Document:

<PAGE>   1
                                                                  EXHIBIT 10.33a

             FIRST AMENDMENT TO CONVERTIBLE NOTE PURCHASE AGREEMENT

         FIRST AMENDMENT, dated as of December 14, 2000 (this "First
Amendment"), to the Convertible Note Purchase Agreement, dated as of April 28,
2000 (the "Note Purchase Agreement"), by and among Bio-Plexus, Inc., a
Connecticut corporation (the "Company"), the Purchasers listed on Exhibit A
thereto, and Appaloosa Management L.P., as Collateral Agent.

                                   WITNESSETH:

         WHEREAS, the Company has issued the Notes to the Purchasers; and

         WHEREAS, in connection with the issuance of the Notes the Company
presented certain operating forecasts in the second revision to its Five Year
Business Plan, dated January 12, 2000 (the "Business Plan"), upon which
Appaloosa relied in setting financial covenants in the Note Purchase Agreement;
and

         WHEREAS, Appaloosa subsequently agreed to suspend such financial
covenant requirements until December 31, 2000 to allow sufficient time for the
Company to hire a new chief executive officer and revise the Business Plan; and

         WHEREAS, the Company's revised Business Plan and the other projections
presented by the Company to Appaloosa since the Closing require that the
financial covenants set forth in the Note Purchase Agreement be revised to more
accurately reflect the revised Business Plan and projections; and

         WHEREAS, the Company desires to amend the financial covenants in the
Note Purchase Agreement for the periods extending beyond December 31, 2000;

         NOW, THEREFORE, in consideration of the premises and mutual covenants
contained herein, the Company, the Purchasers, and the Collateral Agent hereby
agree as follows:

         1. Defined Terms. Unless otherwise defined herein, capitalized terms
which are defined in the Note Purchase Agreement are used herein as therein
defined.

         2. Amendment to the Note.

                  (a) Subsection 6.15 of the Note Purchase Agreement is amended
by deleting the paragraph in its entirety and substituting in lieu therefor the
following:

                  The Company shall maintain the financial covenants specified
in Schedule 6.15.

                  (b) Schedule 6.15 of the Note Purchase Agreement is amended by
deleting the first two charts in their entirety and substituting in lieu
therefor the following charts:
<PAGE>   2
<TABLE>
<CAPTION>
                                          Minimum (Maximum) Operating Profit     Minimum (Maximum) Operating Profit
                 Date                    (Loss) for three-month period ending      (Loss) for twelve-month period
                                                   on date indicated                  ending on date indicated
<S>                                      <C>                                     <C>
          September 30, 1999                              N/A                                    N/A
           December 31, 1999                              N/A                                    N/A
            March 31, 2000                                N/A                                    N/A
             June 30, 2000                                N/A                                    N/A
          September 30, 2000                              N/A                                    N/A
           December 31, 2000                         ($1,622,000)                           ($1,622,000)*
            March 31, 2001                           ($1,391,000)                          ($3,013,000)**
             June 30, 2001                           ($1,011,000)                          ($4,024,000)***
          September 30, 2001                          ($764,000)                            ($4,788,000)
           December 31, 2001                          ($150,000)                            ($3,316,000)
            March 31, 2002                             $450,000                             ($1,475,000)
             June 30, 2002                             $550,000                                $86,000
          September 30, 2002                           $600,000                              $1,450,000
           December 31, 2002                           $600,000                              $2,200,000
            March 31, 2003                            $1,000,000                             $2,750,000
             June 30, 2003                            $1,250,000                             $3,450,000
          September 30, 2003                          $1,500,000                             $4,350,000
           December 31, 2003                          $1,650,000                             $5,400,000
  March 31, 2004 and the last day of
   each calendar quarter thereafter                   $1,700,000                             $6,500,000
</TABLE>

         *        Represents the trailing 3-month period.

         **       Represents the trailing 6-month period.

         ***      Represents the trailing 9-month period.

<TABLE>
<CAPTION>
                                            Minimum Product Sales       Minimum Product Sales
                                           Revenue for three-month     Revenue for twelve-month
                        Date              period ending on the date     period ending on date
                                                  indicated                   indicated
<S>                                       <C>                          <C>
                  December 31, 1999                  N/A                         N/A
                   March 31, 2000                    N/A                         N/A
                    June 30, 2000                    N/A                         N/A
                 September 30, 2000                  N/A                         N/A
                  December 31, 2000               $1,141,000                 $1,141,000*
                   March 31, 2001                 $1,227,000                 $2,368,000**
                    June 30, 2001                 $1,884,000                $4,252,000***
                 September 30, 2001               $2,352,000                  $6,604,000
                  December 31, 2001               $2,921,000                  $8,384,000
                   March 31, 2002                 $4,000,000                 $11,157,000
                    June 30, 2002                 $4,500,000                 $13,773,000
</TABLE>

                                       2
<PAGE>   3
<TABLE>
<CAPTION>
                                            Minimum Product Sales       Minimum Product Sales
                                           Revenue for three-month     Revenue for twelve-month
                        Date              period ending on the date     period ending on date
                                                  indicated                   indicated
<S>                                       <C>                          <C>
                 September 30, 2002               $5,000,000                 $16,421,000
                  December 31, 2002               $5,500,000                 $19,000,000
                   March 31, 2003                 $6,000,000                 $21,000,000
                    June 30, 2003                 $6,500,000                 $23,000,000
                 September 30, 2003               $7,000,000                 $25,000,000
                  December 31, 2003               $7,500,000                 $27,000,000
               March 31, 2004 and the
               last day of each calendar
               quarter thereafter                 $8,500,000                 $32,500,000
</TABLE>

         *        Represents the trailing 3-month period.
         **       Represents the trailing 6-month period.
         ***      Represents the trailing 9-month period.

                  (c) Subsection 6.20 of the Note Purchase Agreement is amended
by deleting clause (e) thereof in its entirety and substituting in lieu
therefor:

                           (e) upon any Holder's request from time to time, such
                           other information (including financial statements,
                           monthly computation of profit and loss, and any other
                           computations) relating to the performance of the
                           provisions of this Agreement and the affairs of the
                           Company and any of its Subsidiaries.

                  (d) Subsection 6.33 of the Note Purchase Agreement is amended
by adding the following text after the final sentence thereof:

                           The Company shall not materially alter or embark upon
                           (other than preliminary non-binding discussions) any
                           new strategic initiatives as a part of its business
                           plan or otherwise, which strategic initiatives shall
                           include, but not be limited to, joint ventures,
                           strategic alliances, licensing agreements,
                           acquisitions, and partnerships of any kind (other
                           than distribution, supply and other similar
                           agreements entered into in the ordinary course of
                           business on commercially reasonable terms), without
                           the express consent of the Collateral Agent.

                  (e) Schedule 6.34 of the Note Purchase Agreement is amended by
adding the following text after the final sentence thereof:

                           Performance Covenants for the Development and Sale of
                           Winged Sets for Blood Collection:

                                       3
<PAGE>   4
                                    The Company shall meet the following
                                    milestones on the dates set forth below with
                                    respect to its Winged Set for Blood
                                    Collection product:

                           (i) Complete installation and start-up of a pilot
                           production line by November 30, 2000;

                           (ii) Produce a minimum 15,000 units of pre-launch
                           Winged Set product samples on the pilot production
                           line by January 31, 2001;

                           (iii) Complete installation and start-up of an
                           automated production line by March 31, 2001; and

                           (iv) Begin commercial sale of the Winged Set product
                           by April 2, 2001 and have shipped a minimum of
                           100,000 units of the Winged Set product for
                           commercial sale (which excludes any sale to an
                           Affiliate or to any other Person on a non-arms length
                           basis) by June 30, 2001.

                  (f) Subsection 11.1 of the Note Purchase Agreement is amended
by deleting the definition of "Product Sales Revenues" in its entirety and
substituting in lieu therefor the following definition:

                           "Product Sales Revenues" shall mean all revenues
                           generated by the Company from the sale of medical
                           products manufactured by the Company (excluding, for
                           the avoidance of doubt, any equipment or other
                           machinery sold or licensed to any Person for the
                           manufacture of any such medical products) calculated
                           in accordance with GAAP.

         3. Representations and Warranties. The Company represents and warrants
that the representations and warranties set forth in Section 2 of the Note
Purchase Agreement are true and complete on and as of the date hereof as if made
on the date hereof (or, if any such representation or warranty is expressly
stated to have been made as of a specific date, as of such specific date). The
Company represents and warrants that as of the date hereof and, after giving
effect to this First Amendment and the transactions contemplated hereby, no
Default or Event of Default has occurred and is continuing. The Company
represents that the execution and delivery of this First Amendment by the
Company and the performance by it of the transactions contemplated hereby have
been duly authorized by all requisite corporate proceedings on the part of the
Company.

         4. Effectiveness. The First Amendment shall become effective as of the
date upon which the Collateral Agent receives the counterpart of this First
Amendment duly executed by the Company.

         5. Continuing Effect of the Transaction Documents. This First Amendment
shall not constitute an amendment of any other provisions of the Note Purchase
Agreement or any other Transaction Documents not expressly referred to herein
and shall not be construed as a waiver or consent to any further or future
action on the part of the Company that would require a waiver or consent of the
Purchasers. Except as expressly amended hereby, the provisions of the Note

                                       4
<PAGE>   5
Purchase Agreement and the other Transaction Documents are and shall remain in
full force and effect. In the event there is any conflict between the terms of
the Note Purchase Agreement and any other Transaction Document, the terms of the
Note Purchase Agreement shall govern.

         6. Counterparts. This First Amendment may be executed by the parties
hereto in any number of separate counterparts, each of which shall be deemed to
be an original, and all of which taken together shall be deemed to constitute
one and the same instrument.

         7. GOVERNING LAW. THIS FIRST AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

                                       5
<PAGE>   6
         IN WITNESS WHEREOF, the parties hereto have caused this First Amendment
to be duly executed and delivered by their respective proper and duly authorized
officers as of the day and year first above written.

                                 BIO-PLEXUS, INC.

                                 By:    /s/  John S. Metz
                                        ---------------------------------------
                                 Name:  John S. Metz
                                 Title: President and Chief Executive Officer

                                 APPALOOSA MANAGEMENT L.P.,
                                        as Collateral Agent

                                 By:    Appaloosa Partners Inc., its General
                                                   Partner

                                 By:    /s/  James E. Bolin
                                        ---------------------------------------
                                 Name:  James E. Bolin
                                 Title: Vice President

                                 APPALOOSA INVESTMENT LIMITED
                                          PARTNERSHIP I

                                 By:    Appaloosa Management L.P., its
                                                 General Partner
                                 By:    Appaloosa Partners Inc., its General
                                                   Partner

                                 By:    /s/  James E. Bolin
                                        ---------------------------------------
                                 Name:  James E. Bolin
                                 Title: Vice President

                                 PALOMINO FUND LTD.

                                 By:    Appaloosa Management L.P.
                                        its Investment Advisor

                                 By:    Appaloosa Partners Inc.
                                        its General Partner

                                 By:    /s/  James E. Bolin
                                        ---------------------------------------
                                 Name:  James E. Bolin
                                 Title: Vice President

                                       6
<PAGE>   7
                                 TERSK LLC

                                 By:    Appaloosa Management L.P.
                                        its Investment Advisor

                                 By:    Appaloosa Partners Inc.
                                        its General Partner

                                 By:    /s/  James E. Bolin
                                        ---------------------------------------
                                 Name:  James E. Bolin
                                 Title: Vice President

                                       7<PAGE>   1
                                                                   EXHIBIT 10.48

                                BIO-PLEXUS, INC.
                               129 Reservoir Road
                                Vernon, CT 06066

                                October 30, 2000

Mr. Carl Sahi
389 High Street
Coventry, CT 06238

Dear Carl:

                  The purpose of this letter is to set forth our agreements with
respect to your ongoing relationship with Bio-Plexus, Inc. (the "Company"). This
letter agreement (the "Letter Agreement") shall constitute the agreement
contemplated by that certain letter agreement dated April 28, 2000 between you
and the Company (the "April 28 Letter"). By signing where indicated below you
acknowledge your agreement with the terms and conditions set forth in this
letter agreement.

                  1. Membership on Board of Directors.

                  You agree that if nominated, you will stand for election to
the Company's Board of Directors, and, if elected, that you will serve on the
Company's Board of Directors, until the 2003 annual meeting of stockholders. In
connection with your service on the Board of Directors you will be entitled to
the standard outside director compensation paid by the Company and to all other
benefits generally available to non-employee directors.

                  2. Accrued Vacation.

                  Within five days of the execution of this Letter Agreement the
Company will pay to you the amount of $70,000, less applicable withholding and
other employment taxes, as partial payment for your unpaid vacation accrued
during your employment with the Company. An additional $22,000 will be paid to
you ratably over a six month period commencing January 1, 2001, in accordance
with the Company's normal payroll practices. You agree that the foregoing
amounts, once paid, shall constitute payment in full of all accrued vacation
owed to you by the Company in connection with your tenure as an employee of the
Company.
<PAGE>   2
Carl Sahi
October 30, 2000
Page 2

                  3. Confidentiality Agreement.

                  On September 14, 2000 you executed and delivered to the
Company the Employee Confidentiality Agreement, Proprietary Information and
Inventions Agreement (the "Confidentiality Agreement") which all employees of
the Company are obligated to sign in connection with the commencement of their
employment with the Company. You and the Company acknowledge and agree that the
Confidentiality Agreement shall be deemed to have been effective as to you and
the Company for all periods during which you were employed with the Company and
shall remain in effect pursuant to its terms subsequent to the execution of this
Letter Agreement and shall apply in connection with your continuing work, if
any, as a consultant for the Company as if you were an employee of the Company.

                  You agree not to contest the enforceability of the
Confidentiality Agreement due to the fact that you executed the Confidentiality
Agreement after you ceased your employment as a full-time employee of Company
and acknowledge that the terms and conditions of the Confidentiality Agreement
and of this Section 3 are reasonable and continue to be effective as provided
herein.

                  Your agreements as provided in this Section 3 are a material
inducement to the Company to deliver this Letter Agreement to you.

                  4. Legal Fees and Expenses.

                  Within five days of your execution and delivery of this Letter
Agreement the Company will pay to you $10,000 in deferment of legal expenses you
have incurred in connection with your separation from the Company.

                  5. Non-competition; Non-solicitation

                           (a) In consideration for the premises and mutual
covenants contained herein and for the compensation set forth in paragraph (c)
of this Section 5, during the period commencing on the date hereof and
continuing through April 28, 2002 (the "Non-compete Term"), you shall not, in
any county and/or city in the State of Connecticut, the United States of America
or any county or political subdivision in any state or country in the world, for
any reason whatsoever, (A) engage in a Competitive Business (as hereinafter
defined) whether such engagement shall be as an employer, officer, director,
owner, employee, consultant, partner, member or other participant; provided,
however, that you shall not be deemed to be engaged in a Competitive Business
solely by your ownership of less than 5% of any class of securities of any
entity or entities which class of securities have been registered under Section
12 of the Securities Exchange Act of 1934, as amended or (B) assist others,
whether as a consultant, agent or independent contractor, in engaging in a
Competitive Business. For purposes of this Agreement,
<PAGE>   3
Carl Sahi
October 30, 2000
Page 3

"Competitive Business" shall mean any business involving the development and/or
manufacture of, or sales and marketing of (i) safety products which are
competitive with the Company's (1) PUNCTUR-GUARD(R) blood collection needle (2)
DROP-IT(R) needle holder, (3) PUNCTUR-GUARD REVOLUTION(R) or (4) the DROP-IT(TM)
Needle Disposal Container, (ii) safety products which are competitive with the
Bio-Plexus Winged Set(R) and Guidewire Introducer products currently being
developed by the Company and (iii) any product directly competitive with the
products developed, manufactured, sold or marketed by (A) Johnson & Johnson
Medical, Inc., (B) TFX Medical, a division of Teleflex Incorporated, as sold to
Bard Access, a division of C.R. Bard or (C) Fresenius Medical Care Holdings,
Inc.("Fresenius"), or any of their respective affiliates or permitted assignees,
in each case based on technology licensed and/or sublicensed, as of the date
hereof, by the Company to such entities; provided that you and the Company
acknowledge and agree that as of the date hereof the Company has not yet entered
into a definitive agreement with Fresenius and that the restrictions set forth
in this Section 5 shall become effective as to you and the Company with respect
to Fresenius upon the execution of such definitive documentation.
Notwithstanding the foregoing, you may act as an employee, consultant, agent or
independent contractor for an entity engaged in a Competitive Business so long
as your role with such entity is not related to the Competitive Business
conducted by such entity.

                  (b) In consideration for the premises and mutual covenants
contained herein and for the compensation set forth in paragraph (c) of this
Section 5, during the Non-compete Term, without the prior written consent of the
Company, you shall not directly induce, recruit, or solicit any officers,
contractors, consultants or employees of the Company to leave the employ of the
Company.

                  (c) In consideration for your agreements contained in this
Section 5, the Company shall (i) pay to you the sum of $60,000 as herein
provided (the "Non-compete Cash Fee") and (ii) issue to you pursuant to the 1991
Long-term Incentive Plan an option (the "Non-Compete Option") to acquire 25,000
shares of the Company's common stock, no par value (the "Common Stock") at an
exercise price per share equal to the closing bid price of a share of Common
Stock on the Nasdaq SmallCap Market as of the date of this Letter Agreement. The
Company shall pay to you the Non-compete Cash Fee in equal monthly installments
ratably over a four-month period commencing on November 15, 2000; provided,
however, that you acknowledge and agree that the $20,000 previously forwarded to
you by the Company in $10,000 installments on or about each of September 15 and
October 15, shall be deemed payments to you of a portion of the Non-Compete Cash
Fee and that, as of the date hereof, the remaining unpaid portion of the
Non-compete Cash Fee is $40,000.
<PAGE>   4
Carl Sahi
October 30, 2000
Page 4

                  6. April 28 Letter

                  By signing where indicated below, Appaloosa Management, L.P.
("Appaloosa") (in its individual capacity and in its capacity as collateral
agent pursuant to the terms of that certain Convertible Note Purchase Agreement,
dated as of April 28, 2000, between Appaloosa, the Company and the other
entities party thereto), you and the Company each acknowledge and agree that
this Letter Agreement satisfies the obligations of you and the Company provided
for in the April 28 Letter. Appaloosa hereby waives any claims or rights it may
have arising out of your and the Company's failure to execute the consulting
agreement called for in the April 28 Letter within thirty days following the
closing of the Company's financing with Appaloosa.

                  It is the intent of you and the Company that Appaloosa be a
third party beneficiary of the rights of the Company pursuant to Sections 3 and
5 of this Letter Agreement.

                  7. Restrictions on Transfers of Securities

                  In return for your agreements set forth in this Letter
Agreement the Company will lift the "window period" trading restrictions set
forth in the Company's insider trading policy which is applicable to you as a
director of the Company. The lifting of the window period trading restrictions
is contingent upon you entering into an arrangement with your broker in
connection with trades in the Company's securities which complies with Rule
10(b)5-1 (a "Rule 10(b)5-1 Program") under the Securities Exchange Act of 1934,
as amended (the "Exchange Act"). There will be no volume or share price
limitations on your trades in the Company's securities so long as such trades
are made pursuant to a Rule 10(b)5-1 Program and otherwise comply with
applicable law. Of course, any trades made by you pursuant to a Rule 10(b)5-1
Program will continue to be reportable under Section 16 of the Exchange Act so
long as you remain a director of the Company.

                  8. Other Terms

                           (a) You acknowledge that the restrictions contained
in Sections 3 and 5 of this Letter Agreement are fair, reasonable and necessary
to protect the legitimate business interests of the Company and that the Company
will suffer irreparable harm in the event of any actual or threatened breach by
you of Sections 3 or 5 of this Letter Agreement. You therefore consent to the
entry of a restraining order, preliminary injunction or other court order to
enforce those paragraphs and expressly waive any security that might otherwise
be required in connection with such relief. You also agree that any request for
such relief by the Company shall be in addition and without prejudice to any
claim for monetary damages which the Company might elect to assert.
<PAGE>   5
Carl Sahi
October 30, 2000
Page 5

                  (b) If any provision of this Letter Agreement is held to be
unenforceable by a court, the remaining provisions shall be enforced to the
maximum extent possible. If a court should determine that any provision of this
Letter Agreement is overbroad or unreasonable, such provision shall be given
effect to the maximum extent possible by narrowing or enforcing in part that
aspect of the provision found overbroad or unreasonable.

                  (c) This Letter Agreement represents the entire agreement of
the parties with respect to the subject matter covered and cannot be modified or
amended except in a writing signed by both parties. The waiver by any party to
this Letter Agreement of a breach of any of the provisions of this Letter
Agreement shall not operate or be construed as a waiver of any subsequent or
simultaneous breach.

                  (d) This Letter Agreement shall be governed by and construed
in accordance with the internal substantive laws, and not the laws of conflict,
of the State of Connecticut. Any legal claim, suit, action or proceeding between
the parties relating in any way to this Letter Agreement may be brought only in
the courts of the State of Connecticut or of the United States of America
located in Connecticut, and you hereby irrevocably consent to exclusive
jurisdiction and venue in such courts and agree not to assert by way of motion,
as a defense or otherwise, any claim that you are not personally subject to the
jurisdiction of the above-named courts, that the suit, action or proceeding is
brought in an inconvenient forum, that the venue of the suit, action or
proceeding is improper or that this Letter Agreement may not be enforced in or
by such courts. Nothing contained herein shall be deemed to prohibit or limit
the right of the Company to sue or take action in any tribunal, wherever
located, having jurisdiction over you or any of your assets.

                  (e) This Letter Agreement shall be binding upon and inure to
the benefit of the parties and their respective successors and permitted
assigns. This Agreement shall not be assignable by either party except with the
prior written consent of the other party.

                  (f) This Letter Agreement may be executed in one or more
counterparts, each of which shall be deemed an original but all of which
together shall constitute one and the same instrument.

                  (g) The language used in this Letter Agreement shall be deemed
to be the language chosen by the parties hereto to express their mutual intent,
and no rule of strict construction will be applied against any party hereto.
<PAGE>   6
Carl Sahi
October 30, 2000
Page 6

                  (h) Subject to receipt of an executed copy of this Letter
Agreement from Appaloosa, the effective date of this Letter Agreement shall be
October 30, 2000. This Letter Agreement shall be void as to you and the Company
if Appaloosa has not delivered to the Company an executed counterpart hereof
within 20 days of the date hereof.

                  Please acknowledge your agreement with the foregoing terms and
conditions by executing where indicated below and returning a duly executed copy
to the Company.

                  On behalf of the Company, thank you for your years of service
to Bio-Plexus. The Company looks forward to a continuing relationship with you
and trusts that the terms set forth herein are acceptable to you.

                                   Very truly yours,

                                   BIO-PLEXUS, INC.

                                   By: /s/  John S. Metz
                                       ------------------------------------
                                       John S. Metz
                                       President and Chief Executive Officer

Agreed and Accepted to

/s/  Carl Sahi
----------------------------
Carl Sahi

Date:    10/30/00
     -----------------------

                                   Solely with respect to
                                   Section 6, Appaloosa
                                   Management, L.P.

                                   By: Appaloosa Partners, Inc., its general
                                         partner

                                   By: /s/    James E. Bolin
                                       ------------------------------------
                                       Name:    James E. Bolin
                                       Title:   Vice President

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00027-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00027-of-00352.parquet"}]]