Wearable Organic Optoelectronic Sensors for Medicine.

DOI: 10.1002/adma.201403560 neuronal photostimulation, [ 16 ] microelectrode arrays [ 10 ] and in vivo measurement of brain activity, [ 17 ] and a report of using an organic light-emitting diodes (OLEDs) light source for photodynamic therapy of skin cancer [ 18 ] in humans. In this communication, we demonstrate that OLEDs and organic photodiodes (OPDs) can be combined to make compact, non-invasive, fl exible sensors for medical applications by simple solution-processing methods, and we describe two examples of such sensors. In the fi rst example, we have developed a thin, fl exible, light weight, and potentially low-cost muscle contraction sensor which can measure signals from intact muscles to control the movement of active prosthetic devices, such as artifi cial limbs. [ 19,20 ] Moreover, we have demonstrated the feasibility of this all-organic, optoelectronic sensor by controlling a robotic arm so that it mimicked the motion of the arm of a healthy volunteer for two types of muscle contractions. Specifi cally, we have shown that the sensor can detect both isotonic and isometric types of muscle contraction and distinguish between them. The clear signal obtained means that movement of a volunteer’s arm can be used to control a robot which copies the volunteer’s movement. We have also performed optical modeling using Monte Carlo simulations to study the effect of anisotropic properties of muscle fi bers on the incident light. In the second example, we have made a fl exible organic optoelectronic bandage to measure tissue oxygenation and demonstrate it by measuring a healthy adult during blood pressure cuff-induced ischemia. It has important implications in the fi eld of neuroimaging, [ 21 ] exercise medicine, [ 22 ] and for understanding of the vascular conditions such as peripheral arterial disease. [ 23 ] This research demonstrates that the combination of OLEDs and OPDs processed on fl exible substrates can open an era of low-cost disposable non-invasive optical sensors for medicine and sports. The optical muscle contraction sensor we designed works by measuring the amount of incident light backscattered from skeletal muscle tissue. Myosin protein in the sarcomeres of muscles has liquid crystalline properties and is responsible for the anisotropic behavior of muscles. [ 24 ] When muscle contracts actin fi bers slide along myosin, and the muscle fi ber becomes short and wide, thereby scattering incident light anisotropically: light traveling parallel to muscle fi bers is scattered differently from light perpendicular to fi bers and this anisotropy can be detected by a surface-mounted light source and detectors positioned along and perpendicular to muscle fi ber. [ 19,25 ] There are several considerations in designing an organic optoelectronic probe (wavelength, geometry, choice of materials, and fabrication). Figure 1 a shows a schematic of the sensor mounted on an arm as a fl exible bandage, which consists of four photodiodes and a light source in the middle. The photodiodes were prepared using polymer thieno[3,4-b]thiophene/benzodithiophene (PTB7) with (6,6)-Phenyl C71 butyric acid methyl ester (PC 70 BM) as the active layer. The polymer PTB7 is an interesting low band gap material used in photovoltaics with power Non-invasive sensors are desirable for a wide range of medical measurements and especially for ubiquitous monitoring of a patient’s health. Medical measurements are typically taken infrequently during a visit to a physician or hospital. However, continuous monitoring (for example, the monitoring of blood pressure) [ 1 ] is preferable as it gives a much more complete picture. Wearable sensors are therefore desired for unobtrusive long-term continuous physiological and health monitoring which is crucial for many chronic illnesses, neurological disorders, depression, drug addiction, and rehabilitation. [ 2,3 ] Furthermore, such sensors are useful for a wide range of medical measurements as they play a crucial role in human–machine interactions, [ 4 ] in vitro diagnostics [ 5 ] and as epidermal electronics systems. [ 6 ] Ideally, wearable sensors should be lightweight, compact, fl exible, non-invasive, simple to make, and low cost. These requirements place numerous simultaneous demands on the sensors. Recently, a wearable pressure sensor using gold nanowires was reported to monitor the blood pulse in real-time, [ 7 ] and Samsung has launched a commercial product in the form of wrist watch to monitor heart rate and blood pressure. In another interesting study, Rogers and coworkers have reported a compact wearable surface electromyography (sEMG) sensor based on silicon electronics to make an epidermal electronics system. [ 6,8 ]