Enhancement of dual zero phonon line emissions in nanodiamonds using quasiperiodic photonic structures.

Color centers in nanodiamonds (NDs) have been largely explored by coupling to a photonic structured matrix (PSM) to amplify visible range emission features, enhancing their use in quantum technologies. Here, we study the emission enhancement of dual near-infrared zero phonon line (ZPL) emission from silicon-boron (SiB) and silicon-vacancy (SiV-) centers in NDs using a spontaneously emerged low index-contrast quasiperiodic PSM, having micron-scale air pores. An intensity enhancement factor of 6.15 for SiV- and 7.8 for SiB ZPLs is attained for the PSM sample compared to a control sample. We find Purcell enhancement of 2.77 times for the PSM sample using spatial-dependent decay rate measurements, supported by localized field intensity confinement in the sample. Such cavity-like emission enhancement and lifetime reduction are enabled by an in-plane order-disorder scattering in the PSM sample substantiated by pump-dependent emission measurements. The results put forward a facile approach to tailor the near-infrared dual ZPL emission from NDs using nanophotonic structures.

Ordered and disordered microstructures of nanoconfined conducting polymers.

We probe the microstructural differences of conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives under geometrical nanoconfinement using a high-resolution electron microscopy (HRTEM) technique. Highly ordered domains of poly(3,4-ethylenedioxythiophene):tosylate PEDOT:Tos, which is polymerized within alumina nanochannels, are observed. These features are in contrast to those of the polymer blend poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) PEDOT:PSS inserted into the nanopores. The extent of the order-disorder parameter in terms of surface crystallization and the number of ordered domains of the long-chain polymers strongly depends on the dopant environment, processing conditions and structural confinement. Atomic force spectroscopy of individual PEDOT nanochannels highlights counterion-dependent surface adhesive factors. The molecular dynamics (MD) simulation of these systems reveals similar polymer chain configurations and the resulting morphology.

Temporal changes in total and metabolically active ruminal methanogens in dairy cows supplemented with 3-nitrooxypropanol.

The purpose of this study was to investigate the effect of 3-nitrooxypropanol (3-NOP), a potent methane inhibitor, on total and metabolically active methanogens in the rumen of dairy cows over the course of the day and over a 12-wk period. Rumen contents of 8 ruminally cannulated early-lactation dairy cows were sampled at 2, 6, and 10 h after feeding during wk 4, 8, and 12 of a randomized complete block design experiment in which 3-NOP was fed at 60 mg/kg of feed dry matter. Cows (4 fed the control and 4 fed the 3-NOP diet) were blocked based on their previous lactation milk yield or predicted milk yield. Rumen samples were extracted for microbial DNA (total) and microbial RNA (metabolically active), PCR amplified for the 16S rRNA gene of archaea, sequenced on an Illumina platform, and analyzed for archaea diversity. In addition, the 16S copy number and 3 ruminal methanogenic species were quantified using the real-time quantitative PCR assay. We detected a difference between DNA and RNA (cDNA)-based archaea communities, revealing that ruminal methanogens differ in their metabolic activities. Within DNA and cDNA components, methanogenic communities differed by sampling hour, week, and treatment. Overall, Methanobrevibacter was the dominant genus (94.3%) followed by Methanosphaera, with the latter genus having greater abundance in the cDNA component (14.5%) compared with total populations (5.5%). Methanosphaera was higher at 2 h after feeding, whereas Methanobrevibacter increased at 6 and 10 h in both groups, showing diurnal patterns among individual methanogenic lineages. Methanobrevibacter was reduced at wk 4, whereas Methanosphaera was reduced at wk 8 and 12 in cows supplemented with 3-NOP compared with control cows, suggesting differential responses among methanogens to 3-NOP. A reduction in Methanobrevibacter ruminantium in all 3-NOP samples from wk 8 was confirmed using real-time quantitative PCR. The relative abundance of individual methanogens was driven by a combination of dietary composition, dry matter intake, and hydrogen concentrations in the rumen. This study provides novel information on the effects of 3-NOP on individual methanogenic lineages, but further studies are needed to understand temporal dynamics and to validate the effects of 3-NOP on individual lineages of ruminal methanogens.

Wavelength-Dependent Charge Carrier Dynamics for Single Pixel Color Sensing Using Graded Perovskite Structures.

We report smart color-sensing devices of two-dimensional lead halide perovskites that exhibit a graded band gap across the film. We observe that the device short-circuit photocurrent is strongly dependent on excitation wavelength λ, and this arises through photoabsorption at different depths in the sample due to the graded bandgaps present. This λ signature in the response of the device is observed in case of steady-state excitation when incident from the high bandgap side of the film, where a complete reversal in the polarity of the photocurrent Iph(t) is obtained as the excitation wavelength is spanned across the visible spectrum. The transient photocurrent reveals λ-specific response arrived from a combination of positive and negative Iph(t) components. The uniqueness of Iph(t) as a function of incident λ can be utilized to examine spectral purity without dispersive optical elements. An equivalent circuit model description provides a possible glimpse into the physical sources involved in contributing to these features.

Red-Emitting Delayed Fluorescence and Room Temperature Phosphorescence from Core-Substituted Naphthalene Diimides.

Unprecedented ambient triplet-mediated emission in core-substituted naphthalene diimide (cNDI) derivatives is unveiled via delayed fluorescence and room temperature phosphorescence. Carbazole core-substituted cNDIs, with a donor-acceptor design, showed deep-red triplet emission in solution processable films with high quantum yield. This study, with detailed theoretical calculations and time-resolved emission experiments, enables new design insights into the triplet harvesting of cNDIs; an important family of molecules which has been, otherwise, extensively been investigated for its n-type electronic character and tunable singlet fluorescence.

Antibiotic resistance and virulence genes in nisin-resistant Enterococcus faecalis isolated from raw buffalo milk modulate the innate functions of rat macrophages.

AIMS: To elucidate the antibiotic resistance and virulence genes of nisin-resistant Enterococcus faecalis isolated from raw buffalo milk and to study the effect of nisin-sensitive and -resistant E. faecalis on the innate immunity of rats. METHODS AND RESULTS: Slanetz-Bartley agar plates containing nisin were used to isolate nisin-resistant E. faecalis. The virulence factors were ascertained using quantitative real-time polymerase chain reaction. Cell viability, phagocytosis, intracellular survival and enzyme assays were performed to investigate the interaction of E. faecalis with rat macrophages. Nisin-resistant E. faecalis was less prone to phagocytosis and survived longer inside the macrophages, due to reduced production of reactive oxygen species and nitric oxide. The viability and activation of macrophages was also reduced in the presence of resistant E. faecalis, as observed by enhanced lactate dehydrogenase production and reduced ß-galactosidase. CONCLUSIONS: Nisin-resistant E. faecalis and its virulence factors were reported in raw buffalo milk. This study shows that nisin-resistant variants exhibited cross resistance to antibiotics and suppressed the innate immune responses of rats by directly affecting macrophage activity. SIGNIFICANCE AND IMPACT OF THE STUDY: This study elucidated the contamination of raw buffalo milk by nisin-resistant E. faecalis, which may pose food safety risk.

Self-powered single semiconductor nanowire photodetector.

Self-powered photodetectors have been fabricated from a single germanium nanowire (NW) in the metal-semiconductor-metal (MSM) device configuration. The self-powered devices show a high photoresponse (responsivity âˆ¼ 103-105 A W-1) in the wavelength range 300-1100 nm. It has been established from I-V characteristics that asymmetry exists in the Schottky barrier height (SBH) at the two MS contacts. We have used simulation to establish that the asymmetric SBH at the metal contacts in an MSM device is a major cause for the 'built-in' axial field that leads to separation of a light generated electron-hole pair in the absence of an applied bias. Thus, even in the absence of external bias, the photogenerated carriers can be separated, which then diffuse to the appropriate electrodes driven by the 'built-in' axial field. We also point out the physical origins that can lead to unequal barrier heights in seemingly identical NW/metal junctions in a MSM device.

Self-Assembled Porous Alumina Based Organic Nanotriode Arrays.

We utilize ordered mesoporous alumina templates for solution processable electronics and demonstrate massively parallel organization of connected three-terminal vertical transistors. The vertical transistor device consists of a connected organic nanotriode array obtained using porous anodized alumina membranes of pore density ≈ 109 pores/cm2. In this structure, a collector-emitter diode gives rise to a space charge limited current, which can be controlled by a third intermediate porous base electrode to give transistor-like characteristics. We study the response characteristics along with 2D device simulations of this novel structure to indicate key parameters involved in the underlying mechanism. Device operation at single transistor level is verified by conductive atomic force microscopy, and the inherent short switching time scales of the vertical structure device is also demonstrated.

Multi-Stimuli-Responsive Charge-Transfer Hydrogel for Room-Temperature Organic Ferroelectric Thin-Film Devices.

The possibility of designing programmable thin-film supramolecular structures with spontaneous polarization widens the utility of facile supramolecular chemistry. Although a range of low molecular mass molecular single crystals has been shown to exhibit ferroelectric polarization, demonstration of stimuli-responsive, thin-film, solution-processable supramolecular ferroelectric materials is rare. We introduce aromatic π-electron donor-acceptor molecular systems responsive to multiple stimuli that undergo supramolecular chiral mixed-stack charge-transfer (CT) coassembly through the tweezer-inclusion-sandwich process supported by hydrogen-bonding interactions. The structural synergy originating from hydrogen-bonding and chiral CT interactions resulted in the development of spontaneous unidirectional macroscopic polarization in the crystalline nanofibrous hydrogel network, under ambient conditions. Moreover, the tunability of these interactions with optical, mechanical, thermal, and electrical stimuli allowed the design of multistate thin-film memory devices. Our design strategy of the supramolecular motif is expected to help the development of new molecular engineering strategies for designing potentially useful smart multicomponent organic electronics.

Dipole-moment-driven cooperative supramolecular polymerization.

While the mechanism of self-assembly of π-conjugated molecules has been well studied to gain control over the structure and functionality of supramolecular polymers, the intermolecular interactions underpinning it are poorly understood. Here, we study the mechanism of self-assembly of perylene bisimide derivatives possessing dipolar carbonate groups as linkers. It was observed that the combination of carbonate linkers and cholesterol/dihydrocholesterol self-assembling moieties led to a cooperative mechanism of self-assembly. Atomistic molecular dynamics simulations of an assembly in explicit solvent strongly suggest that the dipole-dipole interaction between the carbonate groups imparts a macro-dipolar character to the assembly. This is confirmed experimentally through the observation of a significant polarization in the bulk phase for molecules following a cooperative mechanism. The cooperativity is attributed to the presence of dipole-dipole interaction in the assembly. Thus, anisotropic long-range intermolecular interactions such as dipole-dipole interaction can serve as a way to obtain cooperative self-assembly and aid in rationalizing and predicting the mechanisms in various synthetic supramolecular polymers.

Single CuTCNQ charge transfer complex nanowire as ultra high responsivity photo-detector.

We report ultra large photo responsivity ℜ (ratio of photo-generated current to absorbed power) in a single nanowire (NW) device made from a single strand of a nanowire (diameter ~30nm and length ~200nm) of an organomettalic semiconducting charge transfer complex material of CuTCNQ. The device shows responsivity of 8x10(4) A/Watt at 1 volt applied bias with an enhancement over the dark current exceeding 10(5) at zero bias. The observed photo current has a spectral dependence that strongly follows the main absorption peak (close to 405 nm) showing the primary role of absorbed photo-generated carriers.

Investigations on artificially extending the spectral range of natural vision.

Organic semiconductors are being explored as retinal prosthetics with the prime attributes of bio-compatibility and conformability for seamless integration with the retina. These polymer-based artificial photoreceptor films are self-powered with light-induced signal strength sufficient to elicit neuronal firing events. The molecular aspect of these semiconductors provides wide spectral tunability. Here, we present results from a bulk heterostructure semiconductor blend with a wide spectral response range. This combination elicits clear spiking activity from a developing blind-chick embryonic retina in the subretinal configuration in response to white light. The response is largely triggered by the blue-green spectral regime rather than the red-NIR regime for the present polymer semiconductor layer attributes.

Structured hybrid photodetectors using confined conducting polymer nanochannels.

We design and fabricate hybrid organic inorganic perovskite photodetectors that utilize hole transport layer poly(3,4-ethylene dioxythiophene):poly (styrenesulfonate) PEDOT:PSS confined in alumina nanocylinders. This structural asymmetry in the device where the alumina nanopore template is partially filled with PEDOT:PSS provides features that improve certain device characteristics. The leakage component of the current in such devices is considerably suppressed, resulting in enhanced responsivity and detectivity. The funneling aspect of the photogenerated charge carrier transit ultimately leads to fast detectors as compared to conventional perovskite detectors.

Light controlled signaling initiated by subretinal semiconducting-polymer layer in developing-blind-retina mimics the response of the neonatal retina.

Optoelectronic semiconducting polymer material interfaced with a blind-developing chick-retina (E13-E18) in subretinal configuration reveals a response to full-field flash stimulus that resembles an elicited response from natural photoreceptors in a neonatal chick retina. The response manifests as evoked-firing of action potentials and was recorded using a multi-electrode array in contact with the retinal ganglion layer. Characteristics of increasing features in the signal unfold during different retina-development stages and highlight the emerging network mediated pathways typically present in the vision process of the artificial photoreceptor interfaced retina.

Single-pixel, single-layer polymer device as a tricolor sensor with signals mimicking natural photoreceptors.

Color sensing procedures typically involve multiple active detectors or a photodetector coupled to a filter array. We demonstrate the possibility of using a single polymer layer based device structure for multicolor sensing. The device structure does not require any color filters or any subpixelation, and it distinguishes colors without any external bias. The color sensing relies on an appropriate thickness of the active polymer layer that results in a characteristic polarity and temporal profile of the photocurrent signal in response to various incident colors. The device characteristics reveal interesting similarities to the features observed in natural photosensitive systems including retinal cone cells.

Characteristic noise features in light transmission across membrane protein undergoing photocycle.

We demonstrate a technique based on noise measurements which can be utilized to study dynamical processes in protein assembly. Direct visualization of dynamics in membrane protein system such as bacteriorhodopsin (bR) upon photostimulation are quite challenging. bR represents a model system where the stimulus-triggered structural dynamics and biological functions are directly correlated. Our method utilizes a pump-probe near field microscopy method in the transmission mode and involves analyzing the transmittance fluctuations from a finite size of molecular assembly. Probability density distributions indicating the effects of finite size and statistical correlations appear as a characteristic frequency distribution in the noise spectra of bR whose origin can be traced to photocycle kinetics. Valuable insight into the molecular processes were obtained from the noise studies of bR and its mutant D96N as a function of external parameters such as temperature, humidity or presence of an additional pump source.

2D Position-Sensitive Hybrid-Perovskite Detectors.

Hybrid organic-inorganic perovskites (HOIPs) have emerged as a versatile class of semiconductors for numerous optoelectronic applications. Here, we demonstrate light-excitation-dependent two-dimensional (2D) position-sensitive detectors (PSDs) using a mixed-phase perovskite, FA0.83Cs0.17Pb(I0.9Br0.1)3, as the active semiconductor, incorporated within a five-terminal device geometry. The light-induced lateral photovoltage, which is initiated by selective charge transfer across the metal-perovskite barrier interface, is utilized to achieve the excitation-position-dependent electric response. The 2D PSD devices exhibit a spatially dependent linear variation of the photosignal with sensitivity >50 µV mm-1 and a low position detection error (1-2%), making them suitable for applications such as quadrant detectors. Further, it is observed that the device architecture plays a key role in controlling the dynamics and linearity of the HOIP PSDs. The large active area devices (up to ∼2 cm × 2 cm) exhibit a distinct spatial variation of the photosignal. We utilize the functionality of the PSD device for light-tracking applications by implementing a continuous detection scheme.

Monitoring intermediate states of bacteriorhodopsin monolayers using near-field optical microscopy.

We demonstrate single-molecule-level features using near-field optical microscopy on bacteriorhodopsin (bR), a membrane protein that functions as a light-driven proton pump. The photophysical properties of bR are utilized in this imaging technique, using a combination of photoexcitation sources, to accurately identify the active regions and quantify the optical parameters. The studies of bR monolayers are carried out on inert quartz substrates as well as active conducting polymer (polyaniline) substrates. The substrate also plays an important role in the photocycle quantum efficiencies. We speculate on mechanisms governing the higher near-field absorption strength of bR molecules.

An integrated 3D fluidic device with bubble guidance mechanism for long-term primary and secondary cell recordings on multi-electrode array platform.

A 3D fluidic device (3D-FD) is designed and developed with the capability of auto bubble guidance via a helical pathway in a 3D geometry. This assembly is integrated to a multi-electrode array (MEA) to maintain secondary cell lines, primary cells and primary retinal tissue explants of chick embryos for continuous monitoring of the growth and electrophysiology recording. The ability to maintain the retinal tissue explant, extracted from day 14 (E-14) and day 21 (E-21) chick embryos in an integrated 3D-FD MEA for long duration (>100 h) and study the development is demonstrated. The enhanced duration of monitoring offered by this device is due to the controlled laminar flow and the maintenance of a stable microenvironment. The spontaneous electrical activity of the retina, including the spike recordings from the retinal ganglion layer, was monitored over a long duration. Specifically, the spiking activity in embryonic chick retinas of different days (E-14 to 21) is studied, and the presence of light-stimulated firings along with a distinct electroretinogram for E-21 mature retina provides the evidence of a stable microenvironment over a sustained period.

Observation of Bessel beams from electric-field-induced patterns on polymer surfaces.

We report the observation of Bessel-like beams from periodic patterns induced on viscoelastic polymer surfaces by electric field. The patterns resembling a microaxicon array originate from electrohydrodynamic instabilities in polymer films, where the feature dimensions can be easily controlled. The output beam characteristics from these patterns revealed characteristic traits of Bessel beams.