Roman Volinsky

Poly(methyl methacrylate)-Supported Polydiacetylene Films: Unique Chromatic Transitions and Molecular Sensing

Polydiacetylenes (PDAs) constitute a family of conjugated polymers exhibiting unique colorimetric and fluorescence transitions, and have attracted significant interest as chemo- and biosensing materials. We spin-coated PDA films upon poly(methyl methacrylate) (PMMA), and investigated the photophysical properties and sensing applications of the new PDA configuration. Specifically, the as-polymerized blue PDA layer underwent distinct transformations to purple, red, and yellow phases, which could be quantified through conventional color scanning combined with application of image analysis algorithms. Furthermore, we recorded a reversible red-purple PDA transition that was induced by ultraviolet irradiation, a phenomenon that had not been reported previously in PDA film systems. We show that distinct color and fluorescence transitions were induced in the PMMA-supported PDA films by amphiphilic substances-surfactants and ionic liquids-and that the chromatic transformations were correlated to the analyte structures and properties. Overall, this study presents a new chromatic PDA film system in which noncovalent interactions between the PMMA substrate and spin-coated PDA give rise to distinct chromatic properties and molecular sensing capabilities.

Colorimetric/fluorescent bacterial sensing by agarose- embedded lipid/polydiacetylene films

Aim:  Development of a new chromatic (colorimetric/fluorescence) bacterial sensor, for rapid, sensitive and versatile detection of bacterial proliferation.

Phospholipid-induced fibrillation of a prion amyloidogenic determinant at the air/water interface.

The peptide fragment 106-126 of prion protein [PrP(106-126)] is a prominent amyloidogenic determinant. We present analysis of PrP(106-126) fibrillation at the air/water interface and, in particular, the relationship between the fibrillation process and interactions of the peptide with phospholipid monolayers. We find that lipid monolayers deposited at the air/water interface induce rapid formation of remarkably highly ordered fibrils by PrP(106-126), and that the extent of fibrillation and fiber organization were dependent upon the presence of negatively charged and unsaturated phospholipids in the monolayers. We also observe that fibrillation was enhanced when PrP(106-126) was injected underneath preassembled phospholipid monolayers, compared to deposition and subsequent compression of mixed monolayers of the peptide and phospholipids. In a broader context, this study demonstrates that Langmuir systems constitute a useful platform for studying lipid interactions of amyloidogenic peptides and lipid-induced fibrillation phenomena.

Lipid/polydiacetylene films for colorimetric protein surface-charge analysis.

The distribution and organization of charges on a protein surface are fundamental properties which affect protein functions and interactions. We demonstrate a new approach for protein surface-charge analysis through modulating protein interactions with chromatic lipid/polydiacetylene (PDA) films. We show that visible and easily quantifiable blue-red transitions, induced on the film surface through electrostatic interactions between the negatively charged PDA and positive soluble species, constitute an effective means for characterizing protein surface charge. Specifically, protein-film interactions can be significantly modulated by complexation between the tested macromolecules and lipid-embedded multivalent calixarene ligands displaying charged residues, making possible protein discrimination based upon the abundance and organization of surface charge. The lipid/PDA film system, in conjunction with the calixarene-derived ligands, facilitates characterization of protein surface charges and identification of anomalous protein electrostatic properties.

Laser-modulated ordering of gold nanoparticles at the air/water interface.

Beam me up, Scotty! Laser irradiation of Langmuir monolayers of gold nanoparticles (NPs) and elaidic acid led to dramatic reorganization that was dependent on the laser power (see picture, scale bar = 100 microm). Variable-temperature experiments indicate that localized surface heating in an extremely small temperature range, induced by the laser beam, causes ordering of the NPs.

Self-Assembly and Lipid Interactions of Diacylglycerol Lactone Derivatives Studied at the Air/Water Interface

Synthetic diacylglycerol lactones (DAG-lactones) have been shown to be effective modulators of critical cellular signaling pathways. The biological activity of these amphiphilic molecules depends in part upon their lipid interactions within the cellular plasma membrane. This study explores the thermodynamic and structural features of DAG-lactone derivatives and their lipid interactions at the air/water interface. Surface-pressure/area isotherms and Brewster angle microscopy revealed the significance of specific side-groups attached to the terminus of a very rigid 4-(2-phenylethynyl)benzoyl chain of the DAG-lactones, which affected both the self-assembly of the molecules and their interactions with phospholipids. The experimental data highlight the formation of different phases within mixed DAG-lactone/phospholipid monolayers and underscore the relationship between the two components in binary mixtures of different mole ratios. Importantly, the results suggest that DAG-lactones are predominantly incorporated within fluid phospholipid phases rather than in the condensed phases that form, for example, by cholesterol. Moreover, the size and charge of the phospholipid headgroups do not seem to affect DAG-lactone interactions with lipids.

Colorimetric Polymer Films for Predicting Lipid Interactions and Percutaneous Adsorption of Pharmaceutical Formulations

PurposeTo develop and demonstrate a rapid and simple colorimetric film assay for evaluating lipid interactions of pharmaceutical compounds and gel formulations.MethodsThe colorimetric assay comprises glass-supported films of phospholipids and polydiacetylene, which undergo visible and quantifiable blue–red transformations induced by interactions with amphiphilic molecules applied in very small volumes on the film surface. The color transitions are recorded by scanning of the films, and quantified through a simple image analysis algorithm.ResultsWe show that pharmaceutical molecules and gel formulations induce blue–red transformations after short incubation with the lipid/polydiacetylene (PDA) films. Colorimetric dose–response curves exhibit dependence upon the lipid affinity and extent of membrane binding of the pharmaceutical compounds examined. The colorimetric lipid/PDA film assay was employed for distinguishing the contributions of individual molecular components within gel formulations.ConclusionsThe colorimetric data yield insight into the degree of lipid binding of the molecules tested. The film assay is particularly advantageous for analysis of semi-solid (gel or lotion) formulations, elucidating the lipid interaction characteristics of specific molecular components within the mixtures. The new colorimetric film assay constitutes a generic, rapid, and easily applicable platform for predicting and screening interactions of pharmaceutical compounds and complex formulations with lipid barriers.