Thierry Leïchlé

Biosensors and tools for surface functionalization from the macro- to the nanoscale: The way forward

Most of review articles or even books dedicated to biosensing issues are organized by the generally admitted scheme of a biosensor. Subsequently, biological receptors, modified surfaces (and ways to specifically modify those surfaces using established biological and/or chemical recipes), and transduction techniques are thoroughly addressed in this precise order. In this review, we deliberately decided to break the conventional way of providing biosensing review by uniquely addressing biomolecules’ immobilization methods onto a solid surface and biosensing-related transduction techniques. The aim of this review is to provide a contemporary snapshot of the biosensing landscape without neglecting the seminal references or products where needed. The main guiding line of the review is the downscaling (from the macro- to the nanoscale) of biosensors and their respective most known applications. To conclude, a brief overview of the most popularized nanodevices applied to biology is given before attempting to com...

Individual Blood‐Cell Capture and 2D Organization on Microarrays

The image shows living B lymphocytes captured on a microcantilever-arrayed biochip. Antibodies targeting cellular antigens are pyrrole-modified and then electropolymerized into polypyrrole films on a gold surface. The arrayed feature size is close to a lymphocyte size and thus allows efficient cell capture and organization. Gold layers can thus be arrayed in a predetermined manner that gives access to organized blood cells on surfaces. Each line is separated from the other by 50 µm.

Current Switching Coupled to Molecular Spin-States in Large-Area Junctions

The fabrication of large-area vertical junctions with a molecular spin-crossover complex displaying concerted changes of spin degrees of freedom and charge-transport properties is reported. Fabricated devices allow spin-state switching in the spin-crossover layer to be triggered and probed by optical means, while detecting associated changes in electrical resistance in the junctions.

Fabrication and characterization of microlens arrays using a cantilever-based spotter

We present a quantitative study on the fabrication of microlenses using a low-cost polymer dispending technique. Our method is based on the use of a silicon micro-cantilever robotized spotter system. We first give a detailed description of the technique. In a second part, the fabricated microlenses are fully characterized by means of SEM (Scanning Electron Microscope), AFM (Atomic Force Microscopy) non contact optical profilometry and Mach-Zehnder interferometry. Diameters in the range [25-130mum] are obtained with an average surface roughness of 2.02nm. Curvature radii, focal lengths as well as aberrations are also measured for the first time: the fabricated microlenses present focal lengths in the range [55-181mum] and exhibit high optical quality only limited by diffraction behaviour with RMS aberration lower than lambda/14.

A Bistable Microelectromechanical System Actuated by Spin-Crossover Molecules

We report on a bistable MEMS device actuated by spin-crossover molecules. The device consists of a freestanding silicon microcantilever with an integrated piezoresistive detection system, which was coated with a 140u2005nm thick film of the [Fe(HB(tz)3 )2 ] (tz=1,2,4-triazol-1-yl) molecular spin-crossover complex. Switching from the low-spin to the high-spin state of the ferrous ions at 338u2005K led to a reversible upward bending of the cantilever in agreement with the change in the lattice parameters of the complex. The strong mechanical coupling was also evidenced by the decrease of approximately 66u2005Hz in the resonance frequency in the high-spin state as well as by the drop in the quality factor around the spin transition.

Arrays of nanoelectromechanical biosensors functionalized by microcontact printing

The biofunctionalization of nanoelectromechanical systems (NEMS) is critical for the development of new classes of biosensors displaying improved performance and higher levels of integration. In this paper we propose a modified microcontact process (μCP) in order to biofunctionalize arrays of NEMS with a probe molecule on the active sensing areas together with an anti-fouling layer on the passive areas in a single, self-aligned step. We demonstrate the adequate functionalization/anti-fouling of arrays of freestanding nanocantilevers as dense as 10(5) nanostructures cm(-2) by using both fluorescence microscopy and dynamic measurements of the structures resonant frequency. The proper bioactivity of an antibody deposited onto the cantilevers and the blocking property of a bovine serum albumin layer are both assessed by incubating specific and non-specific tagged secondary antibodies followed by fluorescence imaging. Furthermore, measurement of the resonant frequency of the nanocantilevers before and after functionalization and biological recognition demonstrate that using μCP for device functionalization does not damage the nanostructures and preserves the mechanical sensing capability of our NEMS.

Interaction of biomolecules sequentially deposited at the same location using a microcantilever-based spotter.

A microspotting tool, consisting of an array of micromachined silicon cantilevers with integrated microfluidic channels is introduced. This spotter, called Bioplume, is able to address on active surfaces and in a time-contact controlled manner picoliter of liquid solutions, leading to arrays of 5 to 20-μm diameter spots. In this paper, this device is used for the successive addressing of liquid solutions at the same location. Prior to exploit this principle in a biological context, it is demonstrated that: (1) a simple wash in water of the microcantilevers is enough to reduce by >96% the cross-contamination between the successive spotted solutions, and (2) the spatial resolution of the Bioplume spotter is high enough to deposit biomolecules at the same location. The methodology is validated through the immobilization of a 35mer oligonucleotide probe on an activated glass slide, showing specific hybridization only with the complementary strand spotted on top of the probe using the same microcantilevers. Similarly, this methodology is also used for the interaction of a protein with its antibody. Finally, a specifically developed external microfluidics cartridge is utilized to allow parallel deposition of three different biomolecules in a single run.

A dielectrophoretic continuous flow sorter using integrated microelectrodes coupled to a channel constriction

In this article, we propose a novel dielectrophoretic continuous flow sorter using planar micro electrodes coupled to a channel constriction. This design enables a high particle sorting efficiency at low voltages while relying on a simple fabrication and integration process. We have numerically simulated the AC electrokinetic effects and the fluid behavior to predict particle trajectories. Simulation results are in accordance with experimental data: 10 and 5u2009μm polystyrene beads were continuously sorted with <2% errors at flow speeds of 100u2009μm/s. We were also able to change the particle buffer while sorting beads. Finally, to demonstrate the interest of our device for cell sorting, we also sorted dead and living yeast cells according to their different dielectric properties. Living cell concentration was enriched by a factor of 4 versus dead cell concentration after passing the sorting device.

Collective fabrication of an in-plane silicon nanotip for parallel femtoliter droplet deposition

We present an in-plane nanotip incorporated into a microchannel at the tip of microcantilevers for the deposition of femtoliter droplets, thus addressing the miniaturization of biochips. The nanotip fabrication is based on anisotropic etching of Si by tetramethyl ammonium hydroxide with silicon nitride and local oxidation of silicon films as masking layers. This technique does not require high-resolution lithography nor an alignment technique. By using the obtained cantilever array with in-plane nanotips, matrices of water–glycerol droplets with a diameter of 2 µm and an interspot distance of 10 µm are achieved. It is demonstrated that the surface wettability of the nanotip and the substrate is an important factor influencing the droplet size.

Nanostructuring surfaces with conjugated silica colloids deposited using silicon-based microcantilevers

In this paper, the assembly and stability of locally spotted spherical nanoparticles onto various substrates are studied. Arrays of silicon-based microcantilevers, combined with an automated three-stage spotter, are used to deposit picolitre droplets containing 300xa0nm diameter polyethylene glycol and 150xa0nm diameter amino conjugated silica nanospheres onto silicon, allylamine and acrylic acid surfaces. Matrices of colloid spots ranging from 10 to 100xa0µm in diameter have been successfully patterned. SEM characterizations of the nanoparticles geometry and spatial distribution within the spots were carried out, showing the colloid aggregation at the droplets rim and the selective stability of the printed patterns. The expected substrate functionalization was assessed by XPS characterizations of the nanoparticles surfaces. Finally, polyethylene glycol–SiO2 nanoparticle conjugates were used as masks during a selective reactive ion etching of the silicon substrate, and silicon nanopillars have been obtained. This work opens up possibilities of high spatial resolution nanopatterning with nanoparticle conjugates.