Having recently reported the use of a portable surface plasmon resonance (SPR) sensing device to detect anti-EcAII antibodies in undiluted serum from children undergoing therapy for ALL (Aubé et al., <i>ACS Sensors</i><b>2016</b>, <i>1</i> (11), 1358-1365), here we investigate the impact of the quaternary structure and the mode of immobilization of EcAII onto low-fouling SPR sensor chips on the sensitivity and reproducibility of immunosensing.