The Interactions of Graphene with Ionic Solutions and Their Effects on the Differential Capacitance for Sensing Applications

Nano-scale devices continue to challenge the theoretical understanding of microscopic systems. Of particular interest is the characterization of the interface electrochemistry of sensors, which operate as field effect transistors with graphene in contact with the solution. While plenty of experimental research has been conducted in regard to the viability and sensitivity of graphene-based devices, the understanding of the microscopic and macroscopic physics of these sensors has lagged, unlike any other areas of applications for graphene. Although some successful models of these sensors have been developed, relatively little theoretical work to account for the vast extent of experimental work. Typically operated in a regime of high ion concentration and high surface charge density, dielectric saturation, dielectric decrement, and ion crowding become non-negligible at the interface, complicating continuum treatments based upon the Poisson-Boltzmann equation. Modifications to the standard Poisson-Boltzmann theory are explored, with modifications due to dielectric saturation and dielectric decrement considered in tandem with a Bikerman-Friese model to account for the steric effects of ions. In the case of dielectric saturation, a model proposed by Booth is used to characterize the diffuse layer capacitance for both metallic and graphene electrodes immersed in an electrolyte. The dependence of the diffuse layer capacitance on the surface charge density of the electrode exhibits two peaks, in contrast to the experimental results. For dielectric decrement, a dielectric permittivity dependent on the concentration of positive and negative ions is used to determine the diffuse layer capacitance for both metallic and graphene electrodes. The diffuse layer capacitance shows a strong interplay between ion polarizability and steric effects, while exhibiting a single peak. A self-consistent and parameter-free method for the inclusion of a Stern layer is used in both cases, which eliminates the spurious secondary peak in the case of dielectric saturation and reduces the overall magnitude of the capacitance of the diffuse layer in both dielectric saturation and dielectric decrement. When a graphene electrode is used, the total capacitance in all modifications is dominated by V-shaped quantum capacitance of graphene at low potentials, which is a manifestation of the Dirac cone structure of the graphene $\pi$-electron bands. A broad peak develops in the total capacitance at high potentials, which is sensitive to the ion size at dielectric saturation, but is stable with dielectric decrement. In addition to the interactions of graphene with an electrolyte, considerable interest has recently been shown in studying the electric double layer that arises at the interface of doped graphene and a class of electrolytes known as ionic liquids. Ionic liquids are a class of molten ionic salts at room temperature that have low volatility and high ionic concentration, and are characterized by the overscreening and overcrowding effects in their electric double layer. A mean field model for ionic liquids is presented, which takes into account both the ion correlation and the finite ion size effects, in order to calculate the differential capacitance of the ionic liquid interface with single-layer graphene. Besides choosing ion packing fractions that give rise to the camel-shaped and bell-shaped capacitances of the diffuse layer in ionic liquids, the regimes of ``dilute electrolytes'' and asymmetric ionic liquids are considered. As in the case of electrolytes, the main effect of a graphene electrode arises due to its V-shaped quantum capacitance. As a result, the total capacitance of a graphene--ionic liquid interface exhibits a camel-shaped dependence on the total applied potential, even for large ion packing fractions and finite ion correlation lengths. While the minimum at the neutrality point in the total capacitance is``inherited” from the quantum capacitance of graphene, the two peaks that occur at applied potentials of $\sim \pm1$ V are sensitive to the presence of the ion correlation and a Stern layer, which both tend to reduce the height and flatten the peaks in the camel-shaped total capacitance. It is also determined that the largest fraction of the applied potential goes to charging the graphene electrode. When considering the sensitivity of graphene-based sensors to ion concentration and/or pH of the surrounding environment, a site binding model which allows hydrogen and hydroxyl groups to adsorb onto the surface of the device is proposed. Both a regime in which bare graphene is exposed to the electrolyte and a regime where a functionalized oxide, which contains a density of charged impurities to facilitate ion binding, is situated between graphene and the electrolyte are proposed. With regard to the dependence on ion concentration, comparisons between the model and experimental data show good agreement when the finite size of ions is included in the electrolyte. In the case of pH dependence, comparisons between the model and experimental data show excellent agreement, particularly when steric effects are included in the electrolyte. The favourable comparisons here are the first steps in developing a comprehensive model of graphene based biological and chemical sensors

Health-related quality of life and depression among participants in the Sjögren's International Collaborative Clinical Alliance registry.

ObjectiveTo examine health-related quality of life (HRQoL) and depression among participants in an international Sjögren's syndrome (SS) registry, comparing those with and without SS.MethodsCross-sectional study of participants in the Sjögren's International Collaborative Clinical Alliance (SICCA) registry. The 2016 American College of Rheumatology/European League Against Rheumatism SS classification criteria were used to determine disease status. HRQoL was assessed using the Short Form 12, version 2 Health Survey to derive scores for physical component summary (PCS) and mental component summary (MCS). Depression was assessed using the 9-Item Patient Health Questionnaire. Multivariate linear and logistic regression analyses were performed to identify predictors of HRQoL and depression while controlling for potential confounders.ResultsAmong 2401 SICCA participants who had symptoms of dry eyes and dry mouth, 1051 had SS (44%) and 1350 did not (56%). After controlling for confounders, when compared with non-SS participants, those with SS had better PCS (p<0.001, β=2.43, 95% CI 1.57 to 3.29), MCS (p=0.002, β=1.37, 95% CI 0.50 to 2.23) and lower adjusted odds of depression (p<0.001, OR 0.67, 95% CI 0.55 to 0.81). Other significant predictors of HRQoL and depression included employment, country of residence and use of medication with anticholinergic effect or for management of SS-related signs and symptoms.ConclusionOur results suggest that among symptomatic patients, having a diagnosis of SS may be associated with better emotional and psychological well-being compared with patients without a diagnosis. Having a definitive diagnosis of SS may encourage patients to obtain a better understanding of their disease and have coping mechanisms in place to better manage their symptoms

The effects of dielectric decrement and finite ion size on differential capacitance of electrolytically gated graphene

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.cplett.2018.04.030 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We analyze the effects of dielectric decrement and finite ion size in an aqueous electrolyte on the capacitance of a graphene electrode, and make comparisons with the effects of dielectric saturation combined with finite ion size. We first derive conditions for the cross-over from a camel-shaped to a bell-shaped capacitance of the diffuse layer. We show next that the total capacitance is dominated by a V-shaped quantum capacitance of graphene at low potentials. A broad peak develops in the total capacitance at high potentials, which is sensitive to the ion size with dielectric saturation, but is stable with dielectric decrement.Natural Sciences and Engineering Research Council of Canada (ZLM: Grant No. 2016-03689

Strength in diversity: enhancing learning in vocationally-orientated, master's level courses

Postgraduate education in geography, especially at the Master’s level, is undergoing significant changes in the developed world. There is an expansion of vocationally-oriented degree programmes, increasing recruitment of international students, integration of work place skills, and the engagement of non-traditional postgraduate students as departments respond to policies for a more ‘inclusive’ higher education. This paper sets the context by outlining some programmatic changes in selected countries (Australia, the UK, and the USA). We briefly reflect on how postgraduate ‘bars’ or ‘levels’ are defined and explore in detail what ‘diversity’ or ‘heterogeneity’ means in these new postgraduate settings. The paper then explores some examples of practice drawn from our own experiences, whilst recognising that relevance will vary in other contexts. Finally we consider how diversity can be harnessed as a strength that has potential to enhance taught elements of contemporary postgraduate education in and beyond the discipline

Quantifying an aquifer nitrate budget and future nitrate discharge using field data from streambeds and well nests

Novel groundwater sampling (age, flux, and nitrate) carried out beneath a streambed and in wells was used to estimate (1) the current rate of change of nitrate storage, dSNO3 /dt, in a contaminated unconfined aquifer, and (2) future [NO3–]FWM (the flow-weighted mean nitrate concentration in groundwater discharge) and fNO3 (the nitrate flux from aquifer to stream). Estimates of dSNO3 /dt suggested that at the time of sampling (2013) the nitrate storage in the aquifer was decreasing at an annual rate (mean = –9 mmol/m2yr) equal to about one-tenth the rate of nitrate input by recharge. This is consistent with data showing a slow decrease in the [NO3–] of groundwater recharge in recent years. Regarding future [NO3–]FWM and fNO3 , predictions based on well data show an immediate decrease that becomes more rapid after ~5 years before leveling out in the early 2040s. Predictions based on streambed data generally show an increase in future [NO3–]FWM and fNO3 until the late 2020s, followed by a decrease before leveling out in the 2040s. Differences show the potential value of using information directly from the groundwater—surface water interface to quantify the future impact of groundwater nitrate on surface water quality. The choice of denitrification kinetics was similarly important; compared to zero-order kinetics, a first-order rate law levels out estimates of future [NO3–]FWM and fNO3 (lower peak, higher minimum) as legacy nitrate is flushed from the aquifer. Major fundamental questions about nonpoint-source aquifer contamination can be answered without a complex numerical model or long-term monitoring program

The role of trust and health literacy in nurse-delivered point-of-care STI testing for pregnant women living with HIV, Tshwane District, South Africa

Abstract Background Sexually transmitted infections (STIs) during pregnancy result in neonatal morbidity and mortality, and may increase mother-to-child-transmission of HIV. Yet the World Health Organization’s current syndromic management guidelines for STIs leaves most pregnant women undiagnosed and untreated. Point-of-care (POC) diagnostic tests for STIs can drastically improve detection and treatment. Though acceptable and feasible, poor medication adherence and re-infection due to lack of partner treatment threaten the programmatic effectiveness of POC diagnostic programmes. Methods To engender patient-provider trust, and improve medication adherence and disclosure of STI status to sexual partners, we trained study nurses in compassionate care, good clinical practices and motivational interviewing. Using qualitative methods, we explored the role patient-provider communications may play in supporting treatment adherence and STI disclosure to sexual partners. Nurses were provided training in motivational interviewing, compassionate care and good clinical practices. Participants were interviewed using a semi-structured protocol, with domains including STI testing experience, patient-provider communication, and HIV and STI disclosure. Interviews were audio-recorded, transcribed and analyzed using a constant comparison approach. Results Twenty-eight participants treated for Chlamydia trachomatis (CT), Trichomonas vaginalis (TV), and/or Neisseria gonorrhea (NG) were interviewed. Participants described strong communications and trusting relationships with nurses trained in patient-centered care training and implementing POC STI diagnostic testing. However, women described a delayed trust in treatment until their symptoms resolved. Women expressed a limited recall of their exact diagnosis, which impacted their ability to fully disclose their STI status to sexual partners. Conclusions We recommend implementing patient health literacy programmes as part of POC services to support women in remembering and disclosing their specific STI diagnosis to sexual partners, which may facilitate partner treatment uptake and thus decrease the risk of re-infection

Should Research Ethics Encourage the Production of Cost-Effective Interventions?

This project considers whether and how research ethics can contribute to the provision of cost-effective medical interventions. Clinical research ethics represents an underexplored context for the promotion of cost-effectiveness. In particular, although scholars have recently argued that research on less-expensive, less-effective interventions can be ethical, there has been little or no discussion of whether ethical considerations justify curtailing research on more expensive, more effective interventions. Yet considering cost-effectiveness at the research stage can help ensure that scarce resources such as tissue samples or limited subject popula- tions are employed where they do the most good; can support parallel efforts by providers and insurers to promote cost-effectiveness; and can ensure that research has social value and benefits subjects. I discuss and rebut potential objections to the consideration of cost-effectiveness in research, including the difficulty of predicting effectiveness and cost at the research stage, concerns about limitations in cost-effectiveness analysis, and worries about overly limiting researchers’ freedom. I then consider the advantages and disadvantages of having certain participants in the research enterprise, including IRBs, advisory committees, sponsors, investigators, and subjects, consider cost-effectiveness. The project concludes by qualifiedly endorsing the consideration of cost-effectiveness at the research stage. While incorporating cost-effectiveness considerations into the ethical evaluation of human subjects research will not on its own ensure that the health care system realizes cost-effectiveness goals, doing so nonetheless represents an important part of a broader effort to control rising medical costs

Implementation considerations for a point-of-care Neisseria gonorrhoeae rapid diagnostic test at primary healthcare level in South Africa : a qualitative study

ADDITIONAL FILE 1 : IDI protocols. Interview protocols used in this study during the pre-implementation, initial use, 3-month (mid-assessment) and 6-month (post-evaluation) implementation phase.ADDITIONAL TABLE 1 : Consolidated criteria for reporting qualitative studies (COREQ): 32-item checklist for interviews and focus groups.ADDITIONAL TABLE 2 : NPT Constructs as defined for the implementation of the NG-LFA.BACKGROUND : South Africa maintains an integrated health system where syndromic management of sexually transmitted infections (STI) is the standard of care. An estimated 2 million cases of Neisseria gonorrhoeae (N. gonorrhoeae) occur in South Africa every year. Point-of-care diagnostic tests (POCT) may address existing STI control limitations such as overtreatment and missed cases. Subsequently, a rapid lateral flow assay with fluorescence-based detection (NG-LFA) with a prototype reader was developed for N. gonorrhoeae detection showing excellent performance and high usability; however, a better understanding is needed for device implementation and integration into clinics. METHODS : A qualitative, time-series assessment using 66 in-depth interviews was conducted among 25 trained healthcare workers involved in the implementation of the NG-LFA. Findings were informed by the Normalization Process Theory (NPT) as per relevant contextual (strategic intentions, adaptive execution, and negotiation capacity) and procedural constructs (coherence, cognitive participation, collective action, reflexive monitoring) to examine device implementation within primary healthcare levels. Interviews were audio-recorded, transcribed, and then analyzed using a thematic approach guided by NPT to interpret results. RESULTS : Overall, healthcare workers agreed that STI POCT could guide better STI clinical decision-making, with consideration for clinic integration such as space constraints, patient flow, and workload. Perceived NG-LFA benefits included enhanced patient receptivity and STI knowledge. Further, healthcare workers reflected on the suitability of the NG-LFA given current limitations with integrated primary care. Recommendations included sufficient STI education, and appropriate departments for first points of entry for STI screening. CONCLUSIONS : The collective action and participation by healthcare workers in the implementation of the NG-LFA revealed adaptive execution within the current facility environment including team compositions, facility-staff receptivity, and STI management experiences. User experiences support future clinic service integration, highlighting the importance of further assessing patient-provider communication for STI care, organizational readiness, and identification of relevant departments for STI screening.Sub-award via FIND (primary recipient Cecilia Ferreyra), from the Global Antimicrobial Resistance Innovation Fund (GAMRIF) (https://www.gov.uk/government/groups/theglobal-amr-innovation-fund).https://bmchealthservres.biomedcentral.comhj2024Medical MicrobiologySDG-03:Good heatlh and well-bein