Effect of nanoparticle size on the near-surface pH-distribution in aqueous and carbonate buffered solutions

An analytical solution for the effect of particle size on the current density and near-surface ion distribution around spherical nanoparticles is presented in this work. With the long-term aim to support predictions on corrosion reactions in the human body, the spherical diffusion equation was solved for a set of differential equations and algebraic relations for pure unbuffered and carbonate buffered solutions. It was shown that current densities increase significantly with a decrease in particle size, suggesting this will lead to an increased dissolution rate. Near-surface ion distributions show the formation of a steep pH-gradient near the nanoparticle surface (\u3c6 μm) which is further enhanced in the presence of a carbonate buffer (\u3c2 μm). Results suggest that nanoparticles in pure electrolytes not only dissolve faster than bigger particles but that local pH-gradients may influence interactions with the biological environment, which should be considered in future studies

Electrochemical Estimations of the Gold Nanoparticle Size Effect on Cysteine-Gold Oxidation,

Gold nanoparticles are interesting for nanobiomedical applications, such as for drug delivery and as diagnostic imaging contrast agents. However, their stability and reactivity in-vivo are influenced by their surface properties and size. Here, we investigate the electrochemical oxidation of differently sized citrate-coated gold nanoparticles in the presence and absence of L-cysteine, a thiol-containing amino acid with high binding affinity to gold. We found that smaller sized (5, 10 nm) gold nanoparticles were significantly more susceptible to electrochemical L-cysteine interactions and/or L-cysteine-facilitated gold oxidation than larger (20, 50 nm) sized gold nanoparticles, both for the same mass and nominal surface area, under the conditions investigated (pH 7.4, room temperature, stagnant solutions, and scan rates of 0.5 to 450 mV s−1). The electrochemical measurements of drop-casted gold nanoparticle suspensions on paraffin-impregnated graphite electrodes were susceptible to the quality of the electrode. Increased cycling resulted in irreversible oxidation and detachment/oxidation of gold into solution. Our results suggest that L-cysteine-gold interactions are stronger for smaller nanoparticles

Effect of Amino Acids on the Corrosion and Metal Release from Copper and Stainless Steel

Copper (Cu) and stainless steel 316 L are widely used for biomedical applications, such as intrauterine devices and orthopedic/dental implants. Amino acids are abundantly present in biological environments. We investigated the influence of select amino acids on the corrosion of Cu under naturally aerated and deaerated conditions using a phosphate-free buffer. Amino acids increased the corrosion of Cu under both aeration conditions at pH 7.4. Cu release was also significantly (up to 18-fold) increased in the presence of amino acids, investigated at pH 7.4 and 37 °C for 24 h under naturally aerated conditions. Speciation modelling predicted a generally increased solubility of Cu in the presence of amino acids at pH 7.4. 316 L, investigated for metal release under similar conditions for comparison, released about 1,000-fold lower amounts of metals than did Cu and remained passive with no change in surface oxide composition or thickness. However, amino acids also increased the chromium release (up to 52-fold), significantly for lysine, and the iron release for cysteine, while nickel and molybdenum release remained unaffected. This was not predicted by solution speciation modelling. The surface analysis confirmed the adsorption of amino acids on 316 L and, to a lower extent, Cu coupons

Effect of nanoparticle size on the near-surface pH-distribution in aqueous and carbonate buffered solutions

An analytical solution for the effect of particle size on the current density and near-surface ion distribution around spherical nanoparticles is presented in this work. With the long-term aim to support predictions on corrosion reactions in the human body, the spherical diffusion equation was solved for a set of differential equations and algebraic relations for pure unbuffered and carbonate buffered solutions. It was shown that current densities increase significantly with a decrease in particle size, suggesting this will lead to an increased dissolution rate. Near-surface ion distributions show the formation of a steep pH-gradient near the nanoparticle surface (<6 m) which is further enhanced in the presence of a carbonate buffer (<2 m). Results suggest that nanoparticles in pure electrolytes not only dissolve faster than bigger particles but that local pH-gradients may influence interactions with the biological environment, which should be considered in future studies

Electrochemical estimations of the gold nanoparticle size effect on cysteine-gold oxidation

Gold nanoparticles are interesting for nanobiomedical applications, such as for drug delivery and as diagnostic imaging contrast agents. However, their stability and reactivity in-vivo are influenced by their surface properties and size. Here, we investigate the electrochemical oxidation of differently sized citrate-coated gold nanoparticles in the presence and absence of L-cysteine, a thiol-containing amino acid with high binding affinity to gold. We found that smaller sized (5, 10 nm) gold nanoparticles were significantly more susceptible to electrochemical L-cysteine interactions and/or L-cysteine-facilitated gold oxidation than larger (20, 50 nm) sized gold nanoparticles, both for the same mass and nominal surface area, under the conditions investigated (pH 7.4, room temperature, stagnant solutions, and scan rates of 0.5 to 450 mV s−1). The electrochemical measurements of drop-casted gold nanoparticle suspensions on paraffin-impregnated graphite electrodes were susceptible to the quality of the electrode. Increased cycling resulted in irreversible oxidation and detachment/oxidation of gold into solution. Our results suggest that L-cysteine-gold interactions are stronger for smaller nanoparticles

Social media use and impact during the holiday travel planning process

Through an empirical study among holiday travellers, residing in the Former Soviet Union Republics, this paper presents a comprehensive view of role and impact of social media on the whole holiday travel planning process: Before, during and after the trip, providing insights on usage levels, scope of use, level of influence and trust. Findings suggest that social media are predominantly used after holidays for experience sharing. It is also shown that there is a strong correlation between perceived level of influence from social media and changes made in holiday plans prior to final decisions. Moreover, it is revealed that user-generated content is perceived as more trustworthy when compared to official tourism websites, travel agents and mass media advertising

Understanding How Social Entrepreneurs Fit into the Tourism Discourse

This chapter discusses how social entrepreneurs fit into the existing tourism discourse. It examines four areas of literature in particular, tourism entrepreneurs, sustainability, destination development and intrapreneurship, and analyzes how introducing the concept of social entrepreneurs into these discussions is useful, and contributes to our understanding. Furthermore the paper illustrates that as social entrepreneurs are relevant to a broad range of issues in the tourism literature this should prevent the development of research silos where social entrepreneurship scholars seek out their own vein of research. The nexus of common ground and interests, as displayed in this chapter, should enhance the development of research, thought and understanding of social entrepreneurs within the field as a whole The key argument is that research on social entrepreneurs is not just relevant for those interested in entrepreneurs it also effects our thinking on issues such as destination development, relationships between stakeholders, tourism policy and sustainability. The chapter concludes with a wide range of questions for further research

Visitor expenditure estimation for grocery store location planning: a case study of Cornwall

Visitor expenditure is an important driver of demand in many local economies, supporting a range of services and facilities which may not be viable based solely on residential demand. In areas where self-catering accommodation is prevalent visitor demand makes up a considerable proportion of sales and revenue within grocery stores, yet this form of visitor consumption is commonly overlooked in supply and demand-side estimates of visitor spend. As such, store location planning in tourist resorts, decisions about local service provision and the local economic impacts of tourism are based on very limited demand-side estimates of visitor spend. Using Cornwall, South West England as a study area, we outline a methodology and data sources to estimate small-area visitor grocery spend. We use self-catering accommodation provision, utilisation and visitor expenditure rates as key factors driving visitor spend. We identify that the use of visitor accommodation accounts for the spatial and temporal complexities of visitor demand that may be overlooked when using alternative approaches, such as the up-scaling of residential demand. Using a spatial interaction model, we demonstrate that our expenditure estimates can be used to generate store level revenue estimation within tourist resorts, and we make a number of recommendations for service provision and store location planning in these areas