Use of SU8 as a stable and biocompatible adhesion layer for gold bioelectrodes.

Gold is the most widely used electrode material for bioelectronic applications due to its high electrical conductivity, good chemical stability and proven biocompatibility. However, it adheres only weakly to widely used substrate materials such as glass and silicon oxide, typically requiring the use of a thin layer of chromium between the substrate and the metal to achieve adequate adhesion. Unfortunately, this approach can reduce biocompatibility relative to pure gold films due to the risk of the underlying layer of chromium becoming exposed. Here we report on an alternative adhesion layer for gold and other metals formed from a thin layer of the negative-tone photoresist SU-8, which we find to be significantly less cytotoxic than chromium, being broadly comparable to bare glass in terms of its biocompatibility. Various treatment protocols for SU-8 were investigated, with a view to attaining high transparency and good mechanical and biochemical stability. Thermal annealing to induce partial cross-linking of the SU-8 film prior to gold deposition, with further annealing after deposition to complete cross-linking, was found to yield the best electrode properties. The optimized glass/SU8-Au electrodes were highly transparent, resilient to delamination, stable in biological culture medium, and exhibited similar biocompatibility to glass

Microfluidic-optical integrated CMOS compatible devices for label-free biochemical sensing

11 páginas, 17 figuras, 1 tabla.The fabrication, characterization and packaging of novel microfluidic-optical integrated biosensors for label-free biochemical detection is presented in this paper. The integrated device consists of a three-dimensional embedded microchannel network fabricated using enhanced CMOS compatible SU-8 multilevel polymer technology on top of a wafer containing Mach-Zehnder Interferometer (MZI) nanophotonic biosensor devices. PMMA housing provides connection to the macro-world and ensures robust leakage-free flow operation of the devices. This macro-microfluidic module can operate at pressure drops up to 1000 kPa. Fluid flow experiments have been performed in order to demonstrate the robustness of our microfluidic devices. The devices have been designed to operate under continuous flow. Steady-state flow rates ranging from 1 to 100 µl min−1 at pressure drops ranging from 10 to 500 kPa were measured in the laminar flow regime. Experimental results are in good agreement with laminar flow theory. The first interferometric sensing measurements are presented in order to demonstrate the functionality of these novel integrated devices for lab-on-a-chip and label-free biosensing applications. A bulk refractive index detection limit of 3.8 × 10−6 was obtained, close to the minimum detected up to now by label-free biosensor devices without microfluidic integration. As far as we know, this is the first time that a label-free biosensor device is integrated within a microfluidic network using a wafer-level CMOS compatible process technology.This research is sponsored by the Basque and Spanish Governments, under a Torres Quevedo Spanish Fellowship for industrial research and the programs of research and development ofmicro and biotechnologies MICROGUNE and BIOGUNE.Peer reviewe