Schematic diagram of a gold nanomonitor implanted subcutaneously in a mouse.
The use of implantable devices to continuously monitor a sign or drug concentration in the body is a medical application that scientists have been drilling for a long time. This is important for disease control and medication feedback. However, the various implantable devices so far are not suitable to stay in the body for long periods of time and need to be replaced with a new one about every few days or weeks.
In addition, some implantable devices can cause rejection in the body, and some devices have a color that fades after a period of time, resulting in inaccurate measurements.
A study published in Nano Letters on March 30 describes their invention of a gold nanoparticle sensor that can be used stably in the human body for several months after implantation in the skin. Moreover, the nanoparticles can be modified with a variety of specific molecular receptors that can reflect various conditions and indicators of the body. Furthermore, the researchers loaded these particles within artificial polymeric tissues to be implanted under the skin without rejection.
The principal investigator, Carsten Soennichsen of the Johannes Gutenberg-Universität Mainz in Germany, has been working in this field for many years. He explains that gold nanoparticles are highly capable of absorbing and scattering light, changing color depending on their surroundings. This property makes gold nanoparticles ideal for use in implantable medical sensors.
To prevent the nanoparticles from being washed away or broken down by the body’s immune cells, the researchers designed a porous polymer gel similar to human tissue as a carrier for the nanoparticles. When implanted in the skin, the body’s capillaries and cells fill the holes, allowing the sensor to fuse well with human tissue without rejection.
“Our sensor is like an invisible tattoo, about the size of a penny and less than a millimeter thick.” Sonichsen said. They use gold nanoparticles to reflect infrared light, and then a special measuring instrument, outside the body by measuring the infrared light from the skin can understand the reading of the implantable detector.
In this study, the researchers implanted these sensors into some hairless mice and then used them to monitor the concentration of antibiotic drugs in the mice. After the antibiotics entered the mice’s bodies, they flowed through the blood vessels and came into contact with the sensors. The gold nanoparticles inside the sensors have special receptors bound to their surfaces that change color depending on the concentration of the antibiotic drug.
The results of the experiments showed that the sensors steadily reflected the concentration of the antibiotic drug and operated in the mice for several months.
Fading was a common problem before,” said Katharina Kaefer, lead author of the study. However, gold nanoparticles do not fade and their color remains constant. And it’s easy to coat them with a variety of sensor receptors, so they’re ideal as implantable sensor carriers.”
The new technology is versatile and will extend the life of the overall implantable sensor, according to the study. In the future, nanoparticle-based implantable sensors could be used to simultaneously monitor biomarkers and drugs in the body, with a wide range of potential uses in drug development, medical research, and customizing drugs, such as medication regimens for chronic disease patients to manage their conditions.
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