Biosensors are based on the conversion of a biological response to an electrical signal. One of the major challenges is to ascertain that the receptor is not denatured when immobilised (covalently or not) on the device. In this work, a protein receptor (virus) was immobilised on two different surfaces, mica and self-assembled monolayer (SAM), and its height was determined by atomic force microscopy measurements at the atomic level. Results clearly showed that expected dimensions of Tobacco Mosaic Virus (TMV) are obtained after immobilisation onto a soft organic SAM.