In-line fiber optic structures for environmental sensing applications

Fiber optic sensors based on the interaction of surface plasmons or evanescent waves with the surrounding environment are usually obtained by tapering an optical fiber, which significantly weakens the structure, or by use of just the end of the optical fiber. A fiber optic structure that maintains the structural integrity of the optical fiber with a long environmental interaction length is presented. Graded-index optical fiber elements are used as lenses, and a coreless optical fiber acts as the environmental interaction area. These elements are fused by an optical fiber splicer and result in a continuous fiber optic sensing system.     

EOT or Kretschmann configuration? Comparative study of the plasmonic modes in gold nanohole arrays

The debate is still ongoing on the optimal mode of interrogation for surface plasmon resonance (SPR) sensors. Comparative studies previously demonstrated that nanoparticles exhibiting a localized SPR (LSPR) have superior sensitivity to molecular adsorption processes while thin Au film-based propagating SPR is more sensitive to bulk refractive index. In this paper, it is demonstrated that nanohole arrays (1000 nm periodicity, 600 nm diameter and 125 nm depth), which support both LSPR and propagating SPR modes, exhibited superior sensitivity to bulk refractive index and improved detection limits for IgG sensing by using the Kretschmann configuration. The greater sensitivity to IgG detection in the Kretschmann configuration was obtained despite the shorter penetration depth of nanohole arrays excited in the enhanced optical transmission (EOT) configuration. The decay length of the electromagnetic field in EOT mode was estimated to be approximately 140 nm using a layer-by-layer deposition technique of polyelectrolytes (PAH and PSS) and was confirmed with 3D FDTD simulations, which was lengthen by almost a factor of two in the Kretschmann configuration. Spectroscopic data and field depth were correlated with RCWA and FDTD simulations, which were in good agreement with the experimental results. Considering these analytical parameters, it is advantageous to develop sensors based on nanohole arrays in the Kretschmann configuration of SPR.     

Transport of topical anesthetics in vitamin E loaded silicone hydrogel contact lenses

Transport of surface active anesthetic drugs through silicone hydrogel contact lenses containing nanosized vitamin E aggregates is explored for achieving extended anesthetics delivery. Commercial silicone hydrogel contact lenses release most ophthalmic drugs including local anesthetics for only a few hours, which is not adequate. Here we focus on creating dispersion of highly hydrophobic vitamin E aggregates in the lenses as barriers for drug diffusion for increasing the release durations. This approach has been shown previously to be successful in extending the release durations for some common hydrophilic ophthalmic drugs. The topical anesthetic drugs considered here (lidocaine, bupivacaine, and tetracaine) are hydrophilic at physiologic pH due to the charge, and so these cannot partition into the vitamin E barriers. However, these surface active drug molecules adsorb on the surface of the vitamin E barriers and diffuse along the surface, leading to only a small decrease in the effective diffusivity compared to non-surface-active hydrophilic drugs. The drug adsorption can be described by the Langmuir isotherm, and measurements of surface coverage of the drugs on the vitamin E provide an estimate of the available surface area of vitamin E, which can then be utilized to estimate the size of the aggregates. A diffusion controlled transport model that includes surface diffusion along the vitamin E aggregates and diffusion in the gel fit the transport data well. In conclusion, the vitamin E loaded silicone contact lens can provide continuous anesthetics release for about 1-7 days, depending on the method of drug loading in the lenses, and thus could be very useful for postoperative pain control after corneal surgery such as the photorefractive keratectomy (PRK) procedure for vision correction.     

Indium triflate catalyzed one-pot multicomponent synthesis of spiro-hexahydropyrimidines explained by multiple covalent bond formation

A mild, efficient, and expeditious method has been developed for the synthesis of spiro-hexahydropyrimidine derivatives via a three-component, one-pot cyclocondensation reaction of aromatic amines, formaldehyde, and cyclic ketones in 4-6 h using In(OTf)₃ as Lewis acid catalyst for the first time. The reaction involving creation of six new covalent bonds was efficiently promoted by 10 mol % In(OTf)₃ and the catalyst could be recovered easily after the reaction and reused without any loss of its catalytic activity. The advantageous features of this methodology are high atom-economy, operational simplicity, shorter reaction time, and easy handling.     

DNA separation by EFFF in a microchannel

This paper theoretically explores the application of electric field flow fractionation (EFFF) for the size-based separation of DNA strands in a microchannel. An axial electric field cannot separate DNA strands in solution because the electrical mobility of the strands is independent of the length. However, lateral electric fields coupled with an axial Poiseuille flow can separate the DNA strands of different sizes. By using regular perturbation analysis, we obtain the effective diffusivity and the mean velocity of the DNA molecules that are undergoing a pressure driven Poiseuille flow in a 2D channel in presence of a lateral electric field. The mean velocities and the dispersion coefficients are then utilized to determine the scaling for length of the channel and the time required for separation of DNA molecules in different parameter regimes. The results show that EFFF can separate DNA strands in the range of 10 kbp that differ in size by about 2.5 kbp in about half an hour in a 1 cm long channel. While DNA strands can be separated by EFFF, the performance of devices based on EFFF seems to be at best comparable to other techniques such as entropic trapping.     

Role of interstitial “caged” Fe in the superconductivity of FeTe1/2Se1/2

All samples are synthesized through a standard solid state reaction route and are quenched to room temperature systematically at 700 °C, 500 °C, 300 °C, and room temperature (RT); the samples are denoted 700Q, 500Q, 300Q, and RTQ, respectively. The structural, and magnetic properties are studied. Careful Rietveld analysis of the X-ray diffraction patterns revealed that all samples except 700Q crystallized in a single phase with space group P4/nmm; the amount of interstitial Fe (Fe_int) at the 2c site increased from 5% for RTQ to 8% for 500Q. Sample 700Q crystallized in the Fe₇Se₈ phase. The magnetization result revealed that RTQ and 300Q are superconducting at 10 K and 13 K, respectively, while 500Q and 700Q are not superconducting. Magnetic ordering was observed at around 125 K for all the samples. The prominence of in terms of effective moment is sufficiently higher for 500Q and 700Q than for RTQ and 300Q. Summarily, it is found that quenching-induced disorder affects the occupancy of interstitial Fe in FeTe_1/2Se_1/2 and thus both its superconducting and magnetic properties. Further, it clear that limited presence of interstitial Fe at 2c site is not completely contrary to the observation of superconductivity, because the 300Q sample possesses higher T_c (13 K) for higher Fe_int (6%) than the RTQ sample with relatively lower T_c (10 K) having lower Fe_int (5%). Further, the 500Q sample, with much higher Fe_int (8%), is non-superconducting.     

Amitriptyline overdose treatment by pegylated anionic liposomes

Liposomes composed of DOPG, 50:50 DMPC:DOPG, 95:5 and 85:15 DOPG:DPPE-mPEG-2000, and 55:15:30 DMPC:DPPE-mPEG-2000:CH were studied for their ability to sequester amitriptyline in human serum. The effects of lipid type and loading, liposome size, PEG inclusion, protein interaction and storage were considered. Liposome size had no effect on drug uptake, as 40, 100, and 284 nm liposomes bound similar amounts of drug in buffer. The optimal amount of PEG-modified lipid incorporated into liposomes was found to be 5%. 95:5 DOPG:DPPE-mPEG-2000 liposomes loaded at 1.44 mg lipid/mL were most effective at shielding protein interactions while still allowing amitriptyline to diffuse to the bilayer surface and bind. Absolute reductions of 99% in buffer and human serum samples were observed, while the free drug concentration reduction relative to binding in serum without liposomes was nearly 90% across a drug concentration range of 1-20 muM. With such reductions, serum drug concentrations could be rapidly reduced from toxic to therapeutic levels. Furthermore, storage tests revealed that such liposomes may be stored for at least one month without a change in drug binding ability. These findings strongly suggest that predominantly anionic liposomes incorporated with PEG are excellent candidates for amitriptyline overdose treatment.