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Implantable sensors that continuously monitor vital signs and concentrations of drugs in the body have the potential to revolutionize healthcare. Such sensors would enable the constant tracking of disease progression and the efficacy of treatment.
Current implantable sensor technology has severe limitations. For example, existing sensors cannot remain in the body permanently, and must be replaced after a few days or weeks. Scientists at Johannes Gutenberg University Mainz have developed a novel type of implantable sensor which can operate in the body for several months. The sensor is based on color-stable gold nanoparticles that are modified with receptors for specific molecules. Embedded into an artificial polymeric tissue, the nanoparticles are implanted under the skin where they report changes in drug concentrations by changing color.
Implant reports information via color changes
Professor Carsten Soennichsen’s research group has been using gold nanoparticles as sensors to detect tiny amounts of proteins in microscopic flow cells for many years. Gold nanoparticles act as small antennas for light: They strongly absorb and scatter it and, therefore, appear colorful. Soennichsen’s team has exploited this concept for implanted medical sensing.
To prevent the tiny particles from swimming away or being degraded by immune cells, they are embedded in a porous hydrogel with a tissue-like consistency. Once implanted under the skin, small blood vessels and cells grow into the pores. The sensor is integrated in the tissue and is not rejected as a foreign body. “Our sensor is like an invisible tattoo, not much bigger than a penny and thinner than one millimeter,” said Soennichsen.
In their study published in Nano Letters, the team implanted their gold nanoparticle sensors under the skin of hairless rats. Color changes in these sensors were monitored following the administration of various doses of an antibiotic. The drug molecules are transported to the sensor via the bloodstream. By binding to specific receptors on the surface of the gold nanoparticles, they induce color change that is dependent on drug concentration. Thanks to the color-stable gold nanoparticles and the tissue-integrating hydrogel, the sensor was found to remain mechanically and optically stable over several months.
Huge potential of gold nanoparticles as long-lasting implantable medical sensors
“We are used to colored objects bleaching over time. Gold nanoparticles, however, do not bleach but keep their color permanently. As they can be easily coated with various different receptors, they are an ideal platform for implantable sensors,” explained Dr. Katharina Kaefer, first author of the study.
The novel concept is generalizable and has the potential to extend the lifetime of implantable sensors. In future, gold nanoparticle-based implantable sensors could be used to observe concentrations of different biomarkers or drugs in the body simultaneously. Such sensors could find application in drug development, medical research, or personalized medicine, such as the management of chronic diseases.
K. Kaefer et al. Implantable Sensors Based on Gold Nanoparticles for Continuous Long-Term Concentration Monitoring in the Body, Nano Lett (2021) DOI: 10.1021/acs.nanolett.1c00887
Original press release provided by the Johannes Gutenberg University Mainz