Loss of Capacitance Ideality in Label-Free Immuno-Chip

Improved label-free capacitive detection was very recently demonstrated for both ssDNA and antigen target molecules. That improvement is due to ethylene-glycol alkanethiols monolayers used as linkers for anchoring probe molecules. The presence of ethylene-glycol chains into the thin films greatly reduces time drift, detection error, and non-specific signals. It also increases ideality of the electrochemical interface behavior. However, the ideality of probe surfaces is partially lost when dealing with antibodies. The aim of this paper is to show this loss of ideality by means of capacitance measurements upon the frequency as acquired in label-free detection of cancer markers.