SUBSCRIPTION AGREEMENT

      SUBSCRIPTION AGREEMENT ("Subscription Agreement") made as of this 31st day
of January, 2005, by and among Bluestone Ventures Inc., a Nevada corporation
(the "Company"), Amerasia Technology, Inc., a California corporation
("Amerasia"), as General Partner of Electronic Sensor Technology, L.P., a
California limited partnership ("EST"), and the undersigned (the "Subscriber").

      WHEREAS, the Company, Amerasia, L&G Sensor Technology, Inc., a California
corporation (L&G"), Ameritech SDN BHD, a Malaysian corporation ("Ameritech"),
and newly formed subsidiaries of the Company are parties to a certain Agreement
of Merger and Plan of Reorganization, dated as of January 31, 2005 (the "Merger
Agreement"), pursuant to which (i) Amerasia will acquire a 4% interest in EST
from Ameritech, (ii) following such acquisition, Amerasia Acquisition and L&G
Acquisition will merge with and into Amerasia and L&G, the holders of 100% of
the equity interests in EST, with Amerasia and L&G being the respective
surviving company in such mergers, and each of Amerasia and L&G will become a
direct wholly-owned subsidiary of the Company, (iii), EST will become an
indirect wholly-owned subsidiary of the Company, (iv) the existing Amerasia
stockholders will receive 11,000,000 shares of common stock of the Company as
consideration for the merger (the "Merger"), and (v)the existing L&G stockholder
will receive 9,000,000 shares of common stock of the Company as consideration
for the Merger; and immediately after the effective time of the Merger (the
"Closing Date"), the Company will change its name to Electronic Sensor
Technology, Inc. (or other similar name) and will assume, through EST, its
business and operations.

      WHEREAS, to facilitate the Merger, and as a condition to the closing of
the Merger, the Company intends to issue, in a private placement transaction
(the "Offering") pursuant to Regulation D promulgated under the Securities Act
of 1933, as amended (the "Act"), 3,000,000 Units ("Units") of the Company with
each Unit comprised of one share of the Company's common stock, par value $0.001
per share ("Common Stock"), and one warrant to purchase one share of Common
Stock at a purchase price of $1.00 per share for three years, on the terms and
conditions hereinafter set forth, and the Subscriber desires to acquire that
number of Units set forth on the signature page hereof.

      NOW, THEREFORE, and in consideration of the premises and the mutual
covenants hereinafter set forth and for other good and valuable consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties
hereto, intending legally to be bound, do hereby agree as follows:

      1. Subscription Procedure

      1.1 Subject to the terms and conditions hereinafter set forth, the
Subscriber hereby subscribes for and agrees to purchase from the Company such
number of Units as is set forth upon the signature page hereof at a price of
$1.00 per Unit (the "Purchase Price"). The Company agrees to sell such Units to
the Subscriber for the Purchase Price.

      1.2 The subscription period will begin as of January 10, 2005, and will
terminate (if the Closing Date has not earlier occurred) at 5:00 PM Eastern
Standard Time on January 15, 2005, unless extended by the Company and Amerasia

<PAGE>

for up to an additional 90 days (the "Termination Date"). The minimum dollar
amount of Units that may be purchased by the Subscriber is $25,000 unless
Amerasia and the Company waive the minimum purchase requirement. The
consummation of the Offering is subject to the satisfaction of a number of
conditions, as further described in the Offering Memorandum, one or more of
which conditions may not occur.

      1.3 The Purchase Price will be placed in escrow pursuant to an escrow
agreement by and among, the Company, Amerasia and Gottbetter & Partners, LLP, as
escrow agent (the "Escrow Agreement") and shall be paid over to the Company at
the closing of the purchase of the Units in the Offering (the "Closing") to
occur on the Closing Date.

      1.4 The certificates for the Common Stock and warrants underlying the
Units bearing the name of the Subscriber will be delivered by the Company no
later than fifteen (15) days following the Closing Date. The Subscriber hereby
authorizes and directs the Company to deliver the securities to be issued to
such Subscriber pursuant to this Subscription Agreement to the residential or
business address indicated in the Investor Questionnaire attached hereto as
Exhibit A (the "Investor Questionnaire").

      1.5 The Purchase Price for the Units purchased hereunder shall be paid
only by (i) certified check, payable to Gottbetter & Partners, LLP, as escrow
agent or (ii) by wire transfer to Gottbetter & Partners, LLP pursuant to the
following instructions:


         BANK: CITIBANK, N.A., 330 Madison Avenue, New York, New York

         ABA:  021000089

         BENEFICIARY:  Gottbetter & Partners, LLP

         ACCOUNT:  49061322

         REFERENCE:  "EST - [insert your name]"


Gottbetter & Partners Accounting Contact: Vincent DiPaola (212) 400-6916
[vdp@gottbetter.com]

      1.6 The Company and Amerasia may, in their sole discretion, reject any
subscription, in whole or in part, or terminate or withdraw the Offering in its
entirety at any time prior to a closing thereof. The Company shall not be
required to allocate Units among investors on a pro rata, or any other, basis in
the event of over-subscription therefor.

      2. Representations and Covenants of Subscriber

      2.1 The Subscriber recognizes that the purchase of Units involves a high
degree of risk in that (i) the Company will need additional capital but has no
assurance of obtaining such additional necessary capital; (ii) an investment in
the Company is highly speculative and only investors who can afford the loss of
their entire investment should consider investing in the Company and the Units;
(iii) an investor may not be able to liquidate his investment; (iv)
transferability of the Units and the underlying warrants and Common Stock is
extremely limited; and (v) an investor could sustain the loss of his entire
investment.

                                       2
<PAGE>

      2.2 The Subscriber represents that he is an "accredited investor" as such
term is defined in Rule 501 of Regulation D promulgated under the Act, as
indicated by his responses to the Investor Questionnaire, and that he or it is
able to bear the economic risk of an investment in the Units. The Subscriber
must complete the Investor Questionnaire to enable the Company and Amerasia to
assess the Subscriber's eligibility for the Offering.

      2.3 The Subscriber acknowledges that he has prior investment experience,
including investment in non-listed and non-registered securities, or he has
employed the services of an investment advisor, attorney or accountant to read
all of the documents furnished or made available by the Company or Amerasia both
to him and to all other prospective investors in the Units and to evaluate the
merits and risks of such an investment on his behalf, and that he recognizes the
highly speculative nature of this investment.

      2.4 The Subscriber hereby represents that he has been furnished or given
access by the Company or EST during the course of this Offering with or to all
information regarding the Company and EST and their respective financial
conditions and results of operations which he had requested or desired to know;
that all documents which could be reasonably provided have been made available
for his inspection and review; that he has been afforded the opportunity to ask
questions of and receive answers from duly authorized representatives of the
Company and EST concerning the terms and conditions of the Offering, and any
additional information which he had requested.

      2.5 The Subscriber acknowledges that this Offering of Units may involve
tax consequences. The Subscriber acknowledges that he must retain his own
professional advisors to evaluate the tax and other consequences of an
investment in the Units.

      2.6 The Subscriber acknowledges that this Offering of Units has not been
reviewed or approved by the United States Securities and Exchange Commission
("SEC") because the Offering is intended to be a nonpublic offering pursuant to
Section 4(2) of the Act. The Subscriber represents that the Units are being
purchased for his own account, for investment and not for distribution or resale
to others. The Subscriber agrees that he will not sell or otherwise transfer the
Units or the underlying warrants or Common Stock unless it is registered under
the Act or unless an exemption from such registration is available and, upon the
Company's request, the Company receives an opinion of counsel reasonably
satisfactory to the Company confirming that an exemption from such registration
is available for such sale or transfer.

      2.7 The Subscriber understands that neither the Units nor the underlying
warrants or Common Stock have been registered under the Act by reason of a
claimed exemption under the provisions of the Act which depends, in part, upon
his investment intention. The Subscriber realizes that, in the view of the SEC,
a purchase now with an intent to distribute would represent a purchase with an
intent inconsistent with his representation to the Company, and the SEC might
regard such a distribution as a deferred sale to which such exemption is not
available.

      2.8 The Subscriber understands that Rule 144 ("Rule 144") promulgated
under the Act requires, among other conditions, a one year holding period prior
to the resale (in limited amounts) of securities acquired in a non-public
offering, such as the Offering, without having to satisfy the registration
requirements under the Act. The Subscriber understands that the Company makes no
representation or warranty regarding its fulfillment in the future of any
reporting requirements under the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), or its dissemination to the public of any current
financial or other information concerning the Company, as is required by Rule
144 as one of the conditions of its availability. The Subscriber consents that
the Company may, if it desires, permit the transfer of the Units, the underlying
warrants and the Common Stock out of his name only when his request for transfer
is accompanied by an opinion of counsel reasonably satisfactory to the Company
that neither the sale nor the proposed transfer results in a violation of the

                                       3
<PAGE>

Act or any applicable state "blue sky" laws (collectively, "Securities Laws").
The Subscriber agrees to hold the Company, Amerasia and their respective
directors, officers and controlling persons and their respective heirs,
representatives, successors and assigns harmless and to indemnify them against
all liabilities, costs and expenses incurred by them as a result of any
misrepresentation made by him contained herein or in the Investor Questionnaire
or any sale or distribution by the undersigned Subscriber in violation of any
Securities Laws.

      2.9 The Subscriber consents to the placement of one or more legends on any
certificate or other document evidencing his Units and the underlying warrants
and Common Stock stating that it has not been registered under the Act and
setting forth or referring to the restrictions on transferability and sale
thereof.

      2.10 The Subscriber understands that the Company and Amerasia will review
this Subscription Agreement and the Investor Questionnaire and are hereby given
authority by the undersigned to call his bank or place of employment or
otherwise review the financial standing of the Subscriber; and it is further
agreed that the Company and Amerasia reserve the unrestricted right to reject or
limit any subscription and to close the offer at any time.

      2.11 The Subscriber hereby represents that the address of Subscriber
furnished by him at the end of this Subscription Agreement and in the Investor
Questionnaire is the undersigned's principal residence if he is an individual or
its principal business address if it is a corporation or other entity.

      2.12 The Subscriber acknowledges that if the Subscriber is a Registered
Representative of a National Association of Securities Dealers, Inc. ("NASD")
member firm, he must give such firm the notice required by the NASD Conduct
Rules, or any applicable successor rules of the NASD, receipt of which must be
acknowledged by such firm on the signature page hereof. The Subscriber shall
also notify the Company if the Subscriber or any affiliate of Subscriber is a
registered broker-dealer with the SEC, in which case the Subscriber represents
that the Subscriber is purchasing Units in the ordinary course of business and,
at the time of purchase of the Units, has no agreements or understandings,
directly or indirectly, with any person to distribute the Units or the
underlying warrants or Common Stock or any portion thereof.

      2.13 The Subscriber hereby represents that no representations or
warranties have been made to the Subscriber by either the Company or Amerasia or
their agents, employees or affiliates and in entering into this transaction, the
Subscriber is not relying on any information, other than that contained in the
Offering Documents and the results of independent investigation by the
Subscriber.

      2.14 The Subscriber agrees that he will purchase securities in the
Offering only if his intent at such time is to make such purchase for investment
purposes and not with a view toward resale.

                                       4
<PAGE>

      2.15 If the undersigned Subscriber is a partnership, corporation, trust or
other entity, such partnership, corporation, trust or other entity further
represents and warrants that: (i) it was not formed for the purpose of investing
in the Company; (ii) it is authorized and otherwise duly qualified to purchase
and hold the Units and the underlying warrants and Common Stock; and (iii) that
this Subscription Agreement has been duly and validly authorized, executed and
delivered and constitutes the legal, binding and enforceable obligation of the
undersigned.

      2.16 If the Subscriber is not a United States person, such Subscriber
hereby represents that it has satisfied itself as to the full observance of the
laws of its jurisdiction in connection with any invitation to subscribe for the
Units or any use of this Subscription Agreement, including (i) the legal
requirements within its jurisdiction for the purchase of the Units, (ii) any
foreign exchange restrictions applicable to such purchase, (iii) any
governmental or other consents that may need to be obtained, and (iv) the income
tax and other tax consequences, if any, that may be relevant to the purchase,
holding, redemption, sale or transfer of the Units or the underlying warrants or
Common Stock. Such Subscriber's subscription and payment for, and his or her
continued beneficial ownership of the Units or the underlying warrants or Common
Stock will not violate any applicable securities or other laws of the
Subscriber's jurisdiction.

      2.17 The undersigned hereby covenants and agrees that it will not have an
open position (e.g., short sale) in the Units or the underlying warrants or
Common Stock prior to the Registration Statement (as defined below) being
declared effective by the SEC with the intent of covering such open position
with Units, warrants or Common Stock being registered in the Registration
Statement. The undersigned hereby acknowledges and understands that the SEC has
taken the position that such an open position would constitute a violation of
Section 5 of the Act. 2.18 The Subscriber acknowledges that (i) he may learn or
become aware of material, non-public information concerning the Company within
the meaning of Regulation FD promulgated by the SEC, and (ii) the Subscriber is
obtaining such material, non-public information solely for the purpose of
considering whether to purchase the Units pursuant to a private placement that
is exempt from registration under the Act. In accordance with Regulation FD, the
Subscriber agrees to keep such information confidential and not to disclose it
to any other person or entity except the Subscriber's legal counsel, other
advisors and other representatives who have agreed to (X) keep such information
confidential, (Y) use such information only for the purpose set forth above, and
(Z) comply with applicable securities laws with respect to such information. In
addition, the Subscriber further acknowledges that the Subscriber and such legal
counsel, other advisors and other representatives are prohibited from trading in
the Company's securities while in possession of material, non-public information
and agrees to refrain from purchasing or selling securities of the Company until
such material, non-public information has been publicly disseminated by the
Company. The Subscriber agrees to indemnify and hold harmless the Company and
Amerasia and EST and their respective officers, directors, employees,
subsidiaries and affiliates and each other person, if any, who controls any of
the foregoing, against any loss, liability, claim, damage and expense whatsoever
(including, but not limited to, any and all expenses whatsoever reasonably
incurred in investigating, preparing or defending against any litigation
commenced or threatened or any claim whatsoever) arising out of or based upon
any false representation or warranty by the Subscriber, or the Subscriber's
breach of, or failure to comply with, any covenant or agreement made by the
Subscriber herein or in any other document furnished by the Subscriber to the
Company or its officers, directors, employees or affiliates or each other
person, if any, who controls any of the foregoing in connection with this
transaction.

                                       5
<PAGE>

      2.19 The Subscriber understands and acknowledges that (i) the Units are
being offered and sold to Subscriber without registration under the Act in a
private placement that is exempt from the registration provisions of the Act
under Section 4(2) of the Act and (ii) the availability of such exemption
depends in part on, and that the Company will rely upon the accuracy and
truthfulness of, the foregoing representations, and such Subscriber hereby
consents to such reliance.

      3. Representations by the Company, Amerasia and EST

            Except as set forth in the reports filed by the Company pursuant to
the Exchange Act (the "SEC Reports"), each of the Company and, as applicable,
Amerasia and EST severally represent and warrant to the Subscriber that:

      3.1 Organization and Authority. The Company, Amerasia and EST, and each of
their respective subsidiaries, (i) is a corporation or limited partnership duly
organized, validly existing and in good standing under the laws of the
jurisdiction of its incorporation or formation, (ii) has all requisite corporate
or limited partnership power and authority to own, lease and operate its
properties and to carry on its business as presently conducted, and (iii) has
all requisite corporate or limited partnership power and authority to execute,
deliver and perform their obligations under this Subscription Agreement and the
Offering Documents being executed and delivered by it in connection herewith,
and to consummate the transactions contemplated hereby and thereby.

      3.2 Qualifications. The Company, Amerasia, EST, and each of their
respective subsidiaries, is duly qualified to do business as a foreign
corporation or other entity and is in good standing in all jurisdictions where
such qualification is necessary and where failure so to qualify could have a
material adverse effect on the business, properties, operations, condition
(financial or other), results of operations or prospects of the Company,
Amerasia and EST, and each of their respective subsidiaries, taken as a whole.

      3.3 Capitalization of the Company. The capitalization of the Company as of
September 30, 2004, is as described in the Company's Form 10-QSB for the nine
months ended September 30, 2004. The Company has not issued any capital stock
since such date other than pursuant to the conversion or exercise of outstanding
common stock equivalents or as contemplated by the Merger Agreement. No person
has any right of first refusal, preemptive right, right of participation, or any
similar right to participate in the transactions contemplated by the Offering
Documents. Except as a result of the purchase and sale of the Units, as
contemplated in the Merger Agreement or as disclosed in the SEC Reports, there
are no outstanding options, warrants, script rights to subscribe to, calls or
commitments of any character whatsoever relating to, or securities, rights or
obligations convertible into or exchangeable for, or giving any person any right
to subscribe for or acquire from the Company, any shares of Common Stock, or
contracts, commitments, understandings or arrangements by which the Company or
any subsidiary is or may become bound to issue additional shares of Common
Stock, or securities or rights convertible or exchangeable into shares of Common
Stock. The issuance and sale of the Units will not obligate the Company to issue
shares of Common Stock or other securities to any person (other than the
Subscribers) and will not result in a right of any holder of Company securities
to adjust the exercise, conversion, exchange or reset price under such
securities. The outstanding shares of capital stock of the Company have been
duly authorized and validly issued and are fully paid and nonassessable. None of
the outstanding shares of Common Stock or options, warrants, or rights or other
securities entitling the holders to acquire Common Stock has been issued in
violation of the preemptive rights of any security holder of the Company. No
holder of any of the Company's securities has any rights, "demand," "piggy-back"
or otherwise, to have such securities registered by reason of the intention to
file, filing or effectiveness of the Registration Statement (as defined below).
The Units and the underlying warrants to be issued to the Subscriber has been
duly authorized, and when issued and paid for in accordance with this
Subscription Agreement will be valid obligations of the Company, and the Common
Stock to be issued to the Subscriber has been duly authorized, and when issued
and paid for in accordance with this Subscription Agreement will be duly and
validly issued, fully paid and non-assessable. The Common Stock is eligible for
quotation on the NASD OTC Bulletin Board, the Company and the Common Stock meet
the criteria for continued quotation and trading on the OTC Bulletin Board, and
no suspension of trading in the Common Stock is in effect.

                                       6
<PAGE>

      3.4 Corporate Authorization. This Subscription Agreement, assuming due
execution and delivery by the Subscriber, when executed and delivered by the
Company and Amerasia, will be, a valid and binding obligation of the Company and
Amerasia enforceable in accordance with its terms, except as the enforceability
hereof and thereof may be limited by bankruptcy, insolvency, reorganization,
moratorium or other similar laws now or hereafter in effect relating to or
affecting creditors' rights generally and general principles of equity,
regardless of whether enforcement is considered in a proceeding in equity or at
law.

      3.5 Non-Contravention. The execution and delivery of this Subscription
Agreement by the Company and Amerasia, the issuance of the Units and the
warrants and Common Stock underlying the Units and the completion by the Company
and Amerasia of the other transactions contemplated by the Merger Agreement do
not and will not, with or without the giving of notice or the lapse of time, or
both, (i) result in any violation of any provision of the articles of
incorporation or by-laws or similar instruments of the Company or Amerasia or
EST or their respective subsidiaries, (ii) conflict with or result in a breach
by the Company or Amerasia or EST or their respective subsidiaries of any of the
terms or provisions of, or constitute a default under, or result in the
modification of, or result in the creation or imposition of any lien, security
interest, charge or encumbrance upon any of the properties or assets of the
Company or Amerasia or EST or their respective subsidiaries pursuant to, any
indenture, mortgage, deed of trust or other agreement or instrument to which the
Company or Amerasia or EST or any of their respective subsidiaries is a party or
by which the Company or Amerasia or EST or any of their respective subsidiaries
or any of their respective properties or assets are bound or affected, in any
such case which would have a material adverse effect on the business,
properties, operations, condition (financial or other), results of operations or
prospects of the Company, Amerasia and EST and their respective subsidiaries,
taken as a whole, (iii) violate or contravene any applicable law, rule or
regulation or any applicable decree, judgment or order of any court, United
States federal or state regulatory body, administrative agency or other
governmental body having jurisdiction over the Company or Amerasia or EST or any
of their respective subsidiaries or any of their respective properties or assets
which would have a material adverse effect on the business, properties,
operations, condition (financial or other), results of operations or prospects
of the Company, Amerasia, and EST and their respective subsidiaries, taken as a
whole, or (iv) have any material adverse effect on any permit, certification,
registration, approval, consent, license or franchise necessary for the Company,
Amerasia or EST or their respective subsidiaries to own or lease and operate any
of its properties and to conduct any of its business or the ability of the
Company, Amerasia or EST or any of their respective subsidiaries to make use
thereof.

                                       7
<PAGE>

      3.6 Information Provided. The Company hereby represents and warrants to
the Subscriber that the SEC Reports and any other information provided by or on
behalf of the Company to the Subscriber in connection with the transactions
contemplated by this Subscription Agreement, does not contain any untrue
statement of a material fact or omit to state any material fact necessary in
order to make the statements therein, in the light of the circumstances under
which they are made, not misleading, it being understood that for purposes of
this Section 3.6, any statement contained in such information shall be deemed to
be modified or superseded for purposes of this Section 3.6 to the extent that a
statement in any document included in such information which was prepared and
furnished to the Subscriber on a later date or filed with the SEC on a later
date modifies or replaces such statement, whether or not such later prepared and
furnished or filed statement so states. Amerasia hereby represents and warrants
to the Subscriber that any information provided by or on behalf of Amerasia or
EST to the Subscriber in writing in connection with the transactions
contemplated by this Subscription Agreement, does not contain any untrue
statement of a material fact or omit to state any material fact necessary in
order to make the statements therein, in the light of the circumstances under
which they are made, not misleading.

      3.7 Absence of Certain Proceedings. Except as disclosed in the SEC
Reports, there is no action, suit, proceeding, inquiry or investigation before
or by any court, public board or body, or governmental agency pending or, to the
knowledge of the Company or Amerasia, threatened against or affecting the
Company or Amerasia or EST or any of their respective subsidiaries, in any such
case wherein an unfavorable decision, ruling or finding would have a material
adverse effect on the business, properties, operations, condition (financial or
other), results of operations or prospects of the Company, Amerasia or EST, or
which could adversely affect the validity or enforceability of, or the authority
or ability of the Company, Amerasia or EST to perform its obligations under, the
Offering Documents; and to the best of the Company's, Amerasia's and EST's
knowledge there is not pending or contemplated any, and there has been no,
investigation by the SEC involving the Company, Amerasia or EST or any of their
current or former directors or officers.

      3.8 Compliance with Law. Neither the Company nor Amerasia nor EST nor any
of their respective subsidiaries is in violation of or has any liability under
any statute, law, rule, regulation, ordinance, decision or order of any
governmental agency or body or any court, domestic or foreign, except where such
violation or liability would not individually or in the aggregate have a
material adverse effect on the business, properties, operations, condition
(financial or other), results of operations or prospects of the Company and its
subsidiaries, taken as a whole; and to the knowledge of the Company, Amerasia
and EST there is no pending investigation which would reasonably be expected to
lead to such a claim.

      3.9 Tax Matters. The Company, Amerasia and EST and each of their
respective subsidiaries has filed all federal, state and local income and
franchise tax returns required to be filed and has paid all taxes shown by such
returns to be due, and no tax deficiency has been determined adversely to the
Company, Amerasia or EST or any of their respective subsidiaries which has had
(nor does the Company or Amerasia or EST or any of their respective subsidiaries
have any knowledge of any tax deficiency which, if determined adversely to the
Company or Amerasia or any of their respective subsidiaries, might have) a
material adverse effect on the business, properties, operations, condition
(financial or other), results of operations, or prospects of the Company or
Amerasia or any of their respective subsidiaries, taken as a whole.

                                       8
<PAGE>

      4. "Piggy-Back" and "Demand" Registration Rights.

      4.1 "Piggy-Back" Registration Right. Subject to Section 4.5 et seq.,
should the Company decide to register any of its Common Stock or securities
convertible into or exchangeable for Common Stock under the Securities Act (a
"Registration") on a form that is suitable for an offering of shares of Common
Stock by the Company or by third parties and that is not a registration solely
to implement an employee benefit plan on Commission Form S-8, a registration
statement on Commission Form S-4 (or successor form) or a transaction to which
Rule 145 or any other similar rule of the Commission is applicable (such form, a
"Registration Statement"), the Company shall give written notice to the
Subscribers of its intention to effect such a Registration. Subject to Section
4.2 below, the Company shall use all reasonable efforts to effect Registration
under the Securities Act of all Units and the underlying warrants and Common
Stock ("Registrable Securities") that the Subscribers request be included in
such Registration by a written notice delivered to the Company within thirty
(30) days after the notice given by the Company. Each of the Holders agrees that
any Registrable Securities which such Subscriber requests to be included in a
Registration pursuant to this Section 4 shall be included by the Company on the
same form of Registration Statement as selected for the Registration.

      4.2 If a Registration involves an underwritten offering, the Company shall
not be required to register securities in excess of the amount that the
principal underwriter reasonably and in good faith recommends in writing for
inclusion in such offering (a "Cutback"), a copy of which recommendation, and
supporting reasoning, shall be delivered to each Subscriber. If such a Cutback
occurs, the number of shares that are entitled to be included in the
Registration and underwriting shall be allocated in the following manner: (i)
first, to the Company for any securities it proposes to sell for its own
account, (ii) second, to any Person with demand registration rights requiring
such registration, and (iii) third, to the Subscribers and other holders of
Company securities with piggy-back registration rights requesting inclusion in
the Registration, pro rata among the respective holders thereof on the basis of
the number of shares for which each such requesting holder has requested
registration.

      4.3 If the Registration of which the Company gives notice is for an
underwritten public offering, the Company shall so advise the Subscribers as a
part of the written notice given pursuant to Section 4.1. In such event, the
right of any Subscriber to have its Registrable Securities included in the
Registration pursuant to this Section 4 shall be conditioned upon such
Subscriber's participation in such underwriting and the inclusion of such
Subscriber's Registrable Securities in the underwriting to the extent provided
herein. All Subscribers proposing to distribute their securities through such
underwriting shall (together with the Company and its other security holders
with registration rights to participate therein distributing their securities
through such underwriting) enter into an underwriting agreement in customary
form with the representative of the underwriters or the managing underwriter
selected by the Company.

      4.4 If the Company elects to terminate any Registration after a
Registration Statement for such Registration shall have been filed, the Company
will have no obligation to register the Registrable Securities that the
Subscribers sought to have included in such Registration. The Company shall bear

                                       9
<PAGE>

all Registration Expenses of the Subscribers in connection with any
Registration. All underwriting discounts, selling commissions and expense
allowances applicable to the sale by Subscriber of Registrable Securities and
all fees and disbursements of counsel for the Subscriber shall be borne by the
Subscriber.

      4.5 "Demand" Registration Right. Notwithstanding the provisions of Section
4.1 through and including Section 4.4 hereof, at any time after 120 days after
the Closing Date, upon one (1) occasion only, upon the election of those owning
not less than 50% of those outstanding Registrable Securities, the Subscriber
may demand registration under the Securities Act ("Demand Registration") for an
offering of all or any portion of the Registrable Securities by sending written
notice of the demand to the Company. Such notice shall specify the number of the
Registrable Securities sought to be registered. The Company will then use its
commercial best efforts to file with the Securities and Exchange Commission (the
"SEC"), at the earliest possible date ("Filing Date") but no later than sixty
(60) days following such a demand, a registration statement for the Demand
Registration. The Company shall use reasonable best efforts to cause such Demand
Registration Statement to become effective within one hundred and fifty (150)
days after the date so filed with the Securities and Exchange Commission.
Failure to timely file the Demand Registration Statement or obtain its
effectiveness within 150 days of the Filing Date shall require the Company to
make a cash payment, as liquidated damages, to the Subscriber of 1% of the
Purchase Price of the Common Stock sold to the Subscriber under this
Subscription Agreement per month for each full calendar month of such failure.
After the Filing Date and prior to the date the Registration Statement is
declared effective, the Company shall not file with the SEC any other new
registration statement under the Securities Act, other than a Form S-4 or a Form
S-8 registration statement, with respect to any securities of the Company.

      4.6 Registration of Other Securities. Whenever the Company shall effect a
Demand Registration, no shares of Common Stock owned by other stockholders of
the Company other than the Registrable Securities shall be included among the
shares of Common Stock covered by such registration statement other than shares
of Common Stock issued in connection with additional financing of up to $7.0
million subsequent to the Closing Date or unless the Purchaser shall have
consented in writing to the inclusion of such other shares of Common Stock.

      4.7 Expenses. The Company will pay all of the registration expenses of the
Subscribers in connection with any Demand Registration. All underwriting
discounts, selling commissions and expense allowances applicable to the sale by
Subscriber of Registrable Securities and all fees and disbursements of counsel
for the Subscriber shall be borne by the Subscriber.

      4.8 Indemnification.

            (a) To the extent permitted by law the Company will indemnify each
Subscriber, each of its officers, directors, agents, employees and partners, and
each person controlling such Subscriber, with respect to each registration,
qualification or compliance effected pursuant to this Subscription Agreement,
and each underwriter, if any, and each person who controls any underwriter, and
their respective counsel against all claims, losses, damages and liabilities (or
actions, proceedings or settlements in respect thereof) arising out of or based
on any untrue statement (or alleged untrue statement) of a material fact
contained in any prospectus, offering circular or other document prepared by the
Company (including any related registration statement, notification or the like)
incident to any such registration, qualification or compliance, or based on any
omission (or alleged omission) to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading, or
any violation by the Company of the Act or any rule or regulation thereunder
applicable to the Company and relating to action or inaction required of the
Company in connection with any such registration, qualification or compliance,
and will reimburse each such Subscriber, each of its officers, directors,
agents, employees and partners, and each person controlling such Subscriber,
each such underwriter and each person who controls any such underwriter, for any
legal and any other expenses as they are reasonably incurred in connection with
investigating and defending any such claim, loss, damage, liability or action,
provided that the Company will not be liable in any such case to the extent that
any such claim, loss, damage, liability or expense arises out of or is based on
any untrue statement (or alleged untrue statement) or omission (or alleged
omissions) based upon written information furnished to the Company by such
Subscriber or underwriter; provided, however, that the indemnity agreement
contained in this subsection shall not apply to amounts paid in settlement of

                                       10
<PAGE>

any such loss, claim, damage, liability or action if such settlement is effected
without the consent of the Company (which consent shall not be unreasonably
withheld), nor shall the Company be liable in any such case for any such loss,
claim, damage, liability or action to the extent that it arises out of or is
based upon a violation which occurs in reliance upon and in conformity with
written information furnished expressly for use in connection with such
registration by such Subscriber, partner, officer, director, employee, agent,
underwriter or controlling person of such Subscriber, provided, however, that
the obligations of the Company hereunder shall be limited to an amount equal to
the portion of net proceeds represented by the Registrable Securities pursuant
to this Subscription Agreement.

            (b) To the extent permitted by law, each Subscriber whose
Registrable Securities are included in any registration, qualification or
compliance effected pursuant to this Subscription Agreement will indemnify the
Company and Amerasia and their respective directors, officers, agents,
employees, subsidiaries, affiliates and each underwriter, if any, of the
Company's securities covered by such a registration statement, each person who
controls the Company or such underwriter within the meaning of the Act and the
rules and regulations thereunder, each other such Subscriber and each of their
officers, directors, partners, agents and employees, and each person controlling
such Subscriber, and their respective counsel against all claims, losses,
damages and liabilities (or actions in respect thereof) arising out of or based
on any untrue statement (or alleged untrue statement) of a material fact
contained in any such registration statement, prospectus, offering circular or
other document, or any omission (or alleged omission) to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading, and will reimburse the Company and Amerasia and such
Subscribers, directors, officers, partners, persons, underwriters or control
persons for any legal or any other expenses as they are reasonably incurred in
connection with investigating or defending any such claim, loss, damage,
liability or action, in each case to the extent, but only to the extent, that
such untrue statement (or alleged untrue statement) or omission (or alleged
omission) is made in such registration statement, prospectus, offering circular
or other document in reliance upon and in conformity with written information
furnished to the Company by such Subscriber; provided, however, that the
obligations of any Subscriber hereunder shall be limited to an amount equal to
the net proceeds to such Subscriber from Registrable Securities sold under such
registration statement, prospectus, offering circular or other document as
contemplated herein; provided, further, that the indemnity agreement contained
in this subsection shall not apply to amounts paid in settlement of any such
loss, claim, damage, liability or action if such settlement is effected without
the consent of the Subscriber, which consent shall not be unreasonably withheld
or delayed.

                                       11
<PAGE>

            (c) Each party entitled to indemnification under this Section (the
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or any litigation resulting
therefrom, shall be approved by the Indemnified Party (whose approval shall not
unreasonably be withheld or delayed), and the Indemnified Party may participate
in such defense at such Indemnified Party's expense; and provided further that
if any Indemnified Party reasonably concludes that there may be one or more
legal defenses available to it that are not available to the Indemnifying Party,
or that such claim or litigation involves or could have an effect on matters
beyond the scope of this Subscription Agreement, then the Indemnified Party may
retain its own counsel at the expense of the Indemnifying Party; and provided
further that the failure of any Indemnified Party to give notice as provided
herein shall not relieve the Indemnifying Party of its obligations under this
Subscription Agreement unless and only to the extent that such failure to give
notice results in material prejudice to the Indemnifying Party. No Indemnifying
Party, in the defense of any such claim or litigation, shall, except with the
consent of each Indemnified Party, consent to entry of any judgment or enter
into any settlement which does not include as an unconditional term thereof the
giving by the claimant or plaintiff to such Indemnified Party of a release from
all liability in respect to such claim or litigation. Each Indemnified Party
shall furnish such information regarding itself or the claim in question as an
Indemnifying Party may reasonably request in writing and as shall be reasonably
required in connection with defense of such claim and litigation resulting
therefrom.

            (d) If the indemnification provided for in this Section is held by a
court of competent jurisdiction to be unavailable to an Indemnified Party with
respect to any loss, liability, claim, damage or expense referred to herein,
then the Indemnifying Party, in lieu of indemnifying such Indemnified Party
hereunder, shall contribute to the amount paid or payable by such Indemnified
Party as a result of such loss, liability, claim, damage or expense in such
proportion as is appropriate to reflect the relative fault of the Indemnifying
Party on the one hand and of the Indemnified Party on the other in connection
with the statements or omissions which resulted in such loss, liability, claim,
damage or expense as well as any other relevant equitable considerations. The
relative fault of the Indemnifying Party and of the Indemnified Party shall be
determined by reference to, among other things, whether the untrue or alleged
untrue statement of a material fact or the omission to state a material fact
relates to information supplied by the Indemnifying Party or by the Indemnified
Party and the parties' relative intent, knowledge, access to information and
opportunity to correct or prevent such statement or omission.

      4.9 Transfer or Assignment of Registration Rights. The benefits to the
Subscriber hereunder may be transferred or assigned by the Subscriber to a
permitted transferee or assignee of any of the Registrable Securities, provided
that the Company is given written notice that such right has been transferred,
stating the name and address of said transferee or assignee and identifying the
securities with respect to which such registration rights are being transferred
or assigned; provided further that the transferee or assignee of such rights
shall be deemed to have assumed the obligations of the Subscriber under this
Subscription Agreement by the acceptance of such assignment and shall, upon
request from the Company, evidence such assumption by delivery to the Company of
a written agreement assuming such obligations of the Subscriber.

                                       12
<PAGE>

      4.10 Registration Procedures. In the case of the registration effected by
the Company pursuant to this Subscription Agreement, the Company will keep the
Subscriber advised in writing as to the initiation of each registration and as
to the completion thereof. The Company will:

            (a) Prepare and file with the SEC such amendments and supplements to
such registration statement and the prospectus used in connection with such
registration statement as may be necessary to comply with the provisions of the
Act with respect to the disposition of securities covered by such registration
statement;

            (b) Respond as promptly as reasonably practicable to any comments
received from the SEC with respect to a registration statement or any amendment
thereto;

            (c) Notify the Subscriber as promptly as reasonably practicable and
(if requested by any such person) confirm such notice in writing no later than
one trading day following the day (A) when a prospectus or any prospectus
supplement or post-effective amendment to a registration statement is proposed
to be filed and (B) with respect to a registration statement or any
post-effective amendment, when the same has become effective;

            (d) Furnish such number of prospectuses and other documents incident
thereto, including supplements and amendments, as the Subscriber may reasonably
request;

            (e) Furnish to the Subscriber, upon request, a copy of all documents
filed with and all correspondence from or to the SEC in connection with any such
registration statement other than non-substantive cover letters and the like, to
the extent such items do not constitute material, non-public information;

            (f) Use its reasonable best efforts to avoid the issuance of, or, if
issued, obtain the withdrawal of (i) any order suspending the effectiveness of a
registration statement, or (ii) any suspension of the qualification (or
exemption from qualification) of any of the Registrable Securities for sale in
any jurisdiction, at the earliest practicable moment; and

            (g) Use its reasonable best efforts to comply with all applicable
rules and regulations of the SEC.

Notwithstanding the foregoing, if at any time or from time to time after the
date of effectiveness of the Registration Statement, the Company notifies the
Subscriber in writing of the existence of an event or circumstance that is not
disclosed in the Registration Statement and that may have a material effect on
the Company or its business (a "Potential Material Event"), the Subscriber shall
not offer or sell any Registrable Securities, or engage in any other transaction
involving or relating to the Registrable Securities, from the time of the giving
of notice with respect to a Potential Material Event until the Company notifies
the Subscriber that such Potential Material Event either has been added to the
Registration Statement by amendment or supplement or no longer constitutes a
Potential Material Event; provided, that the Company may not so suspend the
right of Subscriber for more than 120 days in the aggregate.

                                       13
<PAGE>

      4.11 Statement of Beneficial Ownership. The Company may require the
Subscriber to furnish to the Company a certified statement as to the number of
shares of Common Stock beneficially owned by such Subscriber and the controlling
person thereof and any other such information regarding the Subscriber, the
Registrable Securities held by the Subscriber and the intended method of
disposition of such securities as shall be reasonably required with respect to
the registration of the Subscriber's Registrable Securities. The Subscriber
hereby understands and agrees that the Company may, in its sole discretion,
exclude the Subscriber's shares of Common Stock from the Registration Statement
in the event that the Subscriber fails to provide such information within ten
(10) trading days of the request therefor by the Company.

      4.12 Compliance. Subscriber covenants and agrees that such Subscriber will
comply with the prospectus delivery requirements of the Act as applicable to
such Subscriber in connection with sales of Registrable Securities pursuant to
the Registration Statement required hereunder.

      5. Miscellaneous

      5.1 Any notice or other communication given hereunder shall be deemed
sufficient if in writing and sent by registered or certified mail, return
receipt requested, addressed to the Company, at Bluestone Ventures, Inc. at
11940 Old Yale Road, Surrey, British Columbia, Canada V3V 3X3 Attention: Edward
Wong, with a copy to (which copy shall not be deemed to provide notice)
Gottbetter & Partners, LLP, 488 Madison Avenue, 12th Floor, New York, New York
10022, Attention: Adam Gottbetter, Esq., prior to the Merger. Following the
Merger, any communication shall be sent by registered or certified mail, return
receipt requested, addressed to the Company at Electronic Sensor Technology,
1077 Business Center Circle, Newbury Park, California 91320, with a copy to
Richardson & Patel LLP, 10900 Wilshire Boulevard, Suite 500, Los Angeles,
California 90024, Attention: Ryan S. Hong, Esq., and to the Subscriber at his
address indicated on the signature page of this Subscription Agreement. Notices
shall be deemed to have been given three (3) business days after the date of
mailing, except notices of change of address, which shall be deemed to have been
given when received.

      5.2 This Subscription Agreement may be amended through a written
instrument signed by the Subscriber, Amerasia and the Company; provided,
however, that the terms of Section 4 of this Subscription Agreement may be
amended without the consent or approval of the Subscriber so long as such
amendment applies in the same fashion to the subscription agreements of all of
the other subscribers for Units in the Offering and at least holders of a
majority of the Units sold in the Offering have given their approval of such
amendment, which approval shall be binding on all holders of Units.

      5.3 This Subscription Agreement shall be binding upon and inure to the
benefit of the parties hereto and to their respective heirs, legal
representatives, successors and assigns. This Subscription Agreement sets forth
the entire agreement and understanding between the parties as to the subject
matter hereof and merges and supersedes all prior discussions, agreements and
understandings of any and every nature among them.

      5.4 Notwithstanding the place where this Subscription Agreement may be
executed by any of the parties hereto, the parties expressly agree that all the
terms and provisions hereof shall be construed in accordance with and governed
by the laws of the State of New York.

                                       14
<PAGE>

      5.5 This Subscription Agreement may be executed in counterparts. It shall
not be binding upon the Company and Amerasia unless and until it is accepted by
the Company and EST. Upon the execution and delivery of this Subscription
Agreement by the Subscriber, this Subscription Agreement shall become a binding
obligation of the Subscriber with respect to the purchase of Units as herein
provided; subject, however, to the right hereby reserved to the Company to enter
into the same agreements with other subscribers and to add or to delete other
persons as subscribers.

      5.6 The holding of any provision of this Subscription Agreement to be
invalid or unenforceable by a court of competent jurisdiction shall not affect
any other provision of this Subscription Agreement, which shall remain in full
force and effect.

      5.7 It is agreed that a waiver by either party of a breach of any
provision of this Subscription Agreement shall not operate, or be construed, as
a waiver of any subsequent breach by that same party.

      5.8 The parties agree to execute and deliver all such further documents,
agreements and instruments and take such other and further action as may be
necessary or appropriate to carry out the purposes and intent of this
Subscription Agreement.

      5.9 The Company agrees not to disclose the names, addresses or any other
information about the Subscribers, except as required by law, provided that the
Company may provide information relating to the Subscriber as required in any
registration statement under the Act that may be filed by the Company pursuant
to the requirements of this Subscription Agreement.

      5.10 The obligation of the Subscriber hereunder is several and not joint
with the obligations of any other subscribers for the purchase of Common Stock
in the Offering (the "Other Subscribers"), and the Subscriber shall not be
responsible in any way for the performance of the obligations of any Other
Subscribers. Nothing contained herein or in any other agreement or document
delivered at the Closing, and no action taken by the Subscriber pursuant hereto,
shall be deemed to constitute the Subscriber and the Other Subscribers as a
partnership, an association, a joint venture or any other kind of entity, or
create a presumption that the Subscriber and the Other Subscribers are in any
way acting in concert with respect to such obligations or the transactions
contemplated by this Subscription Agreement. The Subscriber shall be entitled to
protect and enforce the Subscriber's rights, including without limitation the
rights arising out of this Subscription Agreement, and it shall not be necessary
for any Other Subscriber to be joined as an additional party in any proceeding
for such purpose. The language used in this Agreement will be deemed to be the
language chosen by the parties to express their mutual intent, and no rules of
strict construction will be applied against any party. The Subscriber is not
acting as part of a "group" (as that term is used in Section 13(d) of the 1934
Act) in negotiating and entering into this Subscription Agreement or purchasing
the Common Stock or acquiring, disposing of or voting any of the underlying
shares of Common Stock or the Warrant Shares. The Company hereby confirms that
it understands and agrees that the Subscriber is not acting as part of any such
group.

                            [SIGNATURE PAGE FOLLOWS]


                                       15
<PAGE>

              IN WITNESS WHEREOF, the parties have executed this Subscription
Agreement as of the day and year first written above.


------------------------------              ------------------------------------
Signature of Subscriber                     Signature of Co-Subscriber

------------------------------              ------------------------------------
Name of Subscriber                          Name of Co-Subscriber
[please print]                              [please print]

------------------------------              ------------------------------------
Street Address of Subscriber                Street Address of Co-Subscriber

------------------------------              ------------------------------------
City, State and Zip Code of Subscriber      City, State and Zip Code of
                                            Co-Subscriber
------------------------------              ------------------------------------
Social Security or Taxpayer                 Social Security or Taxpayer
Identification Number of Subscriber         Identification Number of
                                            Co-Subscriber

------------------------------
Number of Shares of Common Stock
Subscribed For


Subscription Agreed to and Accepted by

BLUESTONE VENTURES INC.                      AMERASIA TECHNOLOGY, INC.

By:                                          By:
   ---------------------------------            --------------------------------
Name:                                        Name:
     -------------------------------              ------------------------------
Title:                                       Title:
      ------------------------------               -----------------------------
Date:                                        Date:
     -------------------------------              ------------------------------

ELECTRONIC SENSOR TECHNOLOGY, LP

By:      AMERASIA TECHNOLOGY, INC.,

Its General Partner

By:
   ---------------------------------
Name:                                        Name:
     -------------------------------              ------------------------------
Title:                                       Title:
      ------------------------------               -----------------------------
Date:                                        Date:
     -------------------------------              ------------------------------

                                       16