Microfluidics Enabled Interfacial Capacitive Sensors For Biomedical Applications

Microfluidics-enabled Interfacial Capacitive Sensors for Biomedical Applications

Pressure is a vital indicator in various physiological systems. Therefore, extracting the pressure information (e.g., intraocular pressure, intracranial pressure) becomes important in monitoring these physiological systems. A variety of pressure sensors/transducers have been investigated and most of them rely on resistive, piezoelectric, or capacitive sensing mechanism. However, several major challenges preventing their adoption in advanced medical devices (e.g., surgical instruments) are the needs for high sensitivity, accuracy, fast mechanical response, and high flexibility. In this dissertation, we have introduced a novel microfluidics-enabled interfacial capacitive sensor, referred to as MICS, with ultrahigh pressure sensitivity and resolution, fast mechanical response, and skin-like flexibility at a low-cost for various biomedical applications. Utilizing a high-capacitance electrical double layer (EDL) at the elastic electrode-electrolyte interface, the MICS with a simple device architecture achieves an ultra-large capacitance and an ultrahigh device sensitivity, i.e. more than 1,000 times larger than the traditional solid-state capacitive sensors. Importantly, the influences of the design parameters on the device sensitivity have been thoroughly investigated, as the desired device sensitivity can vary considerably for different applications. In addition, utilizing the low-viscosity sensing liquids on a hydrophobic-modified surface, we have been able to achieve high-frequency responses to external stimuli (up to 1kHz). Moreover, benefiting from the chemical and thermal stability of the sensing liquids, we have largely removed the concerns of environmental sensitivities (e.g., evaporation) and achieved stable sensing units. Furthermore, the simple device architecture -- the entire device consists of only two flexible micropatterned electrode layers and one spacing layer, allows us to massively produce the MICS at low-cost yet high reliability. Besides the investigations on the device performances, we have also explored a multi-functional MICS. Inspired by the physiological tactile sensation, we have successfully devised the MICS to detect the normal and shear pressure as well as to map surface topology at an ultrafine spatial resolution (greater than that of human skin) within a flexible and transparent package. In addition, the MICS has been developed into a wireless pressure sensor, allowing it to be integrated in implantable and remote sensing devices. As demonstrations, we have applied the wireless MICS, encapsulated in a biocompatible silicone rubber, to monitor the intraocular pressure of human eyes. In Vitro tests have been performed, in which the sensor achieves a good sensitivity and accuracy within the target pressure range. In addition, we have devised the MICS in a miniaturized package (0.20mm x 0.16mm x 1.50mm) with an ultrahigh capacitive output. Given its high sensitivity and miniaturized design, this MICS can be readily integrated into existing medical devices (e.g., guide wires) for an invasive physiological pressure monitoring. In conclusion, a novel interfacial capacitive sensing principle is presented in this dissertation, and we believe this novel sensing approach will offer a highly transformative solution to various medical applications (e.g., diagnoses of glaucoma and coronary artery disease) in the near future.

CMOS Capacitive Sensors for Lab-on-Chip Applications

1.1 Overview of Lab-on-Chip Laboratory-on-Chip (LoC) is a multidisciplinary approach used for the miniaturization, integration and automation of biological assays or procedures in analytical chemistry [1–3]. Biology and chemistry are experimental sciences that are continuing to evolve and develop new protocols. Each protocol offers step-by-step laboratory instructions, lists of the necessary equipments and required biological and/or chemical substances [4–7]. A biological or chemical laboratory contains various pieces of equipment used for performing such protocols and, as shown in Fig. 1.1, the engineering aspect of LoC design is aiming to embed all these components in a single chip for single-purpose applications. 1.1.1 Main Objectives of LoC Systems Several clear advantages of this technology over conventional approaches, including portability, full automation, ease of operation, low sample consumption and fast assays time, make LoC suitable for many applications including. 1.1.1.1 Highly Throughput Screening To conduct an experiment, a researcher fills a well with the required biological or chemical analytes and keeps the sample in an incubator for some time to allowing the sample to react properly. Afterwards, any changes can be observed using a microscope. In order to quickly conduct millions of biochemical or pharmacolo- cal tests, the researchers will require an automated highly throughput screening (HTS) [8], comprised of a large array of wells, liquid handling devices (e.g., mic- channel, micropump and microvalves [9–11]), a fully controllable incubator and an integrated sensor array, along with the appropriate readout system.

Frontiers in robotics and AI editor’s picks 2022