A new generation of nanosensors

Nitric oxide (NO) is one of the most important signaling molecules in living cells. Abnormal levels of nitric oxide are recorded in many malignant cells, but very little is known about the behavior of this molecule in both healthy and pathologically altered cells.

Researchers at the Massachusetts Institute of Technology, working under the leadership of Professor Michael Strano, have created a sensor implanted under the skin based on carbon nanotubes that allows monitoring of nitric oxide throughout the year, as well as a soluble sensor for injection into the bloodstream. One of the potential uses of such sensors is to monitor inflammatory reactions, the byproduct of which is nitric oxide.

Carbon nanotubes, which are hollow cylinders of pure carbon with a thickness of 1 nanometer, are a promising material for the manufacture of nanosensors. Employees of the Strano laboratory have recently developed sensors based on carbon nanotubes to detect various molecules, including hydrogen peroxide, as well as toxic compounds such as sarin nerve gas. The mechanism of action of such sensors is based on the natural ability of carbon nanotubes to fluorescence. The sensor is a complex of nanotubes and a compound that selectively binds to a specific target, which enhances or weakens the fluorescence of the complex.

As part of their latest work, the researchers modified a previously created sensor to detect nitric oxide, which is carbon nanotubes wrapped in a DNA chain whose nucleotides are arranged in a certain sequence. The result of the work was the creation of two types of sensors, one of which is designed for intravenous administration and short-term monitoring of nitric oxide levels, and the second is coated with a special gel and is suitable for implantation under the skin for a long-term period.

The suitability of the first variant of sensors for injection is ensured by the molecules of the biocompatible polymer polyethylene glycol (PEG) attached to them, which prevents the aggregation of particles in the bloodstream. When injected into mice, such sensors pass through the vessels of the lungs and heart without harming the body. Subsequently, most of them accumulate in the liver, where they can be used to monitor the concentration of nitric oxide associated with inflammation.

The long–lived sensors (pictured) are nanotubes coated with alginate, a polymer extracted from algae. When implanted under the skin of a mouse, such sensors retain functionality for at least 400 days. They can be used to monitor malignant tumors or other inflammatory diseases, as well as to detect immune reactions in patients with artificial joints or other implants.

To read the monitoring results, researchers shine a laser at the sensor implantation site, emitting a glow in the near-infrared region of the spectrum, which makes it possible to distinguish the fluorescence of nanotubes from background fluorescence.

Currently, the authors are working on adapting their proposed technology for monitoring glucose concentration in the body. The ultimate goal of this line of work is to create sensors that will allow patients with diabetes mellitus to monitor blood glucose in real time.

Article by Nicole M. Iverson et al. In vivo biosensing via tissue-localized near-infrared-fluorescent single-walled carbon nanotubes is published in the journal Nature Nanotechnology.

Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of the Massachusetts Institute of Technology:
New implantable sensor paves way to long-term monitoring. 

05.11.2013