Accurate nanoliter liquid complex admittance characterization up to 40 GHz for biomedical applications

In this paper is demonstrated an accurate liquid sensing technique in the nanoliter-range from 40 MHz to 40 GHz. The sensor is based on an interdigitated capacitor with a microfluidic channel placed on top to confine the liquid. Its sensing volume corresponds to 0.9 nL, whereas the developed microtechnology is fully compatible with a massive parallelization at low cost. Both alcohol and biological aqueous solutions have been precisely defined and distinguished in terms of capacitance and conductance´s contrasts with respect to pure water. Mixtures of 10% and 20% of ethanol exhibit capacitance´s values of 30 fF and 60 fF at 13 GHz respectively. A similar discrimination level is also achievable on the conductance at high frequencies and notably at 40 GHz. As far as biomedical applications are targeted, we also demonstrate the potentialities of Fetal Bovine Serum detection in aqueous solution down to 0,1 % v/v.