基于Parity-Time对称耦合微腔的血糖传感器

Blood Glucose Sensor Based on Parity-Time Symmetry Coupled Cavities

为设计新型光学生物传感器,本课题组构造了基于Parity-Time(PT)对称的耦合谐振腔系统,用于实现对人体血糖浓度的测量。通过结构优化,使系统达到PT对称极点状态,然后利用极点状态下透射率对血糖折射率极其敏感的特性,将对血糖浓度的测量转化为对系统透射率的测量,从而达到血糖传感的目的。本文研究了两种传感方式:一是固定特定极点处的频率,测量系统在不同血糖浓度下的透射率;二是在极点附近的频率范围内扫描,测量特定血糖浓度下透射率的峰值。血糖质量浓度为20~182 mg/dL时,第二种方式下传感器的灵敏度均高于第一种方式;当血糖质量浓度高于182 mg/dL时,第一种方式在1466.40 THz频率下的灵敏度要比第二种方式高。可以将本文对血糖浓度的传感方式推广到对其他生物样本的测量上。

Objective With the continuous improvement of living standards,excessive energy intake increases the rate of diabetes yearly.Additionally,kidney failure,heart disease,and many other diseases can cause blood glucose abnormalities.Therefore,paying attention to the detection of blood glucose and the design of glucose sensors with high performance become essential.Sensors based on photonic crystals(PCs)are widely used in biology and medicine.Most of these sensors are based on the relationship between blood glucose concentration and its refractive index.The change in the refractive index will cause the movement of the transmission peak of PCs.Thus,people can detect blood glucose concentration by measuring the movement of the transmission peak.However,the movement of the transmission peak is too little for detecting with a small change in the refractive index.Thus,the small change in blood glucose concentration is not easily detected with PC sensors.To solve this problem,a coupled-resonator system based on Parity-Time(PT)symmetric configuration is constructed to measure blood glucose concentration.The polar effect of the PT-symmetric structure will be excited through structural optimization.On the pole state,the PT-symmetric structure can achieve huge transmittance and reflectance and is extremely sensitive to the change of structural parameters.When the blood is filled with the coupling layer,the change in blood glucose concentration changes the refractive index;thus,changing the sensor's transmittance.On the pole state,the transmittance of the sensor changes,even for the small change in blood glucose concentration,the transmittance of the sensor changes obviously.This can solve the problem of limited sensitivity and accuracy of traditional blood glucose sensors.It also provides an approach for measuring blood glucose concentration.The design idea of this sensor is not limited to the measurement of blood glucose concentration and provides a universal method for detecting other organisms.Methods The designed model of the sensor is shown in Fig.1.The overall structure was expressed as PAGA_(1)LAP.The two layers P were a pair of coupled prisms with the base angle θ and the refractive index 3.48.Layer A was the air layer with a thickness of d_(a)=400 nm and the refractive index of n_(A)=1.00027.Layers G and L were gain and loss layers,which constitute two-coupled resonators with the same thickness of 1500 nm.The refractive indexes of layers G and L were n_(G)=3205-iτ and n_(L)=3205+iτ,where τ was the gain and loss coefficient.The overall structure met the requirements of the PT-symmetry that the real part of the refractive index was even symmetry and the imaginary part was odd symmetry.The middle layer A_(1)was filled with the object to be measured.The input light was incident on the left prism,and a total reflection occurred on its inner interface.The evanescent waves entered the two-coupled resonators and achieved resonance transmission.The output through the right prism was connected with a photoelectric sensor,which converted the intensity of transmitted light into the current signal for recording.Semiconductor InGaAsP doped with quantum well was used as the gain dielectric layer,and Cr/Ge was covered on the gain dielectric layer to form the loss layer.The transfer matrix method was used to calculate the transmittance and reflectance of the structure.To achieve the purpose of blood glucose sensing,measurement of blood glucose concentration was transformed into the measurement of the system transmittance.Results and Discussions First,we assume that layer A_(1)was filled with air.The result in Fig.2 shows that there are two adjacent transmission peaks with transmittance near 1 corresponding to the two-coupled modes.With τ=0.003904,the two peaks merges into one peak,and the peak value undergoes a jump zoom up to 60 dB.This is the pole state.Next,we assume that layer A_(1) is filled with blood with different glucose concentrations and the corresponding transmittance is calculated.The results are shown in Fig.5.We choose τ=0.006701 to excite the pole effect for the new medium in layer A_(1).The change in the blood glucose concentration leads to different peak values and positions.In this study,we investigate two sensing methods.One is to fix the frequency around a specific pole to measure the system transmittance under different blood glucose concentrations.The other is to detect the peak value corresponding to a specific blood glucose concentration by scanning the transmission spectrum near the pole.The sensing results and the corresponding sensitivities for the two methods are shown in Figs.7 and 9,respectively.When the blood glucose concentration is 20-182 mg/dL,the sensor's sensitivity in the second method is higher than that in the first method.However,when the blood glucose concentration is higher than 182 mg/dL,the sensor's sensitivity sensor in the first method is higher than that in the second method.If the sensor detects blood glucose with a high concentration,the first method can be selected.However,the second method can be selected if the sensor detects blood glucose with low concentration and requires high sensitivity.Conclusions In this study,we design a theoretical model of glucose concentration sensor using the pole effect of the PT-symmetric structure.Unlike the traditional sensor,the designed model does not use spectrum positions as the sensing mechanism but uses transmittance detection as the sensing method.The new sensing mechanism has high precision and sensitivity.Although our model is for blood glucose sensing,it can be extended to general biomaterial sensing,including sensing various diseased cells.Therefore,this study provides a new universal method for biosensors.