Recent Progress of Flexible Image Sensors for Biomedical Applications

Abstract

irradiating X-rays, have become indispensable approaches for diagnosing diseases. [4] Other similar applications may include imaging based on positron emission tomography using gamma rays, [10] deep ultraviolet resonant Raman imaging of a cell, [11] histopathology images using visible light, [12] and electroencephalography through nearinfrared (NIR) light [13] (Figure 1).An image sensor, or an imager, is an essential electronic device that supports such type of bioimaging technology. Image sensors have two main components: single or multiple optical sensors (for detecting light) and circuits (for reading the output from optical sensors). Multiple optical sensors are arranged in an array with specific rows and columns. By reading light signals from the sensors using readout circuits, the spatial and/or temporal distribution-localization of biological information is determined, while its dynamics can be analyzed as an image. Two important applications of such bioimaging techniques are static imaging, which involves techniques, such as X-ray and CT, and dynamic imaging, which concerns object detection such as pulse, [14] blood oxygen levels, [15,16] and blood flow. [17] In static imaging, the imaging speed is not required as only little dynamic movements exist, but it requires high resolution and high sensitivity. Meanwhile, in dynamic imaging, high resolution is not required, but high-speed imaging is essential (Figure 2).Recently, the miniaturization of semiconductor devices has led to the development of imaging devices for wearable electronics. As a typical example, a smartwatch integrates small optical sensors that can continuously monitor biological information, such as pulse, blood pressure, and blood oxygen levels, for the long-term by simply wearing the sensors in direct contact with the skin.The flexibility of image sensors is improving to reduce the discomfort caused by such wearable electronics. Because hard and heavy devices cause relatively high discomfort, their prolonged and continuous use increases the psychological and physical burden on the user. Thus, a flexible imaging device that uses soft materials and thin substrates to reduce the device thickness and weight is an effective approach for load reduction. Further, flexible devices are easier to bend and attach to the bioplane than traditional solid devices. Consequently, problems of inaccuracy or intermittency of data acquisition caused by fluctuations in the physical distance between the target skin surface and the device can be reduced. Therefore, flexible imaging Flexible image sensors have attracted increasing attention as new imaging devices owing to their lightness, softness, and bendability. Since light can measure inside information from outside of the body, optical-imaging-based approaches, such as X-rays, are widely used for disease diagnosis in hospitals. Unlike conventional sensors, flexible image sensors are soft and can be directly attached to a curved surface, such as the skin, for continuous measurement of biometric information wi...

Recent advances in liquid-metal-based wearable electronics and materials

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6‐1: Invited Paper: Measuring Health Parameters with Large‐Area Organic Photodetector Arrays

“…In the flourishing field of flexible and large-area electronics, organic photodetectors (OPDs) have recently emerged as a new branch with potential applications ranging from health monitoring, gesture control, artificial vision, optical communication, and night vision to opto-genetics [1]. Organic thin films can be easily formed over large area using solution coating or printing processes and thus eliminate the need for expensive and time-consuming vacuum processing steps.…”

“…In its simplest form, one only needs two discrete LEDs and a single, broadband photodiode for a spot size measurement. Several groups have made flexible pulse oximeters using organic photodiodes instead of their inorganic counterparts, albeit with a small number of pixels [1,14]. Mechanical flexibility allows for good conformal skin contact and thus high signal quality.…”

Magnetic‐Sensitive Crack Sensor with Ultrahigh Sensitivity at Room Temperature by Depositing Graphene Nanosheets upon a Flexible Magnetic Film

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