New photon technology can allow fluorescent sensors to track molecules deep in the body

Fluorescent sensors, which can be used to label and display a wide variety of molecules, offer a unique look at living cells. However, they can usually only be used in cells grown in a laboratory dish or in tissues close to the surface of the body, as their signal is lost when implanted too deep.

MIT engineers have already figured out a way to overcome this limitation. Using a new photonic technique they developed to excite each fluorescent sensor, they were able to dramatically improve the fluorescent signal. With this approach, the researchers showed that they can implant sensors up to 5.5 centimeters in the tissue and still receive a strong signal.

This type of technology could allow fluorescent sensors to be used to track specific molecules in the brain or other tissues deep in the body, for medical diagnosis or to monitor the effects of drugs, the researchers said.

If you have a fluorescent sensor that can examine biochemical information in cell culture or in thin tissue layers, this technology allows you to translate all of these fluorescent dyes and probes into thick tissue. “

Vladimir Koman, a researcher at MIT and one of the leading authors of the new study

Naveed Bakh SM15, PhD ’20 is also the lead author of the article that appears today in Natural nanotechnologies. Michael Strana, a Carbon P. Dubbs professor of chemical engineering at MIT, is the senior author of the study.

Increased fluorescence

Scientists use many different types of fluorescent sensors, including quantum dots, carbon nanotubes and fluorescent proteins, to mark molecules inside cells. The fluorescence of these sensors can be seen by illuminating laser light on them. However, this does not work in dense, dense tissue or deep in the tissue, as the tissue itself also emits some fluorescent light. This light, called autofluorescence, dims the signal coming from the sensor.

“Autofluorescence of all tissues and this is becoming a limiting factor,” says Koman. “As the signal from the sensor becomes weaker and weaker, it is preceded by tissue autofluorescence.”

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 could be more easily distinguished from tissue autofluorescence. The technique, which they call wavelength-induced frequency filtering (WIFF), uses three lasers to create a laser beam with an oscillating wavelength.

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

One possible application for this type of sensor is to monitor the effectiveness of chemotherapeutic 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, after which they receive the chemotherapeutic drug temozolomide (TMZ) to try to eliminate all other cancer cells.

This drug can have serious side effects and does not work for all patients, so it would be useful to have a way to easily monitor whether it works or not, says Strana.

“We are working on technology to create small sensors that can be implanted near the tumor itself, which can give an indication of how much drug arrives in the tumor and whether it is metabolized. “You can place a sensor near the tumor and check the effectiveness of the drug in the actual tumor environment from outside the body,” he said.

When temozolomide enters the body, it breaks down into smaller compounds, including one known as AIC. The MIT team has designed a sensor that can detect AIC and has shown that it can be implanted at a depth of up to 5.5 centimeters in an animal’s brain. They were able to read the signal from the sensor even through the animal’s skull.

Such sensors can also be designed to detect molecular signatures of tumor cell death, such as reactive oxygen species.

“Any wavelength”

In addition to detecting TMZ activity, researchers have demonstrated that they can use WIFF to enhance signal from a variety of other sensors, including carbon nanotube-based sensors previously developed by Strano’s laboratory to detect hydrogen peroxide, riboflavin and ascorbic acid.

“The technique works at any wavelength and can be used for any fluorescent sensor,” says Strana. “Since you now have a lot more signal, you can implant a depth sensor in the tissue that was not possible before.”

For this study, the researchers used three lasers together to create the oscillating laser beam, but in future work they hope to use an adjustable laser to create the signal and improve the technique even more. This should become more feasible as the cost of adjustable lasers decreases and they become faster, researchers say.

To make fluorescent sensors easier to use in patients, researchers are working on sensors that are bioavailable so they will not need to be surgically removed.

The study was funded by the Koch Institute for Integrative Cancer Research and the Dana-Farber Bridge / Harvard Cancer Center project. Additional funding was provided by the Swiss National Science Foundation, the Japan Society for the Advancement of Science, King Abdullah University of Science and Technology, the Zuckerman STEM Leadership Program, the Israel Science Foundation and the Arnold and Mabel Beckman Foundation.


Massachusetts Institute of Technology

Reference journal:

Koman, V.B., et al. (2022) Wavelength-induced frequency filtering method for fluorescent nanosensors in vivo. Natural nanotechnologies.

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