Embodiments of the invention are related to microfluidic devices for detecting or determining the concentration of biomolecules in an analyte comprising: a channel, wherein a surface of said channel is fabricated to be functionalized with at least one molecule selected to interact with a biomolecule, said channel being configured to interact with a microsphere, wherein a surface of said microsphere is fabricated to be functionalized with at least one same or different molecule selected to interact with said biomolecule; a second channel in fluid communication with said first channel; a system to move fluid containing said microsphere through said first and second channels; and a system to measure a change in electrical impedance or optical microscopy across said second channel as said microsphere moves through said second channel. Other embodiments concern related devices, and methods of making and using.