Acoustic wave devices coated with a biolayer are described for the detection target bio-molecules. The acoustic wave device is connected in an oscillator circuit, and the frequency shift .DELTA.f resulting from a biomolecular event is recorded. Further described are the use of Rayleigh wave surface acoustic wave devices for vapor phase detection as well as quartz crystal microbalance devices for liquid phase measurements. A biofilm on the surface of the acoustic wave device comprises of a layer of antibodies raised against a specific target molecule or antigen. Signatures for detection events are presented in the form of frequency shifts .DELTA.f(t).