In antibody-based biosensors, the nature of the underlying electrode can significantly influence the binding strength of capture antibodies, their association constant and stable. Here, screen printed carbon electrodes (SPCE) have been electroplated with gold (Au) or platinum (Pt) nanostructures and used as a platform for the immobilisation of antibodies for the important cancer biomarker CA125(MUC16). The sensor performs very effectively in human blood plasma with Limits of Detection, LOD, of 419 +/- 31 ngmL(-1) and 386 +/- 27 ngmL(-1) for electrochemically deposited Au and Pt nanostructured interfaces, respectively. Electroplating allows the surface roughness, and hence the total number of moles of antibody immobilised per unit area to be controlled. The deposited Au and Pt layers provide a suitable microenvironment for anti-CA125 adhesion and allow CA125 to be detected. For the Au, the electrochemically active surface area was 0.382 +/- 0.03 cm(2) but is strikingly larger for Pt, 3.250 +/- 0.25 cm(2). For the Au-SPCE, the standard heterogeneous electron transfer rate constant (k(o)) has been determined by fitting the complete cyclic voltammograms after each modification step. The k(o) decreased from 185.0 +/- 3.7 x 10(-5) cm s(-1) to 81 +/- 9.5 x 10(-5) cm s(-1) after anti-CA125 immobilisation, i.e., antibody immobilisation modulates the electron transfer rate rather than simply reducing the electrochemically active area. Significantly, after BSA blocking to prevent non-specific adsorption onto areas of the electrode not modified by anti-CA125, k(o) decreased to 6.2 +/- 0.87 x 10(-5) cm s(-1). In comparison, on Pt-SPCE the k(o) decreased from 132 +/- 4.6 x 10(-5) to 65 +/- 8.5 x 10(-5) cm s(-1) after anti-CA125 immobilisation and decreased further to 5.1 +/- 0.19 x 10(-5) cm s(-1) after BSA blocking. Significantly, on the high-surface-area Au-SPCE electrode, antigen binding does not statistically change the rate of heterogeneous electron transfer. In contrast, at the Pt-modified SPCE, CA125 binding causes the k(o) to decrease by a factor of two - to 2.5 +/- 0.8 x 10(-5) cm s(-1), making Pt-SPCE electrodes coated with anti-CA125 promising for CA125 detection. (c) 2019 Elsevier Ltd. All rights reserved.