The direct label-free detection methods for bioanalytical applications employ much simplied assay formats compared to traditional approaches based on labels as enzymes, uorophores, and radioactivity. The continuous evaluation of the progress of the afnity binding interaction provides more detailed information compared to traditional techniques that measure the amount of the surface-bound label only at the end of the interaction. Furthermore, the direct sensors can be used repeatedly for many assays, thus reducing the running costs. Several physical transducers are capable of measuring surface mass changes resulting from the formation of biomolecular complexes at the sensitive area. Although mostly advanced optical systems are utilized, the piezoelectric (PZ) and acoustic devices  represent a similar but signi- cantly less expensive alternative.