In this study, we theoretically investigate one-dimensional photonic crystal (1D PC) with a defect layer as a biosensor for the detection of COVID-19 (SARS-CoV-2) through human blood. Finite-difference time-domain method (FDTD) is used to calculate the transmission spectrum of the biosensor by using OptiFDTD software. The photonic crystal biosensor performance is measured by the transmission peak shift in resonant wavelength. The effect of the defect layer thicknesses over sensor performance is studied and optimum sensitivity of the 107,0085 nm/RIU, quality factor of 0.3702x103 and detection limit of 3.37086x10-6 RIU is achieved for designed biosensor. The simple structure, easy analysis, and available fabrication techniques make the proposed design a suitable candidate for biosensing applications.