Glucose sensor response curves

Figure 6. Effect of increased alkyl chain length on glucose sensor response glucose calibration curves for the ferrocene-modified poly(siloxane) / glucose oxidase / carbon paste electrodes at E = +300 mV (vs. SCE). The polymeric relay systems are indicated next to each curve, which is the mean result for four electrodes.

Fig. 2.16 Theoretical (full points) and experimental (open points) time response curve for glucose sensors to step change in concentration (from 0 to 1 mM) (adapted from Caras et al., 1985b, p. 1922)...

Glucose sensors II and HI were prepared from the semipermeable membrane of PMSP, poly(1-trimethylsilyl-l-propyne), which has 4 times the oxygen permeability compared with that of FEP membrane. The response properties of sensor H, using a PMSP membrane with 25 Um diameter pinhole, were almost similer to that of the sensor I, so that their calibration curves were not presented in this paper. 

Figure 5. Dynamic response curves of glucose sensor I under various oxygen tensions (%)...

Sensors should always be evaluated in vitro. While this is clearly not a substitute for in vivo testing, it is easier to diagnose fundamental problems without the complications that the biological milieu introduces. Furthermore, if they do not work reliably in vitro, they will not work in vivo. In addition to the linear dynamic range mentioned above, stability and reproducibility of characteristics in sensor production are very important. Linearity can be characterized by comparing the sensitivities (slope of the dose/response curve) at 5 and 15 mM glucose, assuming that they should not deviate by more than 10%. Stability can be measured in several different ways. Sensors can be stored dry and at room temperature between periodic sensitivity checks. This tends to... 

The linear response range of the glucose sensors can be estimated from a Michaelis-Menten analysis of the glucose calibration curves. The apparent Michaelis-Menten constant KMapp can be determined from the electrochemical Eadie-Hofstee form of the Michaelis-Menten equation, i = i - KMapp(i/C), where i is the steady-state current, i is the maximum current, and C is the glucose concentration. A plot of i versus i/C (an electrochemical Eadie-Hofstee plot) produces a straight line, and provides both KMapp (-slope) and i (y-intercept). The apparent Michaelis-Menten constant characterizes the enzyme electrode, not the enzyme itself. It provides a measure of the substrate concentration range over which the electrode response is approximately linear. A summary of the KMapp values obtained from this analysis is shown in Table I. 

Fig. 6. Response curves of a bifunctional FET sensor sensitive to urea and glucose. Response curves for (a) 8.3 mM urea solution, (i) 3.1 mM glucose solution, and (c) solution containing 8.3 mM urea and 3.1 mM glucose. (Reproduced from Hanazato et al. (8), with permission.)...

Fig. 12. Response curves and calibration curve of a glucose-sensitive FET sensor, (a) Response curves using continuous flow apparatus. An arrow indicates onset of analyte solution flow, [b) Response curve under homogeneous condition (see text for details). An arrow indicates addition of glucose, (c) Calibration curve using the flow apparatus. (Reproduced from Shiono et al. (9), with permission.)...

The response of the sensor peaked within 4 min and the calibration curve is applicable within the range of glucose concentrations in normal human serum. Another glucose sensor using sol-gel systems was based upon glucose oxidase in conjunction with a mediator compound (ferrocene or hexacyanoferrate) that transferred an electron to the enzyme [211], This system can be represented as... 

Response curves of Bacillus subtilis- and THchosporon cutaneum-based sensors to glucose-glutamic acid standard solution containing 22 mg/L biochemical oxygen demand (BOD). Reproduced from (420] with permission from Springer-Verlag. 

Figure 8. Response curves of the glucose sensor. The concentration ivas 1.

Coulometric Analysis, Fig. 4 left) Schematic layer-by-layer illustration of FreeStyle glucose sensor, and right) coulometric response by integration of current-time curve at a given concentration of glucose [17]... 

Figure 2. Response curve of the glucose sensor to 1 mM glucose solution with 0.5% TritonX-100 (pH 7.0, 25 C)...

The calibration curves of the sensor IV, which was prepared with a PMSP membrane as an oxygen permeable membrane and an acetyl celulose(AC) membrane as a glucose semipermeable membrane, were shown in Figure 8. This AC membrane was cast by Manjikian s method and treated at a curing temperature of 85°C. The sensor ]V indicated a linear response up to 500 mg/dl of glucose concentration, even under 5 % of oxygen tension, and the output currents were hardly affected by oxygen tension. 

It is clear from these KMapp values, and from the glucose calibration curves, that the response of the sensors begins to deviate from linearity even at glucose concentrations below 10 mM (the response to glucose is expected to be strictly linear for concentrations approximately less than or equal to 0.1KMapp). We have previously... 

The experiments were performed in batch mode with stirring. The sensor was placed in 20.00 mL of buffer in a three electrode configuration. The potential was applied (+150 mV vs SCE) and the response was allowed to reach baseline. The required amount of analyte was added to measure the response to electroactive interferents and to generate a glucose calibration curve. 

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