This article presents the design and development of a novel terahertz (THz) sensor with a graphene-infused metamaterial for precise detection of different refractive indices. The sensor operates in a single-band frequency, with a metamaterial unit cell size set at 1.401 times the effective wavelength (lambda(eff)), and it exhibits a resonant frequency of 4.48 THz. The proposed sensor achieves a remarkable peak absorption of 99%. The sensor is composed of a series of layers, such as graphene, polyimide, copper, and Teflon, to finely tune the absorption response. The sensitivity metrics of the sensor were derived from its absorption response to various refractive index profiles. The sensor's sensitivity is studied with random dielectric substances and specific chemical analytes. The complete characterization of the sensor has been obtained for performance parameters, such as absorptivity versus analyte thickness, refractive indices, and chemical potentials. The outcome of this research affirms the suitability of the developed refractive index-based metamaterial sensor for a broad spectrum of THz sensing applications, highlighting its potential for enhancing THz imaging techniques.