The eye-shaped sensor finds cancer cells early. It works even with small mistakes or heat changes, making it useful for real use.
A new photonic crystal biosensor design with an eye-shaped cavity has demonstrated high sensitivity and stability in detecting cancer cells. It achieves a sensitivity of up to 243 nm per refractive index unit (RIU), a high Q-factor of about 87,070, and a figure of merit (FoM) of 11,800 RIU⁻¹. These values are higher than many earlier designs. The sensor also remains stable under small fabrication errors and temperature changes, making it practical for real-world use.
Photonic crystal biosensors work by controlling and trapping light at very small scales. They use repeating patterns of dielectric materials like silicon to form photonic bandgaps—regions that block certain light wavelengths. This allows them to detect changes in their environment with high precision. When light passes through different types of biological cells, the refractive index changes slightly. Cancerous cells, for example, shift the light’s resonance wavelength in a detectable way, which forms the basis of this sensing method.
Most existing biosensor designs use round or hexagonal cavities to trap light. However, this study proposes using an eye-shaped cavity, which is less commonly explored. The eye shape helps trap light more tightly, leading to higher sensitivity and a better-defined resonance peak. This sharper optical response makes it easier to detect small biological changes, such as those caused by cancer cells.
The sensor structure is based on a two-dimensional grid of silicon rods suspended in air. Each rod is 0.1 µm wide, and the rods are spaced 540 nm apart. Two straight waveguides allow light to enter and exit the device. The eye-shaped cavity, placed between these waveguides, holds the material being tested. Researchers used simulation tools based on the finite element method to adjust the cavity shape and rod positions, improving how sharply and predictably the resonance wavelength shifts during detection.
To measure performance, the team evaluated three key indicators: sensitivity, Q-factor, and figure of merit (FoM). Sensitivity refers to how much the resonance wavelength shifts per unit change in refractive index. The Q-factor shows how sharp and distinct the resonance peak is. The FoM combines both values to represent overall sensor effectiveness.
The simulations showed excellent results. The sensor’s resonance wavelength shifted clearly and predictably as the refractive index changed, allowing small differences in cell properties to be measured. Even when the design was slightly inaccurate—by ±2 nm in the cavity or ±20 nm in the rod spacing—the sensor still worked well. It also stayed stable across a temperature range from 25 °C to 75 °C, meaning heat or material fluctuations had little effect on performance.
This new design successfully combines an unconventional cavity shape with high sensing accuracy and physical resilience. It does not require any extra fluorescent labels or dyes to detect cancer cells, which simplifies the process. Thanks to its tolerance for small errors and environmental shifts, it has strong potential for use in medical diagnostics, especially for early cancer detection.