Since the beginning of the coronavirus disease 2019 (COVID-19) in December 2019 and the current lack to date of specific drugs or vaccinations to cope with the disease, it has become apparent that the surest way of dealing with this is through early diagnosis and management. Current testing has shown to be unable to rapidly and accurately provide the results required to restrict the spread. Here we report the use of an intrinsic silicon thin film transistor functionalised with aptamers designed to attach to the spike protein of COVID-19. It is shown that a linear response can be obtained in a concentration of 10 fM and 10 pM, and that the relative response is independent of the applied potential allowing a sensory system to fine tune the applied potential to facilitate the interpretation of the results.