICE.

         WITNESS the following signature and seal:

                                           CELL ROBOTICS INTERNATIONAL, INC.

                                        By: /s/ Ronald Lohrding
                                           ---------------------------------
                                           President

         THE FOREGOING WAS ACKNOWLEDGED BEFORE ME THIS 13TH DAY OF DECEMBER,
2001 BY RONALD LOHRDING, THE PRESIDENT OF CELL ROBOTICS INTERNATIONAL, INC.

                                            -------------------------------
                                                     Notary Public

                   My commission expires: ____________________

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Maker's address to
which Notices shall be sent:
2715 Broadbent Parkway NE
Albuquerque, New Mexico 87107

Noteholder's address to which
Notices and payments shall be sent:
2400 Hunter's Way
Charlottesville, Virginia 23228

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                             MODIFICATION AGREEMENT

         THIS MODIFICATION AGREEMENT (the "Agreement"), made this 13th day of
December, 2001, is by and between HUMAGEN FERTILITY DIAGNOSTICS, INC., a
Virginia corporation (hereinafter "Humagen") and CELL ROBOTICS INTERNATIONAL,
INC., a Colorado corporation (hereinafter "Cell Robotics").

         WHEREAS, Cell Robotics previously borrowed the sum of $250,000.00 from
Humagen, which said obligation is evidenced by a certain Promissory Note dated
December 6, 1999 (the "Original Note"); and

         WHEREAS, the parties subsequently executed a certain Amendment to
Promissory Note, effective May 10, 2000 (the "Amendment"); and

         WHEREAS, the parties have reached an oral agreement that sets forth a
schedule under which the obligation owed by Cell Robotics will be paid.

         NOW, THEREFORE, the parties hereto execute this Agreement to evidence
their oral agreement, and to provide for the payment by Cell Robotics of
$190,905.00, plus interest, to Humagen.

                                   WITNESSETH:

         1. Payment Schedule. Cell Robotics agrees to pay to Humagen the total
principal sum of $190,905.00, plus interest, in monthly installments of FIFTY
THOUSAND and NO/100 DOLLARS ($50,000.00), commencing on January 31, 2002, and
continuing on the last day of each calendar month thereafter for a period of
three (3) consecutive calendar months. The remaining principal amount then
outstanding, and all then accrued interest, shall be due and payable on April
30, 2002. To evidence this obligation, Cell Robotics shall, simultaneously with
the execution of this Agreement, execute an Amended and Restated Promissory Note
dated the same date herewith in the principal amount of $190,905.00, a copy of
which is attached hereto as Exhibit "A" (the "Amended and Restated Note"). The
Amended and Restated Note shall supercede and replace the Original Note dated
December 6, 1999 and the Amendment.

         2. Forebearance of Litigation. Provided Cell Robotics timely makes the
payments set forth herein and in the Amended and Restated Note, Humagen agrees
to forebear on the institution of legal proceedings to collect the amounts due.
In the event that Cell Robotics defaults under the Amended and Restated Note,
all amounts due thereunder shall be immediately accelerated and Humagen shall be
entitled to enforce its rights set forth under the Amended and Restated Note.

         3. Applicable Law. This Agreement and the Amended and Restated Note are
made in Virginia and shall be construed in accordance with the laws of the
Commonwealth of Virginia.

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         4. Binding Effect. This Agreement shall be binding upon Humagen and
Cell Robotics, their successors and assigns. This Agreement shall inure to the
benefit of the parties hereto, their respective heirs, executors,
administrators, personal representatives, successors and assigns.

         5. Other Documents. Each party hereto promises and agrees to execute
and deliver any instruments and to perform any acts that may be necessary or
reasonably requested in order to give full effect to this Agreement.

         IN WITNESS WHEREOF, the parties have caused this Agreement to be
executed this 13TH day of December, 2001.

                                           HUMAGEN FERTILITY DIAGNOSTICS, INC.,
                                           a Virginia corporation

                                       By: /s/ Debra Bryant
                                          -------------------------------------

                                           CELL ROBOTICS INTERNATIONAL, INC.,
                                           a Colorado corporation

                                       By: /s/ Ronald Lohrding
                                          -------------------------------------

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                                                                    Exhibit 4.03

                             BROOKS AUTOMATION, INC.
                          AMENDMENT TO RIGHTS AGREEMENT

      This Amendment (this "Agreement"), dated as of October 23, 2001, to the
Rights Agreement dated as of July 23, 1997 (the "Rights Agreement"), between
Brooks Automation, Inc., a Delaware corporation (the "Company"), and Equiserve
Trust Company, N.A. successor Rights Agent (the "Rights Agent").

                                    RECITALS

      WHEREAS, the board of directors of the Company has approved a certain
agreement and plan of merger (the "Merger Agreement") by and among the Company,
PRI Automation, Inc., a Massachusetts corporation ("PRI"), Pontiac Acquisition
Corp., a Massachusetts corporation wholly owned by the Company ("Brooks Merger
Sub") at a meeting of the board of directors of the Company held on October 23,
2001 (the "Meeting"), pursuant to which Brooks Merger Sub will be merged with
and into PRI (the "Merger"), and the stockholders of PRI will become
stockholders of the Company.

      WHEREAS, upon the effectiveness of the Merger, PRI may acquire more than
15% of the outstanding shares of the Company's Common Stock, $.01 par value per
share (the "Company's Common Stock").

      WHEREAS, the acquisition of more than 15% of the outstanding shares of the
Company's Common Stock would result in the acquiring entity or entities being
deemed to be an "Acquiring Person" under the Rights Agreement, which would
trigger certain events pursuant to the terms of the Rights Agreement.

      WHEREAS, at the Meeting the board of directors of the Company determined
that it is in the best interest of the Company to amend the Rights Agreement
prior to the Company entering into the Merger Agreement so that PRI and its
Affiliates will not become Acquiring Persons under the Rights Agreement.

      WHEREAS, capitalized terms used but not otherwise defined in this
Amendment No. 1 shall have the meanings given them in the Rights Agreement.

      NOW, THEREFORE, in consideration of the promises and agreements set forth
herein, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

      1. AMENDMENT OF FIRST SUBPARAGRAPH OF SECTION 1. The first subparagraph of
Section 1, definition of "Acquiring Person," is hereby amended and restated so
that such subparagraph reads in its entirety as follows:

            "Acquiring Person" shall mean any Person who or which, together with
            all Affiliates and Associates of such Person, shall be the
            Beneficial Owner of 15% or more of the Common Shares of the Company
            then outstanding, but shall not

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            include (i) the Company, (ii) any Subsidiary of the Company, (iii)
            any employee benefit plan of the Company or any Subsidiary of the
            Company, (iv) any entity holding Common Shares for or pursuant to
            the terms of any such employee benefit plan, (v) Robert J. Therrien,
            any members of his immediate family or any of his or their
            Affiliates or Associates, (vi) any person that is the Beneficial
            Owner of 15% or more of the Common Shares of the Company outstanding
            as of the close of the Nasdaq National Market on the date hereof;
            provided, however, that after such date such person does not become
            the Beneficial Owner of additional Common Shares of the Company in
            an aggregate amount (net of any sales) of the greater of 200,000
            Common Shares or the number of Common Shares equal to 2.6% of the
            then outstanding Common Shares (as measured as of the date of the
            then acquisition of Common Shares by the Beneficial Owner); and
            provided, further that such person shall be treated as any other
            holder of Common Shares of the Company and shall no longer be
            entitled to the exclusion set forth in this clause (vi) after such
            time as such person becomes the Beneficial Owner of less than 15% of
            the Common Shares of the Company then outstanding or (vii) PRI
            Automation, Inc., a Massachusetts corporation ("PRI"), or any of its
            Affiliates if and only if, PRI or such Affiliates shall become the
            Beneficial Owner of 15% or more of the Common Shares of the Company
            then outstanding as a result of the execution of the Agreement and
            Plan of Merger authorized and approved by the Board of Directors of
            the Company at the meeting of the Board of Directors held on October
            23, 2001, as it may be amended from time to time (the "Merger
            Agreement"), or the consummation of the transactions contemplated
            thereby, and/or any options to purchase or proxies to vote Common
            Shares of the Company granted by the Company or any stockholder of
            the Company to PRI in connection with the Merger Agreement or any
            agreements or arrangements entered into by the Company and PRI in
            connection therewith. Notwithstanding the foregoing, (1) no Person
            shall become an "Acquiring Person" as the result of an acquisition
            of Common Shares by the Company which, by reducing the number of
            shares outstanding, increases the proportionate number of shares
            beneficially owned by such Person to 15% or more of the Common
            Shares of the Company then outstanding; provided, however, that if a
            Person shall so become the Beneficial Owner of 15% or more of the
            Common Shares of the Company then outstanding by reason of an
            acquisition of Common Shares by the Company and shall, after such
            share purchases by the Company, become the Beneficial Owner of an
            additional 1% of the outstanding Common Shares of the Company, then
            such Person shall be deemed to be an "Acquiring Person"; (2) if the
            Board of Directors of the Company determines in good faith that a
            Person who would otherwise be an "Acquiring Person," as defined
            pursuant to the foregoing provisions of this paragraph, has become
            such inadvertently, and such Person divests as promptly as
            practicable a sufficient number of Common Shares so that such Person
            would no longer be an "Acquiring Person," as defined pursuant to the
            foregoing provisions of this paragraph, then such Person shall not
            be deemed to have become an "Acquiring Person" for any purposes of
            this Agreement; and (3) an underwriter or underwriters which become
            the Beneficial Owner of 15% or more of the Common Shares of the
            Corporation then outstanding in connection

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            with an underwritten public offering with a view to the public
            distribution of such Common Shares shall not become an "Acquiring
            Person" hereunder."

      2. REAFFIRMATION OF RIGHTS AGREEMENT. Except as specifically amended by
this Amendment, the Rights Agreement shall remain in full force and effect.

                            [SIGNATURES ON NEXT PAGE]

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      IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the date first above written.

                                    BROOKS AUTOMATION, INC.

                                    By:   /s/ Ellen B. Richstone
                                       -----------------------------------------
                                          Name:   Ellen B. Richstone
                                          Title:  Senior Vice President of
                                                  Finance and Administration and
                                                  Chief Financial Officer

                                    EQUISERVE TRUST COMPANY, N.A

                                    By:   /s/ Margaret Prentice
                                       -----------------------------------------
                                          Name:   Margaret Prentice
                                          Title:  Managing Director

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