Immunosensor with fluid control mechanism for salivary cortisol analysis

Abstract

The purpose of this research is to demonstrate a new design for a cortisol immunosensor for the noninvasive and quantitative analysis of salivary cortisol. We propose a cortisol immunosensor with a fluid control mechanism which has both a vertical flow and a lateral flow. The detected current resulting from a competitive reaction between the sample cortisol and a glucose oxidase (GOD)-labeled cortisol conjugate was found to be inversely related to the concentration of cortisol in the sample solution. A calibration curve using the relative detected current showed a R(2)=0.98 and CV=14% for a range of standard cortisol solutions corresponding to the concentrations of native salivary cortisol (0.1-10 ng/ml). The measurement could be accomplished within 35 min and the cortisol immunosensor could be reused. These results show promise for realizing an on-site and easy-to-use biosensor for cortisol. Used for evaluation of human salivary cortisol levels, the cortisol immunosensor measurement corresponded closely with commercially available ELISA method (R(2)=0.92). Our results indicate the promise of the new cortisol immunosensor for noninvasive, point of care measurement of human salivary cortisol levels.

Fig. 1

External view and the structure of the sensor. (a) Close-up of salivary cortisol sensor cartridge. (b) Exploded view of sensor cartridge and fluid control mechanism (WE: working electrode, CE: counter electrode, RE: reference electrode).

Fig. 2

Electrochemical reaction underlying the biosensor recognition element (WE: working electrode).

Figure 3

Detected current characteristics of cortisol sensor with fluid control mechanism. (0 s: glucose injection).

Fig. 4

Calibration curves for the cortisol immunosensor with competitive reaction.

Fig. 5

Refreshing characteristics of the cortisol immunosensor evaluated by the relative detected current.

Fig. 6

Measured results of human salivary cortisol using the cortisol immunosensor (using calibration curve: Fig. 4a, ●: mean).