Label-free impedimetric immunosensors for psoriasin—Increased reproducibility and sensitivity using an automated dispensing system

We describe within this paper the construction of a label-free immunosensor for the protein psoriasin (S100A7), which is associated with a number of clinical conditions such as skin diseases or cancer. Antibodies to psoriasin were immobilised onto screen-printed carbon electrodes that had been pre-modified with the conductive polymer polyaniline. We compared and contrasted a number of different methods of assembly to optimise the construction and properties of the immunosensor. Immunosensors were fabricated using both manual liquid handling (pipette) and an automated liquid dispensing platform, the BioDot AD3200TM. Two immobilisation methods were also utilised; simple electrostatic binding of the antibody to polyaniline as well as a more complex procedure using a biotin–neutravidin bridge. The optimum results in terms of sensitivity and reproducibility were obtained utilising the automated system and the biotin–avidin assembly procedure. The resultant immunosensors could be interrogated using AC impedance without the need for any labelling and demonstrated quantification of psoriasin from 250 pg ml−1 to 10 ng ml−1—a concentration range suitable for determining physiological levels of psoriasin.

► Developed and optimised a label-free immunosensor for psoriasin.
► Antibodies to psoriasin immobilised using avidin–biotin or electrostatic interactions.
► Both manual and automated (BioDot AD3200 micro-dispenser) deposition used.
► Affinity immobilised sensors display much higher sensitivity than electrostatic.
► BioDot produced sensors display higher sensitivity and lower sample-to-sample variation. Levels of psoriasin from 250–10,000 pg ml−1 can be clearly determined.