research activities in 2007 - CSEM

Simultaneous Detection of Four Antibiotic Families in Milk for Customer Safety
G. Voirin, R. Ischer, S. Pasche
A biosensor for the detection of four antibiotic families has been realized and tested with reference milk samples in collaboration with European
partners. The simultaneous detection and identification of antibiotics in contaminated milk has been demonstrated.
In the dairy industry, it is important to avoid contamination of
milk with antibiotics which could modify the fermentation
process of dairy products such as cheese or yogurt, or
possibly cause allergic reactions in consumers (Figure 1). In
the frame of the European project GoodFood [1] , a biosensor
system for the detection of several antibiotics has been
developed in collaboration with other European partners.
CSEM has focused on a biosensor detection system based on
the interrogation of the resonance wavelength of a waveguide
grating coupler (WIOS Wavelength Interrogated Optical
Sensing). The relevant antibiotics were identified during a
survey made in 30 countries around the world. Four antibiotic
families were selected: sulphonamides, fluoroquinolones,
beta-lactams and tetracyclines.
Figure 1: Milk chain from production to consumer, screening test
must be performed as early as possible
The detection system is based on the change of the refractive
index of the sensing surface due to the binding of molecules.
The refractive index change induces a shift in the resonance
wavelength of the waveguide grating coupler which is
interrogated using a periodically swept tunable laser. This
detection method is sensitive to refractive index changes on
the order of 10-6 , or the equivalent of several pg/mm2 of
molecules binding to the sensor surface.
A competitive immunoassay format was chosen for the
detection of the antibiotics. A specific sensing surface was
obtained by using recognition molecules such as antibodies
and receptors, developed by GoodFood partners. Specific
antibodies for the sulphonamide and fluoroquinolone antibiotic
families were obtained by immunization of rabbits, and are
specific for a whole family of antibiotics (a family is a group of
molecules with similar chemical structures). Receptor
molecules specific for the beta-lactams and tetracycline
antibiotic families were specially engineered to present a high
affinity for a group of molecules. For each family, a test
protocol was implemented on the biosensor platform and the
cross reactions with the other reagents and antibiotics were
tested. The goal was to obtain a biosensor platform with
different sensing regions each specific to one antibiotic family,
allowing detection in the different regions simultaneously with
a unique milk sample. Using optical detection allows
measurements on eight separate pads simultaneously.
Figure 2 presents the calibration curves for each antibiotic
resulting from competitive immunoassays.
Figure 2: Calibration curves for sulphonamides, fluoroquinolones,
beta-lactams and tetracyclines
Validation of the detection system was performed in the
laboratory of the Nestlé Research Center in Lausanne in the
frame of a workshop where different methods developed in
GoodFood were compared. Reference milk samples with
known concentration of antibiotics were used for these tests.
The response signal observed with the milk sample on the
different reactive regions of the chip were compared to the
value obtained with milk contaminated at the maximum
residue limit level (MRL). Figure 3 displays the results
obtained for the different reference milks, demonstrating that
the four antibiotics can be detected at the MRL level.
Figure 3: Measurement of different milk samples for the simultaneous
detection of four antibiotics (dotted lines indicates signal at the MRL)
In the frame of the GoodFood project, it was possible to
develop a biosensor platform for the detection of four
antibiotics families simultaneously at the maximum residue
limit set in the legislation. Adapting this technology for Lab-
On-a-Chip [2] will provide a tool for antibiotic screening at the
farm level or before entering the dairy factory.
This work was funded by SER, European Project FP6-IST-1-
508774-IP and OFFT. CSEM thanks them for their support.
[1] www.goodfood-project.org
[2] G. Suárez, et al., “ Food Safety with the Help of a Miniaturized
Laboratory”, in this report, page 64
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