The optoelectronic sensor creatinine and urea


In paper the concept of interaction of cholesteric liquid crystals (CLC) with creatinine and urea to designing the active medium material for optical sensor of biological substances are presented. It is shown that there is a general tendency to reduce the pitch of supramolecular helical structure versus of increasing of concentrations of aqueous solutions for all investigated substances. A decision to designing the scheme of signal converter of optical sensors with frequency selection is proposed. In basis of the proposed decision is impedance converter provided the inductive nature of the impedance circle of load photodiode and therefore suppressing of direct component of the photocurrent.
The significant changes of wavelength transmittance minimum are taking place at higher concentration of creatinine or urea in water and at lower concentration this aqueous solution in LC mixture.
The principal advantage of the proposed circuit solutions is the possibility of forming of resonant characteristics. It provides the highest possible for a given type of operational amplifier values of resonant frequencies and conversion ratios signal. Frequency-selective characteristics of the impedance converter can improve the signal-to-noise ratio up to 60 dB.

Author: Wojciech Surtel
Conference: Title