On-chip mid-infrared optical sensing with GeSbSe waveguides and resonators.

We fabricated single mode Ge28Sb12Se60 waveguides and resonators using e-beam lithography and achieved a propagation loss of 3.88 dB/cm at 3.66 µm. We compared BCl3 and CHF3 etch chemistries and determined CHF3 produced 1.5 dB/cm higher propagation losses at 3.6 µm due to C-H bond absorption. We use fabricated waveguides to detect an aromatic aldehyde dissolved in a non-polar solvent with a limit of detection of 1.09 µmol/mL. We then reduce this detection limit to 0.25 µmol/mL using the enhancement produced by a chalcogenide ring resonator.

Fabrication and characterization of high quality GeSbSe reflowed and etched ring resonators.

We demonstrate the fabrication of high Q Ge28Sb12Se60 ring resonators in an all chalcogenide platform through electron-beam lithography, lift-off and thermal reflow. We achieve a Q factor of (3.9 ± 0.2) × 105 in the reflowed ring resonators and (2.5 ± 0.2) × 105 in the reactive ion etched ring resonators at 1550 nm. We measure the line roughness of these devices to estimate the scattering loss. We determine the material and scattering losses of the waveguide and find an additional 1.1 dB/cm excess loss from surface absorption. We fabricate Ge23Sb7S70 waveguides with 0.6 dB/cm of losses and show that Ge23Sb7S70 waveguides do not experience the same kind of excess loss when fabricated under the same conditions. This indicates the excess loss is related to the chemical composition of Ge28Sb12Se60 compound.

Adaptive immunity to human coronaviruses is widespread but low in magnitude.

OBJECTIVES: Endemic human coronaviruses (hCoVs) circulate worldwide but cause minimal mortality. Although seroconversion to hCoV is near ubiquitous during childhood, little is known about hCoV-specific T-cell memory in adults. METHODS: We quantified CD4 T-cell and antibody responses to hCoV spike antigens in 42 SARS-CoV-2-uninfected individuals. Antigen-specific memory T cells and circulating T follicular helper (cTFH) cells were identified using an activation-induced marker assay and characterised for memory phenotype and chemokine receptor expression. RESULTS: T-cell responses were widespread within conventional memory and cTFH compartments but did not correlate with IgG titres. SARS-CoV-2 cross-reactive T cells were observed in 48% of participants and correlated with HKU1 memory. hCoV-specific T cells exhibited a CCR6+ central memory phenotype in the blood, but were enriched for frequency and CXCR3 expression in human lung-draining lymph nodes. CONCLUSION: Overall, hCoV-specific humoral and cellular memory are independently maintained, with a shared phenotype existing among coronavirus-specific CD4 T cells. This understanding of endemic coronavirus immunity provides insight into the homeostatic maintenance of immune responses that are likely to be critical components of protection against SARS-CoV-2.

Third-harmonic generation enhancement in an ITO nanoparticle-coated microresonator.

We report a ∼3-fold enhancement of third-harmonic generation (THG) conversion efficiency using indium tin oxide (ITO) nanoparticles on the surface of an ultra-high-Q silica microsphere. This is one of the largest microcavity-based THG enhancements reported. Phase-matching and spatial mode overlap are explored numerically to determine the microsphere radius (∼29 µm) and resonant mode numbers that maximize THG. Furthermore, the ITO nanoparticles are uniformly bonded to the cavity surface by drop-casting, eliminating the need for complex fabrication. The significant improvement in THG conversion efficiency establishes functionalized ITO microcavities as a promising tool for broadband frequency conversion, nonlinear enhancement, and applications in integrated photonics.

Enhancement of third-order nonlinearity of thermally evaporated GeSbSe waveguides through annealing.

Chalcogenides are a promising platform for infrared nonlinear optics but are susceptible to structural changes during fabrication that affect their linear and nonlinear optical properties. We analyze the structure and optical properties of thermally evaporated and annealed chalcogenide films. Thermally evaporated Ge28Sb12Se60 has an increased selenium content, bandgap, and concentration of heteropolar bonds. The concentration of heteropolar bonds can be reduced by annealing above the glass transition temperature, resulting in improved optical nonlinearity. We demonstrate a 4-fold enhancement of third-order nonlinearity in Ge28Sb12Se60 chalcogenide waveguides by thermal annealing and a decrease in propagation loss from 2.5 dB/cm to 1 dB/cm as an added benefit.

Mass spectral studies of the biologically active stereoisomer family of e,e,e-(methanofullrene(60-63)-carboxylic acids.

Fullerene-based compounds are being developed for an extensive range of biomedical applications, and may provide a completely new class of biologically useful reagents. In support of our continuing investigation and characterization of one such compound, e,e,e-fullerene(60)-63-tris malonic acid (1) we optimized the conditions for obtaining mass spectra. Both positive and negative ion mass spectra are obtained using electrospray ionization (ESI). However, the spectra are dramatically different in the different ionization modes. We studied the effect of solvent media, acid content as well as the concentration of the compound (1) on mass fragmentation pattern both in positive and negative mode. The best mass spectra were obtained when 1 was sprayed from a solution containing a weak organic acid added to aqueous methanol (1:1) in positive mode. We also analyzed the ion current as function of capillary voltage for selected ion. Fragment ions formed by the direct loss of carboxyl groups from the doubly-charged dimer occur for the loss of one, two and six carboxyl groups. Of these, the loss of one carboxyl is the most abundant. The dominant mechanism for the formation of singly-charged fragment ions arises from splitting of the doubly-charged dimers into singly-charged monomers with subsequent carboxyl losses.

High quality chalcogenide-silica hybrid wedge resonator.

Chalcogenide glasses, with high nonlinearity and low loss, have captured research interest as an integrated device platform for near- and mid-infrared nonlinear optical devices. Compared to silicon-based microfabrication technologies, chalcogenide fabrication processes are less mature and a major challenge is obtaining high quality devices. In this paper, we report a hybrid resonator design leveraging a high quality silica resonator to achieve high Q factors with chalcogenide. The device is composed of a thin chalcogenide layer deposited on a silica wedge resonator. The hybrid resonators exhibit loaded Q factors up to 1.5 x 105 in the near-infrared region. We also measured the effective thermo-optic coefficient of the device to be 5.5x10-5/K, which agreed well with the bulk value. Thermal drift of the device can be significantly reduced by introducing a titanium dioxide cladding layer with a negative thermo-optic coefficient.

Back to basics: hand hygiene and isolation.

PURPOSE OF REVIEW: Hand hygiene and isolation are basic, but very effective, means of preventing the spread of pathogens in healthcare. Although the principle may be straightforward, this review highlights some of the controversies regarding the implementation and efficacy of these interventions. RECENT FINDINGS: Hand hygiene compliance is an accepted measure of quality and safety in many countries. The evidence for the efficacy of hand hygiene in directly reducing rates of hospital-acquired infections has strengthened in recent years, particularly in terms of reduced rates of staphylococcal sepsis. Defining the key components of effective implementation strategies and the ideal method(s) of assessing hand hygiene compliance are dependent on a range of factors associated with the healthcare system. Although patient isolation continues to be an important strategy, particularly in outbreaks, it also has some limitations and can be associated with negative effects. Recent detailed molecular epidemiology studies of key healthcare-acquired pathogens have questioned the true efficacy of isolation, alone as an effective method for the routine prevention of disease transmission. SUMMARY: Hand hygiene and isolation are key components of basic infection control. Recent insights into the benefits, limitations and even adverse effects of these interventions are important for their optimal implementation.

The incidence of HBV and HCV infection in Australian travelers to Asia.

We analyzed paired pre- and post-travel sera in a cohort of Australian travelers to Asia and demonstrated the acquisition of hepatitis C virus (HCV) and hepatitis B virus (HBV) infection. The incidence density in nonimmune travelers for HCV infection was calculated as 1.8 infections per 10,000 traveler-days and for HBV infection 2.19 per 10,000 traveler-days.

John Bennett Fenn: a curious road to the prize.

John Bennett Fenn shared the 2002 Nobel Prize in Chemistry for his development of electrospray ionization (ESI). There are several excellent, in-depth biographical reviews of Fenn's scientific career Fenn (Angew. Chem., Int. Ed. 42, 3871-3894, 2003) and Fenn (Annu. Rev. Phys. Chem. 47, 1-41, 1996). The focus of this report is to trace the random walk nature of Fenn's career path and to highlight those critical events along that path that led him to the important work for which he was recognized, the development of ESI as a means of ionizing large molecules and interfacing the liquid chromatograph to the mass spectrometer. In addition, this report should hopefully convey something of the curious, generous, kind, and outgoing nature of the man.

The identification of synthetic homopolymer end groups and verification of their transformations using MALDI-TOF mass spectrometry.

Recent advances in the resolving power of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) enable the detailed characterization of linear homopolymers, and in particular provide invaluable data for the determination of their end-group functionalities. With the growing importance of macromolecular coupling reactions in building complex polymer architectures, the ability to accurately monitor end-group transformations is becoming increasingly important for synthetic polymer chemists. This tutorial demonstrates the application of MALDI-TOF MS in determining both end-group functionalities and their transformations for linear homopolymers. Examples of both polycaprolactone and polystyrene are examined, and the strengths and weaknesses of various approaches to data analysis are given.

Use of the "RAM" susceptibility testing method for rapid detection of clarithromycin resistance in the Mycobacterium avium complex.

Standard susceptibility testing of the Mycobacterium avium complex (MAC) can require 7 to 14 days from initial isolation. We evaluated a high-performance liquid chromatography-based susceptibility test for rapid determination of clarithromycin (CLR) resistance in MAC. This method can be completed in 72 h of incubation. A total of 110 MAC strains were tested using the following concentrations of CLR: 4, 16, and 64 microg/mL, for a total of 330 tests. Microbroth dilution was used as the reference method. Rapid analysis of mycolic acid ("RAM") concordance with the reference method for CLR susceptibility was 98% (254/258) and 100% for CLR resistance (72/72). The 4 discordant results occurred with 2 strains, which demonstrated intermediate resistance with an MIC of 16 microg/mL. This study demonstrates that "RAM"-based susceptibility testing for determination of CLR resistance in MAC is both rapid and accurate, providing a significant reduction in turn-around-time from 7 to 14 days to 72 h of incubation.

Application of SIMSTEX to oligomerization of insulin analogs and mutants.

The propensity of various insulins and their analogs to oligomerize was investigated by mass spectrometric methods including measurement of the relative abundances of oligomers in the gas phase and the kinetics of H/D amide exchange. The kinetics of deuterium uptake show a good fit when the exchanging amides are placed in three kinetic groups: fast, intermediate, and slow. r-Human insulin, of the insulins investigated, has fewer amides that exchange at intermediate rates and more that exchange at slow rates, in accord with its higher extent of association in solution. We adapted PLIMSTEX (protein ligand interactions by mass spectrometry, titration, and H/D exchange) to determine protein/ligand affinities in solution, to determine self-association equilibrium constants for proteins, and to apply them to various insulin analogs. We term this adaptation SIMSTEX (self-association interactions using mass spectrometry, self-titration and H/D exchange); it gives affinity constants that compare well with the literature results. The results from SIMSTEX show that some mutants (e.g., GlnB13) have an increased tendency to self-associate, possibly slowing down their action in vivo. Other mutants (e.g., lispro and AspB9) have lower propensities for self-association, thus providing potentially faster-acting analogs for use in controlling diabetes.

Ion-exchange chromatography followed by ESI-MS for quantitative analysis of sugar monophosphates from glucose catabolism.

The aim of this work is to establish a quantitative method to determine the ratio of [U-(13)C] labeled to unlabeled hexose monophosphates isolated from yeast extracts. This is accomplished by anion exchange chromatography and mobile phase desalting followed by electrospray (ESI) mass spectrometry. We test the method with the analysis of a sample of biological origin. Previously developed analytical techniques are not adequate to accomplish mass spectrometric analysis of these and other small monosaccharide systems because of interference from salt clusters. By lowering the ionic strength of the mobile phase and using a simplified injection system to the mass spectrometer, we were able to obtain data on the relative abundance of the hexose monophosphates.