A cell glows red after being injected with nanosensors that fluoresce in the presence of sodium. Credit: Heather Clark, Draper Laboratory
Tattoos are all the rage these days. But scientists at Draper Laboratory (Cambridge, MA) are working toward the development of a different sort of “tattoo”—one that will monitor diabetics’ blood-sugar level.
Headed by Heather Clark, analytical chemist and task leader of Draper’s biomedical engineering group, a team of researchers is working to develop a biosensor that can be injected into the skin much like tattoo dye. Under infrared light, the device will fluoresce, informing diabetics whether or not they need to inject insulin following a meal. The monitoring technology will fall somewhere between noninvasive sensors for detecting glucose through the skin via infrared light and implanted devices for continually monitoring blood sugar and dispensing insulin.
The concept consists of 120-nm beads coated with a biocompatible material. Each bead contains a fluoroescent dye and sensor molecules that are designed to detect specific chemicals such as glucose and sodium. When injected into the skin, the sensor molecule pulls the target chemical into the polymer from the interstitial fluid that surrounds the cells. To compensate for the newly acquired positive charge of a sodium ion, for example, a dye molecule releases a positive ion, causing the molecule to fluoresce. The level of fluorescence increases with the concentration of the chemical target. Scientists can employ different recognition molecules to measure different targets, including chloride, calcium, and glucose.
The video below shows sodium rushing into heart-muscle cells grown in a dish. As happens during a normal heartbeat, sodium flowing into the heart coincides with contraction and modulates the sensors’ fluorescence (video by Heather Clark, Draper Laboratory).
The technology is unique, explains Clark, “because it doesn’t have any components to be used up.” Glucose strips, for example, detect glucose using an enzyme that must be replaced continually. “Other monitors, even nanosensors, have a limited lifetime, which makes implanting them difficult.”
The researchers have already conducted successful animal tests of a sodium-sensing version of the nanosensor that may eventually be used to monitor dehydration. When injected into the skin of mice, the polymer beads fluoresce in response to saline injections. While the glucose monitor has been shown to work in a solution, animal tests are still pending.
Although the technology looks promising, the researchers have much work ahead of them before the sensor is ready for human testing. While the beads didn’t appear to trigger an immune reaction in initial animal tests, notes Clark, more studies must be performed.
In the meantime, Clark projects that a future sensor may be injected into the surface layers of the skin, shallower than tattoo inks, “so that it sloughs off over time.” A fluorescence monitor resembling an optical mouse would then be used to measure the light emitted by the tattoo, and the sensor would be reinjected periodically.
