The Dow Jones index closed above the $40,000 mark on Friday. When insiders purchase or sell shares, it indicates their confidence or concern around the company's prospects. Investors and traders interested in penny stocks can consider this a factor in their overall investment or trading decision.

Below is a look at a few recent notable insider transactions for penny stocks. For more, check out Benzinga's insider transactions platform.

Tecogen

• The Trade: Tecogen Inc. (OTC:TGEN) Director John Hatsopoulos bought a total of 3,000 shares at an average price of $0.75. To acquire these shares, it cost around $2,248.
• What's Happening: On May 8, Tecogen reported revenues of $6.2 million and net loss of $1.1 million for the quarter ended March 31.
• What Tecogen Does: Tecogen Inc, designs, manufactures, markets, and maintains high-efficiency, ultra-clean cogeneration products. It operates in three business segments, namely Products, Services, and Energy Production.

Standard BioTools

• The Trade: Standard BioTools Inc. (NASDAQ:LAB) Director Casdin Partners FO1-MSV, LP acquired a total of 1,352,072 shares at an average price of $2.56. To acquire these shares, it cost around $3.46 million.
• What's Happening: On May 8, Standard BioTools posted downbeat quarterly sales.
• What Standard BioTools Does: Standard BioTools Inc develops, manufactures, and sells technologies that help biomedical researchers in their search for developing medicines faster.

OPKO Health

• The Trade: OPKO Health, Inc. (NASDAQ:OPK) 10% owner Frost Gamma Investments Trust acquired a total of 163,997 shares at an average price of $1.29. The insider spent around $211,195 to buy those shares.
• What's Happening: On May 7, OPKO Health reported worse-than-expected first-quarter financial results.
• What OPKO Health Does: OPKO Health Inc is a diversified biotechnology company that operates pharmaceutical and diagnostic development programs. Opko's diagnostics business includes a core genetic testing operation.