Study On The Interface Of Biosensors Based On The Aqueous-Liquid Crystal Interface

Liquid Crystal?LC?is a particular state of matter which is an intermediate between an isotropic liquid and a crystal.With unique optical anisotropy and fluidity,LC molecules are extremely sensitive to physical and chemical changes of the bounding interface.Changes in structure and constitutions of interfaces caused by molecular binding events trigger ordering transitions in LCs,and result in visible optical signals.Therefore,LC molecules are generally used as a responsive element for the analysis and detection of various biological binding events,with advantages of label-free,low cost,and nature amplification.LC-based biosensors are mainly based on the LC-solid interface or aqueous-LC interface.In contrast to the LC-solid interface,the aqueous-LC interface has its extreme characteristics:the mobility of LC molecules allows rapidly lateral rearrangement;it is convenient for the dynamics study;and it offers a better bio-reaction environment.Thus,it has been widely applied in the detection of various biomolecules,such as nucleic acid,protein,and small molecules.Biosensing systems based on aqueous-LC interface generally consist of the aqueous phase,aqueous-LC interface,and the thin film of bulk LCs?²0?m?.In order to optimize reaction condition,ions are usually introduced into the aqueous phase.However,the introduction of ions generally causes changes in the aqueous-LC interface,affecting LC orientation and results.Focusing on above problems,this paper is designed to get insight into the effect of ions on the LC ordering at the aqueous-LC interface.The main contents as follows:?1?The effects of different surfactants on the ordering transitions of LC at the aqueous-LC interface.Three surfactants with same head group and different alkyl chains(octadecyltrimethylammonium bromide(C₁₈),dodecyltrimethylammonium bromide(C₁₂),octyltrimethylammonium bromide?C₈?)were used.The effects of length of alkyl chains and concentration on the LC ordering,and the dynamic responses were investigated.Results show that the longer length of alkyl chain the surfactants or the higher concentration of surfactant is,the stronger impact on the LC orientation is.?2?The effects of ions on the ordering transitions of LC at the aqueous-LC interface.Both kosmotropic?K?and chaotropic?C?ions defined by the Hofmeister effect were selected.Several key factors?ions types,concentrations,pH?linking to the LC ordering have been studied systematically.Results show that both K and C ions can induce homeotropic ordering in LCs;every ion solution has a distinct critical concentration sufficient for homeotropic ordering in LCs;the critical concentration of C ions almost lower than that of K ions;when pH>7?the ionic solution?,it will induce homeotropic ordering.We also concluded the mechanism of the specific ionic effects on the ordering transitions of LCs at the aqueous-LC interface:the ion concentrations gradient between the aqueous phase and the aqueous-LC interface caused the formation of an internal electric fields which trigger the LC ordering transitions.?3?The combined effects of ions and surfactants on the ordering transitions of LC at the aqueous-LC interface.Four ions(Na⁺,HPO₄^2-,Cl^-,Mg²⁺)widely used in the biological detection were used.Results show that ions and surfactants have synergistic effects on the ordering transitions.Based on the specific effects,we draw out the critical concentration curves as a guide to the design and application of associated biosensors and a parameters reference.