Homeotropic Alignment of Lyotropic Chromonic Liquid Crystals Using Noncovalent Interactions

Joonwoo Jeong,Tom C Lubensky,Peter J Collings,A T Charlie Johnson,Ganghee Han,Arjun G Yodh

doi:10.1021/la404893t

Abstract

We report on the homeotropic alignment of lyotropic chromonic liquid crystals (LCLCs). Homeotropic anchoring of LCLCs is difficult to achieve, and this challenge has limited development of applications for LCLCs. In this work, homeotropic alignment is achieved using noncovalent interactions between the LCLC molecules and various alignment layers including graphene, parylene films, poly(methyl methacrylate) films, and fluoropolymer films. The LCLC molecules are unique in that they self-assemble via noncovalent interactions in water into elongated aggregates which, in turn, form nematic and columnar liquid crystal (LC) phases. Here we exploit these same noncovalent interactions to induce homeotropic anchoring of the nematic LCLC. Homeotropic alignment is confirmed by polarized optical microscopy and conoscopy. We also report on novel transient stripe textures that occur when an initial flow-induced planar alignment transforms into the equilibrium homeotropic alignment required by boundary conditions. An understanding of this behavior could be important for switching applications.

Highlights

Triple negative breast cancers (TNBC) are heterogeneous tumors that share common phenotypic features: low expression of the estrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2 (HER2)
Smart probes that only fluoresce upon enzymatic activation specific to malignant cells are currently at the forefront of cancer imaging research, offering potential for improved selectivity.[10−15] phosphatidylcholine-specific phospholipase C (PC−PLC) shows a high degree of selectivity to phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) when a bulky substituent is attached to the sn-2 position of these phospholipids.[27−29] This principle is exploited in our probe, pyropheophorbide a-phosphatidylethanolamine-QSY21 (Pyro-PtdEtn-QSY, Figure 1a), which is selectively cleaved in the presence of PC−PLC.[38]
Full quenching of the probe prior to PC−PLC activation was confirmed by the absorbance and fluorescence spectra of lipidbased nanoparticles (LNPs), incorporating Pyro-PtdEtn-QSY and pyropheophorbide a-phosphatidylcholine (Pyro-PtdCho, a nonquenched positive control probe, Figure 1b)

Summary

■ INTRODUCTION

Triple negative breast cancers (TNBC) are heterogeneous tumors that share common phenotypic features: low expression of the estrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2 (HER2). We have developed smart near-infrared (NIR) fluorescent phospholipid probes that fluoresce after selective cleavage by PC−PLC.[27,29,38] Smart probes that only fluoresce upon enzymatic activation specific to malignant cells are currently at the forefront of cancer imaging research, offering potential for improved selectivity.[10−15] PC−PLC shows a high degree of selectivity to phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) when a bulky substituent is attached to the sn-2 position of these phospholipids.[27−29] This principle is exploited in our probe, pyropheophorbide a-phosphatidylethanolamine-QSY21 (Pyro-PtdEtn-QSY, Figure 1a), which is selectively cleaved in the presence of PC−PLC.[38]. Full quenching of the probe prior to PC−PLC activation was confirmed by the absorbance and fluorescence spectra of LNPs, incorporating Pyro-PtdEtn-QSY and pyropheophorbide a-phosphatidylcholine (Pyro-PtdCho, a nonquenched positive control probe, Figure 1b). The therapeutic potential of the probe was assessed by measuring the dark toxicity of the probe and by performing PDT experiments, which include cell proliferation and colony formation assays following irradiation with light

■ RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ REFERENCES