  Metasurfaces providing resonances arising from quasi-bound states in the
continuum have been proposed as sensors in the THz band due to the existence of
strong resonances characterized by high quality factors. Controlling
geometrical parameters, the quality factor can be adjusted and, theoretically,
designed at will. However, losses in materials critically bound the metasurface
performance and limit the quality factor of the resonances. For this reason,
all-dielectric metasurfaces have been proposed as an alternative to
metal-dielectric structures to reduce losses and achieve extreme
functionalities. When implemented by low-loss materials, these structures are
usually considered lossless and proposed as ultrasensitive sensors in the THz
band. In this paper, we examine the effect of losses in all-dielectric
metasurfaces considering realistic materials and study the limitations in the
quality factor. In addition, we compare the performance of these structures as
sensors with a nanostructure supporting extraordinary optical transmission. Our
results show that material loss, even in low-loss materials, severely limits
the sensing performance in all-dielectric metasurfaces, and that their
performance can be surpassed by structures supporting extraordinary optical
transmission.
