Methods and apparatus for analyzing bioprocess fluids are provided. A plurality of particles coated with a plurality of capture agents having an affinity for one or more biological markers is combined with bioprocess fluid to form a plurality of analyte-particle complexes. The system also includes a transport arrangement for transporting the sample to a sensor surface, and optionally a magnetic field inducing structure constructed and arranged to establish a magnetic field at and adjacent to the sensor surface. The resonant sensor produces a signal corresponding to an amount of analyte-particle complexes that are bound to the sensor surface.