Disclosed is a method of detecting the presence of an oligomer analyte in
a liquid sample, the method comprising the steps of: (a) contacting a
sample comprising the oligomer or aggregate with an oscillating sensor
surface, which surface may optionally be coated with a receptor that
binds directly or indirectly to at least one component of the oligomer or
aggregate, so as to cause direct or indirect binding of the oligomer or
aggregate to the surface; (b) using a detection circuit to measure or
calculate at least two of the following parameters: series resonance
frequency (f.sub.0), and hence the series resonance frequency shift
(.DELTA.F); motional resistance (R.sub.M), and hence the motional
resistance shift .DELTA.R; motional inductance (L.sub.M); motional
capacitance (C.sub.M); parallel capacitance (C.sub.0); frequency
half-band half-width (.GAMMA.); Q-factor (=f/(2.GAMMA.); dissipative
factor (1/Q); impedance or admittance phase (.phi.) and hence phase shift
(.DELTA..phi.); and impedance or admittance amplitude (Z, or Y) and hence
amplitude change (.DELTA.Z, or .DELTA.Y); (c) and analysing the
calculated values to derive data which vary according to the presence
and/or amount of oligomer in the sample; (d) and, optionally, repeating
the measurements continuously or intermittently to derive data which vary
according to the presence and/or amount of oligomer or aggregate in the
sample to be calculated as a function of elapsed time.