The aim of the TAU project is to develop a functional glass substrate with integrated thin-film heaters and thin-film temperature sensors to be used for the accurate and localized temperature control of lab-on-chip devices for space applications.
Lab-on-chip devices are indeed ideal candidates for the use in space missions where experiment automation, system compactness, limited weight and low sample and reagent consumption are required. In this context, precise temperature control is a fundamental requirement for most of the bioanalytical tasks that must be carried out during the experiments. Temperature control, however, represents one of the most power consuming tasks if conventional approaches are considered.
The proposed active glass substrate is meant to be used as cover-glass for the sealing of microfluidic chips and it will offer an optimized and energy efficient solution for the thermal control of microfluidic devices. The main requirements include: good optical transparency to allow the use of optical analytical methods on the lab-on-chip; an accurate measurement of the local chip temperature; uniform heating of the target lab-on-chip area. These requirements will be met by combining a transparent thin-film heater and a set of hydrogenated amorphous silicon (a-Si:H) p-i-n diodes fabricated on the same glass substrate. The transparent resistive heater will be made of Indium Tin Oxide (ITO) deposited by RF magnetron sputtering. Due to the negligible Thermal Coefficient of Resistance of ITO films, the measurement of the temperature cannot be accomplished through resistance measurements as for metallic heaters. For this reason, a-Si:H diodes deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) will be used for accurate temperature measurement. The layout of heaters and sensors will be optimized to achieve a uniform temperature profile over the area of interest and to maximize the energy efficiency by heating only the volume of interest of the chip.
The proposed research project addresses one of the most important points of most analytical devices, namely the temperature control. The proposed smart cover glass is intended to be used with a variety of microfluidic chips in order to add on-chip temperature control functionality. This can be achieved by simply replacing the standard cover-glass used to seal the chips with the smart cover that will be developed in this project. This aspect becomes of particular relevance if lab-on-chip devices for space applications are considered. Indeed, conventional approaches imply the fine temperature regulation of the entire payload volume, resulting in high power consumption. The proposed device, instead, will implement an energy-efficient control of the local chip temperature by heating only the volume of fluid of interest which is in close contact with the smart cover glass.
The advantages brought by the proposed solution can be exploited also in terrestrial applications such as point-of-care testing for medical diagnostics and population screening.
In addition, the technical knowledge gained during the execution of the project in terms of fabrication process optimization and system integration aspects, will represent a significant step toward the development of portable multifunctional analytical devices for both space and terrestrial applications.