Construction Of Portable Enzyme-free Electrochemical Glucose Sensor Based On Metal-organic Framework

Currently,point-of-care testing（POCT）devices are expensive and require trained professionals to operate.This creates a challenge for diabetic patients who require daily glucose monitoring to manage their condition effectively.Many commercially available glucose meters use enzyme-based electrochemical sensing electrodes as their detection front end.However,the use of enzymes can negatively impact the stability and manufacturing cost of glucose detection electrodes,presenting additional challenges.Therefore,the development of an enzyme-free electrochemical glucose sensor and its integration into a portable electrochemical detection system as the detection front-end can greatly benefit diabetic patients in managing their health.This approach would result in a portable,accurate,easy-to-operate,and cost-effective glucose detection device.Such a device would enable diabetic patients to monitor their glucose levels easily,aiding them in their self-health management efforts.The main tasks are as follows:（1）An enzyme-free electrochemical glucose sensor was constructed using a copper-based metal-organic framework（Cu-MOF）and platinum nanoparticles（PtNPs）catalytic action on glucose.The Cu-MOF/PtNPs were modified onto a gold electrode（GE）by layer-by-layer electrodeposition.The sensor was validated to have a catalytic effect on glucose in an alkaline environment and the detection mechanism was explained based on the Initial Hydrogen Atom Mediator（IHOAM）model.The morphology and energy spectrum of the electrodes were characterized using field emission scanning electron microscopy（FESEM）.In addition,the impedance changes during electrode construction were analyzed by electrochemical impedance spectroscopy（EIS）.After optimizing the fabrication conditions of the sensor,the glucose detection performance of the sensor was examined via differential pulse voltammetry（DPV）.The oxidation current on the Cu-MOF/PtNPs/GE sensor exhibited a two-segment linear relationship with glucose concentration in the range of 0.4-25.0m M.The linear fitting equations for low-concentration（0.4-10.0 m M）and high-concentration（10.0-25.0 m M）ranges were I_L=11.1972c（m M）+19.7268,R²=0.9901,and I_H=3.2248c（m M）+95.8843,R²=0.9832,respectively,with a sensitivity of 158.41μA·m M^-1·cm^-2 and a limit of detection（LOD）of 0.06 m M.Finally,the glucose detection performance of the sensor was examined in human serum samples,and the results were found to be similar to those obtained using a commercial blood glucose meter.The standard addition method was used to determine the recovery of the sensor,which was found to be in the range of 97.00-108.98%,with a relative standard deviation（RSD）between 1.31-3.59%.These results demonstrate that the sensor has great potential for practical applications.（2）A zinc-based MOF（Zn-MOF）was used to increase the active adsorption sites on the surface of the GE,and multi-walled carbon nanotubes（MWCNTs）were used to improve the conductivity of the electrode surface.Two electro-deposition methods were used to modify the GE surface with Zn-MOF and MWCNTs,resulting in the construction of a Zn-MOF/MWCNTs/GE enzyme-free electrochemical glucose sensor.The detection mechanism of the sensor for glucose in an alkaline environment was explained through CV experiment and p H-potential relationship experiment.Changes in the surface morphology and elemental composition during the sensor construction process were observed using FESEM.The surface electron transfer impedance was quantified using EIS.After optimizing some of the fabrication conditions and the applied potential in i-t measurements,the performance of the sensor in detecting glucose using i-t was examined.The oxidation current on the Zn-MOF/MWCNTs/GE sensor exhibited a two-segment linear relationship with glucose concentration.The linear fitting equations for low-concentration（0.02-1.27 m M）and high-concentration（1.27-8.14 m M）ranges were I_L=2.46c（m M）+0.3596,R²=0.9919;and I_H=0.8980c（m M）+3.5099,R²=0.9908,respectively.The LOD of the sensor was found to be0.0037 m M,with a sensitivity of 34.64μA·m M^-1·cm^-2.The selectivity,reproducibility,and stability of the sensor were examined using i-t measurements.The detection performance of the sensor in human serum samples was validated,and the error with respect to the values obtained using a commercial blood glucose meter was only 1.76%.The sensor was used in standard addition experiments,resulting in a recovery rate of98.52-102.65%and an RSD of 1.72-8.00%in serum samples,demonstrating its potential for practical applications in real-world testing scenarios.（3）A portable electrochemical detection system based on DPV was constructed using an STM32F103C8T6 microcontroller,which was connected to the Cu-MOF/PtNPs/GE sensor.The detection system generated a voltage that linearly increased within a specific range and a fixed amplitude pulse signal,which were applied to the constant potential three-electrode circuit.As the oxidation reaction of glucose occurred on the modified electrode,the detection system converted the weak current signal into a voltage signal,continuously sampling the data,and finally displaying the sampling data as a DPV waveform,with peak potential and peak current on the OLED screen.By connecting the portable electrochemical detection system to the enzyme-free glucose sensor Cu-MOF/PtNPs/GE,glucose solutions of different concentrations were detected.The linear relationship between glucose concentration and DPV peak current was obtained:I=7.633c（m M）+40.08,R²=0.986,achieving the enzyme-free and convenient detection of glucose.The glucose concentration of the glucose injection was tested using this testing system,and the error was only 2.96%compared to the value measured by a commercial blood glucose meter.