The development of electronics has changed our daily life for last few decades. The conventional electronic devices are usually based on wafers; they are, in principle, rigid and in the planar form with Young’s modulus of a few hundreds GPa. On the other hand, our biology system is much soft with Young’s modulus within kPa range. Thus, there is mechanical mismatch between the electronic devices and soft human body, which tackles the use of the electronics as biomedical devices for diagnosis and therapy. In this study, we introduce a few approaches to minimize the mechanical mismatch by enhancing the flexibility of devices for electronics-based biomedical devices.
In the first chapter, the In2O3 based conformal biomolecular sensors were introduced with highly robust and stable performance. The platform of biosensors was based on field effects transistors which is one of the most popular device types because of its sensitivity and selectivity. In addition, aqueous chemistry was utilized without organic solvent to eliminate organic byproduct, which ensures highly dense In2O3 film with ultrathin-thick (3.5 nm). Also, the oxide surface of In2O3 was able to be easily functionalized for selective detection. Glucose and pH were detected with the ultrathin In2O3 based transistor as a possible demonstration. In addition, we designed the structure of In2O3 based transistors with the ultra-low stiffness value, which ensures the extreme flexibility of the devices and conformal contact on unconventional substrates.
In the second section, wearable pulse sensor was exploited with flexible waveguide plates and micro light emitting diodes (μ-LEDs). Since the pulse sensor is a non-invasive tool monitoring the heart rate and arterial blood oxygen concentration, the development of wearable pulse sensor can be useful for wearable biomedical devices to diagnose our body system. For flexible devices, the waveguide plates were made of soft elastomer. Through the pattern made on the elastomer, the condition for total reflection of emitted light from μ-LEDs was changed to emit more light from the surface of the waveguide plates. The flexible waveguide plates consisting of two different μ-LEDs were placed on one side and organic photodetectors were placed on another side to understand the arterial blood oxygen saturation. Also, breath condition was monitored by using the wearable biomedical devices to further conform the possibility of our devices for photodiagnosis. Also, devices worked well under 50 % stretching test.
In the last section, the wearable light emission device was utilized for phototherapy which is to use light for clinical purpose. The bilirubin was chosen as a target molecule, known as an indicator of mal-function of liver. Using our flexible biomedical devices, we successfully triggered the reaction kinetic of bilirubin and control the level of bilirubin. In addition, it was used to give the drug selectivity using photon-accelerated caged molecules, a caged fluorophore (5-carboxyfluorescein-bis-(5-carboxymethoxy-2-nitrobenzyl) ether. This is a proof-of-concept for drug targeting.
Recent advances for wearable clinics and healthcare systems have brought a new opportunity for new types of biomedical devices available for recognition, prevention, and treatment. I strongly believe that current our study in this dissertation will be helpful for biomedical devices to move forward toward to commercialization.