Preparation of QP4VP-b-LCP liquid crystal block copolymer and its application as a biosensor

Abstract

The interface between nematic liquid crystal, 4-cyano-4'-pentylbiphenyl (5CB), and water in a transmission electron microscopy (TEM) grid cell coated with QP4VP-b-LCP (quaternized poly(4-vinylpyridine) (QP4VP) and poly(4-cyanobiphenyl-4'-oxyundecylacrylate) (LCP)) was examined for protein and DNA detection. QP4VP-b-LCP was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Quaternization of P4VP with iodomethane (CH3I) made it a strong cationic polyelectrolyte and allowed QP4VP-b-LCP to form complexes with oppositely charged biological species. Several proteins, such as bovine serum albumin (BSA), hemoglobin (Hb), α chymotrypsinogen-A (ChTg), and lysozyme (LYZ), were tested for nonspecific protein detection. By injecting the protein solutions into the TEM grid cell, the initial homeotropic orientation of the TEM grid cell changed to a planar orientation above their isoelectric points (PIs) due to electrostatic interactions between QP4VP (+charge) and proteins (-charge), which did not occur below the PIs of the tested proteins. Their minimum concentrations at which the homeotropic to planar configurational change (H-P change) occurred were 0.01, 0.02, 0.03, and 0.04 wt.% for BSA, ChTg, Hb, and LYZ, respectively. One of the strong anionic polyelectrolytes, deoxyribonucleic acid (DNA) (due to the phosphate deoxyribose backbone) was also tested. A H-P change was observed with as little as 0.0013 wt.% salmon sperm DNA regardless of the pH of the cell. A H-P change occurred in 5CB and was observed by polarized optical microscopy. This simple and inexpensive setup for nonspecific biomaterial detection provides the basic idea for developing effective selective biosensors by introducing specific binding groups, such as the aptamer and antibody.

Visible Light Induced RAFT Polymerization of 2‐Vinylpyridine without Exogenous Initiators or Photocatalysts

“…As one of the types of important polymeric materials, poly(vinylpyridine) (PVP) is extensively utilized in a wide variety of applications, such as coordinative reagent for transition metals, [ 18 ] molecular imprinting polymers, [ 19 ] conductive polymers after dopping, [ 20 ] microfi ltration membranes, [ 21 ] and biosensor materials. [ 22 ] Exploring a method for the facile synthesis of well-defi ned PVP under mild conditions is undoubtedly desirable. McCormick and co-workers [ 23 ] reported RAFT polymerizations of VP by utilizing azoisobutyronitrile as the initiator at 60 °C.…”

Specific detection of avidin–biotin binding using liquid crystal droplets

“…For example, the poly(dimethylaminoethylmethacrylate) (PDMAEMA)-coated 5CB in a TEM grid could measure a 10 g/mL BSA aqueous solution [25]. The quarternized poly(4-vinylpyridin) (QP4VP) brushes at the 5CB/aqueous interface enabled the detection of ∼100 g/mL protein solutions [27], and the PAA brushes detected a 32 g/mL lysozyme solution [2]. The low sensitivity observed in this study may be due to the strong affinity of avidin to biotin.…”

A Single-Substrate Biosensor with Spin-Coated Liquid Crystal Film for Simple, Sensitive and Label-Free Protein Detection

“…In addition, the intensity of the optical response to BSA was enhanced when a 3.4 µm-thick E7 film was spin-coated on DMOAP slides modified with ultraviolet light or when the high-birefringence LC HDN was used instead of E7 to form the sensing LC film, resulting in an improvement in LOD from 10 −8 to 10 −9 g/mL BSA (data not shown). In addition to LC-solid interface sensing, a few works have been conducted at the LC-aqueous interface for BSA detection with LOD of ~45 nM using the typical LC-infiltrated TEM grids configuration [42,43]. Notably, it is of perspective to extend the proposed LC-on-a-single-substrate configuration to implementation of protein assay at the LC-aqueous interface because the side open to the air can form an LC-aqueous interface analogous to that of LC-infiltrated TEM grids.…”