Abstract
This paper presents a new analysis of optical sensors based on surface plasmon resonance (SPR) phenomenon and nematic liquid crystal (LC) sensitive layer in the partially ordered state. In particular, the paper studies the influence of degradation in the LC ordering state on the behavior of the plasmon resonance parameters. The degradation in the LC ordering is represented by the order parameter. The explicit treatment of the order parameter is critical when trying to differentiate between a change in alignment and a degradation of alignment in LC in response to the presence of an external stimulus in LC based sensors. When a reduction in ordering occurs, ignoring the order parameter can produce misleading results. This sensor has potential applications in chemical and biological systems. The paper presents a tracking method for the state of alignment and degree of ordering of the partially ordered LC film. This can be achieved via the SPR propagation constant and the critical angle at the interface between a metal and an LC film.
Highlights
Liquid crystal (LC)-based sensors have been proven to be successful in sensing and identifying toxic chemicals, explosive and radioactive materials, and biological agents at very low levels in gasses and liquids, and on surfaces in real time [1,2,3,4,5,6]
In [7], the authors performed an experiment in detecting vapor-phase Dimethyl methylphosphonate (DMMP) by monitoring the intensity of polarized light transmitted through 40 -pentyl-4-cyanobiphenyl (5CB) liquid crystal film
A change in the structure at the liquid crystal (LC)/agents interface caused by binding of a chemical or biological agent or biomolecular interactions is amplified into a significant change in the average molecular alignment of the LC film
Summary
Liquid crystal (LC)-based sensors have been proven to be successful in sensing and identifying toxic chemicals, explosive and radioactive materials, and biological agents at very low levels in gasses and liquids, and on surfaces in real time [1,2,3,4,5,6]. The proposed SPR-LC sensor does not require visual inspection; a simpler system with autonomous operation and reduced possible false alarms are achievable This sensor offers the ability to identify and track the average LC deformation and is capable of providing information about the order parameter in partially ordered LC phase. We propose an optical transduction technique that utilizes LC in partially ordered and fully ordered phases along with SPR configuration This method has the potential to identify and track the LC profile deformations (the average LC director as well as the ordering degree) rather than merely sensing the LC director alteration. When a reduction in ordering occurs, ignoring this parameter can produce misleading results
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