- Hydrogels are considered an optimum material for protein chip surfaces, since they provide a quasi-liquid environment which allows protein activity to be maintained and shows good spot morphology as well as excellent immobilization capacity. In the following, we present a polyurethane (PU) chip that electrostatically binds IgG. The PU surface is optimized with regard to layer thickness (∼200 nm), hydrogel (2%) and immobilized antibody concentration (0.5 mg mL−1; 0.3 ng spot−1), pH and ionic strength of the print buffer as well as to blocking solution. Evaluation is done in a direct IgG immunoassay using the Nexterion slide H as a reference. It is shown that higher IgG loading is achieved on the PU chip than on slide H, no matter whether 1× PBS (pH 7.2), Sörensen (pH 5.8) or Nexterion buffer was used as a spotting solution. Moreover, the crossreactivity with goat IgG, human IgG and monoclonal anti-CRP spotted in Nexterion buffer was as low as ≤0.74% (slide H: ≤3.34%).