Label-free biodetection by optical diffraction
Label-free biodetection techniques are the matter of intense research field in bioassays area. We have developed a label-free detection method based on optical diffraction. Probes molecules are immobilised on functionalized glass slides by soft lithography to generate molecular gratings that efficiently diffract light from a laser beam. Diffraction efficiency increases with the thickness of the molecular gratings. According to this principle, the measured diffraction intensity is found to increase when probe-target interactions take place at the surface of the molecular gratings. To collect and compare diffracted intensity before and after interaction, we have developed a dedicated scanner to measure the 1st order diffracted beam.
- Label-free biodetection
- Low-cost fabrication
- Amandine M.C. Egea, Laurent Mazenq, Emmanuelle Trévisiole, Vincent Paveau and Christophe Vieu, Optical label free biodetection based on the diffraction of light by nanoscale protein gratings, Microelectronic Engineering, 2013, V.111, p.425-427
- Patent : Jean-Christophe Cau, Helene Lalo, Jean-Pierre Peyrade, Childerick Severac and Christophe Vieu Method of seeking at least one analyte in a medium likely to contain it, 2010, WO 2010/029139
- H. Lalo, Thèse INSA, Toulouse, 2009
- J.C. Cau, Thèse INSA, Toulouse, 2009
- J. Foncy, Thèse INSA, Toulouse, 2013
Microfluidic interface for microarray diagnostic
Keywords : microfluidics, reversible magnetic clamp, multiplexed immunoassay, allergen microarray
Reference: Reversible magnetic clamp of a microfluidic interface for the seric detection of food allergies on allergen microarrays, J. Foncy, E. Crestel, J-P Borges, A. Estève, J-C Cau, C. Vieu, L. Malaquin and E. Trévisiol, Microelectronic Engineering (2016).
To provide a robust platform for fluid handling, most microfluidic devices usually involve irreversible bonding methods to achieve a leak free interface between the microchannels and the holding substrate. Such an approach induces a major drawback when biological interactions are performed on a microarray format as it is difficult to recover the biochip for further fluorescence scanner analysis. This work describes an automated microfluidic platform using a reversible magnetic clamp for multiplexed immunodiagnostis. The microfluidic device is composed of a magnetic PDMS layer (containing iron powder) coated by PDMS, which is reversibly clamped to an epoxysilane glass slide containing an array of various antigens. The microfluidic device was validated for in vitro diagnosis of food allergies on an allergen microarray after serum interaction. The statistical analysis of spot intensities(Signal to noise ratios) on the microarray displayed excellent reproducibility. In addition to the reduction of volumes provided by miniaturization, this approach is versatile, easy-to- produce and provide an effective platform for multiplexed immunodiagnosis based on conventional fluorescent detection schemes.
Fig 1: Schematic view of the microfluidic device. Magnetic PDMS cartridge and the microarray are hold together by magnetic force using array of magnets under the device. a) Microfluidic cartridge composed by PDMS and a magnetic PDMS layer, b) microarray composed by an epoxysilane glass slide containing an array of various antigens (85 spots), c) the microfluidic cartridge and the microarray reversibly sealed by a magnetic field to ensure a conform and hermetic contact, d) section view of the device, e) View of the microfluidic interface.
Reversible magnetic clamp of a microfluidic interface and a glass slide spotted with a microarray of allergens for serum detection of food allergies
The PDMS microfluidic cartridge is transparent above the channels allowing optical imaging in the microfluidic device while the reversibility of the magnetic clamp allows the reading of the microarray after microfluidic removal using a conventional fluorescent scanner.
No leakage was observed below 150 mBar with the magnetic clamp.
The functionality of the device was validated for in vitro diagnosis of food allergies in the serum of a patient.
Fig 2: a) Microarray fluorescence image of the interacting spots after removal of the microfluidic reversible chip, b) signal to noise ratio quantification after food allergy immunodiagnostic using the microfluidic device. The patient was allergic to cow milk, coat milk and yolk eggs.
Nanostructured mold replication - Low cost
Soft lithography at nanoscale requires a nanostructured silicon or resist master mold generated by advanced and expensive lithography and complex transfer techniques like ion etching. Such a fabrication is prohibitive for the industrial use of polydimethylsiloxane (PDMS) stamps in soft lithography. Our work focuses on a straightforward – low cost – technology to duplicate silicon master molds with nanoscale structures. Hence, master silicon molds patterned with nanometer scale lines can be replicated into epoxy resist and polyurethane by the following process.
Principle of the duplication method
The PDMS stamp made from a silicon master mold is used as template to copy this original mold into epoxy resist or polyurethane by UV nanoimprint lithography and demonstrated a faithful replication of the silicon mold nanostructures.Moreover, the biomolecule gratings patterns obtained by µCP using the PDMS stamps molded on epoxy resist or polyurethane replicated molds are identical to those obtained with the original silicon master mold.
Epoxy resist or polyurethane are very attractive and cost-effective substrates to reproduce at large scale PDMS stamps initially made on a nanostructured silicon master mold.
- Amandine M.C. Egea and Christophe Vieu, Microcontact printing of biomolecular gratings from SU-8 masters duplicated by Thermal Soft UV NIL, Microelectronic Engineering, 2011, V.88, p.1935-1938.
- Julie Foncy, Jean-Christophe Cau, Carlos Bartual-Murguia Jean Marie François, Emmanuelle Trévisiol and Childérick Sévérac, Comparison of polyurethane and epoxy resist master mold for nanoscale soft lithography, Microelectronic Engineering, 2013, V.100, p.183-187