Abstract: An implantable unit includes fluorescent sensor molecules, each of which includes a binding site for an analyte, a donor fluorophore, and an acceptor fluorophore; and a first light source. An external system includes an external reading unit, which includes a light sensor; and a processor, which is configured to (i) during a first time period: (a) drive the first light source to generate light having a first illumination peak wavelength appropriate for excitation of the donor fluorophore, and (b) receive, from the light sensor, a first measurement of the fluorescent light emitted from the acceptor fluorophore, (ii) during a second time period: (a) drive a second light source to generate light having a second illumination peak wavelength appropriate for direct excitation of the acceptor fluorophore, and (b) receive, from the light sensor, a second measurement of the fluorescent light emitted from the acceptor fluorophore, and (iii) calculate the concentration of the analyte based on the measurements.

Abstract: A method is provided, including implanting a chamber containing cells in a subject, and subsequently administering, to the subject, a drug capable of killing the cells. For example, the drug may be administered after the cells cease to function for their intended purpose, or if the cells escape from the implanted chamber. Alternatively, the drug may be administered to kill the cells while the cells are in the implanted chamber. Other embodiments are also described.

Abstract: A protein is provided, including a glucose binding site, cyan fluorescent protein (CFP), and yellow fluorescent protein (YFP). The protein is configured such that binding of glucose to the glucose binding site causes a reduction in a distance between the CFP and the YFP. Substance monitoring apparatus (210) is also provided, including a semi-permeable barrier (212), adapted to be implanted in a body of a subject and to allow passage therethrough of a substance, while inhibiting passage therethrough of immune cells; and microorganisms (214), disposed within the semi-permeable barrier (212) so as to produce a measurable response to a level of the substance. A sensor (220) is adapted to measure the measurable response and not to measure a response of any mammalian cells that may be disposed within the semi-permeable barrier (212).