Ultrasounds (US) are one of the most used imaging techniques in medicine for assessing the physiological and pathological state of soft tissue. Apart from therapeutic applications, most of the interaction of the acoustic beams with tissues occur passively and without substantial modification to the physiology of the latter. However, US can also be used to remotely power implantable devices with sensing capabilities. In this study, we propose small-form devices interfaced with functionalized electrochemical electrodes for the detection of pH and lactate levels, powered by ultrasounds and data transmission through a Frequency Shift Keying (FSK) modulation technique. A custom-made piezoelectric transducer is responsible for converting the acoustic waves into electrical voltage at the device with operational levels as low as 0.5 V (power consumption of 10 μW) obtained from implantation distances of 50 mm inside tissue. This conjugated with the high sensitivity of the developed electrochemical sensors allows to detect and transmit local parameter variations below 0.1 pH (4.2 mV) and 1 mM lactate (70 nA). Potential applications include real-time access to intrabody tissue monitoring post-operatively, with the view of assessing proper soft tissue healing or infection detection by bacteria, as well as tissue cancer screening in structures such as the human breast.
Keywords: Frequency shift keying; Implantable devices; Lactate sensor; Power harvesting; Soft tissue monitoring and healing; Ultrasounds; pH sensor.
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