Influence of the dielectric substrate on the effective optical constants of silver plasmonic films.

The effective optical properties of plasmonic thin films can be used to model the far-field response of nanostructured materials to an incident electromagnetic field. In the present work, optically thin nanostructured silver (Ag) plasmonic films were fabricated on transparent dielectric substrates of soda-lime glass, sapphire, and fused silica using oblique angle deposition. The influence of the underlying dielectric substrate on the effective optical properties of the nanostructured layer was investigated by an ellipsometric-optical model based on Mueller matrix ellipsometry. The wavelength-dependent uniaxial optical responses of the nanostructured Ag films fabricated on sapphire were modeled with three Gaussian and one Tanguy oscillator, representing key optical phenomena over the range from 300 to 1000 nm. In comparison with the same Ag films on glass, the results confirm that the effective optical properties cannot be considered in isolation from the substrate. As expected, the extinction peak associated with the localized surface plasmon resonance was redshifted by approximately 220 nm per unit of the substrate refractive index. Importantly, it was found that the direction of incidence also influences the film behavior, with a substantial redshift in the extinction peak for light directed through the dielectric compared to free-space illumination. This property can have a significant effect on the far-field performance of these films.

Effective optical constants of anisotropic silver nanoparticle films with plasmonic properties: erratum.

This erratum reports a correction to Fig. 5 in the original manuscript, Opt. Lett.41, 5495 (2016)OPLEDP0146-959210.1364/OL.41.005495.

Effective optical constants of anisotropic silver nanoparticle films with plasmonic properties.

Mueller matrix ellipsometry has been used to determine the effective optical constants of island-like Ag films deposited by thermal evaporation. These films depart substantially from bulk silver with a prominent localized surface plasmon resonance. Moreover, despite the isotropic appearance, they exhibit uniaxial optical properties with the optical axis inclined by 83.4° from the substrate normal toward the direction of the incoming vapor flux. The uniaxial model supports the plasmon resonance peaks revealed by in-plane absorbance measurements of the films. The uniaxial behavior suggests that the resonances along the ordinary axes are weakly coupled between neighboring particles, whereas the extraordinary resonance is relatively strongly coupled. Therefore, the anisotropy should be considered in the practical applications of these plasmonic films.

Influence of carbon steel grade on the initial attachment of bacteria and microbiologically influenced corrosion.

The influence of the composition and microstructure of different carbon steel grades on the initial attachment (≤ 60 min) of Escherichia coli and subsequent longer term (28 days) corrosion was investigated. The initial bacterial attachment increased with time on all grades of carbon steel. However, the rate and magnitude of bacterial attachment varied on the different steel grades and was significantly less on the steels with a higher pearlite phase content. The observed variations in the number of bacterial cells attached across different steel grades were significantly reduced by applying a fixed potential to the steel samples. Longer term immersion studies showed similar levels of biofilm formation on the surface of the different grades of carbon steel. The measured corrosion rates were significantly higher in biotic conditions compared to abiotic conditions and were found to be positively correlated with the pearlite phase content of the different grades of carbon steel coupons.

The effect of metal microstructure on the initial attachment of Escherichia coli to 1010 carbon steel.

Metallurgical features have been shown to play an important role in the attachment of microorganisms to metal surfaces. In the present study, the influence of the microstructure of as-received (AR) and heat-treated (HT) 1010 carbon steel on the initial attachment of bacteria was investigated. Heat treatment was carried out with the aim of increasing the grain size of the carbon steel coupons. Mirror-polished carbon steel coupons were immersed in a minimal medium inoculated with Escherichia coli (ATCC 25922) to investigate the early (15, 30 and 60 min) and relatively longer-term (4 h) stages of bacterial attachment. The results showed preferential colonisation of bacteria on the grain boundaries of the steel coupons. The bacterial attachment to AR steel coupons was relatively uniform compared to the HT steel coupons where an increased number of localised aggregates of bacteria were found. Quantitative analysis showed that the ratio of the total number of isolated (i.e., single) bacteria to the number of bacteria in aggregates was significantly higher on the AR coupons than the HT coupons. Longer-term immersion studies showed production of extracellular polymeric substances by the bacteria and corrosion at the grain boundaries on both types of steel coupon tested.

Temperature measurement in the microscopic regime: a comparison between fluorescence lifetime- and intensity-based methods.

Thermally sensitive fluorescent indicators have been proposed to monitor temperature changes in microfluidic systems, mainly based on fluorescence intensity or lifetime. However, measuring temperature in a structured environment, such as biological tissue, presents additional challenges due to the chemical and structural complexity. Here, we investigate the potential for resolving temperature distributions within the volume of a single cell. Rhodamine B (RhB) dye was employed as a temperature indicator to compare fluorescence intensity- and lifetime-based techniques. The relationship between the fluorescence lifetime and temperature was found to be highly dependent on the biological environment. The intensity-based method allowed the temperature distribution to be mapped with partial success within the volume of a single cell. Under ideal circumstances, the temperature can be mapped pixel by pixel with a resolution better than ±0.3°C within the cell cytoplasm, but this accuracy was reduced to ±1.8°C by environmental variations. These results suggest that the fluorophore should be encapsulated and immobilized in the biological tissue in order to reduce the influence of environmental factors on temperature measurements at the cellular level.

Bacterial attachment on optical fibre surfaces.

Optical fibres have received considerable attention as high-density sensor arrays suitable for both in vitro and in vivo measurements of biomolecules and biological processes in living organisms and/or nano-environments. The fibre surface was chemically modified by exposure to a selective etchant that preferentially erodes the fibre cores relative to the surrounding cladding material, thus producing a regular pattern of cylindrical wells of approximately 2.5 mum in diameter and 2.5 mum deep. The surface hydrophobicity of the etched and non-etched optical fibres was analysed using the sessile pico-drop method. The surface topography was characterised by atomic force microscopy (AFM), while the surface chemistry was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Six taxonomically different bacterial strains showed a consistent preference for attachment to the nano-scale smoother (R(q) = 273 nm), non-etched fibre surfaces (water contact angle, theta = 106 degrees +/- 4 degrees). In comparison, the surfaces of the etched optical fibres (water contact angle, theta = 96 degrees +/- 10 degrees) were not found to be amenable to bacterial attachment. Bacterial attachment on the non-etched optical fibre substrata varied among different strains.

Nanostructured optical fibre arrays for high-density biochemical sensing and remote imaging.

Optical fibre bundles usually comprise a few thousand to tens of thousands of individually clad glass optical fibres. The ordered arrangement of the fibres enables coherent transmission of an image through the bundle and therefore enables analysis and viewing in remote locations. In fused bundles, this architecture has also been used to fabricate arrays of various micro to nano-scale surface structures (micro/nanowells, nanotips, triangles, etc.) over relatively large areas. These surface structures have been used to obtain new optical and analytical capabilities. Indeed, the imaging bundle can be thought of as a "starting material" that can be sculpted by a combination of fibre drawing and selective wet-chemical etching processes. A large variety of bioanalytical applications have thus been developed, ranging from nano-optics to DNA nanoarrays. For instance, nanostructured optical surfaces with intrinsic light-guiding properties have been exploited as surface-enhanced Raman scattering (SERS) platforms and as near-field probe arrays. They have also been productively associated with electrochemistry to fabricate arrays of transparent nanoelectrodes with electrochemiluminescent imaging properties. The confined geometry of the wells has been loaded with biosensing materials and used as femtolitre-sized vessels to detect single molecules. This review describes the fabrication of high-density nanostructured optical fibre arrays and summarizes the large range of optical and bioanalytical applications that have been developed, reflecting the versatility of this ordered light-guiding platform.

Audit of performance of size 1.5 ProSeal laryngeal mask airways in infants less than six months undergoing inguinal herniotomy.

Many anaesthetists have found the size 1.5 classic Laryngeal Mask Airway unsuitable for use in children under 10 kg, whereas recent studies evaluating the ProSeal Laryngeal Mask Airway (PLMA) show high success rates, even during laparoscopic surgery. Our routine practice has been to use tracheal intubation for inguinal herniotomy in children weighing less than 10 kg. Following the introduction of the PLMA to our hospital, we decided to audit our use of the PLMA 1.5 in this group of patients. We included 20 consecutive infants, aged less than six months and weighing 5 to 10 kg. We recorded patient, anaesthetic and insertion details, device performance data and complications. No aspect of anaesthetic practice was changed by involvement in this audit. The PLMA was inserted successfully at the first attempt in 85% (17/20) of infants. Overall successful insertion occurred in 90% (18/20) and satisfactory airway maintenance was provided for the duration of anaesthesia in 90% (18/20). The mean leak pressure was 24 cmH2O (range 15 to 30 cmH2O). We found the 1.5 PLMA provided a satisfactory airway in 90% of infants. This report adds to the evidence that the PLMA 1.5 can provide a satisfactory alternative to intubation in selected infants.

Optical fibre SERS sensors.

Surface-enhanced Raman scattering (SERS) has established itself as an important analytical technique. However, efforts to transfer the technology from the laboratory to the production line, clinic or field have been frustrated by the lack of robust affordable substrates and the complexity of interfacing between sample and spectrometer. Prompted by the success of optical fibre systems for implementing normal Raman scattering spectroscopy in remote locations and biomedical applications, attention has now shifted to the development of SERS-active optical fibres. Other workers have attempted to develop SERS probes with extended interaction lengths and both far-field and near-field SERS imaging techniques for high-resolution chemical mapping of surfaces. This review discusses the development of these technologies and presents the current state of the art. Although recent developments show great promise, some outstanding challenges and opportunities remain to be addressed.

Nanoimprinted optical fibres: Biotemplated nanostructures for SERS sensing.

Optical fibre surface-enhanced Raman scattering (SERS) sensors offer a potential solution for monitoring low chemical concentrations in remote or in situ sensing scenarios. The SERS effect relies on the interaction of analyte molecules with nanostructured metal surfaces. We demonstrate a nanoscale biotemplating approach to fabricating these sensors, using nanoimprint lithography to replicate cicada wing antireflective nanostructures onto the end faces of standard silica optical fibres. These SERS-compatible nanoarrays are coated with silver to make them SERS active, and thiophenol and rhodamine 6G are used as test analytes, from which strong SERS spectra are collected using both direct endface illumination and through-fibre interrogation. This combination of biological templates with nanoscale replication and optical fibres demonstrates a high-resolution, low-cost approach to fabricating high-performance optical fibre SERS sensors.

Differences in colonisation of five marine bacteria on two types of glass surfaces.

The retention patterns of five taxonomically different marine bacteria after attachment on two types of glass surfaces, as-received and chemically etched, have been investigated. Contact angle measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectrometry (XPS) were employed to investigate the impact of nanometer scale surface roughness on bacterial attachment. Chemical modification of glass surfaces resulted in a approximately 1 nm decrease in the average surface roughness (R(a)) and the root-mean-squared roughness (R(q)) and in a approximately 8 nm decrease in the surface height and the peak-to-peak (R(max)) and the 10-point average roughness (R(z)). The study revealed amplified bacterial attachment on the chemically etched, nano-smoother glass surfaces. This was a consistent response, notwithstanding the taxonomic affiliation of the selected bacteria. Enhanced bacterial attachment was accompanied by elevated levels of secreted extracellular polymeric substances (EPS). An expected correlation between cell surface wettability and the density of the bacterial attachment on both types of glass surfaces was also reported, while no correlation could be established between cell surface charge and the bacterial retention pattern.

Prospective comparison of sevoflurane and desflurane in formerly premature infants undergoing inguinal herniotomy.

BACKGROUND: Formerly premature infants having inguinal herniotomy have been at a high risk of postoperative apnoea, newer less soluble anaesthetic agents may reduce this risk. METHODS: Thirty infants, under 37 weeks gestation and under 47 weeks post-conceptional age, undergoing inguinal herniotomy had an inhalational induction with sevoflurane and were randomly allocated to sevoflurane (group S) or desflurane (group D) for maintenance. All infants received i.v. atracurium 0.5 mg kg(-1), rectal acetaminophen 20 mg kg(-1) and caudal bupivacaine 0.25% 1 ml kg(-1). Infants were monitored for apnoeas (using nasal thermistry and impedance), haemoglobin oxygen desaturations and bradycardias for 12 h before and after operation with an Alice 4 polysomnograph. Emergence timings were recorded. RESULTS: There was no difference between pre- and postoperative incidence of apnoeas in either group, and no group difference between desflurane and sevoflurane in terms of pre- and postoperative ventilatory events or in the number of apnoeas in the postoperative period (nine patients in group D and five patients in group S had apnoeas). Median times to first movement, tracheal extubation, eye opening and first cry were all faster with group D (group D: 3.0, 10.0, 9.0 and 11.0 min and group S: 7.0, 15.1, 13.5 and 16.1 min, respectively). No infant had problems with airway irritation on emergence and no infant required airway intervention for apnoea. CONCLUSIONS: Infants wake faster from general anaesthesia when maintained with desflurane as compared with sevoflurane, but no difference in postoperative respiratory events was demonstrated between the groups.

Emergence and recovery in children after desflurane and isoflurane anaesthesia: effect of anaesthetic duration.

BACKGROUND: We hypothesized that increasing duration of inhalation anaesthesia is associated with slower emergence and recovery in children, and that this effect would be less marked with desflurane in comparison with isoflurane. METHODS: Fifty-four infants and children assigned in groups according to age and expected length of operation were prospectively randomized to receive either isoflurane (I) or desflurane (D) for anaesthesia. After standard induction, the anaesthesia was maintained using an age-related 1.0 minimum alveolar concentration (MAC) equivalent for either agent in air and oxygen. Local analgesia was used as appropriate. End-tidal volatile agent concentration was recorded until extubation. Clinical evaluation of recovery was made by observers, blinded to group allocation. RESULTS: For patients <4 yr of age, the median (95% CI) times in minutes to first movement [5.27 (D), 9.22 (I)], eye opening [9.42(D), 13.3(I)] and extubation [7.18 (D), 12.5 (I)] were significantly shorter (P<0.05) for desflurane. In the group >4 yr of age, the median (95% CI) times in minutes to first movement [4.42 (D), 11.6 (I)], eye opening [8.55(D), 18.0(I)] and extubation [7.08 (D), 16.7 (I)] were significantly shorter (P<0.001) for desflurane. Times to leave recovery were not significantly different for the group <4 yr of age, but were significantly shorter for desflurane in the group >4 yr of age (P<0.01). The isoflurane, but not desflurane, had a time-dependent effect on arousal. There were no significant differences in incidence of airway irritation or emergence delirium between the two agents. CONCLUSIONS: The rate of recovery in children after exposure to desflurane was faster than those patients receiving isoflurane; recovery from desflurane, but not isoflurane, was relatively unaffected by the duration of anaesthesia.

Double-blind randomized controlled trial of caudal versus intravenous S(+)-ketamine for supplementation of caudal analgesia in children.

BACKGROUND: The postoperative analgesic efficacy of S(+)-ketamine after caudal or i.v. administration following sub-umbilical surgery in children was studied to investigate its principal site of analgesic action. METHODS: Sixty children undergoing caudal block during general anaesthesia for hernia repair or orchidopexy were prospectively randomized to one of three groups: the bupivicaine group received plain bupivacaine 0.25% 1 ml x kg(-1); the caudal ketamine group received caudal plain bupivacaine 0.25% 1 ml x kg(-1) with S(+)-ketamine 0.5 mg x kg(-1); the i.v. ketamine group received caudal plain bupivacaine 0.25% 1 ml x kg(-1) plus S(+)-ketamine 0.5 mg x kg(-1) i.v. Postoperative measurements included analgesic requirements and modified objective pain score for the first 24 h. RESULTS: The median time to first analgesia was significantly longer in the caudal ketamine group (10 h) than in the i.v. ketamine (4.63 h) or bupivacaine (4.75 h) groups (P=0.01). Significantly fewer doses of analgesia were required over the first postoperative 24 h by subjects in the caudal ketamine group (median 1) compared with the i.v. ketamine (median 2) or bupivacaine (median 2.5) groups (P<0.05). There was no difference between the groups in the incidence of postoperative nausea and vomiting or psychomotor reactions. CONCLUSIONS: We have demonstrated that the addition of caudal S(+)-ketamine to bupivacaine prolongs the duration of postoperative analgesia. However, the same dose of i.v. S(+)-ketamine combined with a plain bupivacaine caudal provides no better analgesia than caudal bupivacaine alone, indicating that the principal analgesic effect of caudal S(+)-ketamine results from a local neuroaxial rather than a systemic effect.

Double-blind randomized placebo-controlled trial of the effect of ketamine on postoperative morphine consumption in children following appendicectomy.

BACKGROUND: Ketamine has an opioid sparing effect following surgery in adults. This study investigated whether a similar effect is seen following appendicectomy in paediatric patients. METHODS: Seventy-five ASA 1 or 2 children aged 7-16 years were recruited, and randomly allocated to one of three groups. Following a standard anaesthetic for appendicectomy, all were prescribed patient controlled analgesia (PCA) morphine with paracetamol and nonsteroidal anti-inflammatory drugs (NSAIDS) as required for postoperative analgesia. In addition the control group received a saline infusion postoperatively, the ketamine bolus group received 500 micro g.kg-1 intravenous (i.v.) ketamine preincision and a saline infusion postoperatively, and the ketamine infusion group received 500 micro g.kg-1 i.v. ketamine preincision and a ketamine infusion at 4 micro g.kg-1 min-1 postoperatively. Morphine consumption, rescue analgesia requirement and side-effects were recorded postoperatively. RESULTS: There was no difference in morphine consumption between the groups. The ketamine infusion group required more doses of rescue analgesia and reported more side-effects than the control group. Five patients, all in the ketamine infusion group, reported hallucinations. CONCLUSIONS: In this paediatric population intravenous ketamine did not have a morphine sparing effect. The increased incidence of side-effects, especially hallucinations, reported by patients given a ketamine infusion may limit the further use of postoperative ketamine in children.

Double-blind, placebo-controlled analgesic study of ibuprofen or rofecoxib in combination with paracetamol for tonsillectomy in children.

BACKGROUND: The analgesics used for paediatric tonsillectomy may be associated with side-effects such as sedation, respiratory depression and vomiting (opioids) or increased bleeding [non-steroidal anti-inflammatory drugs (NSAIDs)]. In our institution, we employ a combination of paracetamol, NSAID and opioid, although there is no published evidence of analgesic benefit from adding NSAIDs to paracetamol in children. METHODS: This randomized, double-blinded clinical study examined the analgesic effectiveness of combining paracetamol (20 mg kg(-1)) with rofecoxib (0.625 mg kg(-1)), ibuprofen (5 mg kg(-1)) or placebo as premedication for (adeno)tonsillectomy (n=98) in children aged 3-15 yr. Intravenous fentanyl 1-2 microg kg(-1) was given intraoperatively. Regular oral paracetamol (15 mg kg(-1), 4 hourly) was given after operation and could be supplemented on request from the child with oral ibuprofen 5 mg kg(-1) or oral codeine 1 mg kg(-1). The primary outcome variable was need for early supplementary analgesia (within 2 h after surgery). RESULTS: The addition of ibuprofen to paracetamol reduced the need for early analgesia from 72% to 38% of children (difference 34%; 95% confidence interval 4-64%). The addition of rofecoxib to paracetamol did not significantly alter the need for early analgesia (68 vs 72%). Pain scores were higher in those children who required early analgesia. There were no differences between the groups in operative blood loss or complications, total 24-h analgesic consumption, pain scores at 4 and 8 h, vomiting or antiemetic use. CONCLUSION: This study provides evidence to support the combination of ibuprofen (but not rofecoxib) with paracetamol for perioperative analgesia in children.