IMMUNOLOGICAL SENSORS



PIEZOELECTRIC SENSORS

µLibra quartz-based microbalance uses as transductors AT-cut crystals with fundamental oscillation frequency of 10 MHz. The surface of transductor is coated by a thin golden layer as electrode.

Onto the golden electrodes biomolecules, such as antibodies, can be bound, by means of both passive adsorption, or covalent binding by a thiocompounds self-assembled monolayer (SAM), or by silanization (APTES, GOPS) with or without cross-linkers. Moreover, thanks to the highly specific binding between streptavidin (linked to the gold electrode) and biotin (antibody-conjugated), a very stable complex is obtained.

Immunoassays by QCM, in general, can be carried out by using label-free molecules (not modified by reporter molecules) since the binding event is merely revealed by means of the oscillation frequency shift due to the mass adsorbed onto the electrodes. Nevertheless, QCM immunoassays can be carried out by using a sandwich design. In this case, the signal is easy amplified by using e.g. a secondary colloidal gold-conjugated antibody.



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ELECTROCHEMICAL IMMUNOSENSORS

Immunoelectrochemical assays are not widely used, but they become more and more interesting considering the possibility to produce miniaturized and low-cost electrodes.These can be made in large-scale production by using low-cost materials and employing the screen-printing technology that uses carbon or other conductive substances as inks.

Several electrochemical reaction can be used to reveal the antigen-antibody binding, based on the reporter molecule used (enzymatic substrates producing electroactive products or colloidal gold).

The reaction is measured by means of the differential pulsed voltammetry (DPV), which can be easy performed with commercial available potentiostats. The use of screen-printed electrodes and the possibility to perform the analysis in a flow-cell, allow to reduce the volume required for reaction, resulting in a noteworthy optimization of precious reagents and samples.


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