Surface assemblies based on carbon nanotubes in a piezoelectric immunosensor for the highly sensitive determination of ractopamine
Abstract
The article proposes piezoelectric immunosensors based on surface ensembles of multi-walled carbon
nanotubes (CNTs) for the determination in a direct format of an immunoassay of trace concentrations of
ractopamine banned to be used in the Russian Federation as a feed additive to increase the productivity of
livestock and a fat-burning agent for producing lean meat, Content on the health of consumers. The conditions
for the formation of a recognition layer of a piezoelectric sensor based on carbon nanotubes for the
highly sensitive determination of ractopamine in direct immunoassay format have been studied. The recognition
layer was formed in several stages, including the modification of the sensor electrode by
2-mercaptoethylamine, the formation of ensembles based on multi-walled carbon nanotubes, and the immobilization
of monoclonal antibodies to ractopamine on their surface. Preliminary treatment of carbon nanotubes
with concentrated nitric and sulfuric acids, as well as activation of carboxyl groups by carbodiimide method,
provides their strong binding to amino groups of a substrate based on 2-mercaptoethylamine and amino
groups of monoclonal antibodies to ractopamine used as recognition elements of the sensor. The concentrations of colloidal solutions of two types of carbon nanotubes in dimethylformamide are established, which
ensure maximum values of the concentration sensitivity of the piezoelectric sensor when determining ractopamine.
The increase in the concentration of CNTs at the stage of formation of the recognition layer leads to
a simbatic change in the mass and thickness of the film coating, in the case of using colloidal solutions of
CNTs with a concentration of 500 mg/dm3
, the oscillation of the sensor oscillations is observed. The maximum
value of Sc was noted when using solutions of CNT 1 and CNT-2 100 mg/dm3
and 144 mg/dm3
, respectively.
The influence of concentration of monoclonal antibodies used in the immobilization stage was
studied. The choice of the working concentration of antibodies was carried out at the maximum saturation of
the sorption layer, with the concentration of monoclonal antibodies equal to 3.2 ng/cm3
, the limiting density
of the active binding sites on the surface of the sensor electrode is reached. Surface topography is estimated
by atomic force microscopy, a significant increase in the average arithmetic roughness Ra of the CNT-based
recognition layer as compared to the substrate based on 2-mercaptoethylamine is established, which indicates
the possibility of placing more detectable molecules of monoclonal antibodies on the sensor electrode. The
range of detectable contents of ractopamine by means of a piezoelectric sensor is (ng/cm3
) 0.09-25, the detection
limit is 0.03
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References
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