Once the electrode has been modified the bioreceptor, i.e. antibodies or antigens, can be immobilised onto the surface. As previously mentioned, bioreceptors such as enzymes can be immobilised onto the surface during the electrode modification step, usually within a polymer layer. Although this technique is generally not adopted for immunosensors due to steric hinderance, some groups have successfully detected analytes through entrapped antibodies or antigens. John et al. deposited PPy on a platinum electrode with anti-human serum albumin (HSA). formed a semiinsulating layer on Au with insulative polymer o-phenylenediamine and antibodies for hepatic fibrosis biomarker.