Aims & Objectives: In this work, we employed the transfer-matrix method to obtain the transmittance spectrum of a one-dimensional photonic crystal composed of polymer materials. As we increase the blood plasma concentration and the thickness of the cavity, we discover a defect mode within the photonic band gap that is specifically tuned for long wavelengths. Methods: Photonic Crystals (PCs) are artificial heterostructures with a spatial periodicity of their refractive indices. Conversely, employing PCs as alternative biosensing devices for monitoring human health through different blood components has also become popular Results: Fig. (a) shows the transmittance spectrum as a function of blood plasma concentration for a fixed value of the cavity thickness and the applied pressure (0 MPa). As glucose increases from 0 to 50 g/L, a shift of the defect mode toward longer wavelengths is observed in Fig. (b). Fig. (c) shows the behavior of the transmittance spectrum as the pressure increases from 0 to 120 MPa. A defect mode blueshift is observed while keeping the PBG width unchanged, as seen in Fig. (d).Conclusions: This work aimed to investigate the effects of the variations in pressure, blood plasma concentration, and increased cavity thickness on the confined mode in the PBG. Following the use of the Transfer-matrix method for a 1D-PC composed of polymer materials, defect mode tuning at long wavelengths was observed as the blood plasma concentration and cavity thickness increased. Additionally, a decrease in the energy stored in the cavity was observed as the applied pressure increased. Keywords: Transmittance spectrum, blood plasma concentration, photonic band gap, photonic crystal