Label-free detection of charged macromolecules by using a field-effect-based sensor platform: Experiments and possible mechanisms of signal generation

The possibilities and limitations of a direct electrical detection of charged macromolecules using a field-effect-based sensor platform is evaluated, mainly focusing on capacitive EIS (electrolyte-insulator-semiconductor) devices. The experimentally obtained results on the detection of DNA immobilisation and hybridisation as well as the monitoring of layer-by-layer adsorbed charged polyelectrolyte (PE) multilayers have been discussed by using two basic possible mechanisms of signal generation, namely the intrinsic charge of the macromolecules and the charge redistribution within the intermolecular spaces or in the multilayer. The effects of the layer-by-layer adsorption conditions (unbuffered and pH buffer solution), and the number and polarity of charged layers on the sensor response have been systematically investigated by means of capacitance–voltage (C–V), constant–capacitance (ConCap) and impedance spectroscopy (IS) methods. PACS 82.47.Rs; 82.80.Fk; 85.30.Tv; 87.15.Kg; 87.14.Gg