Analyte capture in an array of functionalized droplets for a regenerable biosensor.

We describe in this work an advanced microfluidic chip for the capture of bioanalyte on the surface of droplets arranged in a dense array. We show the procedure for generating, functionalizing, and arranging the droplets inside the device for capturing a specific bioanalyte. Then, we demonstrate the capacity of the array to capture analyte from a cross-flowing liquid, using a biotin/streptavidin model. The paper also proposes to use the droplets array, after integration with acoustic detection, as a regenerable detection interface for bioanalyte sensing. We model the arrangement of droplet in dense array and show that they present a larger effective capture surface and shorter capture distance than standard flat surface biosensor of the same footprint. As the droplets can be easily evacuated and replaced inside the device analysis chamber, the proposed biosensor would allow biointerface regeneration and chain measurement without dismounting the device.

Improving immunosensor performances using an acoustic mixer on droplet microarray.

A major drawback of protein microarrays is the lack of control of ligand immobilization at the surface of the chip which limits their performances and thus their impacts in in vitro diagnosis. To improve antibody (Ab) grafting during the spotting process on commercialized gold SPRi chips, we propose to produce a chaotic flow in every spotted droplet, by using an acoustic field, in order to disrupt the steady state of the reaction of Ab grafting. Our results show that acoustic mixing during Ab binding at the biochips surface increases their biorecognition performances of a mean factor of 2.7 in comparison with Ab layer grafted in a passive mode. Moreover, it increases statistically the homogeneity of the response over all the surface of the chips.

Sensitivity of a Lamb wave sensor with 2 microm AlN membrane.

Anti-symmetrical Lamb wave mode A0 presents a large sensitivity to mass loading and can be used in contact with liquids with a small attenuation. The advantages of this system are the possibility to get a large mass sensitivity. The sensitivity increases when the thickness of membrane decreases. Therefore the problem is to obtain thin piezoelectric membranes. A membrane of AlN with a thickness of 2 microm has been made. The measured mass sensitivity with a fluid is 200 cm(2) g(-1). In a practical use point of view, the problem in this kind of sensor is its temperature sensitivity. In order to reduce effective temperature sensitivity, a device with thin metallic strips is presented. On the same membrane two different waves with perpendicular propagating directions are produced. Experimentally, temperature sensitivity is rather different depending on the propagation direction but mass sensitivity is almost the same, this allows distinguishing temperature effects from those due to mass loading on the frequency shift measurements.

Action of low frequency vibration on liquid droplets and particles.

Liquids handling is an important issue in biomedical analysis. Two different devices for acoustic manipulation of droplets have already been tested. The first one, more classical, uses a high frequency travelling wave and acoustic streaming. The second one uses low frequency flexural standing waves in a plate. This means of liquid handling is original and easy to implement but the physical principle is not obvious. In order to understand more precisely the phenomena involved we present new observations on droplet displacement between two planes and on the behaviour of a droplet on an inclined vibrating plane with this method. The physical principle involved is discussed. The common acoustic radiation pressure formulation is expressed via the non-linear theory of sound propagation, but in our case the acoustic wavelength is much smaller than the height of a water droplet. To get a better understanding of the phenomenon, further experiments on the internal liquid flow and behaviour of particles in the droplet have been performed. These will be compared with results obtained with particles in a thin water-filled vibrating glass tube. The general conclusion is that the phenomenon is practical to use for droplet displacement even if its complex mechanism is not completely understood.

Displacement of droplets and deformation of thin liquid layers using flexural vibrations of structures. Influence of acoustic radiation pressure.

In this paper observations concerning some effects of vibrating structures on fluids are presented, followed by a tentative theoretical analysis. First, a brief description of a caterpillar-like structure is made. This structure is almost equivalent to an infinite beam which allows the choice of positions of the nodal lines of a vibrating mode. Displacement of liquid droplets using switching between two modes of this structure is then presented. This phenomenon is supposed to be induced by acoustic radiation pressure. Possible extensions of this principle are then discussed. After this, results are reported concerning deformations of thin liquid layers.