NORCROSS, Ga., Jan. 5 -- Abbott Laboratories has purchased $2.5 million in convertible redeemable preferred stock of SpectRx Inc., bringing Abbott's total purchase of SpectRx stock to $5.25 million. SpectRx reported that the stock purchase was part of an agreement between the two companies to jointly develop a continuous glucose monitor for diabetics. The agreement assigns to Abbott exclusive worldwide marketing rights to continuous monitoring applications and to single-use monitoring applications of the technology. SpectRx will receive a royalty on sales of disposable devices, and will have the option to manufacture continuous monitoring devices for Abbott. The monitor uses a surface-worn patch containing a glucose sensor -- based on SpectRx's biophotonic technology -- to measure glucose levels in interstitial fluid (ISF). ISF is collected through an array of micropores created with a laser in the stratum corneum, or dead outer layer of skin. According to SpectRx, prototypes of the device have shown it capable of providing one reading per minute.