Polymer–Surfactant Driven Interactions and the Resultant Microstructure in Protein-Containing Liquid Crystal Droplets

Abstract

Integration of molecular liquid crystals (LCs) with functional proteins can provide new class of materials for potential applications in optical biosensing. However, hydrophobic nematic LCs (length ∼ 1−2 nm) and hydrophilic proteins, size ∼ O (nm), do not intermix without chemical modification of at least one of them. Bioconjugation of proteins with a polyethylene glycol-based polymeric surfactant (PS) can provide a core−shell system that is sequestered within nonaqueous LC (4-cyano-4′-pentylbiphenyl) microdroplets. However, the nature of interactions between the components and detailed understanding of the resultant hybrid microstructure remains unclear.Here, using a combination of isothermal titration calorimetry (ITC), fluorescence microscopy, and infrared-imaging spectroscopy, we show that strong hydrophobic interactions between the LC and PS drives the sequestration of a myoglobin−PS (Mb−PS; dispersed in the aqueous phase) into the LC spherical microdroplets or even into a bulk LC phase. The average values of both, the binding constant and the standard molar enthalpy change, are increased by approximately a factor of 2.5 times when the unmodified Mb is conjugated to the PS. Small-angle X-ray scattering studies reveal that LC molecules act as a solvent for the Mb−PS conjugate; furthermore, the LC long-range order is disturbed due to mixing, as exemplified by the change in its coherence length from 8.9 to 5.7 nm. Detailed allatomistic molecular dynamic simulations for a three-component PS−water−LC system show a change in interaction energy of −144 kJ mol −1 PS −1 upon the contact of PS chains (initially dispersed in water) with LC and agree with the ITC experiments.

Patterning of Protein-Sequestered Liquid-Crystal Droplets Using Acoustic Wave Trapping

“…First, myoglobin-polymer surfactant bioconjugates were prepared by following a two-step surface modification procedure as reported in our previous publications. , The procedure is mentioned in detail in SI Methods and is schematically shown in Figure a. Briefly, the first step involves covalent tagging of rhodamine B isothiocyanate (RITC: R) dye to unmodified myoglobin (uMb) followed by covalent coupling of N , N ′-dimethyl-1,3-propanedimine (DMAPA: Diamine) to the surface-accessible aspartic and glutamic amino acid residues to form cationized-RITC-labeled myoglobin (R-cMb).…”

“…An aqueous PS (50 mg mL –1 ) solution was added dropwise to cationized protein solution (molar ratio of protein to PS is 1:2), and the resultant solution mixture was stirred for 24 h. Further, the solution was centrifuged and dialyzed against phosphate buffer to remove unbound PS molecules, which resulted in a stable protein-PS nanobioconjugate solution (Mb-PS, GOx-PS, and HRP-PS). Dye-labeled (RITC: R or FITC: F) protein-PS bioconjugates (R-Mb-PS/R-GOx-PS/F-HRP-PS) were prepared by covalent labeling of dye to lysine amino acid residues at the unmodified protein surface by following the previously well-established procedures, , followed by cationization and PS bioconjugation steps.…”

Construction of a liquid crystal biosensor based on Fe3O4 nano-signal amplification and its application in HCG detection

“…Abbott proposed and successfully constructed a LC biosensor, which has been widely used in the elds of small molecular substances, [20][21][22] nucleic acids, 23,24 proteins 25 and heavy metal ions due to its advantages of high sensitivity, good specicity, fast response, simple operation and low detection limit. Compared to conventional detection methods, LC biosensors signicantly reduce the detection limit of the target.…”

Formation of topological defects in nematic shells with a dumbbell-like shape

“…[16][17][18] As a consequence, the topological defects' arrangement in nematic shells can be used as an efficient mechanism to tune the optical response of colloidal structures. [18][19][20] Recently, several studies investigated geometrical-induced defects in nematic shells presenting an anisotropic shape. [21][22][23][24][25][26] In particular, symmetry breaking causes the curvature of liquid crystal shells to vary, which tends to modify both the arrangement 22,23 and number of valence centers.…”

“…16–18 As a consequence, the topological defects' arrangement in nematic shells can be used as an efficient mechanism to tune the optical response of colloidal structures. 18–20…”