DNA Biosensor Based on Double-Layer Discharge for the Detection of HPV Type 16

DNA electrochemical biosensors represent a feasible alternative for the diagnosis of different pathologies. In this work, the development of an electrochemical method for Human Papillomavirus-16 (HPV-16) sensing is reported based on potential relaxation measurements related to the discharge of a complex double layer of a DNA-modified gold electrode. The method used allows us to propose an equivalent circuit (EC) for a DNA/Au electrode, which was corroborated by electrochemical impedance spectroscopy (EIS) measurement. This model differs from the Randles circuit that is commonly used in double-layer simulations. The change in the potential relaxation and associated charge transfer resistance were used for sensing the DNA hybridization by using the redox pair Fe(CN)64-/Fe(CN)63+ as an electrochemical indicator. In order to determinate only the potential relaxation of the composed double layer, the faradic and double-layer current contributions were separated using a rectifier diode arrangement. A detection limit of 0.38 nM was obtained for the target HPV-16 DNA sequences. The biosensor showed a qualitative discrimination between a single-base mismatched sequence and the fully complementary HPV-16 DNA target. The results indicate that the discharge of the double-layer detection method can be used to develop an HPV DNA biosensor

Biosensor system with an integrated CMOS microelectrode array for high spatio-temporal electrochemical imaging, A

2019 Fall.Includes bibliographical references.The ability to view biological events in real time has contributed significantly to research in life sciences. While optical microscopy is important to observe anatomical and morphological changes, it is equally important to capture real-time two-dimensional (2D) chemical activities that drive the bio-sample behaviors. The existing chemical sensing methods (i.e. optical photoluminescence, magnetic resonance, and scanning electrochemical), are well-established and optimized for existing ex vivo or in vitro analyses. However, such methods also present various limitations in resolution, real-time performance, and costs. Electrochemical method has been advantageous to life sciences by supporting studies and discoveries in neurotransmitter signaling and metabolic activities in biological samples. In the meantime, the integration of Microelectrode Array (MEA) and Complementary-Metal-Oxide-Semiconductor (CMOS) technology to the electrochemical method provides biosensing capabilities with high spatial and temporal resolutions. This work discusses three related subtopics in this specific order: improvements to an electrochemical imaging system with 8,192 sensing points for neurotransmitter sensing; comprehensive design processes of an electrochemical imaging system with 16,064 sensing points based on the previous system; and the application of the system for imaging oxygen concentration gradients in metabolizing bovine oocytes. The first attempt of high spatial electrochemical imaging was based on an integrated CMOS microchip with 8,192 configurable Pt surface electrodes, on-chip potentiostat, on-chip control logic, and a microfluidic device designed to support ex vivo tissue experimentation. Using norepinephrine as a target analyte for proof of concept, the system is capable of differentiating concentrations of norepinephrine as low as 8µM and up to 1,024 µM with a linear response and a spatial resolution of 25.5×30.4μm. Electrochemical imaging was performed using murine adrenal tissue as a biological model and successfully showed caffeine-stimulated release of catecholamines from live slices of adrenal tissue with desired spatial and temporal resolutions. This system demonstrates the capability of an electrochemical imaging system capable of capturing changes in chemical gradients in live tissue slices. An enhanced system was designed and implemented in a CMOS microchip based on the previous generation. The enhanced CMOS microchip has an expanded sensing area of 3.6×3.6mm containing 16,064 Pt electrodes and the associated 16,064 integrated read channels. The novel three-electrode electrochemical sensor system designed at 27.5×27.5µm pitch enables spatially dense cellular level chemical gradient imaging. The noise level of the on-chip read channels allow amperometric linear detection of neurotransmitter (norepinephrine) concentrations from 4µM to 512µM with 4.7pA/µM sensitivity (R=0.98). Electrochemical response to dissolved oxygen concentration or oxygen partial pressure (pO2) was also characterized with deoxygenated deionized water containing 10µM to 165 µM pO2 with 8.21pA/µM sensitivity (R=0.89). The enhanced biosensor system also demonstrates selectivity to different target analytes using cyclic voltammetry to simultaneously detect NE and uric acid. In addition, a custom-designed indium tin oxide and Au glass electrode is integrated into the microfluidic support system to enable pH measurement, ensuring viability of bio-samples in ex vivo experiments. Electrochemical images confirm the spatiotemporal performance at four frames per second while maintaining the sensitivity to target analytes. The overall system is controlled and continuously monitored by a custom-designed user interface, which is optimized for real-time high spatiotemporal resolution chemical bioimaging. It is well known that physiological events related to oxygen concentration gradients provide valuable information to determine the state of metabolizing biological cells. Utilizing the CMOS microchip with 16,064 Pt MEA and an improved three-electrode system configuration, the system is capable of imaging low oxygen concentration with limit of detection of 18.3µM, 0.58mg/L, or 13.8mmHg. A modified microfluidic support system allows convenient bio-sample handling and delivery to the MEA surface for sensing. In vitro oxygen imaging experiments were performed using bovine cumulus-oocytes-complexes cells with custom software algorithms to analyze its flux density and oxygen consumption rate. The imaging results are processed and presented as 2D heatmaps, representing the dissolved oxygen concentration in the immediate proximity of the cell. The 2D images and analysis of oxygen consumption provide a unique insight into the spatial and temporal dynamics of cell metabolism

CMOS MULTI-MODAL INTEGRATED SYSTEMS FOR FUTURE BIOELECTRONICS AND BIOSENSORS

Cells are the basic structural biological units of all known living organisms. They are highly sophisticated system with thousands of molecules operating in hundreds of pathways to maintain their proper functions, phenotypes, and physiological behaviors. With this scale of complexity, cells often exhibit multi-physiological properties as their cellular fingerprints from external stimulations. In order to further advance the frontiers in bioscience and biotechnologies such as stem cell manufacturing, synthetic biology, and regenerative medicine, it is required to comprehend complex cell physiology of living cells. Therefore, a comprehensive set of technologies is needed to harvest quantitative biological data from given cell samples. Such demands have stimulated extensive research on new bioelectronics and biosensors to characterize their functional information by converting their biological activities to electrical signals. As a result, various bioelectronics and biosensors are reported and employed in many in vivo and in vitro applications. Since sensing electrodes of the devices are physically in touch with biological/chemical samples and record their signals, long-term biocompatibility and chemical/mechanical stability is of paramount importance in numerous biological applications. Furthermore, the devices should achieve high sensitivity/resolution/linearity, large field-of-view (FoV), multi-modal sensing, and real-time monitoring, while maintaining small feature size of devices to use small volume of biological/chemical samples and reduce cost. As a result, My Ph.D research aims to study interfacial electrochemical impedance spectroscopy (EIS) of electrodes with different combination of materials/sizes and to design novel multi-modal sensing/actuation array architectures with CMOS compatible in-house post-processing to address the design challenges of the bioelectronics and biosensors.Ph.D

Ultra-Low-Power Sensors and Receivers for IoT Applications

The combination of ultra-low power analog front-ends and CMOS-compatible transducers enable new applications, such as environmental monitors, household appliances, health trackers, etc. that are seamlessly integrated into our daily lives. Furthermore, wireless connectivity allows many of these sensors to operate both independently and collectively. These techniques collectively fulfil the recent surge of internet-of-things (IoT) applications that have the potential to fundamentally change daily life for millions of people.In this dissertation, the circuit and system design of wireless receivers and sensors is presented that explores the challenges of implementing long lifespan, high accuracy, and large coverage range IoT sensor networks. The first is a wake-up receiver (WuRX), which continuously monitors the RF environment to wake up a higher-power radio upon detection of a predetermined RF signature. This work both improves sensitivity and reduces power over prior art through a multi-faceted design featuring an impedance transformation network with large passive voltage gain, an active envelope detector with high input impedance to facilitate large passive voltage gain, a low-power precision comparator, and a low-leakage digital baseband correlator.Although pushing the prior WuRX performance boundary by orders of magnitude, the first work shows moderate sensitivity, inferior temperature robustness, and large area with external lumped components. Thus, the second work shows a miniaturized WuRX that is temperature-compensated, yet still consumes only nano-watt power and millimeter area while operating at 9 GHz. To further reduce the area, a global common-mode feedback is utilized across the envelope detector and baseband amplifier that eliminates the need for off-chip ac-coupling components. Multiple temperature-compensation techniques are proposed to maintain constant bandwidth of the signal path and constant clock frequency. Both WuRXs operate at 0.4 V supply, consume near-zero power and achieve ~-70 dBm sensitivity.Lastly, the first reported CMOS 2-in-1 relative humidity and temperature sensor is presented. A unified analog front-end interfaces on-chip transducers and converts the inputs into a frequency vis a high-linearity frequency-locked loop. An incomplete-settling switched-capacitor-based Wheatstone bridge is proposed to sense the inputs in a power-efficient fashion