Fabrication And Applications Of Micro Metal Devices On Polymeric Microfluidic Chips

Microfluidic chips made of polymers have been widely employed in the recent years because they are less expensive and easier to fabricate compared to those made of glass or silica. According to microfluidics'property of miniaturization, integration and portability of analytical instruments, metal apparatuses integrated for various functions are obviously required in microfluidic systems.Fabrication of micro metal devices in microchips through LIGA technique requires clean-room conditions and complicated facilities, which makes the process tough and costly. At the same time, organic solvents harmful for polymer surfaces are inevitably employed in the LIGA process, which is not favorable for preparation of metal devices on polymeric chips. As a result, most microchips integrated with metal devices are hybridized of glass and PDMS, the surface properties of which are completely different. The PDMS/glass hybrid chips can only support inhomogeneous electroosmotic flow (EOF), which might deteriorate the separation efficiency.In present work, electroless plating is employed to fabricate micro metal devices on PET and PDMS sheets, both of which are widely used in fabricating microchips. Properties of the fabricated metal devices are characterized, and polymeric microchips with homogeneous channel surfaces properties and integrated micro metal devices are fabricated, which are then used in chemical and biochemical applications.The thesis is composed of four chapters:In chapter 1, recent progress in polymeric microchips and fabrication of micro metal devices on microfluidic chips are reviewed with respect to fabrication of microchannels in polymers, bonding the polymeric microchips, the functions of metal devices on microchips, as well as their applications and fabrication methods. In chapter 2, amorphous PET was exploited to fabricate full-PET microchips integrated with gold microelectrodes. Surface modification via UV light irradiation and air plasma was studied and both of the two methods were found to be able to improve the surface wettability, enhance the supported electroosmotic flow (EOF), and increase thermal bonding strength of PET sheets, with the latter being more efficient and less time-consuming than the former UV light during the surface modification. On the basis of the study mentioned above gold film electrodes were fabricated on PET sheets, and the micro-structured PET sheet was bonded with the PET sheet carrying micro gold electrode was bonded without assistant layers at a low temperature (65℃), forming a full-PET capillary electrophoresis-amperometric detection (μCE-AD) microfluidic chip.The developedμCE-AD PET chip was used for separation and detection of dopamine (DA) and catechol(CA). The separation efficiencies of DA and CA are 3.2×104 and 4.3x104 plates/m, respectively, and detection limits achieved are 0.87 and 1.28μmol/L, respectively. Electropherograms for five consecutive runs of DA and CA show that the RSDs of migration time are 0.5% and 0.3%, respectively. Compared to the PET chips bonding with assistant layers, the analytical performances of present fabricated chip are significantly improved.It is rather difficult to prepare metal devices directly on PDMS substrates because the low surface energy of PDMS renders the adhesion between the deposited metal layer and PDMS substrate quite weak. In chapter 3, protocols for fabrication of fine and reliable metal devices on PDMS surfaces are studied. Different UV induced surface activation methods and their effects on the finally plated gold films are discussed. Among the tested methods, the UV-induced polymerization and grafting of PAA on the PDMS surface is the most effective for region-selective electroless plating. It provides the active carboxylic moieties which can be used as the scaffold for immobilization of metal nano particle catalysts necessary for region-selective electroless plating. The prepared micro gold devices show strong adhesion to the PDMS substrate, excellent electrochemical properties, and allow the SAMs of thiol-compounds to be perfectly formed on their surface. The minimum width of the prepared micro gold devices is no worse that 10μm, which could be improved if finer photo-masks and collimated UV light are used.The full PDMS chip showed good analytical performance. With DA and CA being the model analysts, the RSD of detection signals for DA and CA are 2.1% and 2.4%, respectively (each at 100μM, n=21). The separation efficiency achieved at the applied electric field of 308 V/cm is 21,237 plates/m (H=4.7×10-5 m for DA), which is significantly higher than that (8600 plates/m) obtained at approximately similar electric fields (250V/cm) with a PDMS/glass hybrid chip. The uniform EOF supported by the homogeneous PDMS channels is one of the reasons for the improvement in the separation efficiency.The fabricated gold device is also used d as an electric heater in microchips and its heating performance is examined.In chapter 4, on the basis of chapter 3's work, the Au-PDMS substrate which can be immobilized in the well-plate is fabricated and the feasibility of using it in cell culture is preliminarily studied. Similar cell growth and proliferation is observed on the Au-PDMS substrate prepared by the method established in chapter 3 as in the control experiment, which suggests the fabricated Au-PDMS could be used in cell culture. This result shows the potential for the Au-PDMS substrate to be used for electrical stimulation induced stem cell differentiation during cell culture process in PDMS microfluidic chips.The main novelty of the present work is summarized as:1. Realizing full-PET microchip thermal bonding at a relatively low temperature with the help of air plasma surface modification and prepared PETμCE-ED chip with integrated micro gold electrode via UV surface modification induced electroless plating. The fabricated PET chip shows good analytical performances inμCE-ED application.2. Developing the protocol of integrating reliable micro metal devices on PDMS substrates on the basis of UV induced PAA grafting. Compared to the reports, this protocol proves its feasibility in ordinary chemistry laboratories without the need of the clean room and expensive facilities, and the prepared micro gold devices show satisfying mechanical behavior, excellent electrochemical properties, and good biological compatibility, which could be used as electric conductors, electrochemical detectors and sensors, electric heater and cell culture containers.3. Preliminarily testing performances of the electrolessly fabricated Au-PDMS substrate in cell culture experiment, and establishing the platform for cell culture and electrical stimulation of stem cell in PDMS microchips.