<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