Chiroptical planar metasurfaces have become a promising platform for exploring chirality-based applications and functionalities in nanophotonics due to their capability to enhance light-matter interactions at the nanoscale. Most existing research experiences an inverse correlation between quality factor ($Q$-factor) and circular dichroism (CD) that involves the copolarized (${\mathrm{CD}}_{\mathrm{Chi}}$) and cross-polarized (${\mathrm{CD}}_{\mathrm{Ani}}$) components, thereby limiting the practical applications of multifunctional and tunable optical sensing capabilities. Here planar chiral silicon metasurfaces, incorporating $\mathsf{I}$-shaped and $\mathsf{L}$-shaped meta-atoms, are numerically demonstrated and employed to yield a positive correlation between the $Q$-factor and CD, as well as reveal high-$Q$ and ultrasensitive chiral sensing in the near-infrared regions. In particular, leveraging distinct symmetry-breaking approaches, the $Q$-factor, ${\mathrm{CD}}_{\mathrm{Chi}}$, and ${\mathrm{CD}}_{\mathrm{Ani}}$ exhibit positive correlation with the related asymmetry parameters. Moreover, by embedding with the phase-change material ${\mathrm{VO}}_2$, dynamic modulation of ${\mathrm{CD}}_{\mathrm{Chi}}$ and ${\mathrm{CD}}_{\mathrm{Ani}}$ can be finely adjusted via varying the configurations and the thickness of the ${\mathrm{VO}}_2$. In addition, the steerable chiroptical responses can be engineered to achieve high-$Q$ and ultrahigh-sensitivity chiral sensing in the near-infrared regions. These findings not only provide a unique approach for the realization of high-$Q$ and ultrasensitive metadevices but promote the advancement of multifunctional biochemical and environmental sensing applications.

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• Chirality
• Light-matter interaction
• Metasurfaces
• Nanophotonics