Electrically controlled variation of receptor affi

Authors: Yulia Efremenko Vladimir M Mirsky

Publish Date: 2016/07/20

Volume: 408, Issue: 26, Pages: 7283-7287

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Abstract

A concept of virtual sensor array based on electrically controlled variation of affinity properties of the receptor layer is described It was realized on the base of integrated electrochemical chemotransistor containing polyaniline as the receptor layer Electrical control of the redox state of polyaniline was performed in fiveelectrode configuration containing four electrodes for conductivity measurements and one Ag/AgCl reference electrode All the electrodes were integrated on the same glass chip A roomtemperature ionic liquid was used for the electrical connection between the reference electrode and chemosensitive material Conductivity measurements demonstrated effective potentialcontrolled electrochemical conversions of the receptor material between different redox states Binding of trimethylamine at three different potentials corresponding to the different states of the receptor material was studied Concentration dependencies and binding kinetics were analyzed The results demonstrated that the kinetic as well as the equilibrium binding properties of the receptor layer can be controlled by electrical potential thus providing a possibility to form a virtual sensor array using only a single sensing elementChemical compounds applied as receptors in chemical sensors should fulfill a number of requirements An application for detection of low concentrations of analyte requires a high value of affinity constant A fast sensor recovery is possible if the kinetic desorption constant of the bond analyte is high enough Therefore taking into account that the binding constant is the ratio of kinetic constants of adsorption and desorption it can be concluded that the binding energy cannot be increased by selection of materials with a higher kinetic desorption constantAn additional prerequisite is the high selectivity of the analyte binding In general it is also defined by the affinity and receptors with a higher affinity provide a higher selectivity Despite intensive work in this field 1 2 that is essentially supported by a wide application of combinatorial and highthroughput techniques 3 4 and a large number of different compounds which have been synthesized for this purpose some of affinity properties are reviewed in 5 it is still difficult to find a selective receptor for a particular application Therefore a number of low selective receptors are combined into arrays to improve the selectivity of the whole system The affinity properties of single sensing elements in the array should be very different ideally—orthogonal but a high binding selectivity is not required Such approach can be relatively easily implemented into the most optical sensors which enable very simple parallelization of single sensing elements But in the case of conductometric or electrochemical sensors an increase of the number of these elements leads to a strong increase in the complexity of the whole sensor system This is not only a large hindrance in the application of this perspective approach but also a motivation to find a more technological solutionEarlier we have reported that the problem of poor recovery of highly sensitive chemical sensors can be solved by application of electrochemical transistors 6 7 In this work we describe an extension of this approach to the formation of virtual arrays of chemical sensors This novel type of chemical sensors was realized on the basis of electrochemical chemotransistor containing polyaniline PANI as the receptor layer It is a wellcharacterized chemosensitive material 8 An interaction of polyaniline with different analytes leads to essential changes in its physical properties which can be detected using different methods The highest signaltonoise ratio for transducing the binding of analytes to polyaniline is observed for conductivity measurements 6 9 10 Different measurement configurations were suggested 6 Simultaneous application of two and fourpoint measurements S24 technology allows one to make independent measurements of bulk and contact resistance thus providing an internal sensor integrity control A performance of the conductometric transduction was extended using additional electrodes controlling the redox state of the conducting polymer 6 7 11 12 13 This configuration designed as an electrochemical transistor was further upgraded by the implementation of a S24 technique 10 allowing us to combine its advantages with internal integrity control 6The suggested approach can be applied for different receptors and for different analytes In the current work we use PANI as the receptor and trimethylamine TMA as the analyte TMA is practically important in chemical analytics as one of the main indicators of the spoilage of fish products Applications of PANI as a receptor for this analyte were earlier applied in chemical sensors based on quartz microbalance 14 An implementation of the technology of integrated electrochemical transistors allowed us to reach a very high sensitivity and to demonstrate electrically controlled variations of sensor affinityWe describe here a novel concept for chemical sensors based on conducting polymers a virtual sensor array consisting of a single chemosensitive element which can be electrochemically converted into materials with different affinity properties This approach demonstrates that an application of electrochemical chemotransistors can be considered as a possible solution not only for acceleration of sensor recovery 7 but also for a decrease of complexity of sensor arrays

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