Plasmonic sensors show great potential in healthcare with nanohole arrays being most suited to highly sensitive, multiplexed label-free biosensing in point-of-care diagnostics. Extraordinary optical transmission (EOT) occurs when incident light is coupled to plasmonic modes in a nanohole array. When biomolecules bind to the surface of the nanohole array the refractive index surrounding it changes. We use optical microspectrometry and imaging to measure the EOT resonance wavelength shift due to the presence of these biomolecules. We demonstrate the biosensing capabilities of our plasmonic sensor with the detection of molecular and protein binding events, and cancer biomarkers.