Jean-Christophe Camart

Integrated microfluidics based on multi-layered SU-8 for mass spectrometry analysis

We present a design for integrated lab-on-chip microsystems dedicated to mass spectrometry analysis based on the fabrication of watertight microchannels for the circulation of liquids. In this paper, we demonstrate how to fabricate complete polymer microchannels using the negative photoresist SU-8 which has the advantage of being compatible with protein analysis by mass spectrometry. Our method of fabrication requires novel technological steps involving SU-8 multi-layer processing, improved SU-8 adhesion and the use of SU-8 wafer bonding for the watertight closing of the microchannels with a Pyrex wafer. This technique also encompasses the design of various microfluidic elements such as tapered recesses for the housing of capillary tubes allowing the connection of the channels to external systems. Following this, the capillary tubes were used to test the hydrodynamic behaviour of the channels and consequently the efficiency of our technological process in achieving fully watertight structures within our flow rate and pressure specifications.

Variation of absorption coefficient and determination of critical dose of SU-8 at 365 nm

The absorption coefficient of thick-films of the negative photoresist SU-8 is observed to be time dependent during photolithographic exposure by I-line ultraviolet light (λ=365nm); varying linearly from 38±1cm−1 to 49±1cm−1 for a surface exposure dose of 415mJ∕cm2. We develop a general model which enables the exposure dose to be calculated at a given photoresist depth for a given exposure time. We determine the critical exposure dose for the subsequent polymerization of SU-8 having an arbitrary thickness to be 49.4±3.9mJcm−2.

Surface acoustic wave two-dimensional transport and location of microdroplets using echo signal

Digitalized microfluidics is dealing with microdroplet actuation and location. We propose the implementation of a surface acoustic wave (SAW) echo method so as to move and to locate a microdroplet from a single interdigital transducer (IDT). A prototype working at 20MHz demonstrates the ability of this method to achieve the goal with submillimeter accuracy quite sufficient for aimed biologic applications. The tested platform fitted with one IDT built on a LiNbO3 substrate allows the tracking of water droplets actuated by SAW running free or squeezed under a cover for biological treatments in a lab on chip.

Modeling of planar applicators for microwave thermotherapy

In order to improve the external applicators used for microwave thermotherapy controlled by microwave radiometry in medical applications, we propose specific planar applicators developed for heating: either annular ones to be used at the frequency equal to 915 MHz or in the shape of a horseshoe (short-circuited ring) for 434 MHz. The final goal of this paper is the realization of a honeycomb network for the treatment of larger areas and greater volumes.

6I-1 Novel Echo Method Implementation to Locate Microdroplets Transported by SAW

Digitalized microfluidics is now seen as a relevant solution to implement programmable and addressable biology. It is based on liquid microdroplet manipulation for performing basic operations such as transporting, splitting, merging and mixing. In our aimed applications, the moving droplets contain proteins and must cross bio-active micropads to achieve specific operations (Renaudin et al., 2006). We thus need the droplet position for blind hitting these micropads. This paper addresses the issue of both transporting and locating liquid droplets by SAW. It is also known that SAW permit to locate a droplet from its transmitted signal. But implementation of this method requires a complex configuration of InterDigital Transducers (IDTs) and an arduous command of circuits (Alzuaga et al., 2003) or slanted finger IDTs working in a specific frequency bandwidth (Wu and Chang, 2005). We propose hereafter for the first time the droplet location from its SAW reflected signal. The implementation of this new echo method only requires a single standard IDT. The IDT can work alternately as a SAW emitter for actuation and as a receptor for the droplet reflected signal or echo. First a radiofrequency pulsed excitation RFPEa is sent to displace the droplet. Once actuation is stopped a dedicated RFPEl is sent for droplet location and the position is determined from the delay sigma between excitation and the corresponding reflected signal. A LiNbO3 platform working at 20 MHz and fitted with four IDTs demonstrates the ability of this new method to achieve 5 mul droplet 2D displacement and location with submillimeter accuracy quite sufficient for biologic purpose in current lab-on-chips. The tested platform allows the tracking of water droplets running free or squeezed under a top cover. We have brought a new solution to the 2D-monitoring of microdroplets and thus hope helping to set a better coupling of SAW with microfluidics in lab-on-chips dedicated to biological applications so as to take advantage of SAW possibilities