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Formation of extracellular polymeric substances (EPS) is a crucial step for bacterial biofilm growth. Dependence of EPS composition on the growth substrate and the conditioning of the latter is thus of primary importance. Here, we present results of studies on the growth of biofilms of two different strains each, of the Gram negative bacteria Escherichia coli and Klebsiella pneumoniae, on four polymers used commonly in indwelling medical devices – Polyethene, Polypropylene, Polycarbonate, and Polytetrafluoroethylene immersed in Bovine Serum Albumin (BSA) for 24 hrs. The polymer substrates are studied before and after immersing in BSA for 9 hrs and 24 hrs, using contact angle measurement (CAM) and Field Emission Scanning Electron Microscopy (FE-SEM) to extract, respectively, the ‘philicity’ (defined as ϕ ≡ sin (θ-90°), where θ is contact angle of the liquid on the solid at a particular temperature and ambient pressure) and spatial Hirsch parameter H (defined from the relation, F(r) ~ r2H, where F(r) is the mean squared density fluctuation at the sample surface). H =, 0.5 signifies no correlation, anti-correlation, and correlation, respectively. The substrates are seen to transform from large hydrophobicity to near amphiphilicity with the formation of BSA conditioning surface layer, and the H-values distinguish the length scales of ~ 100 nm, 500 nm, and 2000 nm, with the anti-correlation increasing with length scale. Biofilms grown on the BSA-covered surfaces are studied with CAM, FE-SEM, Fourier Transform Infrared (FTIR) and Surface Enhanced Raman Spectroscopy (SERS). Most notably, the ϕ-values are independent of the bacterial species and strain but dependent on the polymer, as is also shown strikingly by both types of spectra, while H-values show some bacterial variation. Thus, the EPS composition and consequently the wetting properties of the corresponding bacterial biofilms seems to be decided by the interaction of the conditioning BSA layer with a specific polymer used as the growth substrate.

We report the formation, through self-organization, of a two-dimensional assembly of crystalline silicon nanoparticles (SiNPs) made amphiphilic by attaching the long-chain fatty acid — Stearic Acid, at air-water interface. The bulk film of amphiphilized SiNP (ASiNP), floating on water surface, exhibits intense luminescence, under ultraviolet (UV) excitation, that can be viewed with the naked eye. A monolayer of ASiNP on water surface can be transferred horizontally onto any arbitrary substrate through a modified inverse Langmuir-Schaefer (MILS) deposition technique and it retains its luminescence. Brewster Angle Microscopy (BAM) of the film on water and Imaging Ellipsometry (IE) of transferred film show circular domains of diameter ∼ 100 μm, whereas Atomic Force Microscopy (AFM) of the latter show fractal patterns of height ∼ 1 nm and lateral size ∼ 10 nm, within these domains. Transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED) patterns reveal crystalline Si with very small sizes in the range of 2-10 nm having a lateral spread of several hundreds of nanometers. Spectroscopic investigations by UV-visible spectrometer of functionalized Si films reveals features that are very different from that of bulk Si and clearly bear signature of nanostructures. These thin films hold immense potential for applications in opto-electronic devices.

Au nanoparticle (NP)-decorated titanium dioxide (TiO2) thin films (Au-TO), prepared by a unique surfactant-assisted 2D self-assembling technique of Au NP layering onto a titanium dioxide matrix (TO) with molecular-level control, in conjunction with a classic sol–gel route, showed a significant decrease in the optical band gap (ΔEg = ∼0.6 eV) of Au-TO films compared to the conventional sol–gel-prepared pristine counterpart. Strong dependence on surfactant type and deposition temperature of the 2D Au NP layer was observed upon a band gap decrease of the films. Unlike spin-coated Au NP overlayers on TiO2, which resulted in Au NP agglomeration, in this modified inverted Langmuir–Schaefer (MILS) technique, the organic surfactant induced 2D patterned confinement of Au NP layers on TiO2, causing an increase in the active surface area of the Au NP–TiO2 interface. Results of X-ray diffraction and near-edge X-ray absorption fine structure spectroscopy indicated changes in crystal structure as well as in electronic ...

Hydrophobic dodecanethiol capped gold nanoparticles (AuNPs) are found to self-assemble into two-dimensional patterns in monolayers of amphiphiles spread at the air-water interface of a Langmuir trough. In this communication we investigate the role of the nanoparticle-monolayer (FNMA) and monolayer-monolayer (FMMA) lipophilic attraction in influencing morphology and dynamics of AuNP cluster patterns in fatty acid monolayers. FNMA and FMMA are progressively varied by changing n, where n is the number of -CH2 groups in the alkyl tails of the amphiphilic fatty acid (CH3(CH2)nCOOH) molecules forming the monolayer. Compressibility measurements on the pristine and nanoparticle-laden monolayers show that, while the compressibility of the pristine monolayer decreases with increasing n, pointing to a progressive increase in FMMA, the effect of nanoparticles (increase in compressibility or lowering of FMMA) is discernible only for 14 < n < 22. The corresponding pattern morphology, observed with a Brewster Angle Microscope (BAM) at an in-plane resolution of 450 nm for 6 hours, reveals that there are essentially three stages in pattern evolution, lamellae of Au nanoclusters spread over the fatty-acid monolayer background (the λ state) followed by a network of nanoclusters with high node density (the ν state) and finally rings (circular/elongated) of random sizes with very low node density (the ρ state), evolving from an initial unsegregated state, without appreciable change in the average nanoparticle number density over the field of view. Increasing FNMA alongwith FMMA is found to shift a certain state to later times, thus playing the role of a viscous drag and introducing a delay in the timeline. The mean square fluctuation of BAM intensity remains flat and then decays as f(ξ) = ξ(2H) over smaller length scales, where ξ is the spatial separation and H the Hurst exponent. The study of f(ξ) over time reveals the growth of a sub-diffusive regime (H < 0.5) at the intermediate length scale, in almost all the films coinciding with the emergence of the ρ state. The growth of this sub-diffusive regime is slower for stronger FNMA and FMMA, the interactions thus acting as control parameters in dictating the time structure of the spatio-temporal patterns.

Thin films of patterned, thiol capped Au nanoparticle (NP) over layer on titanium dioxide (TiO 2 ) matrix (Au-TO-Ov), prepared by a unique surfactant assisted 2D self-assembling technique with molecular level control, in conjuncture with sol-gel route showed significant decrease in optical band gap and enhanced crystallinity compared to sol-gel prepared pristine TiO 2 . Combined results of scanning electron microscopy, UV-Vis spectroscopy, Raman spectroscopy and near edge x-ray absorption fine structure spectroscopy indicated that decrease in optical band gap was associated with changes in local electronic structure of Au-TO films. No such changes were observed for the film with AuNP as underlayer (Au-TO-Un). Dependence of structure and band gap, on order of Au NP layer is attributed to difference in hydrophilic and hydrophobic interactions occurring at AuNP-TiO 2 interface. Unlike spin coated Au NPs on TiO 2 , which resulted in Au NP agglomeration, or in-situ doping of Au NPs in titanium dioxide precursor by sol-gel method, which indicated a slight increase in band gap, Langmuir-Schaefer method caused significant changes in local structure and hence band gap of the system brought about by these weak Van der Waal's interactions. This cheaper, scalable technique of surfactant aided deposition of 2D layers of Au NPs on semiconducting oxides may be used for development of multilayered structures with promising light harvesting and unidirectional energy transfer (LUET) applications.

Au Nanoparticle (NP) decorated TiO2 thin films, prepared by a unique surfactant assisted 2D self-assembling technique with molecular level control, showed significant decrease in optical band gap as well as enhanced crystallinity compared to its sol-gel prepared pristine counterpart. Spin coated Au NP overlayers on titania in absence of surfactant, on the other hand, had no appreciable effect on either band gap or crystal structure compared to undoped TiO2 films. Apart from exhibiting band gap tuning of TiO2, this cheap, scalable technique of surfactant aided deposition of 2D layers of Au NPs on semiconducting oxides, may be used for development of multilayered structures with promising light harvesting and unidirectional energy transfer (LUET) applications.

Hydrophobic dodecanethiol capped Au nanoparticles (AuNPs) form two-dimensional patterns in monolayers of amphiphilic fatty acids ([Formula: see text]) at the air water interface. An interplay between the various lipophilic interactions, in turn, decides the NP cluster size, where stronger NP-monolayer and monolayer-monolayer attraction in fatty acid monolayers with longer tail length oppose nanoparticle aggregation resulting in a decrease in cluster size in both in-plane and out-of-plane directions. The decrease in the in-plane cluster size is steepest for 14

Liquid disordered $({L}_{d})$ to liquid ordered $({L}_{o})$ phase transition in myristic acid [MyA, ${\text{CH}}_{3}{({\text{CH}}_{2})}_{12}\text{COOH}$] Langmuir monolayers was studied macroscopically as well as mesoscopically to locate the critical point. Macroscopically, isotherms of the monolayer were obtained across the $20{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}\text{--}38{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ temperature $(T)$ range and the critical point was estimated, primarily from the vanishing of the order parameter, at $\ensuremath{\approx}38{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Mesoscopically, domain morphology in the ${L}_{d}\text{\ensuremath{-}}{L}_{o}$ coexistence regime was imaged using the technique of Brewster angle microscopy (BAM) as a function of $T$ and the corresponding power spectral density function (PSDF) obtained. Monolayer morphology passed from stable circular domains and a sharp peak in PSDF to stable dendritic domains and a divergence of the correlation length as the critical point was approached from below. The critical point was found to be consistent at $\ensuremath{\approx}38{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ from both isotherm and BAM results. In the critical regime the scaling behavior of the transition followed the two-dimensional Ising model. Additionally, we obtained a precritical regime, over a temperature range of $\ensuremath{\approx}8{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ below ${T}_{c}$, characterized by fluctuations in the order parameter at the macroscopic scale and at the mesoscopic scale characterized by unstable domains of fingering or dendritic morphology as well as proliferation of a large number of small sized domains, multiple peaks in the power spectra, and a corresponding fluctuation in the peak $q$ values with $T$. Further, while comparing temperature studies on an ensemble of MyA monolayers with those on a single monolayer, the system was found to be not strictly ergodic in that the ensemble development did not strictly match with the time development in the system. In particular, the critical temperature was found to be lowered in the latter. These results clearly show that the critical behavior in fatty acid monolayer phase transitions have features of both complex and nonequilibrium systems.

Dodecanethiol-capped gold nanoparticles (AuNPs) are self-organized in two different amphiphilic monolayers one of which is a single-tailed fatty acid Stearic acid (StA) and the other a double-tailed lipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). In the StA-AuNP film the AuNPs self-organize to form an interconnected network of nanoclusters on compression while in the DMPC-AuNP film the AuNPs aggregate to form random, isolated clusters in the film. The long time evolution of the films at constant surface pressure reveals ring structures in the former and diffusion limited aggregates in the latter that with time evolve into an irregular porous maze of AuNPs in the DMPC film. The difference in structure of the AuNP patterns in the two films can be attributed to a difference in the lipophilic interactions between the NPs and the amphiphilic molecules. The mean square intensity fluctuations f(ln) calculated along a typical line for the 2D structures in both the films at initial and final stages of lo...

A mixture of dodecanethiol-capped Au nanoparticles (AuNPs) and the amphiphilic fatty acid, stearic acid, spread as a monomolecular layer on water surface, is observed with Brewster angle microscopy (BAM) to form a two-dimensional network of AuNP clusters through demixing, at concentration of AuNPs by weight (ρ[over ¯])>10% and the surface pressure (π)≥10mNm^{-1}. For π=15mNm^{-1}, the number of nodes (n) remains unchanged till ∼2 hours and then changes over to a lower n state, where the pattern consists of almost perfect circles with greater in-plane thickness of the AuNP lamellae. For the higher n state the mean-square fluctuation of BAM intensity remains flat and then decays as f(ξ)=ξ^{2α} with α∼0.6 (correlated fluctuations) over the length scales of 400μm-6μm and below 6μm, respectively. For the lower n state the fluctuation decays almost over the entire length scale with α=0.3, indicating emergence of aperiodicity from quasiperiodicity and a changeover to anticorrelated fluctuations. These patterns can be looked at as two distinct chaotic trajectories in the I-I^{'} phase space of the system (I being the scattered light intensity at any position of the pattern and I^{'} its gradient) with characteristic Lyapunov exponents.

A two-dimensional network of thiol-capped Au nanoparticle (AuNP) clusters is self-organized on a Stearic Acid (amphiphilic fatty acid) Langmuir monolayer on water surface. The AuNP clusters are found to form a pattern of connected and enclosed microspaces in the stearic acid template. The network features can be controlled by changing the surface pressure of the monolayer during compression. The two-dimensional dynamics of this network has been studied over a long timescale using Brewster Angle Microscopy (BAM). The dynamics is very slow, indicating the stability of the network system, and is essentially driven by the tendency to lower the number of nodes or joints in the network.

Thiol capped gold nanoparticles (Au NPs) form a simple two dimensional (2D) liquid on water surface but this thin film is unstable under compression. Amphiphilic stearic acid (StA) molecules on water surface, on the other hand, form a complex and more stable 2D liquid. We have initiated a study on a mixture of StA and Au NPs in a monolayer through Surface Pressure (π) – Specific Molecular Area (A) isotherms and Brewster Angle Microscopy (BAM). A mixture of Stearic Acid and Au nanoparticles (10% by weight) produces a monolayer on water surface that acts as a 2D liquid with phases that are completely reversible with negligible hysteresis.

Surface pressure versus Specific Molecular Area (Π-A) Isotherms for Langmuir Monolayers of stearic acid (StA), and stearic acid containing 10% and 50% (by mass) of dodecanethiol-capped Au nanoparticles (StAu10 and StAu50, respectively), have been recorded. The isotherms show a decrease in the magnitude of the slopes in both the 'liquid' L2 and L2. phases and the 'solid' S phase, as well as a decrease in the differences between slopes of all the adjacent phases, indicating a change from a complex to a simpler two dimensional liquid, progressively from StA to StAu10 to StAu50. Brewster Angle Microscopy (BAM) images show, for StA, formation of a continuous twodimensional body while, for StAu50, formation of aligned nanoparticle clusters, with compression.