Optical trapping and light scattering in atmospheric aerosol science

Aerosol particles are ubiquitous in the atmosphere, and currently contribute a large uncertainty to climate models. Part of the endeavour to reduce this uncertainty takes the form of improving our understanding of aerosol at the microphysical level, thus enabling chemical and physical processes to be more accurately represented in larger scale models. In addition to modeling efforts, there is a need to develop new instruments and methodologies to interrogate the physicochemical properties of aerosol. This perspective presents the development, theory, and application of optical trapping, a powerful tool for single particle investigations of aerosol. After providing an overview of the role of aerosol in Earth's atmosphere and the microphysics of these particles, we present a brief history of optical trapping and a more detailed look at its application to aerosol particles. We also compare optical trapping to other single particle techniques. Understanding the interaction of light with single particles is essential for interpreting experimental measurements. In the final part of this perspective, we provide the relevant formalism for understanding both elastic and inelastic light scattering for single particles. The developments discussed here go beyond Mie theory and include both how particle and beam shape affect spectra. Throughout the entirety of this work, we highlight numerous references and examples, mostly from the last decade, of the application of optical trapping to systems that are relevant to the atmospheric aerosol.

Ultrafast Proton Transport between a Hydroxy Acid and a Nitrogen Base along Solvent Bridges Governed by the Hydroxide/Methoxide Transfer Mechanism

Aqueous proton transport plays a key role in acid–base neutralization and energy transport through biological membranes and hydrogen fuel cells. Extensive experimental and theoretical studies have resulted in a highly detailed elucidation of one of the underlying microscopic mechanisms for aqueous excess proton transport, known as the von Grotthuss mechanism, involving different hydrated proton configurations with associated high fluxional structural dynamics. Hydroxide transport, with approximately 2-fold-lower bulk diffusion rates compared to those of excess protons, has received much less attention. We present femtosecond UV/IR pump–probe experiments and ab initio molecular dynamics simulations of different proton transport pathways of bifunctional photoacid 7-hydroxyquinoline (7HQ) in water/methanol mixtures. For 7HQ solvent-dependent photoacidity, free-energy–reactivity correlation behavior and quantum mechanics/molecular mechanics (QM/MM) trajectories point to a dominant OH^–/CH₃O^– transport pathway for all water/methanol mixing ratios investigated. Our joint ultrafast infrared spectroscopic and ab initio molecular dynamics study provides conclusive evidence for the hydrolysis/methanolysis acid–base neutralization pathway, as formulated by Manfred Eigen half a century ago. Our findings on the distinctly different acid–base reactivities for aromatic hydroxyl and aromatic nitrogen functionalities suggest the usefulness of further exploration of these free-energy–reactivity correlations as a function of solvent polarity. Ultimately the determination of solvent-dependent acidities will contribute to a better understanding of proton-transport mechanisms at weakly polar surfaces and near polar or ionic regions in transmembrane proton pump proteins or hydrogen fuel cell materials.

Stacking-induced fluorescence increase reveals allosteric interactions through DNA

From gene expression to nanotechnology, understanding and controlling DNA requires a detailed knowledge of its higher order structure and dynamics. Here we take advantage of the environment-sensitive photoisomerization of cyanine dyes to probe local and global changes in DNA structure. We report that a covalently attached Cy3 dye undergoes strong enhancement of fluorescence intensity and lifetime when stacked in a nick, gap or overhang region in duplex DNA. This is used to probe hybridization dynamics of a DNA hairpin down to the single-molecule level. We also show that varying the position of a single abasic site up to 20 base pairs away modulates the dye–DNA interaction, indicative of through-backbone allosteric interactions. The phenomenon of stacking-induced fluorescence increase (SIFI) should find widespread use in the study of the structure, dynamics and reactivity of nucleic acids.

Ultrafast proton transport in water-methanol mixtures

Femtosecond UV/IR pump-probe experiments and ab initio molecular dynamics simulations of 7-hydroxyquinoline in water-methanol mixtures demonstrate an unexpectedly dominant OH-/CH3O- transport pathway but consistent with a solvent-dependent photoacidity free energy-reactivity correlation behaviour.

Measuring the size and complex refractive index of an aqueous aerosol particle using electromagnetic heating and cavity-enhanced Raman scattering

We describe a dual-beam optical trap that can simultaneously determine the complex refractive index and the radius of weakly absorbing aerosol particles.

Single-Molecule Fluorescence Detection of a Synthetic Heparan Sulfate Disaccharide

The first single-molecule fluorescence detection of a structurally-defined synthetic carbohydrate is reported: a heparan sulfate (HS) disaccharide fragment labeled with Alexa488. Single molecules have been measured whilst freely diffusing in solution and controlled encapsulation in surface-tethered lipid vesicles has allowed extended observations of carbohydrate molecules down to the single-molecule level. The diverse and dynamic nature of HS-protein interactions means that new tools to investigate pure HS fragments at the molecular level would significantly enhance our understanding of HS. This work is a proof-of-principle demonstration of the feasibility of single-molecule studies of synthetic carbohydrates which offers a new approach to the study of pure glycosaminoglycan (GAG) fragments.

Self-inflating bags versus T-piece resuscitator to deliver sustained inflations in a preterm lamb model

OBJECTIVE

In neonatal resuscitation, the use of a sustained inflation (SI) may facilitate lung aeration. Previous studies comparing different resuscitation devices have shown that one model of self-inflating bag (SIB) could not deliver an SI. We aimed to compare the delivery of an SI using four SIBs with that of a T-piece.

STUDY DESIGN

In intubated preterm lambs, we compared four models of SIB fitted with a positive end expiratory pressure (PEEP) valve to a T-piece using a gas flow of 8 L/min. Four operators aimed to deliver three SIs of 20 cm H₂O for 30 s. The study was repeated with the PEEP valve removed and again with no flow. We measured duration of SI, average inflation pressure (IP) and analysed the shape of the pressure curves.

RESULTS

204 combinations were analysed. Mean (SD) duration of SI was Ambu 6(2)s, Laerdal 14(8)s, Parker Healthcare 5(1)s, Mayo Healthcare 33(2)s and T-piece 33(1)s. Mean (SD) average IP was Ambu 17(3)cm H₂O, Laerdal 17(3)cm H₂O, Parker Healthcare 12(5)cm H₂O, Mayo Healthcare 21(2)cm H₂O and T-piece 20(0)cm H₂O. Duration of SI and average IP was significantly different between SIBs (all p<0.001). The findings were substantially unchanged when PEEP valve and flow were removed (all p>0.05). Only the Mayo system delivered SIs with duration and average IP not significantly different from the T-piece (p>0.05).

CONCLUSIONS

The performance of the four SIBs tested varied considerably. Some are able to deliver an SI even in the absence of gas flow. This may be useful in a resource-limited setting with no gas supply.

Cochlear implantation in older patients: outcomes and comparisons

OBJECTIVES

A review of adults receiving cochlear implants (Cls) at the Yorkshire Cochlear Implant Service (YCIS) was performed to assess whether age affects use or outcomes.

METHODS

A retrospective analysis of all patients over the age of 50 implanted and habilitated at the YCIS was undertaken. Outcome measures included quality of life (QoL) questionnaires and speech perception tests: CUNY sentences and BKB sentences. Comparisons were made between patients implanted age 50 to 59 (A), 60 to 69 (B) and 70 and over (C). Patients with English as a second language and those implanted for less than 9 months were excluded. Data was analysed using a repeated measure regression model.

RESULTS

80 adults were included; A, 31; B, 29; C, 20. Significant improvements were seen in speech perception scores in all groups from pre-implant to 3 months. No statistically significant difference was found between the 3 groups in any outcome measure. QoL scores overall showed increased independence and greater participation in social activities with all patients feeling their implant had been successful.

DISCUSSION

Increased life expectancy and availability of cochlear implants (Cls) has led to greater numbers of older patients being eligible for implantation. Our results show improved speech perception and QoL outcomes in all groups. The lack of statistically significant differences between age groups supports the benefits of Cls in the older population. Older age should not be a discriminating factor in candidacy for cochlear implantation and referral of older patients to implant centres should be encouraged.

Does the location of colorectal carcinoma differ between screened and unscreened populations?

AIM

Screening for colorectal malignancy using faecal occult blood testing is established across the UK. In NHS Grampian the programme was introduced in 2007. Previous studies have reported no difference in anatomical locations of cancers detected by screening programmes compared with those in unscreened populations. This study aims to review the location of tumours detected in an established screening programme compared with those diagnosed through symptomatic presentation within the same population.

METHOD

All patients discussed at the regional multidisciplinary meeting between June 2007 and August 2011 were included. Data were collated prospectively from multidisciplinary team records while site of tumour was documented from radiology, endoscopy, operative and pathology reports. Comparative statistics (χ(2) ) were performed using spss 19.

RESULTS

Of 1487 patients included 255 were detected via the screening programme and 1232 from symptomatic presentation. More left sided tumours (splenic flexure to rectosigmoid) were detected via screening (P=0.005). Of non-screened patients (n=1232), 456 (37%) tumours were right sided (caecum to distal transverse colon), 419 (34%) were left sided and 357 (29%) were in the rectum. This compares with the screened group (n=255): right sided 74 (29%), left sided 113 (44%) and rectal 68 (27%).

CONCLUSION

More left sided tumours appear to be detected in screened patients compared with symptomatic presentation, contrary to previously published work. These results may be worthy of further consideration given the ongoing debate on the optimal means of screening.

The use of ice-lollies for pain relief post-paediatric tonsillectomy. A single-blinded, randomised, controlled trial

OBJECTIVES

To assess whether the use of ice-lollies after tonsillectomy with or without adenoidectomy in children aged 2-12 reduces pain in the immediate postoperative period.

DESIGN

A prospective, randomised, single-blinded study design consisting of two groups with an intention to treat analysis.

SETTING

Tertiary referral centre.

PARTICIPANTS

Children aged 2-12 undergoing tonsillectomy with or without adenoidectomy.

MAIN OUTCOME MEASURES

Pain assessment by nursing staff in the form of the validated modified Children's Hospital of Eastern Ontario Pain Scale at 15, 30 and 60 min and 4 h.

RESULTS

Ninety-two patients were recruited into the study with 46 allocated to receive an ice-lolly and 41 not to receive an ice-lolly after exclusion of those with incomplete data. The two groups were comparable for number, age, sex and diagnosis. The pain score at every time interval was lower in the group that had received the ice-lolly compared with the group that had not. This was statistically significant at 30 (P = 0.008) and 60 min (P = 0.049).

CONCLUSION

Our data suggest that ice-lollies are a cheap, effective and safe method of reducing postoperative pain up to one hour following paediatric tonsillectomy.

The influence of calcium to phosphate ratio on the nucleation and crystallization of apatite glass-ceramics

The nucleation and crystallization behavior of a series of glasses based on 4.5SiO2-3Al2O3-YP2O5-3CaO-1.51CaF2 was studied. The parameter Y was varied to give calcium to phosphate ratios between one and two. All of the glasses studied crystallized firstly to fluorapatite (Ca5PO4)3F). The glass with a calcium to phosphate ratio of 1.67, corresponding to apatite, bulk nucleated to give fluorapatite (FAP). The glasses with calcium : phosphate ratios either less than that of apatite, or greater than that of apatite all exhibited surface nucleation of FAP. However, following a nucleation hold of one hour at approximately 50 K above the glass transition temperature these glasses exhibited bulk nucleation of FAP.

Making it to work: towards employment for the young adult with autism

In the last few decades there has been an increase in the reported prevalence of autism and its correlates within what is now termed autistic spectrum disorder (ASD): from 20 in every 10,000 children being estimated by Wing and Gould (1979) to 91 in every 10,000 by the National Autistic Society (NAS) (1999). While changes in criteria may account for some of this it is accepted that such children are increasingly being identified and knowledge of autism is growing. Semi-structured interviews were conducted with nine teaching staff from seven different schools for children with special needs to elicit information in relation to preparing young adults with ASD for the world of work. Results indicated educational practices are being modified for children with autism. Currently the most specifically tailored packages are offered in schools for children with severe learning difficulties.