Silk Fibroin Based Wearable Glucose Sensor:Design,Construction And Performance

Glucose is the key energy source and precursor for the synthesis of other molecules in human body,but excess high concentration will lead to diabetes.In recent years,the number of diabetes patients in the world has risen sharply,and there are still a large number of potential patients.Therefore,early tracking and prevention of hyperglycemia are particularly important.Effective detection data of glucose concentration relies on high-performance sensors.At present,the reported glucose sensors have high accuracy but poor wearability,which cannot meet the real-time continuous online detection of human glucose concentration.Therefore,it is urgent to develop and design new flexible wearable glucose sensors.Flexible wearable sensors can better fit human body,integrating sensing performance and wearing comfort,thus enabling more in-depth and continuous monitoring of human health status.Textile product is soft,comfortable to wear,and more suitable for the human body,making it an ideal sensor as a substrate material.In this project,silk product was chosen as the substrate to construct silk-based flexible wearable glucose sensors,via surface activation with acid and subsequent in-situ deposition of Prussian blue（PB）.This technique could not only maintain its original good flexibility and wearability,but also endowigi certain conductivity and sensing performance.PB functionalized silk fibers were successfully prepared through in-situ deposition of PB（PB@ASF）.The number of deposition time has a significant impact on its morphology.The result of potassium ferrocyanide uptake experiment showed that,the adsorption capacity gradually increased with the increase of deposition time.In the initial stage（deposition cycles from 1 to 2,L₁～L₂ times）,the concentration of potassium ferrocyanide solution changed slightly,with an adsorption capacity of only 0.03 mg/g.A small amount of particle deposition was visible on the fiber surface.Raising deposition cycles obviously resulted in significant increase in the adsorption quantity of potassium ferricyanide,leeding to more deposition of PB particles on fiber surface.When deposition cycle was 6,the adsorption amount of potassium ferrocyanide reached 0.31 mg/g;the residue rate increased from 1.57%to 18.76%;PB particles were uniformly deposited in 72.38 nm.The results of FITR,XRD,TG showed that the in-situ deposition process only modified the surface of silk fiber without changing its internal structure.Moreover,after 6 times of deposition,silk fibers showed temporary hydrophobicity,and improved thermal and mechanical properties,with a significant increase in mechanical properties by 123.89 MPa and 89.15%.Then,the influence of moisture contenton conductivity of fiber indicated that,water content has a great impact on electrical resistance of fibers.80%moisture content could reduced the electrical resistance by 3 orders of magnitude,indicating an ionic conduction for PB@SF electrodes.When deposition cycle is 6,electrical resistance decreased to the minimum at 99.5 KΩ,proving the best electrical conductivity.As-prepared PB@ASF electrode has good responsiveness to H₂O₂,with confidence intervals above 95%.With the increase of deposition cycles from 1 to 6,the sensitivity increased from 9.12×10^-3 m A·m M^-1·cm^-2 to 21.82×10^-3 m A·m M^-1·cm^-2,whilst 7 deposition cycles resulted in an decrease in sensitivity.Meanwhile,6 deposition cycles also led to the best response to hydrogen peroxide,with a significant electrochemical response in the range of0.8～7.0 mmol/L,and a detection limit of 0.01 mmol/L（S/N=3）.It also showed good cycling performance（RSD=1.4%）under 30 CV cycle tests,and superior stability（96.12%of the initial peak value after 7 days）as well as excellent reproducibility（only 1.9%of the peak deviation for three-group samples）.It was concluded that depositing PB 6 times could bring about the highest sensitivity of 716.54×10^-3 m A·m M^-1·cm^-2.The peak current densities of PB@SF electrodes were almost the same(17.71 m A·cm^-2,17.24 m A·cm^-2,17.72 m A·cm^-2)under three different fiber status,i.e.horizontal,vertical,and spiral status,indicating excellent flexibility.PB@ASF fabric-based wearable glucose sensor was fabricated via in-situ deposition and dipping coating.Results had shown that,the moisture permeability rate was 77.06 g·m^-2·h^-1after 1 h with mass loss of 0.194 g.Simililarly,after moisture permeability,the mass loss reached 0.193 g and moisture permeability rate was 75.88 g·m^-2·h^-1.The little difference indicated that the moisture permeability of the silk fabric after sedimentation treatment has not changed significantly.The sensitivity and correlation of GOx fabric-based wearable glucose sensors reach their maximum at p H of 6.8,exhibiting unique electrocatalytic activity towards glucose.By using the i-t electrochemical measurement method,the sensitivity（2-17 mmol/L）reached 55.33×10^-3 m A·m M^-1·cm^-2 at an applied potential of 0.45 V,with a detection limit of only 2 m M.In addition,the glucose sensor has good repeatability（97.93%）on three different sensors with the same preparation method,with a peak current loss of about 4.92%over a week.It has good stability,a cycling performance of 96.72%,and good specificity for glucose.The response curves of the sensors to glucose at different bending angles almost overlap,with the peak current unchanged,indicating that the GOx fabric-based wearable glucose sensor has good flexibility.