Biosensors based on novel nonlinear delta-function photonic crystals comprising weak nonlinearities.

In this research, we propose a novel nonlinear delta-function photonic crystal for detecting sodium iodide (NaI) solution of different concentrations. The suggested structure comprises 50 delta stacks of GaP in an aqueous solution of NaI. These stacks are considered to have weak defocusing nonlinearity in the order of 10-6 (V/m)-2. Due to nonlinearity of the design, a defect-like resonance is formed within the photonic band gap. Thus, the detection of NaI with different concentrations can be easily investigated without the inclusion of a defect through the photonic crystal structure. The effects of both the linear part of the refractive index of GaP layers and nonlinear coefficient on the transmittance value are thoroughly discussed. The numerical findings investigate that the resonant peak begins to split at some critical nonlinearity. In our proposed structure, splitting occurs at about - 12 × 10-6 (V/m)-2. In this regard, the suggested sensor provides a high sensitivity of 409.7 nm/RIU and a wonderful detection limit of 0.0008.

A 1D binary photonic crystal sensor for detecting fat concentrations in commercial milk.

Our goal in this study is to design an efficient sensor to detect the fat volume in commercial milk. We used a one-dimensional binary photonic crystal to design the sensor and the Transfer Matrix Method to study theoretically its optical response as the refractive index of milk samples changes due to the change in fat concentration. We found that the proposed sensor is efficient in sensing the fat concentration in milk. The optimum defect layer thickness is found to be 1.20 µm and the sensitivity of the sensor improved as the angle of incidence of radiation increased up to 60°. Besides, we proposed an empirical formula that can be used to estimate the fat concentration in milk. The efficiency of our sensor is based on the quick response of the sensor to the changes in the fat concentration in milk. The output signal of the sensor would be processed in a signal processing unit that will give an accurate estimation of the fat concentration in milk. The sensor is easy to fabricate, cost-effective, and user-friendly.

Detection and sensing of hemoglobin using one-dimensional binary photonic crystals comprising a defect layer.

Believing that the detection of hemoglobin possesses a vital role in the discovery of many diseases, we present in this work a simple method for sensing and detecting hemoglobin based on one-dimensional photonic crystals. Implementing hemoglobin as a defect layer inside the proposed photonic crystal results in a resonant peak evolving within the bandgaps. The strong dependence of these resonant peaks on concentration and the consequent refractive index are the essential bases of the detection process. The role played by these parameters together with the angle of incidence on performance and efficiency of our sensor is demonstrated. In the vicinity of the investigated results, we demonstrate the values of sensitivity, figure of merit (FOM), signal-to-noise ratio (SNR), and resolution to optimize the performance of our sensor. The numerical results show a significant effect of polarization mode on performance of this sensor. For TE polarization with an angle of incidence equal to 45°, we investigated sensitivity of 167nmRIU-1, SNR of 0.23, FOM of 0.63RIU-1, and resolution of 257 nm.