Surfactant–DNA interactions at the liquid crystal–aqueous interface

Abstract

The presence of single-stranded (ssDNA) vs. double-stranded (dsDNA) DNA at a surfactant-laden aqueous-nematic liquid crystal (LC) interface results in distinctly different orientations of the LC molecular axis; this is of practical interest as a method to detect DNA hybridization. Results presented here provide new insights into the molecular-level mechanisms of these phenomena. The adsorption of ssDNA to a cationic surfactant-laden aqueous-LC interface caused LC reorientation, leading to coexistence between homeotropic and planar (birefringent) oriented regions. Fluorescence microscopy revealed that ssDNA preferentially partitioned into the birefingent regions, presumably causing a decreased surface coverage of surfactant and the resultant planar LC orientation. Both electrostatic and hydrophobic effects were found to be critical to inducing LC reorientation. In particular, insufficient ssDNA adsorption occurred in the absence of a cationic surfactant (e.g. with no surfactant or with a non-ionic surfactant), demonstrating the importance of electrostatic interactions with the polyanionic ssDNA. Even in the presence of a cationic surfactant, however, polyanions without hydrophobic side-group moieties (poly[acrylic acid] and dsDNA) caused no LC reorientation, while polyanions with hydrophobic side groups (polystyrene sulfonate and ssDNA) initiated the desired LC reorientation. These observations are consistent with the fact that interfacial hybridization of adsorbed probe ssDNA to complementary target ssDNA caused a reorientation from planar back to homeotropic. We propose that ssDNA forms an electrostatic interfacial complex with cationic surfactant where the hydrophobic nucleobases associate directly with the LC phase, effectively competing with surfactant molecules for interfacial sites. Upon hybridization, the hydrophobic character of the ssDNA is lost and the nucleobases no longer associate directly with the LC phase, allowing the surfactant molecules to pack more closely at the interface.

Chemical and biological sensing using liquid crystals

“…A third example involves the use of LC interfaces decorated with cationic surfactants to report hybridization of oligonucleotides [70-72]. This approach builds from past studies that have demonstrated that cationic amphiphiles form organized assemblies with DNA in bulk solution [70-72].…”

“…This approach builds from past studies that have demonstrated that cationic amphiphiles form organized assemblies with DNA in bulk solution [70-72]. Whereas a complex formed between octadecyltrimethylammoniurn bromide (OTAB) and single-stranded DNA (ssDNA) at the aqueous interface of nematic 5CB caused a tilted orientation of the LC, exposure of the ssDNA/OTAB interfacial complex to its ssDNA complement resulted in the nucleation, growth, and coalescence of regions that caused homeotropic LC alignment (Figure 12E).…”

Adsorption of rationally designed “surf-tides” to a liquid-crystal interface

“…8,12,14 Future studies will aim to address several key characteristics mentioned throughout this work, specifically: (1) optimize and further improve the sensitivity of the experimental setup to allow the detection of decreased analyte concentrations (2) examine the role that overall net charge has on the sensitivity and dynamics of interfacial adsorption by synthesizing ''inverse'' peptides with opposing charges at the same residue locations while keeping the surfactant constant (3) investigate the adsorption of peptides into insoluble layers (i.e. The LC experimental platform shows sufficient sensitivity to optically observe molecular adsorption of two very similar molecules over macroscopic length scales.…”

“…Moreover, the ordering results in an easily visualized change in the polarization state, allowing LC-based systems to be readily commercialized. 4 More recently, the application of nematic LCs in contact with aqueous phases to serve as a model oil/aqueous interface has allowed for the optical examination of the adsorption of surfactants, 5 lipids, 6 polymers, 7 nucleic acids, 8 and proteins. 2 These LC materials possess degrees of anisotropy that result in distinct macroscale characteristics, including viscoelastic behavior and diamagnetic/dielectric properties.…”

DNA Hybridization‐Mediated Liposome Fusion at the Aqueous Liquid Crystal Interface

“…Liquid crystals (LCs) have become a valuable tool for monitoring interfacial phenomena at both solid and aqueous interfaces. [ 14 ] Examples include self-assembly processes, [15][16][17] the dynamic behavior of hydrophobic polyanions, [ 18,19 ] protein binding [ 20,21 ] and surfactant phase behavior. [ 22 ] Studies have revealed that certain surfactants (e.g.…”