research activities in 2007 - CSEM

Food Safety with the Help of a Miniaturized Laboratory
G. Suárez, S. Pasche, R. Ischer, G. Voirin, N. Schmid, J. Auerswald
A miniaturized laboratory, often referred to as a “lab-on-a-chip”, based on the Wavelength Interrogated Optical Sensing (WIOS) system has been
developed for the simultaneous detection of several residual antibiotics in fresh milk.
One of the major challenges in food safety is integrating
quality control into the process of production and/or
commercialization. Specifically, the analysis must be accurate,
fast, cost-efficient, disposable and easy to operate by the nonskilled
technician. In the milk industry in particular, levels of
residues of veterinary medicinal products, of which antibiotics
represent a significant part, are strictly regulated by the
European Union legislation. More precisely, a series of four
families of antibiotics are found to be of particular interest:
・・lactams, tetracyclines, sulfonamides and
fluoroquinolones. In the framework of this CCMX
(Competence Centre for Materials Science and Technology)
project, the side-by-side development of a label-free multidetection
system and an integrated microfluidic cartridge
converges to simultaneous and fast detection (< 15 min) of
four antibiotics in the field environment.
The label-free multidetection system is based on WIOS
technology developed at CSEM and allows sensitive detection
of biomolecules adsorbed on the waveguide chip. The
selective adsorption of molecules from the solution induces a
change of refractive index at the interface which is monitored.
Competitive immunoassays based on the specificity of either
antibodies or receptors have previously been developed for
the simultaneous multi-detection of antibiotics and have been
optimized in the framework of the European project
GoodFood [1] . The other aspect of this work consists of
developing and fabricating a microfluidic cartridge that
integrates both the sensor chip and the reagents required for
the assay. Currently the cartridge is fabricated from a piece of
plastic (PMMA) of dimensions 10 x 4 x 0.7 cm in which
channels and reservoirs are machined by micromilling.
Prior to the analysis, a small volume of milk (≈ 1 ml) is
introduced into a vial containing the assay reagents. The vial
is closed with a rubber-cap and introduced upside down into
the sample vial holder located on the microfluidic cartridge.
Two needle-inlets on the base of the vial holder pierce the
rubber-cap and connect the sample to the fluidic system.
Figure 1: Setup of the analysis system
In terms of fluidics, the overall setup of Figure 1 is based on
the use of a single syringe pump working in aspiration mode
coupled with a multiposition valve connected to atmospheric
64
pressure. The basic idea behind the setup is to control which
liquid (sample, buffers…) is driven through the cartridge
channels by submitting its reservoir to the atmosphere while a
negative pressure is applied at the other end of the cartridge.
Moreover, the use of a 3-port valve on the pump allows for
two possible pathways on the cartridge: the loading path (to
deviate residual air from the sensing chip) and the sensing
path which addresses the liquid to the sensing regions for
reaction/measurement. Waste reservoirs ensure that no
residual liquid goes out of the cartridge. With this simple setup
neither the valve nor the pump are directly in contact with the
solutions used during the assay; thus, no contamination
occurs.
Figure 2: Picture of the whole detection setup with microfluidic
cartridge inserted into holder interface (grey box)
The system (Figure 2) was tested successfully with spiked
milk samples demonstrating the automated detection of two
antibiotic families (sulfonamides and fluoroquinolones)
(Figure 3).
Figure 3: Typical signals obtained for antibiotics detection in milk
This system that is currently under optimization for antibiotics
detection in milk remains easily adaptable to further
applications (eg. food analysis or biomedical diagnosis).
This work was funded by CCMX-MMNS Lab-On-a-Chip
project, European Project FP6-IST-1-508774-IP and OFFT.
CSEM thanks them for their support.
[1] G. Voirin, et al., “Simultaneous Detection of Four Antibiotic
Families in Milk for Customer Safety”, in this report, page 61
www.goodfood-project.org