A needle-type glucose biosensor based on PANI nanofibers and PU/E-PU membrane for long-term invasive continuous monitoring

A minimally invasive glucose biosensor capable of continuous monitoring of subcutaneous glucose has been developed in this study. This sensor was prepared using electropolymerized conductive polymer polyaniline (PANI) nanofibers as an enzyme immobilization material and polyurethane (PU)/epoxy-enhanced polyurethane (E-PU) bilayer coating as a protective membrane. The sensor showed almost the same sensitivity (63 nA/mM) and linearity (0-20 mM with the correlation coefficient r2 of 0.9997) in both PBS and bovine serum tests. When stored in 37 °C bovine serum, the sensor's sensitivity gradually increased about 30% of the initial value within the first 13 days and then remained stable for the rest of the study period of 53 days. In vivo implantation experiments using mice models showed real-time response to the variation of blood glucose with an average signal delay of about 8 min. Continuous monitoring showed that the sensor response increased for the first 12 days and then entered a stable period for 14 days. The sensor's baseline (530±10 nA) and the total response to 1 ml 50% dextrose injection were almost the same (267±15 nA) in the stable period. The in vivo stable performances indicated that the sensor could be used as an implantable device for long-term invasive monitoring of blood glucose.