A rhombus-shaped holes-based photonic sensor is proposed and analyzed using the finite-difference time-domain method embedded in the commercial simulator RSoft. By changing the refractive indices in the biosensor under testing, the transmission properties of light are changed according to the changes in glucose concentrations. Various sensitivities are obtained and given as 604.5, 589.91, 537.86, and 520.5  nm  /  RIU, corresponding to both quality (Q) factors as high as 4.414  ×  10⁵, 2.1  ×  10⁵, 8.34  ×  10⁵, and 3.247  ×  10⁶ and a detection limit of 5.89  ×  10^−  7, 1.27  ×  10^−  6, 3.44  ×  10^−  7, and 8.99  ×  10^−  8, respectively. The obtained results were within the cavity region. Therefore, the Q factor and the sensitivity were significantly improved for the proposed structure, which makes this proposed design a potential and promising label-free biosensing device for the biomedical prognosis.