Integrated microsystems for continuous glucose monitoring, interstitial fluid sampling and digital microfluidics
Time: Fri 2020-02-14 10.00
Subject area: Electrical Engineering
Doctoral student: Federico Ribet , Mikro- och nanosystemteknik
Opponent: Professor Boris Stoeber, University of British Columbia, Vancouver, Canada
Supervisor: Niclas Roxhed, Mikro- och nanosystemteknik; Göran Stemme, Mikro- och nanosystemteknik
Interdisciplinary research between medicine and microsystem engineering creates new possibilities to improve the quality of life of patients or to further enhance the performance of already existing devices. In particular, microsystems show great potential for the realization of biosensors and sampling devices to monitor bioanalytes with minimal patient discomfort. Microneedles offer a minimally invasive and painless solution to penetrate the epidermis and provide access to dermal interstitial fluid (ISF), to monitor various substances without the need for more invasive and painful extraction of blood. Diabetes, for example, requires continuous monitoring of the glucose levels in the body (CGM) to avoid complications. Although glucose is traditionally measured in finger-prick blood, CGM, which is performed in ISF, has been proven to be beneficial in the management of the disease. However, current commercial solutions are still relatively large and invasive. In this work, an electrochemical glucose sensor 50 times smaller than competing commercial devices was combined with a hollow silicon microneedle and shown to be able to measure glucose levels in the dermis in vivo. A scalable manufacturing method for the assembly of the two separately fabricated components and their electrical interconnection was also demonstrated. At the same time, a single data point may be sufficient in other situations, such as when only the presence of a certain biomarker or drug needs to be assessed. Although continuous monitoring is not required in these cases, the patient would still benefit by avoiding blood extraction. However, there are no simple devices currently available to reliably sample and store ISF. A painless microneedle-based sampling device designed to extract 1 μL of ISF from the dermis was realized. The sampled liquid is metered and stored in a paper matrix embedded in a microfluidic chip. The sample could then be analyzed using state-of-the-art tools, such as mass spectrometry.On the other hand, device miniaturization also creates issues for sensor performance. In certain types of electrochemical gas sensors, such as nitric oxide sensors used for asthma monitoring, the reduced size results in a shorter device lifetime. These sensors typically operate with a liquid electrolyte, subject to evaporation, and their long-term stability tends to be proportional to the electrode size. To address this issue, a gas diffusion and evaporation controlling platform to be integrated with this type of sensors was proposed. Such a platform opens or seals the sensing compartment on demand, potentially enabling sensor recalibration and evaporation reduction when the sensor is not in use. The device is based on electrowetting-on-dielectric actuation of low-vapor-pressure ionic liquid microdroplets on partially perforated membranes. The platform was then modified to create a zero-insertion loss and broad-band-operation laser shutter.