Real-time measurement of glucose using chrono-impedance technique on a second generation biosensor.

Chrono-impedance technique (CIT) was implemented as a new transduction method for real time measurement of glucose in a biosensor system based in carbon paste (CP)/Ferrocene (FC)/glucose oxidase (GOx). The system presents high selectivity because the optimal stimulation signal composed by a 165mV DC potential and 50mV(RMS) AC signal at 0.4Hz was used. The low DC potential used decreased the interfering species effect and the biosensor showed a linear impedance response toward glucose detection at concentrations from 0mM to 20mM,with 0.9853 and 0.9945 correlation coefficient for impedance module (|Z|) and phase (Φ), respectively. The results of quadruplicate sets reveal the high repeatability and reproducibility of the measurements with a relative standard deviation (RSD) less than 10%. CIT presented good accuracy (within 10% of the actual value) and precision did not exceed 15% of RSD for high concentration values and 20% for the low concentration ones. In addition, a high correlation coefficient (R(2)=0.9954) between chrono-impedance and colorimetric methods was obtained. On the other hand, when two samples prepared at the same conditions were measured in parallel with both methods (the measurement was repeated four times), it should be noticed that student's t-test produced no difference between the two mentioned methods (p=1). The biosensor system hereby presented is highly specific to glucose detection and shows a better linear range than the one reported on the previous article.

Evaluation of chrono-impedance technique as transduction method for a carbon paste/glucose oxidase (CP/GOx) based glucose biosensor.

The chrono-impedance technique (CIT) for real time determination of glucose concentration in a first generation glucose oxidase/carbon paste electrode was implemented. The biosensor was polarized with a signal composed of 900 mV DC potential and 50 mV(RMS) AC signal at 0.4 Hz. A frequency response analyzer was used to measure the complex impedance (magnitude |Z| and phase (Φ)) of the biosensor-bulk interface. Real time measurements were performed while glucose was added to the bulk within a concentration range of 0-40 mM. The cumulative impedance dose-response curves were used to construct calibration curves, both for magnitude and phase. The best fitting was obtained with a hyperbolic equation. Four biosensors were built obtaining five calibration curves for each of them. A single test measurement (unknown glucose concentration) was also obtained after each calibration procedure. Glucose concentrations were estimated with the calibration curves and also measured by colorimetry, the latter being the reference method. Besides, one-way ANOVA test evaluated repeatability. Difference between means was not statistically significant (p>0.01) for both magnitudes (|Z| and Φ). The Student's t-test assessed the differences significance, which produced in all cases p levels lower or equal than 0.44. Thus, CIT was proved to be a reliable method to measure glucose concentration in real time. Moreover, it showed high repeatability and compared well against colorimetry (r(2)=0.98).