UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 16, 2016 (May 15, 2016)

Luminex Corporation

(Exact name of registrant as specified in its charter)

(512) 219-8020

(Registrant’s telephone number, including area code)

Not applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 1.01 Entry into a Material Definitive Agreement.

Merger Agreement

On May 15, 2016, Luminex Corporation, a Delaware corporation (the “Company”), Nanosphere, Inc., a Delaware corporation (“Nanosphere”), and Commodore Acquisition, Inc., a Delaware corporation and a wholly-owned subsidiary of the Company (“Merger Subsidiary”) entered into an Agreement and Plan of Merger (the “Merger Agreement”).

Pursuant to the Merger Agreement, and upon the terms and subject to the conditions thereof, the Company has agreed that it will commence a cash tender offer (the “Offer”) to acquire all of the shares of Nanosphere’s common stock, par value $0.01 per share (“Common Stock”) for a purchase price of $1.35 per share, net to the holders thereof, in cash (the “Offer Price”), without interest, subject to the terms and conditions of the Merger Agreement.

The Merger Agreement may be terminated under certain circumstances, including in specified circumstances in connection with superior proposals. Upon the termination of the Merger Agreement, under specified circumstances, Nanosphere will be required to pay the Company a termination fee of $2,250,000.

The Company has agreed to commence the Offer as promptly as reasonably practicable from the date of the Merger Agreement (but in no event later than fifteen (15) business days from the date of the Merger Agreement). The consummation of the Offer will be conditioned on (i) at least a majority of the issued and outstanding shares of the Common Stock as of the merger date having been validly tendered into and not withdrawn from the Offer, and (ii) other customary conditions.

The Merger Agreement provides that, as soon as practicable (but not more than three (3) business days) following the consummation of the Offer, Merger Subsidiary will merge with and into Nanosphere (the “Merger”), with Nanosphere surviving the Merger as a wholly-owned subsidiary of the Company. The Merger will be governed by Section 251(h) of the General Corporation Law of the State of Delaware (“DGCL”), with no stockholder vote required to consummate the Merger. In the Merger: (i) each tendered issued and outstanding share of Common Stock other than shares of Common Stock owned directly by the Company, Merger Subsidiary or Nanosphere (if any) or owned indirectly by any wholly-owned subsidiary of any of the foregoing (if any), shall be paid an amount equal to the Offer Price (the “Merger Consideration”), and (ii) each untendered issued and outstanding share of Common Stock (excluding shares held by a holder of Common Stock who, in the event Section 251(h) of the DGCL becomes unavailable as a means to effect the Merger, has not voted in favor of adoption of this Agreement or consented thereto in writing) which are held by a Person who is entitled to appraisal rights and who has properly exercised appraisal rights of such shares in accordance

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with Section 262 of the DGCL (such shares of Common Stock being referred to collectively as the “Dissenting Shares” until such time as such holder fails to perfect or otherwise loses such holder’s appraisal rights under the DGCL with respect to such shares) for so long as they shall be Dissenting Shares, shall be converted into the right to receive an amount equal to the Merger Consideration. Upon consummation of the Merger, shares of the issued and outstanding convertible preferred stock, par value $0.01 per share (the “Preferred Stock”) will be entitled upon conversion soley to an amount per share equal to the Offer Price (on an as if converted basis) without interest. The Merger Agreement also provides for the waiver of the non-compete covenants in the employment agreements of Michael McGarrity, Nanosphere’s President and Chief Executive Officer, and Kenneth Bahk, Nanosphere’s Chief Strategy Officer.

The foregoing description of the Merger Agreement is not complete and is qualified in its entirety by reference to the Merger Agreement, which is filed as Exhibit 2.1 to this Current Report on Form 8-K and is incorporated herein by reference.

The Merger Agreement and the foregoing description of the Merger Agreement have been included to provide investors and stockholders with information regarding the terms of the Merger Agreement. It is not intended to provide any other factual information about the Company. The representations, warranties and covenants contained in the Merger Agreement were made only as of specified dates for the purposes of such agreement, were solely for the benefit of the parties to such agreement and may be subject to qualifications and limitations agreed upon by such parties. In particular, in reviewing the representations, warranties and covenants contained in the Merger Agreement and discussed in the foregoing description, it is important to bear in mind that such representations, warranties and covenants were negotiated with the principal purpose of allocating risk between the parties, rather than establishing matters as facts. Such representations, warranties and covenants may also be subject to a contractual standard of materiality different from those generally applicable to stockholders and reports and documents filed with the U.S. Securities and Exchange Commission (the “SEC”). Investors and stockholders are not third-party beneficiaries under the Merger Agreement. Accordingly, investors and stockholders should not rely on such representations, warranties and covenants as characterizations of the actual state of facts or circumstances described therein. Information concerning the subject matter of such representations, warranties and covenants may change after the date of the Merger Agreement, which subsequent information may or may not be fully reflected in the parties’ public disclosures.

Item 7.01. Regulation FD Disclosure.

On May 16, 2016, Homi Shamir, the Chief Executive Officer of the Company, sent a letter to the employees of Nanosphere and a letter to the employees of Luminex. A copy of the letter to the employees of Nanosphere is furnished as Exhibit 99.1 hereto, and a copy of the letter to the employees of Luminex is furnished as Exhibit 99.2 hereto.

On May 16, 2016, the Company and Nanosphere issued a joint press release announcing the execution of the Merger Agreement described above. A copy of the press release is furnished as Exhibit 99.3 hereto.

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Item 8.01. Other Events.

In connection with the execution of the Merger Agreement, the directors and executive officers of Nanosphere (collectively, the “Stockholders”) have entered into certain Support Agreements, each dated as of May 15, 2016, with the Company (the “Support Agreements”). Subject to the terms and conditions of the Support Agreements, each Stockholder agreed, among other things, to tender shares of common stock of Nanosphere (representing in the aggregate approximately 3.8% of Nanosphere’s total issued and outstanding shares of common stock) into the Offer, and, subject to certain exceptions, not to transfer their shares that are subject to the Support Agreements in any competing offer. The Support Agreements will terminate with respect to a Stockholder upon the first to occur of (i) the valid termination of the Merger Agreement, (ii) the completion of the Merger, (iii) entry into an amendment or modification of the Merger Agreement or any waiver of Nanosphere’s rights under the Merger Agreement, in each case that results in a decrease in the Offer Price or (iv) mutual written consent of the Company and such Stockholder.

The foregoing description of the Support Agreements does not purport to be complete and is qualified in its entirety by reference to the Form of Support Agreement, which is furnished as Exhibit 99.4 hereto and is incorporated herein by reference.

Important Information

The tender offer described in this communication has not yet commenced. This communication is provided for informational purposes only and does not constitute an offer to purchase or the solicitation of an offer to sell any securities. At the time the tender offer is commenced, the Company and Merger Subsidiary intend to file with the SEC a Tender Offer Statement on Schedule TO containing an offer to purchase, a form of letter of transmittal and other documents relating to the tender offer, and Nanosphere intends to file with the SEC a Solicitation/Recommendation Statement on Schedule 14D-9 with respect to the tender offer. The Company, Merger Subsidiary, and Nanosphere intend to mail these documents to the Nanosphere common stockholders. Investors and shareholders should read those filings carefully when they become available as they will contain important information about the tender offer. Those documents, as well as the Company’s other public filings with the SEC, may be obtained without charge at the SEC’s website at www.sec.gov and at the Company’s website at www.luminexcorp.com.

Cautionary Statement Regarding Forward-Looking Statements

Certain statements in this press release, including statements regarding the proposed transaction between the Company and Nanosphere, the Company’s and Nanosphere’ financial results and estimates and/or business prospects, the combined company’s plans, objectives, expectations and intentions, leadership in biological testing technologies in the clinical diagnostic and life science industries and the expected size, scope and growth of the combined company’s operations and the markets in which it will operate, expected synergies, as well as the expected timing and benefits of the transaction, may contain words such as “expects,” “may,” “potential,” “upside,” “approximately,” “project,” “would,” “could,” “should,” “will,” “anticipates,” “believes,”

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“intends,” “estimates,” “targets,” “plans,” “envisions,” “seeks” and other similar language and are considered forward-looking statements or information under applicable securities laws. These statements are based on the Company’s current expectations, estimates, forecasts and projections about the proposed transaction and the operating environment, economies and markets in which the Company and Nanosphere operate, are subject to important risks and uncertainties that are difficult to predict and the actual outcome may be materially different. These statements reflect beliefs and assumptions that are based on the Company’s and Nanosphere’ perception of historical trends, current conditions and expected future developments as well as other factors management believes are appropriate in the circumstances. In making these statements, the Company and Nanosphere have made assumptions with respect to the ability of the Company and Nanosphere to achieve expected synergies and the timing of same, the ability of the Company and Nanosphere to predict and adapt to changing customer requirements, preferences and spending patterns, the ability of the Company and Nanosphere to protect their intellectual property, future capital expenditures, including the amount and nature thereof, trends and developments in the clinical diagnostic and life science industries, business strategy and outlook, expansion and growth of business and operations, credit risks, anticipated acquisitions, future results for the Company being similar to historical results, expectations related to future general economic and market conditions and other matters. The Company’s and Nanosphere’ beliefs and assumptions are inherently subject to significant business, economic, competitive and other uncertainties and contingencies regarding future events and as such, are subject to change. The Company’s beliefs and assumptions may prove to be inaccurate and consequently the Company’s actual results could differ materially from the expectations set out herein.

Actual results or events could differ materially from those contemplated in the forward-looking statements as a result of the following:

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Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

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Signature

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Dated: May 16, 2016

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EXHIBIT INDEX

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