Engineers boost signals from fluorescent sensors

Fluorescent sensors, which can be used to label and image a wide variety of molecules, offer a unique glimpse inside living cells. However, they typically can only be used in cells grown in a lab dish or in tissues close to the surface of the body, because their signal is lost when they are implanted too deeply.

MIT engineers have now come up with a way to overcome that limitation. Using a novel photonic technique they developed for exciting any fluorescent sensor, they were able to dramatically improve the fluorescent signal. With this approach, the researchers showed they could implant sensors as deep as 5.5 centimeters in tissue and still get a strong signal.

This kind of technology could enable fluorescent sensors to be used to track specific molecules inside the brain or other tissues deep within the body, for medical diagnosis or monitoring drug effects, the researchers say.

“If you have a fluorescent sensor that can probe biochemical information in cell culture, or in thin tissue layers, this technology allows you to translate all of those fluorescent dyes and probes into thick tissue,” says Volodymyr Koman, an MIT research scientist and one of the lead authors of the new study.

Naveed Bakh SM ’15, PhD ’20 is also a lead author of the paper, which appears today in Nature Nanotechnology. Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT, is the senior author of the study.

Enhanced fluorescence

Scientists use many different kinds of fluorescent sensors, including quantum dots, carbon nanotubes, and fluorescent proteins, to label molecules inside cells. These sensors’ fluorescence can be seen by shining laser light on them. However, this doesn’t work in thick, dense tissue, or deep within tissue, because tissue itself also emits some fluorescent light. This light, called autofluorescence, drowns out the signal coming from the sensor.

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