MIT researchers improved the signal emitted by fluorescent nanosensors to be implanted deep into tissues to help diagnose diseases such as cancer

Typically, fluorescent sensors are used only in cells grown in the laboratory or in tissues close to the surface of the body, because their signal is lost when they are implanted too deeply. Now, chemical engineer Michael Strano, Volodymyr Koman and Naveed Bakh of MIT have developed a new photonics technique that greatly enhances the fluorescent signal from sensors as deep as 5.5 centimeters in tissues.

This technology, the researchers argue, could make it possible to probe biochemical information in cell culture or in layers of thin tissueby tracking specific molecules within the brain or elsewhere for medical diagnosis or monitoring of drug effects.

In the study, published in Nature Nanotechnology, several types of fluorescent sensors, including quantum dots, carbon nanotubes and fluorescent proteins, are used to label cell molecules. The fluorescence of these sensors can be seen by projecting laser light onto them.

The difficulty is that in the deeper layers, the fabric itself emits a fluorescent light in turn. This light, called autofluorescence, dulls the signal from the sensor. To overcome this limitation, the MIT team devised a way to modulate the frequency of the fluorescent light emitted by the sensor so that it can be more easily distinguished from tissue autofluorescence.. The technique, referred to by them as wavelength-induced frequency (WIFF) filtering, uses three lasers to create a single laser beam with an oscillating wavelength.

When this oscillating beam is projected onto the sensor, it causes the fluorescence emitted by the sensor to double its frequency. This allows you to easily distinguish the fluorescent signal from the background autofluorescence. Using this system, the researchers were able to improve the signal-to-noise ratio of the sensors by more than 50 times.

One possible application for this type of detection is the monitoring of the effectiveness of chemotherapy drugs. To demonstrate this potential, the researchers focused on glioblastoma, an aggressive type of brain cancer. Patients with this type of cancer usually undergo surgery to remove as much of the tumor as possible, then they are given the chemotherapy drug temozolomide (TMZ), which can have serious side effects, to try to clear any remaining cancer cells.

“We are working on the technology to make small sensors that could be implanted close to the tumor itself, which can give an indication of how much drug is getting to the tumor and whether it is being metabolized. “The technique works at any wavelength and can be used for any fluorescent sensor,” says Strano. To help make fluorescent sensors easier to use in human patients, researchers are now developing biologically resorbable sensors so they don’t have to be surgically removed.

Image by Nattanan Kanchanaprat from Pixabay


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