Adrian Laborde

Development of a lab-on-chip electrochemical biosensor for water quality analysis based on microalgal photosynthesis

The present work was dedicated to the development of a lab-on-chip device for water toxicity analysis and more particularly herbicide detection in water. It consists in a portable system for on-site detection composed of three-electrode electrochemical microcells, integrated on a fluidic platform constructed on a glass substrate. The final goal is to yield a system that gives the possibility of conducting double, complementary detection: electrochemical and optical and therefore all materials used for the fabrication of the lab-on-chip platform were selected in order to obtain a device compatible with optical technology. The basic detection principle consisted in electrochemically monitoring disturbances in metabolic photosynthetic activities of algae induced by the presence of Diuron herbicide. Algal response, evaluated through oxygen (O2) monitoring through photosynthesis was different for each herbicide concentration in the examined sample. A concentration-dependent inhibition effect of the herbicide on photosynthesis was demonstrated. Herbicide detection was achieved through a range (blank - 1 µM Diuron herbicide solution) covering the limit of maximum acceptable concentration imposed by Canadian government (0.64 µM), using a halogen white light source for the stimulation of algal photosynthetic apparatus. Superior sensitivity results (limit of detection of around 0.1 µM) were obtained with an organic light emitting diode (OLED), having an emission spectrum adapted to algal absorption spectrum and assembled on the final system.

Microchannel-connected SU-8 honeycombs by single-step projection photolithography for positioning cells on silicon oxide nanopillar arrays

We report on the fabrication, functionalization and testing of SU-8 microstructures for cell culture and positioning over large areas. The microstructure consists of a honeycomb arrangement of cell containers interconnected by microchannels and centered on nanopillar arrays designed for promoting cell positioning. The containers have been dimensioned to trap single cells and, with a height of 50 µm, prevent cells from escaping. The structures are fabricated using a single ultraviolet photolithography exposure with focus depth in the lower part of the SU-8 resist. With optimized process parameters, microchannels of various aspect ratios are thus produced. The cell containers and microchannels serve for the organization of axonal growth between neurons. The roughly 2 µm-high and 500 nm-wide nanopillars are made of silicon oxide structured by deep reactive ion etching. In future work, beyond their cell positioning purpose, the nanopillars could be functionalized as sensors. The proof of concept of the novel microstructure for organized cell culture is given by the successful growth of interconnected PC12 cells. Promoted by the honeycomb geometry, a dense network of interconnections between the cells has formed and the intended intimate contact of cells with the nanopillar arrays was observed by scanning electron microscopy. This proves the potential of these new devices as tools for the controlled cell growth in an interconnected container system with well-defined 3D geometry.

High-K thin films as dielectric transducers for flexural M/NEMS resonators

We show that a nanometer-thick high-K material can be used as an electromechanical transducer to actuate the flexural mode of micro/nanoresonators. In this study, a 15 nm silicon nitride layer is employed on top of 320 nm thick silicon beams. The devices, smaller by 2 orders of magnitude than in previous studies [1], are successfully driven into vibration at resonance frequencies greater than 1 MHz, nanometer amplitudes, and quality factors greater than 2,000 in vacuum. We also deduce the transduction efficiency from a thermomechanical displacement noise calibration. This work paves the way for efficient electromechanical transduction scheme at the nanoscale, which would be further strengthened by the use of high-K dielectric materials obtained by atomic layer deposition.

Light emitting devices and integrated electrochemical sensors on lab-on-chip for toxicity bioassays based on algal physiology

In the frame of water toxicity analysis, a portable, glass-based, lab-on-chip was developed, integrating threeelectrode electrochemical microsensors and organic lightemitting diodes (OLED). The basic detection principle consists in monitoring electrochemically O2-related, algal metabolism in presence of herbicides. Thus, aiming on Diuron herbicide detection, a concentration-dependent inhibition effect on photosynthetic oxygen production rate was evidenced in the [0 - 1 μM] range. Finally, OLEDbased integrated system demonstrates higher detection characteristics than those using external white light source (sensitivity: 0.48 versus 0.26 nA/s/μM) and is highly promising for further integration of optical and electrochemical sensors enabling double complementary detection.