Smart contact lenses are becoming increasingly popular for non-invasive monitoring of health status. Contact lens being in direct contact with the eye ball and body fluids can provide a unique platform for continuous monitoring of physiological information. An international team of engineers has developed an ultrathin sensor layer which will even take the conventional smart contact lenses to the next level. The ultrathin sensor layer (few to monolayer) can be mounted directly onto contact lenses. The sensor when placed on contact lenses can maintain direct contact with a body fluid which is tears. Due to its mechanical robustness it will neither interfere with vision nor blinking.
The ingenious smart contact lens sensor layer contains:
- A photo detector for collecting optical information
- A temperature sensor for diagnosing and monitoring potential corneal disease
- A glucose sensor for tracking glucose levels in tears
Bioelectronics and biomedical devices are of immense importance for real time monitoring and diagnosis of health status. Biomedical devices which can be implanted in the body or are flexible and can be easily worn without effecting body movements are gaining attention. Biomedical devices are usually mounted with biosensors which are capable of real time tracking of physiological information like heart rate, body temperature, oxygen saturation etc. Contact lens is a widely used wearable device. They are mostly used for vision correction, therapeutic and aesthetic purposes. Contact lenses remain in direct contact with the body fluids (tears) and the eyeball for a long time. Thus it provides a unique platform for real time tracking of physiological parameters. Other conventional smart patches or wrist bands usually collect data from the skin or sweat which may not be a reliable data source. On the other hand tears are rich in biomarkers (proteins) making tears a far more reliable source of data for monitoring health status. Biomarkers are basically biomolecules (protein, hormones, DNA) which serve as an indicator of an underlying disease or health condition. Thus smart contact lenses which collect data from tears could monitor the health status more accurately than other biomedical devices.
Previously designed smart contact lenses had bulky and rigid sensors. These sensors had to be placed between two layers of contact lenses. The sensors used microfluidic sensing channels to contact tears. Thus the previously designed contact lenses had a number of disadvantages. These disadvantages have been overcome by the ingenious ultrathin sensors developed by the international team of engineers.
The advantages of the novel ultrathin sensor layer are:
- High detection sensitivity
- Easy to assemble
- Good biocompatibility
- Mechanical robustness
- No need for sandwiching between layers can be mounted directly on contact lens
- Being mounted directly on contact lens the sensors can be in direct contact with tears which ensures higher detection sensitivity; no need for microfluidic sensing channels for the sensor to contact tears.
According to the team smart contact lenses mounted with this ultrathin sensor will neither interfere with blinking nor vision. This gives the smart contact lenses fitted with this ultrathin sensor an edge over other smart contact lenses. According to the research team smart contact lenses should be comfortable to wear and have negligible mechanical stiffness with respect to the eye ball. This smart contact lens is highly transparent, flexible and is multifunctional.
Clinical trials have shown that tears contain biomarkers for systemic glucose levels. The smart contact lens is mounted with highly sensitive glucose sensor. With the help of the smart contact lenses glucose level can be monitored from tears instead of blood. This will take noninvasive monitoring of glucose level and diabetes diagnosis to the next level. It is essential to monitor blood glucose levels. Disorder in regulation of blood levels leads to diabetes and its associated complications.
The smart contact lens has embedded photo detectors which can receive optical data, monitor light intensity and assist in vision. It also has sensors for monitoring intraocular pressure which is important for diagnosing ocular diseases such as dry eye diseases and inflammation. It is also embedded with temperature sensors for tracking corneal temperature which is important for postoperative infection monitoring. These sensors and detectors embedded in the smart contact lens are of significance in case of monitoring, diagnosis and treating ocular diseases.
The research team has also tested the smart contact lens in the lab for cytotoxicity. It has shown good biocompatibility making it suitable for medical and healthcare application. The embedded sensors, detectors, circuit chips and the contact lens itself have to be stable and biocompatible to ensure the user does not face irritation and inflammation.
Wearable biomedical device are gaining a lot of attention. The ultrathin sensor layer developed by the team has overcome the disadvantages of the previous generation of smart contact lens. It can be mounted directly onto the contact lens. The smart contact lens fitted with ultrathin sensor layer will ensure real time non-invasive monitoring of physiological parameters. Real time monitoring of the health status with wearable biomedical devices could revolutionize the efficiency of healthcare system by ensuring proper and timely diagnosis.
Shiqi Guo, Kaijin Wu, Chengpan Li, Hao Wang, Zheng Sun, Dawei Xi, Sheng Zhang, Weiping Ding, Mona E. Zaghloul, Changning Wang, Fernando A. Castro, Dong Yang, Yunlong Zhao. Integrated contact lens sensor system based on multifunctional ultrathin MoS2 transistors. Matter, 2020; DOI: 10.1016/j.matt.2020.12.002