Electrically polarized nanoscale surfaces generate reactive oxygenated and chlorinated species for deactivation of microorganisms.

Because of the decreasing supply of new antibiotics, recent outbreaks of infectious diseases, and the emergence of antibiotic-resistant microorganisms, it is imperative to develop new effective strategies for deactivating a broad spectrum of microorganisms and viruses. We have implemented electrically polarized nanoscale metallic (ENM) coatings that deactivate a wide range of microorganisms including Gram-negative and Gram-positive bacteria with greater than 6-log reduction in less than 10 minutes of treatment. The electrically polarized devices were also effective in deactivating lentivirus and Candida albicans. The key to the high deactivation effectiveness of ENM devices is electrochemical production of micromolar cuprous ions, which mediated reduction of oxygen to hydrogen peroxide. Formation of highly damaging species, hydroxyl radicals and hypochlorous acid, from hydrogen peroxide contributed to antimicrobial properties of the ENM devices. The electric polarization of nanoscale coatings represents an unconventional tool for deactivating a broad spectrum of microorganisms through in situ production of reactive oxygenated and chlorinated species.

Compatibility of pulse protein in the formulation of plant based yogurt: a review of nutri-functional properties and processing impact.

With the increased environmental concerns and health awareness among consumers, there has been a notable interest in plant-based dairy alternatives. The plant-based yogurt market has experienced rapid expansion in recent years. Due to challenges related to cultivation, higher cost of production and lower protein content researchers have explored the viability of pulse-based yogurt which has arisen as an economically and nutritionally abundant solution. This review aims to examine the feasibility of utilizing pulse protein for yogurt production. The nutritional, antinutritional, and functional characteristics of various pulses were discussed in detail, alongside the modifications in these properties during the various stages of yogurt manufacturing. The review also sheds light on pivotal findings from existing literature and outlines challenges associated with the production of pulse-based yogurt. Pulses have emerged as promising base materials for yogurt manufacturing due to their favorable nutritional and functional characteristics. Further, the fermentation process can effectively reduce antinutritional components and enhance digestibility. Nonetheless, variations in sensorial and rheological properties were noted when different types of pulses were employed. This issue can be addressed by employing suitable combinations to achieve the desired properties in pulse-based yogurt.

One-Pot Synthesis of Semiconducting Quantum Dots-Organic Linker-Carbon Nanotubes for Potential Applications in Bulk Heterojunction Solar Cells.

Materials and composites with the ability to convert light into electricity are essential for a variety of applications, including solar cells. The development of materials and processes needed to boost the conversion efficiency of solar cell materials will play a key role in providing pathways for dependable light to electric energy conversion. Here, we show a simple, single-step technique to synthesize photoactive nanocomposites by coupling carbon nanotubes with semiconducting quantum dots using a molecular linker. We also discuss and demonstrate the potential application of nanocomposite for the fabrication of bulk heterojunction solar cells. Cadmium selenide (CdSe) quantum dots (QDs) were attached to multiwall carbon nanotubes (MWCNTs) using perylene-3, 4, 9, 10-tetracarboxylic-3, 4, 9, 10-dianhydride (PTCDA) as a molecular linker through a one-step synthetic route. Our investigations revealed that PTCDA tremendously boosts the density of QDs on MWCNT surfaces and leads to several interesting optical and electrical properties. Furthermore, the QD-PTCDA-MWCNTs nanocomposites displayed a semiconducting behavior, in sharp contrast to the metallic behavior of the MWCNTs. These studies indicate that, PTCDA interfaced between QDs and MWCNTs, acted as a molecular bridge which may facilitate the charge transfer between QDs and MWCNTs. We believe that the investigations presented here are important to discover simple synthetic routes for obtaining photoactive nanocomposites with several potential applications in the field of opto-electronics as well as energy conversion devices.

Simultaneous Writing and Erasing Using Probe Lithography Synchronized Erasing and Deposition (PLiSED).

Simultaneous writing and erasing of two and three molecules in one single step at the microscale using Polymeric Lithography Editor (PLE) probes is demonstrated. Simultaneous writing and erasing of three molecules was accomplished by rastering a nanoporous probe that was loaded with rhodamine B and fluorescein over a quinine-coated glass substrate. The solvated quinine molecules were erased and transported into the probe matrix, whereas both rhodamine and fluorescein molecules were simultaneously deposited and aligned with the path of the erased quinine on the substrate. The simultaneous writing and erasing of molecules is referred to as PLiSED. The writing and erasing speed can be easily tuned by adjusting the probe speed to as large as 10,000 µm2/s. The microscale patterns on the orders of square millimeter area were fabricated by erasing fluorescein with an efficiency (ηe) > 95% while simultaneously depositing rhodamine molecules at the erased spots. The roles of the probe porosity, transport medium, and kinetics of solvation for editing were also investigated─the presence of a transport medium at the probe-substrate interface is required for the transport of the molecules into and out of the probe. The physical and mechanical properties of the polymeric probes influenced molecular editing. Young's modulus values of the hydrated hydrogels composed of varying monomer/cross-linker ratios were estimated using atomic force microscopy. Probes with the highest observed erasing capacity were used for further experiments to investigate the effects of relative humidity and erasing time on editing. Careful control over experimental conditions provided high-quality editing of microscale patterns at high editing speed. Combining erasing and deposition of multiple molecules in one single step offers a unique opportunity to significantly improve the efficiency and the accuracy of lithographic editing at the microscale. PLiSED enables rapid on-site lithographic rectification and has considerable application values in high-quality lithography and solid surface modification.

The ERG1A K+ Channel Is More Abundant in Rectus abdominis Muscle from Cancer Patients Than that from Healthy Humans.

BACKGROUND: The potassium channel encoded by the ether-a-gogo-related gene 1A (erg1a) has been detected in the atrophying skeletal muscle of mice experiencing either muscle disuse or cancer cachexia and further evidenced to contribute to muscle deterioration by enhancing ubiquitin proteolysis; however, to our knowledge, ERG1A has not been reported in human skeletal muscle. METHODS AND RESULTS: Here, using immunohistochemistry, we detect ERG1A immunofluorescence in human Rectus abdominis skeletal muscle sarcolemma. Further, using single point brightness data, we report the detection of ERG1A immunofluorescence at low levels in the Rectus abdominis muscle sarcolemma of young adult humans and show that it trends toward greater levels (10.6%) in healthy aged adults. Interestingly, we detect ERG1A immunofluorescence at a statistically greater level (53.6%; p < 0.05) in the skeletal muscle of older cancer patients than in age-matched healthy adults. Importantly, using immunoblot, we reveal that lower mass ERG1A protein is 61.5% (p < 0.05) more abundant in the skeletal muscle of cachectic older adults than in healthy age-matched controls. Additionally, we report that the ERG1A protein is detected in a cultured human rhabdomyosarcoma line that may be a good in vitro model for the study of ERG1A in muscle. CONCLUSIONS: The data demonstrate that ERG1A is detected more abundantly in the atrophied skeletal muscle of cancer patients, suggesting it may be related to muscle loss in humans as it has been shown to be in mice experiencing muscle atrophy as a result of malignant tumors.

IFN-γ and CIITA modulate IL-6 expression in skeletal muscle.

Interleukin 6 (IL-6) is a secreted cytokine that is an important mediator of the immune response in numerous tissues, including skeletal muscle. IL-6 is considered a myokine as it can be secreted by muscle. IL-6 is secreted following exercise, where it exerts both pro-myogenic effects as well as anti-myogenic effects such as promoting atrophy and muscle wasting. The regulation of IL-6 in skeletal muscle is not well understood. The purpose of this study was to determine if IFN-γ and TNF-ɑ stimulate IL-6 in skeletal muscle. We found that both IFN-γ and TNF-α stimulate IL-6 in skeletal muscle, but the stimulation is not cooperative as seen in monocytes. We have previously shown that the IFN-γ stimulated class II major histocompatibility complex transactivator (CIITA) mediates many of the effects of IFN-γ in skeletal muscle and we show here that CIITA directly stimulates IL-6. The regulation of IL-6 by CIITA is clearly complex, as we found that CIITA both stimulates and restrains IL-6 expression. To show that these effects could be observed in a physiological setting, mice were treated with IFN-γ and we found that both CIITA and IL-6 were upregulated in skeletal muscle.

Chemically Engineered Synthetic Lipid Vesicles for Sensing and Visualization of Protein-Bilayer Interactions.

From pathogen intrusion to immune response, the cell membrane plays an important role in signal transduction. Such signals are important for cellular proliferation and survival. However, measurement of these subtle signals through the lipid membrane scaffold is challenging. We present a chromatic model membrane vesicle system engineered to covalently bind with lysine residues of protein molecules for investigation of cellular interactions and signaling. We discovered that different protein molecules induced differential spectroscopic signals, which is based on the chemical and physical properties of protein interacting at the vesicle surface. The observed chromatic response (CR) for bound protein molecules with higher molecular weight was much larger (∼5-15×) than those for low molecular weight proteins. Through mass spectrometry (MS), we found that only 6 out of 60 (10%) lysine groups present in bovine serum albumin (BSA) were accessible to the membrane of the vesicles. Finally, a "sphere-shell" model representing the protein-vesicle complex was used for evaluating the contribution of van der Waals interactions between proteins and vesicles. Our analysis points to contributions from van der Waals, hydrophobic, and electrostatic interactions toward observed CR signals resulting from molecular interactions at the vesicle membrane surface. Overall, this study provided a convenient, chromatic, semiquantitative method of detecting biomolecules and their interactions with model membranes at sub-nanomolar concentration.

Freestanding 3D Mesostructures, Functional Devices, and Shape-Programmable Systems Based on Mechanically Induced Assembly with Shape Memory Polymers.

Capabilities for controlled formation of sophisticated 3D micro/nanostructures in advanced materials have foundational implications across a broad range of fields. Recently developed methods use stress release in prestrained elastomeric substrates as a driving force for assembling 3D structures and functional microdevices from 2D precursors. A limitation of this approach is that releasing these structures from their substrate returns them to their original 2D layouts due to the elastic recovery of the constituent materials. Here, a concept in which shape memory polymers serve as a means to achieve freestanding 3D architectures from the same basic approach is introduced, with demonstrated ability to realize lateral dimensions, characteristic feature sizes, and thicknesses as small as ≈500, 10, and 5 µm simultaneously, and the potential to scale to much larger or smaller dimensions. Wireless electronic devices illustrate the capacity to integrate other materials and functional components into these 3D frameworks. Quantitative mechanics modeling and experimental measurements illustrate not only shape fixation but also capabilities that allow for structure recovery and shape programmability, as a form of 4D structural control. These ideas provide opportunities in fields ranging from micro-electromechanical systems and microrobotics, to smart intravascular stents, tissue scaffolds, and many others.

A fluorometric skin-interfaced microfluidic device and smartphone imaging module for in situ quantitative analysis of sweat chemistry.

The rich composition of solutes and metabolites in sweat and its relative ease of collection upon excretion from skin pores make this class of biofluid an attractive candidate for point of care analysis. Wearable technologies that combine electrochemical sensors with conventional or emerging semiconductor device technologies offer valuable capabilities in sweat sensing, but they are limited to assays that support amperometric, potentiometric, and colorimetric analyses. Here, we present a complementary approach that exploits fluorometric sensing modalities integrated into a soft, skin-interfaced microfluidic system which, when paired with a simple smartphone-based imaging module, allows for in situ measurement of important biomarkers in sweat. A network array of microchannels and a collection of microreservoirs pre-filled with fluorescent probes that selectively react with target analytes in sweat (e.g. probes), enable quantitative, rapid analysis. Field studies on human subjects demonstrate the ability to measure the concentrations of chloride, sodium and zinc in sweat, with accuracy that matches that of conventional laboratory techniques. The results highlight the versatility of advanced fluorescent-based imaging modalities in body-worn sweat microfluidics platforms, and they suggest some practical potential for these ideas.

Probing Liquid-Solid and Vapor-Liquid-Solid Interfaces of Hierarchical Surfaces Using High-Resolution Microscopy.

Liquid-solid (LS) and vapor-liquid-solid (VLS) interfaces are important for the fundamental understanding of how surface chemistry impacts industrial processes and applications. Superhydrophobic surfaces, from structural hierarchies, were fabricated by coating flat smooth surfaces with hollow glass microspheres. These surfaces are referred to as structural hierarchical-modified microsphere surfaces (SHiMMs). Two-phase LS and three-phase VLS interfaces of water droplets on SHiMMs, with an apparent static contact angle (aSCA) of ∼160°, were probed at microscale using environmental scanning electron microscopy (ESEM) and high-resolution optical microscopy (OM). Both ESEM and OM confirmed the presence of air pockets in 3-150 µm range at the VLS triple-phase of the droplet peripheral contact line. The wetting characteristics of the LS interface in the interior of the water droplet were probed using energy-dispersive spectroscopy, which corroborated well with the VLS triple-phase observations, confirming the presence of both the microscale air pockets and fractional complete wetting of the SHiMMs. The superhydrophobic water droplets on the SHiMMs also exhibited relatively high adhesion to the SHiMMs-a tilt angle of 10°-40° was needed for detaching the droplets off the surfaces. Semiquantitative three-phase contact-line analysis and experimental data indicated high-water aSCA, and large adhesion on the microscale-roughened SHiMMs is attributed to pinning of the probe liquid both at the triple VLS and interior LS interfaces. The control over microroughness and surface chemistry of the SHiMMs will allow tuning of both the static and dynamic liquid-surface interactions.

Polymeric lithography editor: Editing lithographic errors with nanoporous polymeric probes.

A new lithographic editing system with an ability to erase and rectify errors in microscale with real-time optical feedback is demonstrated. The erasing probe is a conically shaped hydrogel (tip size, ca. 500 nm) template-synthesized from track-etched conical glass wafers. The "nanosponge" hydrogel probe "erases" patterns by hydrating and absorbing molecules into a porous hydrogel matrix via diffusion analogous to a wet sponge. The presence of an interfacial liquid water layer between the hydrogel tip and the substrate during erasing enables frictionless, uninterrupted translation of the eraser on the substrate. The erasing capacity of the hydrogel is extremely high because of the large free volume of the hydrogel matrix. The fast frictionless translocation and interfacial hydration resulted in an extremely high erasing rate (~785 µm2/s), which is two to three orders of magnitude higher in comparison with the atomic force microscopy-based erasing (~0.1 µm2/s) experiments. The high precision and accuracy of the polymeric lithography editor (PLE) system stemmed from coupling piezoelectric actuators to an inverted optical microscope. Subsequently after erasing the patterns using agarose erasers, a polydimethylsiloxane probe fabricated from the same conical track-etched template was used to precisely redeposit molecules of interest at the erased spots. PLE also provides a continuous optical feedback throughout the entire molecular editing process-writing, erasing, and rewriting. To demonstrate its potential in device fabrication, we used PLE to electrochemically erase metallic copper thin film, forming an interdigitated array of microelectrodes for the fabrication of a functional microphotodetector device. High-throughput dot and line erasing, writing with the conical "wet nanosponge," and continuous optical feedback make PLE complementary to the existing catalog of nanolithographic/microlithographic and three-dimensional printing techniques. This new PLE technique will potentially open up many new and exciting avenues in lithography, which remain unexplored due to the inherent limitations in error rectification capabilities of the existing lithographic techniques.

Immunogenicity of antigen-conjugated biodegradable polydiacetylene liposomes administered mucosally.

In this work, we report a protocol for synthesizing nanosize ovalbumin-functionalized polydiacetylene (PDA) liposomes (LP-Ova). We show that LP-Ova administered per-orally (p.o.) and subcutaneously (s.c.), without the use of adjuvants, induces high serum IgG1 titers. As reported previously using polystyrene nanoparticles (NPs), p.o.-primed mice developed high titers of IgG2c and intestinal IgA following s.c. boosting immunization with LP-Ova. Mice that received a single s.c. immunization with LP-Ova did not develop serum IgG2c or intestinal IgA antibodies. Additionally, in s.c.-immunized mice serum IgG1 titers decreased significantly by 3 months after immunization. In contrast, in mice primed p.o. and boosted s.c. with LP-Ova, serum IgG1/IgG2c, and intestinal IgA antibody titers remained stable. Administration of LPs exerted no adverse effects on immunized mice as no morbidity or signs of toxicity were observed for the duration of the studies. These results indicate that antigen-conjugated liposomes are immunogenic and confirm a previous report that mucosal priming followed by a s.c. boosting immunization is the most effective strategy for inducing long-lasting mucosal IgA, as well as a polarized Th1/Th2 systemic response. In addition to being biodegradable and easily functionalized by conjugation, liposomes have a hollow core which can also be loaded with cargo, allowing for a targeted delivery of multiple antigens (or drugs) simultaneously. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 557-565, 2017.

Fabrication and characterization of non-linear parabolic microporous membranes.

Large scale fabrication of non-linear microporous membranes is of technological importance in many applications ranging from separation to microfluidics. However, their fabrication using traditional techniques is limited in scope. We report on fabrication and characterization of non-linear parabolic micropores (PMS) in polymer membranes by utilizing flow properties of fluids. The shape of the fabricated PMS corroborated well with simplified Navier-Stokes equation describing parabolic relationship of the form L - t1/2. Here, L is a measure of the diameter of the fabricated micropores during flow time (t). The surface of PMS is smooth due to fluid surface tension at fluid-air interface. We demonstrate fabrication of PMS using curable polydimethylsiloxane (PDMS). The parabolic shape of micropores was a result of interplay between horizontal and vertical fluid movements due to capillary, viscoelastic, and gravitational forces. We also demonstrate fabrication of asymmetric "off-centered PMS" and an array of PMS membranes using this simple fabrication technique. PMS containing membranes with nanoscale dimensions are also possible by controlling the experimental conditions. The present method provides a simple, easy to adopt, and energy efficient way for fabricating non-linear parabolic shape pores at microscale. The prepared parabolic membranes may find applications in many areas including separation, parabolic optics, micro-nozzles / -valves / -pumps, and microfluidic and microelectronic delivery systems.

Polydiacetylene nanovesicles as carriers of natural phenylpropanoids for creating antimicrobial food-contact surfaces.

The ultimate goal of this study was developing antimicrobial food-contact materials based on natural phenolic compounds using nanotechnological approaches. Among the methyl-ß-cyclodextrin-encapsulated phenolics tested, curcumin showed by far the highest activity toward Escherichia coli with a minimum inhibitory concentration of 0.4 mM. Curcumin was enclosed in liposome-type polydiacetylene/phosholipid nanovesicles supplemented with N-hydroxysuccinimide and glucose. The fluorescence spectrum of the nanovesicles suggested that curcumin was located in their bilayer region. Free-suspended nanovesicles tended to bind to the bacterial surface and demonstrated bactericidal activity toward Gram-negative (E. coli) and vegetative cells of Gram-positive (Bacillus cereus) bacteria reducing their counts from 5 log CFU mL(-1) to an undetectable level within 8 h. The nanovesicles were covalently bound to silanized glass. Incubation of E. coli and B. cereus with nanovesicle-coated glass resulted in a 2.5 log reduction in their counts. After optimization this approach can be used for controlling microbial growth, cross-contamination, and biofilm formation on food-contacting surfaces.

Investigating surface topology and cyclic-RGD peptide functionalization on vascular endothelialization.

The advantages of endothelialization of a stent surface in comparison with the bare metal and drug-eluting stents used today include reduced late-stent restenosis and in-stent thrombosis. In this article, we study the effect of surface topology and functionalization of tantalum (Ta) with cyclic-(arginine-glycine-aspartic acid-d-phenylalanine-lysine) (cRGDfK) on the attachment, spreading, and growth of vascular endothelial cells. Self-assembled nanodimpling on Ta surfaces was performed using a one-step electropolishing technique. Next, cRGDfK was covalently bonded onto the surface using silane chemistry. Our results suggest that nanotexturing alone was sufficient to enhance cell spreading, but the combination of a nanodimpled surfaces along with the cRGDfK peptide may produce a better endothelialization coating on the surface in terms of higher cell density, better cell spreading, and more cell-cell interactions, when compared to using cRGDfK peptide functionalization alone or nanotexturing alone. We believe that future research should look into how to implement both modifications (topographic and chemical modifications) to optimize the stent surface for endothelialization.

Homo-dimerization and ligand binding by the leucine-rich repeat domain at RHG1/RFS2 underlying resistance to two soybean pathogens.

BACKGROUND: The protein encoded by GmRLK18-1 (Glyma_18_02680 on chromosome 18) was a receptor like kinase (RLK) encoded within the soybean (Glycine max L. Merr.) Rhg1/Rfs2 locus. The locus underlies resistance to the soybean cyst nematode (SCN) Heterodera glycines (I.) and causal agent of sudden death syndrome (SDS) Fusarium virguliforme (Aoki). Previously the leucine rich repeat (LRR) domain was expressed in Escherichia coli. RESULTS: The aims here were to evaluate the LRRs ability to; homo-dimerize; bind larger proteins; and bind to small peptides. Western analysis suggested homo-dimers could form after protein extraction from roots. The purified LRR domain, from residue 131-485, was seen to form a mixture of monomers and homo-dimers in vitro. Cross-linking experiments in vitro showed the H274N region was close (<11.1 A) to the highly conserved cysteine residue C196 on the second homo-dimer subunit. Binding constants of 20-142 nM for peptides found in plant and nematode secretions were found. Effects on plant phenotypes including wilting, stem bending and resistance to infection by SCN were observed when roots were treated with 50 pM of the peptides. Far-Western analyses followed by MS showed methionine synthase and cyclophilin bound strongly to the LRR domain. A second LRR from GmRLK08-1 (Glyma_08_g11350) did not show these strong interactions. CONCLUSIONS: The LRR domain of the GmRLK18-1 protein formed both a monomer and a homo-dimer. The LRR domain bound avidly to 4 different CLE peptides, a cyclophilin and a methionine synthase. The CLE peptides GmTGIF, GmCLE34, GmCLE3 and HgCLE were previously reported to be involved in root growth inhibition but here GmTGIF and HgCLE were shown to alter stem morphology and resistance to SCN. One of several models from homology and ab-initio modeling was partially validated by cross-linking. The effect of the 3 amino acid replacements present among RLK allotypes, A87V, Q115K and H274N were predicted to alter domain stability and function. Therefore, the LRR domain of GmRLK18-1 might underlie both root development and disease resistance in soybean and provide an avenue to develop new variants and ligands that might promote reduced losses to SCN.

Modulating molecular and nanoparticle transport in flexible polydimethylsiloxane membranes.

The ability to fabricate flexible filtration membranes that can selectively separate particles of different sizes is of considerable interest. In this article, we describe a facile, reproducible and simple one-step method to produce pores in polydimethylsiloxane (PDMS) membranes. We embedded micron-sized NaHCO(3) particles in 50 micron thick PDMS films. After curing, the membranes were immersed in concentrated HCl acid. Pores were generated in the membrane by the evolution of CO(2) gas from the reaction of NaHCO(3) and HCl. High resolution Scanning Electron Microscope images clearly reveal the presence of openings on the surface and the cross-section of the membranes. Fluorescence and back-scattered electron imaging of porous PDMS membrane with embedded gold nanoparticles and comparison with non-porous PDMS membranes provided unambiguous evidence of pores in the membrane. Transport studies of molecular fluoresceinate ions, ions (sodium and chloride) and 240 nm polystyrene nanoparticles through these membranes demonstrate passable pores and existence of channels within the body of the membrane. Mechanically stretching the porous PDMS membrane and comparing the flow rates of fluoresceinate ions and the polystyrene beads through the stretched and unstretched membranes allowed a direct proof of the modulation of transport rate in the membranes. We show that stretching the membranes by 10% increases the flow rate of fluorescein molecules by 2.8 times and by a factor of approximately ~40% for the polystyrene nanoparticles.

Real-time monitoring of ligand-receptor interactions with fluorescence resonance energy transfer.

FRET is a process whereby energy is non-radiatively transferred from an excited donor molecule to a ground-state acceptor molecule through long-range dipole-dipole interactions. In the present sensing assay, we utilize an interesting property of PDA: blue-shift in the UV-Vis electronic absorption spectrum of PDA (Figure 1) after an analyte interacts with receptors attached to PDA. This shift in the PDA absorption spectrum provides changes in the spectral overlap (J) between PDA (acceptor) and rhodamine (donor) that leads to changes in the FRET efficiency. Thus, the interactions between analyte (ligand) and receptors are detected through FRET between donor fluorophores and PDA. In particular, we show the sensing of a model protein molecule streptavidin. We also demonstrate the covalent-binding of bovine serum albumin (BSA) to the liposome surface with FRET mechanism. These interactions between the bilayer liposomes and protein molecules can be sensed in real-time. The proposed method is a general method for sensing small chemical and large biochemical molecules. Since fluorescence is intrinsically more sensitive than colorimetry, the detection limit of the assay can be in sub-nanomolar range or lower. Further, PDA can act as a universal acceptor in FRET, which means that multiple sensors can be developed with PDA (acceptor) functionalized with donors and different receptors attached on the surface of PDA liposomes.

Investigating ligand-receptor interactions at bilayer surface using electronic absorption spectroscopy and fluorescence resonance energy transfer.

We investigate interactions between receptors and ligands at bilayer surface of polydiacetylene (PDA) liposomal nanoparticles using changes in electronic absorption spectroscopy and fluorescence resonance energy transfer (FRET). We study the effect of mode of linkage (covalent versus noncovalent) between the receptor and liposome bilayer. We also examine the effect of size-dependent interactions between liposome and analyte through electronic absorption and FRET responses. Glucose (receptor) molecules were either covalently or noncovalently attached at the bilayer of nanoparticles, and they provided selectivity for molecular interactions between glucose and glycoprotein ligands of E. coli. These interactions induced stress on conjugated PDA chain which resulted in changes (blue to red) in the absorption spectrum of PDA. The changes in electronic absorbance also led to changes in FRET efficiency between conjugated PDA chains (acceptor) and fluorophores (Sulphorhodamine-101) (donor) attached to the bilayer surface. Interestingly, we did not find significant differences in UV-vis and FRET responses for covalently and noncovalently bound glucose to liposomes following their interactions with E. coli. We attributed these results to close proximity of glucose receptor molecules to the liposome bilayer surface such that induced stress were similar in both the cases. We also found that PDA emission from direct excitation mechanism was ~2-10 times larger than that of the FRET-based response. These differences in emission signals were attributed to three major reasons: nonspecific interactions between E. coli and liposomes, size differences between analyte and liposomes, and a much higher PDA concentration with respect to sulforhodamine (SR-101). We have proposed a model to explain our experimental observations. Our fundamental studies reported here will help in enhancing our knowledge regarding interactions involved between soft particles at molecular levels.

Ultracompact beam splitters based on plasmonic nanoslits.

An ultracompact plasmonic beam splitter is theoretically and numerically investigated. The splitter consists of a V-shaped nanoslit in metal films. Two groups of nanoscale metallic grooves inside the slit (A) and at the small slit opening (B) are investigated. We show that there are two energy channels guiding light out by the splitter: the optical and the plasmonic channels. Groove A is used to couple incident light into the plasmonic channel. Groove B functions as a plasmonic scatter. We demonstrate that the energy transfer through plasmonic path is dominant in the beam splitter. We find that more than four times the energy is transferred by the plasmonic channel using structures A and B. We show that the plasmonic waves scattered by B can be converted into light waves. These light waves redistribute the transmitted energy through interference with the field transmitted from the nanoslit. Therefore, different beam splitting effects are achieved by simply changing the interference conditions between the scattered waves and the transmitted waves. The impact of the width and height of groove B are also investigated. It is found that the plasmonic scattering of B is changed into light scattering with increase of the width and the height of B. These devices have potential applications in optical sampling, signal processing, and integrated optical circuits.