How Piezofilm Technology Works

Vivacta’s revolutionary diagnostic system is based on a specially prepared PVDF or polyvinylidinefluoride (plastic) film which acts as a sensor of molecules binding to it. The film has piezo (or pyro) electric properties such that an electric charge is generated across the surface of the film following its thermal deformation. The charge can be measured even in response to very small heating effects and this explains the extreme sensitivity of the Vivacta system and its ability to detect the presence of target substances (analytes) at very low concentrations.

The film is mounted in a 6.0 x 4.5cm cartridge which is also a blood collection device able to draw up a pin prick (30µL) of blood along a capillary tube leading to a chamber immediately below the piezofilm. The system is established to measure whole blood. However, other formats are also possible to accommodate alternative sample matrices including serum, plasma and urine.

Once a blood sample is drawn into the cartridge, the cartridge is placed in a compact desktop reader which simultaneously illuminates the sample and measures the charge across the piezofilm.

Before being mounted in the cartridge, the piezofilm is coated with antibodies which specifically bind the target analyte (substance being tested). The inside surface of the capillary tube is coated with a dried-down layer of a second antibody (this time linked to carbon particles) also specifically able to bind the analyte but at a different molecular site from the antibodies bound to the piezofilm.

As the blood sample moves from the capillary tube to the test area within the cartridge, the carbon-antibody-conjugate dissolves in the blood sample. Once the sample, mixed with the carbon conjugates, reaches the piezofilm, a chemical reaction begins. The analyte, if present in the sample being tested, binds to both antibodies at the same time. The reaction results in a “sandwich” in which the analyte is compressed between the two sets of antibodies.

The sandwich reaction causes the carbon particles to become linked to the piezofilm. During the reaction, the desktop reader illuminates the sample every few milliseconds using a flashing light-emitting diode (LED) installed within the instrument, adjacent to where the cartridge is inserted. Carbon particles linked to the film absorb the light and convert it to heat which deforms the film to generate a charge. As more carbon particles become linked to the film, each pulse of light results in greater heat transfer and so greater charge. The rate of change of charge is proportional to the concentration of analyte in the sample. The measurement of charge over time across the piezofilm measures the analyte’s concentration in the sample. This measure is direct in the case of immunometric (sandwich) assays, which are appropriate for measuring large molecules such as proteins or antibodies, and inverse in the case of competitive assays which are appropriate for measuring small molecules, including many drugs.

In summary, piezofilm detection monitors the rate at which a target analyte (substance to be measured) binds to the piezofilm surface. This binding rate is related to the concentration of analyte in the sample.