Micromanufacturing of Conductive Polymer Electrodes for Sensing Microsystems

Abstract

Wearable technologies are receiving a growing attention from research and industry in many different scientific areas [1]. Many of the commercialized devices are mainly based on the detection of gravitational, electric or acoustic impulse and environmental sensors [2]. However, for various healthcare applications it is of vital importance to be able to analyse bodily fluids, detecting microscopic biomarkers in order to monitor health conditions in a continuous, not-invasive and localized way. For this reason, the realization of the realization of in-situ wearable electrochemical bio-sensors is highly needed since it will open the possibility of mass screening and personalized medicine [1]. Conductive polymers are well suited for wearable bio-sensor applications, due to their unique electrical and optical properties that can be selected by choosing among a broad range of available materials [3][4][5]. Moreover, they provide also biocompatibility, low cost and easy manufacturability. This thesis presents a low cost and simple method for fabricating an all polymeric device for pH monitoring. Indeed, pH is one of the keys indicator of wound infection and it is important to study its evaluation during wound healing in order to select the right therapy. The device consists of a microfluidic channel, for uid handling, and polymeric electrodes made of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), one of the most promising conductive electrodes. The PEDOT layer has been created by spin-coating on a cyclic ole_n copolymer (COC) substrate and has been characterized by both contact and optical interferometry. In order to increase adhesion, isopropanol has been added to PEDOT before spin-coating and a post-process treatment with ethylene glycol has demonstrated to be crucial to increase the PEDOT conductivity and decrease its solubility in water, Electrodes coupled with microchannels were fabricated by mean of a single hot embossing process. The thesis presents a comparison between a standard hot embossing process with a soft embossing one (in which the mold is polymeric). Two different processes for fabrication the mold are discussed: direct milling of aluminum for the hard mold and soft lithography with polydimethilsiloxane on a polystyrene master. The polymeric electrodes obtained after embossing have been characterized by means of electrical and electrochemical measurements. In order to impart pH sensitivity, a pH sensitive layer of polyaniline has been electropolimerized on the PEDOT working electrode and characterized by means of SEM imaging and electrochemistry. Finally, the response of the device to a relevant range of pH is tested and validated by monitoring its potentiometric response. In conclusion, this thesis describes the development and characterization of an all polymeric microfluidic pH sensing system with integrated electrodes manufactured by means of a single-step embossing process.