Abstract
Abstract Sensitivity, selectivity, reliability, and measurement range of a sensor are vital parameters for its wide applications. Fast growing number of various detection systems seems to justify worldwide efforts to enhance one or some of the parameters. Therefore, as one of the possible solutions, multi-domain sensing schemes have been proposed. This means that the sensor is interrogated simultaneously in, e.g., optical and electrochemical domains. An opportunity to combine the domains within a single sensor is given by optically transparent and electrochemically active transparent conductive oxides (TCOs), such as indium tin oxide (ITO). This work aims to bring understanding of electro-optically modulated lossy-mode resonance (LMR) effect observed for ITO-coated optical fiber sensors. Experimental research supported by numerical modeling allowed for identification of the film properties responsible for performance in both domains, as well as interactions between them. It has been found that charge carrier density in the semiconducting ITO determines the efficiency of the electrochemical processes and the LMR properties. The carrier density boosts electrochemical activity but reduces capability of electro-optical modulation of the LMR. It has also been shown that the carrier density can be tuned by pressure during magnetron sputtering of ITO target. Thus, the pressure can be chosen as a parameter for optimization of electro-optical modulation of the LMR, as well as optical and electrochemical responses of the device, especially when it comes to label-free sensing and biosensing.
Highlights
Rapid and reliable biosensing solutions are highly desired nowadays [1]
We have clearly shown that properties expected for efficient optical and electrochemical interrogation are practically opposite
We found that charge carrier density corresponding to crystallinity of indium tin oxide (ITO) is a critical parameter responsible for double-domain interrogation
Summary
Rapid and reliable biosensing solutions are highly desired nowadays [1]. Such devices, especially when they make point-of-care testing possible, are mainly expected to identify pathogen outbreaks [2]. Wide range, low detection limit, short response time, small size and low fabrication costs are among highly anticipated parameters of the biosensor [3] To satisfy all these requirements and limit false positive results, a set of sensors together with advanced data processing is typically applied [4]. To receive simultaneously electrical and optical readouts surface of the sensor must be both electrically conductive and susceptible to optical effects that are influenced by a measurand For these purposes the most often explored phenomenon, among many others, is the surface plasmon resonance (SPR), where excitation and propagation of plasmon at a surface of thin gold film is influenced by optical properties of an analyte covering the surface [6]. In the dual-domain configuration the same gold film plays a role of an electrode in EC setup, where the
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