The outbreak of the Covid-19 virus has faced the world with a new and dangerous challenge due to its contagious nature. Hence, developing sensory technologies to detect the coronavirus rapidly can provide a favorite condition for pandemic control of dangerous diseases. In between, because of the nanoscale size of this virus, there is a need for a good understanding of its optical behavior, which can give an extraordinary insight into the more efficient design of sensory devices. For the first time, this paper presents an optical modeling framework for a Covid-19 particle in the blood and extracts its optical characteristics based on numerical computations. We first model a Covid-19 particle based on the available information and the established theoretical concepts from a biophysics perspective. In order to obtain the optical properties of the Covid model, the light reflectance of the structure is then simulated for different geometrical sizes, including the diameter of the Covid particle and the size of the spikes surrounding it. Interestingly, the achieved results indicate some optical phenomena, such as redshift under the geometric variations of the Covid particle model. Furthermore, the density of Covid particles is investigated when the light is incident on different sides of the sample. Following this, we propose a nanosensor based on graphene, silicon, and gold nanodisks and demonstrate the functionality of the designed devices for detecting Covid particles inside the blood samples. Indeed, the presented nanosensor design can be promoted as a practical procedure for creating nanoelectronic kits and wearable devices with considerable potential for fast virus detection.