Prospects for the Use of Gold Nanoparticles to Increase the Sensitivity of an Acoustic Sensor in the Detection of Microbial Cells

The interaction of microbial cells with antibody–gold nanoparticle conjugates in conductive suspensions was experimentally studied by using an acoustic slot-mode sensor. The sensor consisted of a piezoelectric plate with a propagating acoustic wave and a liquid container located above this plate with a given gap. An analysis of the measured parameters of the sensor revealed that the specific interaction of bacterial cells with the conjugates led to a stronger change in the sensor output signal than the specific interaction of bacterial cells with antibodies. The measurements were made for Azospirillum brasilense Sp7 cells in buffer with an initial conductivity of 5–30 μS/cm. The limit of cell detection with the conjugates was 103 cells/mL, and the analysis took about 4 min. The advantage of the sensor is the possibility of repeated use and cleaning of the liquid container without damaging the sensor’s elements. These results are promising for use in rapid test systems for the direct detection of microbial cells in actual samples of liquids in medical diagnostics.