Christian Druon

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.

A planar on-chip micro-nib interface for NanoESI–MS microfluidic applications

We present a novel nanoelectrospray emitter tip based on the principle of a nib rather than a nozzle for nano-electrospray ionization–mass spectrometry (ESI–MS) applications. The fabrication of the micro-nibs relies on micromachining techniques using the epoxy-based negative photoresist SU-8. A double exposure photolithographic process has been employed to form a nib in a membrane-like structure. The nibs contained a capillary slot measuring 20 µm at the tip end. The nib sources were successfully tested on an ion trap mass spectrometer using standard peptide samples at low concentrations, down to 1 µM. High voltage (HV) supply was achieved using platinum wire inserted in a liquid reservoir. A Taylor cone was clearly seen protruding from the nib tip and was determined by the dimensions of the capillary slot.

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.

Microfluidic design rules for capillary slot-based electrospray sources

We formulate microfluidic design principles for electrospray ionization sources based on a rectangular capillary slot formed by two triangular cantilevers. Spontaneous imbibition of the test liquids into the slot by capillary action provides a robust mechanism for liquid transport from a reservoir to the cantilever tip where an electrospray is generated upon application of a voltage. The correct functioning of the source requires the liquid bridging the slot to have a negative Laplace pressure. Imbibition is controlled by the ratio of slot width to height w∕h and the intrinsic contact angles θw, θs of the liquid with the slot walls and the cantilever faces, respectively. Based on these parameters we derive a simple criterion for the complete filling of the slot.

High pressure-resistant SU-8 microchannels for monolithic porous structure integration

Integrated lab-on-chip (LOC) microsystems dedicated to proteomic analysis require specific pretreatment steps such as protein trypsic digestion, concentration, desalting or separation of biological samples. These steps can be achieved thanks to porous monolithic polymers. This paper deals with the integration of such a polymer into SU-8 microchannels by using a multi-material technology (SU-8, Pyrex and silicon). A solution for the fabrication of complete polymer microchannels which are high pressure- and solvents-resistant is proposed. This technique uses the negative photoresist SU-8 which is compatible with the protein analysis performed here. Our process requires a novel technological step using a silane coupling agent. This modification of the SU-8/Pyrex interface leads to the fabrication of a 100 µm × 160 µm section microchannel (length of 3 cm), closed with a Pyrex® lid by SU-8 bonding resistant to 80 bar. An improvement of the SU-8/monolithic structure is also demonstrated thanks to a specific treatment of the polymer enabling good anchoring of the monolith in the microchannels, and the pressure-resistance tests were also achieved with the monolithic structure integrated in the microchannels. A digestion step of a protein sample of benzoylarginine ethyl ester in a SU-8 microchannel was achieved after the functionalization of a monolith anchored in the microchannel. Analysis by UV/VIS spectroscopy of this in situ digestion has been reported.

Novel microwave device for nondestructive electrical characterization of semiconducting layers

A microwave measurement technique, using a novel cell which enables the sheet resistance (R⧠), the carrier density (n), and the mobility (μ) of epitaxial layers to be measured, is proposed. The system, controlled by a microcomputer, performs this characterization by measuring galvanomagnetic effects. The sample is only lightly pressed on the cell. The electrical contacts between the sample and the cell are capacitive. This method is thus nondestructive and requires no technological process. The data treatment necessitates knowledge of factors which are determined from a calibration procedure made only once. For the GaAs samples reported here, the accuracy is better than 5% for R⧠, 15% for μ, and 20% for n.

Micro-conveying station for assembly of micro-components

This paper describes a micro-conveying station for micro-component assembly. It incorporates micro-grippers joined up a micro-conveyer stage. The micro-grippers are fabricated from a mechanical structure in polymer using micro-stereophotolithography process and actuated by shape memory alloy wires. The micro-grippers can work in a space of 10 mm diameter and can carry out opening and closing movements. Neural network identification and PID control are proposed for the closed-loop control the micro-grippers, and trajectory control is realized on one finger. The micro-conveyer stage uses surface acoustic waves generated from interdigital transducers to move a slider onto the surface of the substrate with a high degree of resolution (nanometer) and in several centimetres of operation length. A mechanical model for the energy transfer from the acoustic wave to the slider is proposed. A good agreement between the theory and the experiment is obtained.

Theoretical and experimental study of linear motors using surface acoustic waves

This paper presents the theory, simulation results and experimental study of the slider displacement at nanometer scale in linear ultrasonic motors using surface acoustic waves that can be used as microconveyors. To our knowledge, this is the first attempt to describe the energy transfer from the acoustic wave to the slider in these motors. The model shows that the mechanism is sequential with alternative phases of levitation and contact with step-like behavior of the slider velocity. To validate the model, several microconveyors using Lamb and Rayleigh waves are fabricated. These waves are generated from interdigital transducers with, respectively, 10 and 20 MHz frequencies, which are the highest in ultrasonic micromotors. The control of motion is obtained by varying the duration of the driving signal applied across interdigital transducers. The measured displacement varies from several nanometers to several centimeters. Comparison between experimental and theoretical results shows a good agreement. This model gives a quantitative description of slider motion. In another way, it allows the deduction of key parameters for energy transfer. As an example, a study of slider contact shape is performed.

Study by electron paramagnetic resonance of charge transfer complexes formed by adsorption of TCNE on type X- and Y-zeolites

Electron paramagnetic resonance (e.p.r.) was used to study charge-transfer complexes formed by adsorption of tetracyanoethylene (TCNE) on type X- and Y-zeolites.The results obtained show that the paramagnetism appearing when TCNE is adsorbed on the zeolite is linked to the aluminium atoms and that two types of paramagnetic centres always appear simultaneously. However, the type constituted by the TCNE– ion is more dependent on the nature of the cation and the presence of solvent. All these results can be interpreted by admitting the formation of a charge transfer complex with two paramagnetic electrons when TCNE is adsorbed on the surface of the zeolite. One of these electrons is bound to a TCNE– ion and comes from an aluminium atom.The second paramagnetic type is constituted by the second unpaired electron which necessarily appears at the same time as the first and is located in the structure of the zeolite, probably near the aluminium atom donor.

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