Agriculture Reference
In-Depth Information
enhancing the shelf life of a product, easier and faster analysis, characterization of
food components as nanoscale, etc. There will be some samples about
nanobiosensor usage in food.
The beta-lactam group is one of the most important families of antibiotic used in
veterinary medicine in the treatment of septicaemia, pulmonary and urinary infec-
tions. The presence of penicillin residues in a food of animal origin like meat and
milk might have several drawbacks: possible hypersensitivity reaction to the
consumer, unfavourable microbiological effects in the dairy industry and antibiotic
resistance. Maximum residue limits (MRL) were set at 4
μ
gl
1
for penicillin G,
penethamate (penicillin G), amoxicillin and ampicillin (penicillin A) and at
30
gl
1
for cloxacillin, oxacillin, dicloxacillin and nafcillin in milk (penicillin
M) (
EEC 508
and
EEC 804
, 1999). A biosensor-based immunoassay for the
screening of penicillin residues in milk was developed. The Biacore biosensor
which was used was based on SPR detection. One commercial antibody against
ampicillin which had a much higher affinity for open beta-lactam ring than for
closed ring was chosen. Two different pretreatments were tested prior to the
biosensor assay to open the ring in order to increase the assay sensitivity. These
two ways were enzymatic (penicillinase) and chemical pretreatments of the sam-
ples. Limits of detection for ampicillin in milk were 33 and 12.5
μ
gl
1
after
enzymatic and chemical pretreatments, respectively. There were no cross-reactions
with cephalosporins and other families of proteins or antibiotics in milk and in the
buffer after both the pretreatments. Percentages of cross-reactivity with nine tested
penicillins were frequently clearly higher in milk than in buffer. Furthermore, a lack
of sensitivity after penicillinase pretreatment was observed. On the other hand,
penicillin M and penicillin G might be detected below or at their respective MRLs
(30 and 4
μ
gl
1
in milk), and amoxicillin and ampicillin might be detected only at
about three MRLs after chemical pretreatment. Besides, the enzymatic pretreatment
was much easier to perform and led to more stable results from the point of view
(Guadin et al.
2001
).
For the detection of veterinary drug residues in food, the most commonly used
biological element is the antibody/antigen affinity pair, already widely used in the
immunochemical screening of samples by other techniques. At this stage, the
biosensor is called an immunosensor. For the detection of antibiotics, the
immunosensors used frequently exploit optical or electrochemical transducer sys-
tems. The former may be amperometric, potentiometric or conductometric/capac-
itive. Potentiometric devices measure changes in ion concentration and pH when an
antigen in a sample interacts with an antibody immobilized on an electrode. The
potential difference between the electrode bearing the antibody and a reference
electrode is a function of the concentration of analyte in the sample. An ampero-
metric biosensor measures the current produced when an electroactive species is
reduced or oxidized at an antibody-coated or antigen-coated electrode to which an
analyte or antibody binds specifically. Capacitive or conductometric biosensors
measure the alteration of the electrical conductivity in a solution at a constant
voltage, caused by biochemical reactions that specifically consume or generate
ions. As these transducers are generally non-specific and have a poor signal/noise
μ
