A method of detecting a target biological entity 100 in a biofluid using a sensor, wherein the biofluid comprises the biological entity and nanoparticles 122. The sensor comprises a substrate bearing a pair of electrodes 110, 112 having an affinity with the nanoparticles. The region between the electrodes defines a sensing region 104. The method comprises treating the biofluid with the nanoparticles to obtain bound nanoparticle-entity assemblies. The bound nanoparticle-entity assemblies are introduced to the sensor. The sensor is conditioned in the presence of the bound nanoparticle-entity assemblies by applying an activation voltage between the electrodes 110, 112. The activation voltage increases a degree of connection between the surface of the electrodes and at least one bound nanoparticle-entity assembly. The presence of the target biological entity is determined by detecting a current through the bound nanoparticle-entity assembly. The activation voltage can fuse the bound nanoparticle-entity assemblies linking the electrodes. A nanoparticle sensing voltage can be less than the activation voltage. An electric field can be used to concentrate the bound nanoparticle-entity assemblies in the sensing region. The dimensions of the nanoparticles can be greater than the lateral distance separating the electrodes.
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