Monolithic optofluidic ring resonator lasers created by femtosecond laser nanofabrication

We designed, fabricated, and characterized a monolithically integrated optofluidic ring resonator laser that is mechanically, thermally, and chemically robust. The entire device, including the ring resonator channel and sample delivery microfluidics, was created in a block of fused-silica glass using a 3-dimensional femtosecond laser writing process. The gain medium, composed of Rhodamine 6G (R6G) dissolved in quinoline, was flowed through the ring resonator. Lasing was achieved at a pump threshold of approximately 15 μJ mm(-2). Detailed analysis shows that the Q-factor of the optofluidic ring resonator is 3.3 × 10(4), which is limited by both solvent absorption and scattering loss. In particular, a Q-factor resulting from the scattering loss can be as high as 4.2 × 10(4), suggesting the feasibility of using a femtosecond laser to create high quality optical cavities.

Quasi-phase matched second-harmonic generation through thermal poling in femtosecond laser-written glass waveguides

Quasi-phase matched second-harmonic generation at 532 nm is demonstrated in a channel waveguide that is written in bulk fused silica using a femtosecond laser. The second-order nonlinear grating is fabricated using uniform thermal poling followed by periodic erasure inside an e-beam deposition system caused, by what we believe to be, x-rays. A SHG conversion efficiency of 2 x10(-5) %/W-cm(2) was obtained for a 1 cm long device, corresponding to an effective nonlinear coefficient of 0.0075 pm/V.

Scanning thermal microscopy and Raman analysis of bulk fused silica exposed to low-energy femtosecond laser pulses

Low energy femtosecond laser pulses locally increase the refractive index and the hydro-fluoric acid etching rate of fused silica. These phenomena form the basis of a direct-write method to fabricate integrated glass devices that are of particular interest for optofluidics and optomechanical applications. Yet the underlying physical mechanism behind these effects remains elusive, especially the role of the laser polarization. Using Scanning Thermal Microscope and Raman spectrometer we observe in laser affected zones, a localized sharp decrease of the thermal conductivity correlated with an increased presence of low-number SiO(2) cycles. In addition, we find that a high correlation exists between the amount of structural changes and the decrease of thermal conductivity. Furthermore, sub-wavelength periodic patterns are detected for high peak power exposures. Finally, our findings indicate that, to date, the localized densification induced by femtosecond laser pulses remains well below the theoretical value achievable in mechanically densified silica.

Fabrication and characterization of microstructures with optical quality surfaces in fused silica glass using femtosecond laser pulses and chemical etching

We present a study of the sidewall surface quality inside microchannels fabricated in fused silica glass by femtosecond laser pulses and chemical etching. Multiple combinations of laser exposure and etching solution parameters were examined. Results of scanning electron microscopy, atomic force microscopy, and optical reflection analyses of the surfaces are presented. The results obtained demonstrate the feasibility of optical quality surface fabrication, which in turn demonstrates the feasibility of fabricating complex integrated devices containing microfluidic channels and optical waveguides in the glass substrates.

Nanoindentation and birefringence measurements on fused silica specimen exposed to low-energy femtosecond pulses

Femtosecond laser pulses used in a regime below the ablation threshold have two noticeable effects on Fused Silica (a-SiO2): they locally increase the material refractive index and modify its HF etching selectivity. The nature of the structural changes induced by femtosecond laser pulses in fused silica is not fully understood. In this paper, we report on nanoindentation and birefringence measurements on fused silica exposed to low-energy femtosecond laser pulses. Our findings further back the hypothesis of localized densification effect even at low energy regime.

Waveguide electro-optic modulator in fused silica fabricated by femtosecond laser direct writing and thermal poling

An integrated electro-optic waveguide modulator is demonstrated in bulk fused silica. A Mach-Zehnder interferometer waveguide structure is fabricated by direct writing with a femtosecond laser followed by thermal poling. A 20 degrees electro-optic phase shift is achieved at an operating wavelength of 1.55 microm with an applied voltage of 400 V and an interaction length of 25.6 mm, which correspond to an estimated effective electro-optic coefficient of 0.17 pm/V for the TE-polarized mode.

Microfluidic sorting system based on optical waveguide integration and diode laser bar trapping

Effective methods for manipulating, isolating and sorting cells and particles are essential for the development of microfluidic-based life science research and diagnostic platforms. We demonstrate an integrated optical platform for cell and particle sorting in microfluidic structures. Fluorescent-dyed particles are excited using an integrated optical waveguide network within micro-channels. A diode-bar optical trapping scheme guides the particles across the waveguide/micro-channel structures and selectively sorts particles based upon their fluorescent signature. This integrated detection and separation approach streamlines microfluidic cell sorting and minimizes the optical and feedback complexity commonly associated with extant platforms.

Optimization of optical limiting devices based on excited-state absorption

Limiting devices protect sensitive optical elements from laser-induced damage (LID). Passive devices use focusing optics to concentrate the light through a nonlinear optical (NLO) element (or elements) to reduce the limiting threshold. Unfortunately, these NLO elements may themselves undergo LID for high inputs, restricting the useful dynamic range (DR). Recently, efforts at optimizing this DR have focused on distributing the NLO material along the propagation path z of a focused beam, resulting in different portions of the device (in z) exhibiting NLO response at different inputs. For example, nonlinear absorbers closer to the lens, i.e., upstream, protect device elements downstream near the focal plane. This results in an undesirable increase in the threshold, although the lowest threshold is always obtained with the final element at focus. Thus there is a compromise between DR and threshold. This compromise is determined by the material. We concentrate on reverse saturable absorber (RSA) materials (molecules exhibiting larger excited-state than ground-state absorption). We look at both tandem devices and devices in which the concentration of the NLO material is allowed to spatially vary in z. These latter devices require solid-state hosts. The damage threshold of currently available solid-state hosts is too low to allow known RSA materials to reach their maximum absorption, which occurs when all molecules are in their excited state. This is demonstrated by approximate analytical methods as well as by a full numerical solution of the nonlinear wave propagation equation over extremely large distances in z (up to 10(3)Z(0), where Z(0) is the Rayleigh range of the focused beam). The numerical calculations, based on a one-dimensional fast Fourier transform, indicate that proper inclusion of diffraction reduces the effectiveness of reverse saturable absorption for limiting, sometimes by more than a factor of 10. Liquid-based devices have higher damage thresholds (damage occurs to the cuvette wall) and, thus, larger nonlinear absorption. However, RSA material in liquid hosts may suffer from larger thermal lensing.

Biological and physicochemical characterization of recombinant human erythropoietins fractionated by Mono Q column chromatography and their modification with sialyltransferase

Ten erythropoietin (EPO) fractions differing in sialic acid content, ranging from 9.5 to 13.8 mol mol-1 of EPO, were obtained from baby hamster kidney cell-derived recombinant human EPO by Mono Q column chromatography. The mean pI values of the EPO fractions determined by IEF-gel electrophoresis systematically shifted from 4.11 to 3.31, coinciding with the sialic acid content, without a change in the constitution of asialo N-linked oligosaccharides of each fraction. Although a linear relationship between the in vivo bioactivity and the sialic acid content of the fractionated samples was observed until 12.1 mol mol-1 of EPO, there was no further increase in their activity over 12.4 mol mol-1 of EPO. On the other hand, an inverse relationship between the in vitro bioactivity and sialic acid content of EPO was observed. Also, we showed that the in vivo bioactivity of some fractions with low sialic acid contents was increased after treatment with alpha 2,6-sialyltransferase, but the in vivo bioactivity of the other fractions with high sialic acid contents was either decreased or not affected.

Measurement of the optical damage threshold in fused quartz

The damage thresholds of five different types of quartz glass used for the production of spectroscopic cuvettes for liquids were determined with single temporal and spatial mode nanosecond pulses at 532 nm. One of the glasses had a damage threshold of ≃420 J/cm(2), which was more than twice that of the other glasses.

The loss of in vivo activity of recombinant human erythropoietin by active oxygen species

The effects of active oxygen species on the in vivo activity of recombinant human erythropoietin (EPO) treated by Fenton system, xanthine (X) plus xanthine oxidase (XO) system and hydrogen peroxide (H2O2) has been studied by means of counting the increase in number of hemolyser-resistant cells (HRCs) in EPO-injected mice. The results showed that both Fenton and X plus XO systems caused a significant reduction of the activity in proportion to the concentration of generated active oxygen species. Meanwhile, the treatment of EPO with H2O2 alone resulted in a relatively slight reduction of the activity. Electrophoretic studies on the structure of EPO revealed that its main protein band on sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) disappeared in proportion with the extent of exposure to active oxygen generating systems. Both Fenton and X plus XO systems caused a significant loss of fluorescence in the pyridylamino (PA-) sugar chain in proportion to the concentration of generated active oxygen species, and no degradation products in the sugar chain part of the PA-sugar chain were detected. This showed that aromatic groups in EPO were sensitive to attack by active oxygen species. These results provide evidence that hydroxyl radical and other active oxygen species have a potential to react with EPO, leading to a reduction of its in vivo activity.

Effects of aminoglycoside antibiotics on cholinergic autonomic nervous transmission

The effects of eight aminoglycoside antibiotics, gentamicin, neomycin B, ribostamycin, dibekacin B, kanamycin A, streptomycin, tobramycin and amikacin, and two non-aminoglycoside antibiotics, tetracycline and ampicillin, on cholinergic autonomic nervous transmission were studied using isolated guinea-pig ileum preparation. The aminoglycoside antibiotics blocked the transmurally elicited twitches of the ileum in a concentration-dependent manner. The blocking effect of aminoglycosides was biphasic, i.e., an initial reduction followed by a spontaneous partial recovery. Dibekacin was the most potent parasympathetic inhibitor, followed by neomycin B, tetracycline, gentamicin, streptomycin, kanamycin A, tobramycin, ribostamycin, and amikacin. Ampicillin had no blocking effect. The tested antibiotics did not affect acetylcholine (ACh)-induced contraction of the ileum, except for high concentrations of neomycin B, gentamicin, and streptomycin. The three antibiotics shifted the dose-response curves for ACh to the right without affecting the maximal contraction. Naloxon, yohimbine, hexamethonium and choline chloride failed to eliminate the blocking effect of the antibiotics on twitches of the ileum induced by transmural stimulation. However, increase of the extracellular Ca ion concentration virtually abolished the blockade. Dibekacin blocked the evoked but not the spontaneous release of ACh and shifted the dose-response curve of CaCl2-dependent transmurally elicited contractions of the ileum to the right. These results suggest that the site for the block of aminoglycosides is mainly the cholinergic nerve terminal, where they reduce the available Ca ions required for the release of ACh.

Characterization of haemolyser-resistant cells increased in the blood of erythropoietin-treated mice

Recently, we reported a new in vivo assay method for erythropoietin (Epo) by means of counts of the number of haemolyser-resistant cells (HRCs) increased in Epo-injected mice. Here, we attempted to characterize the HRCs. Flow-cytometric studies revealed that HRCs obtained from Epo-injected mice expressed the transferrin receptor on their surface membranes. Furthermore, a fluorophotometric study suggested that the number of transferrin receptor-positive cells increased in a dose-dependent manner in response to treatment with Epo. On the other hand, flowcytometric and fluorophotometric studies of glycophorin A on HRCs using a rabbit antiglycophorin A antibody also showed a high expression of glycophorin A on them as compared with on HRCs from vehicle-treated animals (control). The results indicated that HRCs could be defined by their expression of both transferrin receptors and glycophorin A. We concluded that HRCs might be immature reticulocytes.

Pharmacokinetics of sulfadimethoxine in skin of broiler-chicken after single and multiple intravenous injections

Pharmacokinetics of sulfadimethoxine (SDMX) in skin of broiler chicken after intravenous and in-drinking-water administrations were investigated to examine the reason for a longer residue of SDMX in the skin which was observed in the residue study after administration via drinking water at a concentration of 1,000 ppm. The decay curve of SDMX in the skin after single intravenous injection of 200 mg/kg, the highest dose, was fitted to the two compartment model with T1/2 of 4.4 hrs in the first elimination phase and 173 hrs in the second one. The extrapolated concentrations in the skin at 24 hrs after the injection were calculated to be 69.0 micrograms/g for the 1st phase and 0.11 micrograms/g for the 2nd phase. The decay curves in the skin after single injection of 30 and 100 mg/kg were fitted to the one compartment model with T1/2 of 3.2 and 5.7 hrs, respectively. Dividing a high dose into 3 to 5 doses and injecting sequentially with intervals of the previously measured T1/2, SDMX concentrations in the skin were about half of those in the plasma and ran parallel. The plasma concentration-time curves after single intravenous injection of SDMX more than 100 mg/kg showed nonlinear kinetics with concentrations over 100 micrograms/ml for 12-30 hrs after the injection. By administration of SDMX via drinking water, a sustained residue curve of SDMX in the skin at 1,000 ppm reported previously was not observed at 500 ppm.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfadimethoxine residue in broiler-chicken skin

The disposition and elimination of sulfadimethoxine (SDMX) in the skin of broiler-chickens were investigated. The administration of SDMX, in drinking water, at a concentration of 1,000 ppm for 5 days demonstrated that the SDMX was eliminated much more slowly from the skin than from the other tissues or plasma. These results were duplicated and confirmed in another experiment, in which a single dose of 200 mg/kg BW of SDMX was administered via a stomach tube. No significant difference in the SDMX residue level was observed between the broiler-chickens that had their skin surface sealed versus the non-sealed animals and that had ingested SDMX in their drinking water. This illustrated the higher SDMX residue in the skin was not attributable to external SDMX contamination from the drinking water, feces or urine. In addition, there was no significant difference among the SDMX residue concentrations in the thoracic, dorsal and leg skin samples, following an intravenous injection of SDMX (30 mg/kg BW). This indicated that the SDMX was distributed evenly throughout the entire skin area of the broiler-chickens.

High-sensitivity, single-beam n(2) measurements

We present a simple yet highly sensitive single-beam experimental technique for the determination of both the sign and magnitude of n(2). The sample is moved along the z direction of a focused Gaussian beam while the repetitively pulsed laser energy is held fixed. The resultant plot of transmittance through an aperture in the far field yields a dispersion-shaped curve from which n(2) is easily calculated. A transmittance change of 1% corresponds to a phase distortion of approximately lambda/250. We demonstrate this method on several materials using both CO(2) and Nd:YAG laser pulses.

In-vitro interactions of FCE 22101 with aminoglycosides against gram-negative rods

Agar dilution MICs of FCE 22101 were measured for 894 consecutively-isolated Gram-negative rods from clinical specimens (413 Escherichia coli, 104 Klebsiella spp., 54 Enterobacter spp., 19 Citrobacter spp., 131 Proteus spp., 43 Acinetobacter spp., 9 Serratia spp., 3 Providencia spp., 4 Yersinia spp., 3 Hafnia spp. and 111 Pseudomonas spp.). Excluding Pseudomonas spp., 98% of these isolates were susceptible to 8 mg/l FCE 22101. Resistance (MIC greater than 8 mg/l) varied from 11% in Serratia spp. to 0% in Citrobacter spp. Interactions between FCE 22101 and gentamicin, tobramycin and amikacin were tested by the chequerboard method for 150 of the isolates. The geometric mean sigma FICs were 0.80 for FCE + gentamicin, 0.78 for FCE + tobramycin and 0.79 for FCE + amikacin. Synergy, defined at FIC index (sigma FIC) less than 0.5, for at least one combination, was found in only 16/150 (11%) of the isolates. Most other isolates showed an additive response (sigma FIC = greater than 0.5-1). No antagonism was detected. No significant difference was observed between the various species tested, except that sigma FIC values were lower (geometric mean sigma FIC = 0.61-0.68) for non-fermentative species than for fermentative species (geometric mean sigma FIC = 0.83-0.86). Likewise, geometric sigma FIC values were lower (0.67-0.69) for isolates resistant to FCE and/or aminoglycosides than for those susceptible to both components (sigma FIC 0.85-0.88).

Expression of H1 outer-membrane protein of Pseudomonas aeruginosa in relation to sensitivity to EDTA and polymyxin B

During growth in magnesium (Mg++)-deficient mineral media, Pseudomonas aeruginosa cells synthesise large amounts of H1 outer-membrane protein and are resistant to polymyxins and EDTA. It has been suggested that H1 protein replaces Mg++ as an outer-membrane-stabilising component in Mg++-deprived cells, thereby removing the EDTA target and blocking an adsorption site for polymyxins. Induction of H1 protein synthesis also occurred in P. aeruginosa cells grown in Antibiotic No. 3 Broth (Ab3B), although this medium is not Mg++-deficient. Generally, significant induction of H1 protein did not occur in P. aeruginosa cultures grown in other complex media such as Proteose Peptone and Nutrient Broth, which contained less Mg++ than Ab3B, nor in Isosensitest Broth or Mueller Hinton Broth, which contained higher Mg++ concentrations. H1-protein-induced P. aeruginosa cells from Ab3B cultures, unlike those from Mg++-deficient mineral-broth culture, remained fully sensitive to polymyxin B and, with one exception, to EDTA. It is concluded that induction of H1 protein does not itself confer resistance to polymyxin B, and has no more than a minor role in EDTA resistance. Other cell-wall changes, such as phospholipid modifications and the absence of Mg++, probably account for the resistance of Mg++-deprived cells.

National survey of antibiotic resistance in Pseudomonas aeruginosa

The antibiotic susceptibility of 1866 consecutive non-replicate clinical isolates of Pseudomonas aeruginosa from 24 British hospitals was examined. Antibiotics tested and resistance breakpoints selected were: carbenicillin (MIC greater than 128 mg/l), azlocillin (greater than 32 mg/l), cefotaxime (greater than 16 mg/l), cefoperazone (greater than 16 mg/l), ceftazidime (greater than 16 mg/l), amikacin (greater than 4 mg/l) and gentamicin (greater than 2 mg/l). Resistance frequencies detected were: carbenicillin 9.6%, azlocillin 3.9%, cefotaxime 19.0%, cefoperazone 4.3%, ceftazidime 0.3%, amikacin 3.8%, and gentamicin 5.5%.

Mechanisms of beta-lactam resistance in British isolates of Pseudomonas aeruginosa

The mechanisms of resistance to beta-lactam antibiotics in 191 isolates of Pseudomonas aeruginosa were examined. These represented the most resistant organisms of 1866 isolates collected during a national survey of antibiotic resistance in this species. One hundred and seventy-two isolates were selected because they were resistant to carbenicillin (MIC greater than 128 mg/L) and 19 because the MICs of cefotaxime were greater than the MICs of carbenicillin. Of the carbenicillin-resistant isolates, 35 produced plasmid-mediated beta-lactamases known to be active against carbenicillin and seven produced unusual beta-lactamases; in 131 strains, resistance could not be attributed to beta-lactamase production and was considered to be intrinsic. The unusual antibiogram in which the MIC of cefotaxime was greater than the MIC of carbenicillin was associated with overproduction of the chromosomally-determined Sabath and Abrahams ' beta-lactamase. Selection of strains with this last mechanism represents a novel resistance problem and one which may increase with increased use of newer antipseudomonal beta-lactams.