Design of switchable "smart" surfaces for biomedical and nanotechnological applications

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, June 2005.Includes bibliographical references.Chapter 1. An Introduction to Self-Assembled Monolayers & Surface Characterization A brief summary of the formation, structure, and characterization techniques of self assembled monolayers (SAMs) is described. The characterization techniques include contact angle goniometry, ellipsometry, grazing-angle Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), sum-frequency generation spectroscopy (SFG), and atomic force microscopy (AFM). Chapter 2. A Reversibly Switching Surface The design of surfaces that exhibit dynamic changes in interfacial properties such as wettability in response to an electrical potential is described. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed both at a molecular level using sum-frequency generation spectroscopy and at a macroscopic level using contact angle measurements. This type of surface design enables amplification of conformational transitions at a molecular level to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open new opportunities in interfacial engineering.Chapter 3. A Synthetic Chemical Route for the Formation of Homogeneously- Mixed Self-Assembled Monolayers A novel way to produce self-assembled monolayers (SAMs) uniformly mixed on the molecular length scale is described.(cont.) Initially, a precursor SAM was formed from molecules that are derived from 16-mercaptohexadecanoic acid (MHA) and contain a globular end group. Self-assembly of these molecules resulted in a SAM that is densely packed with respect to the space-filling end groups, but shows low-density packing with respect to the hydrophobic chains. Subsequent cleavage of the space-filling end groups established a low-density SAM of MHA. A mixed monolayer of MHA and n-butanethiol was formed by backfilling the low-density monolayer of MHA with the corresponding alkanethiol. The new "mixed" SAM was characterized by optical ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FT-IR), cyclic voltammetry (CV), and reductive desorption voltammetry. The results indicate a uniformly mixed monolayer as compared to a SAM generated by coadsorption of mixtures of the same MHA and n-butanethiol molecules. This approach provides a way to produce SAMs that are uniformly mixed using a synthetic chemical route, which affords considerable flexibility in composition and also in the ratio of the different molecules in the mixed SAM. Chapter 4.(cont.) Design of Oligonucleotide Arrays Using Homogeneously Mixed Self - Assembled Monolayers We have employed two quantitative techniques, quart-crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance imaging (SPR) to quantify the hybridization efficiency of a 25-mer oligonucleotide probe to two different surfaces: a dense 16-mercaptohexadecanoic acid self-assembled monolayer (MHA SAM) and a homogeneously-mixed (HM) SAM generated from the method described in Chapter 3 that allows for regular spacing of functional -COOH groups. This reduced density of functional groups led to reduced attachment of oligonucleotide probes to the surface, increasing the area per probe, and allowed more space in which complimentary sequence can bind. Reducing the density of immobilized probes led to the improvement in hybridization efficiency as demonstrated in both SPR and QCM-D results, which are comparable to previous reports. Our method paves the way for customizing binding efficiency and target probe density based on the distance between functional groups. By changing the headgroup size of the precursor monolayer, different distances between functional group can be formed, allowing for an ability to tailor distances between molecules. This method may allow for improvement in DNA array technology.Chapter 5. Long-Term Stability of Self-Assembled Monolayers in Biological Media The study of long term stability of self-assembled monolayer (SAM) in biological media is of importance in evaluating its usefulness for applications in implantable biochips, biosensors, or biological microelectromechanical system (bioMEMs) devices for drug delivery.(cont.) To minimize biofouling effects, researchers have investigated protein/cell adhesion resistant surface-bound materials such as poly(ethylene glycol) or oligo(ethylene glycol) terminated self-assembled monolayers. However, no long term study in biological media has been done. To address the issue of moderate to long-term stability of SAMs for bioMEMS device modification, alkanethiol and oligo(EG) terminated alkanethiol monolayers were prepared and studied after immersion in either phosphate buffer saline (PBS) or calf serum. Here, undecanethiol (CllH23SH) and tri(ethylene glycol) terminated undecanethiol (HO(C2H40)3C H22SH) self-assembled monolayers (SAMs) on clean gold surfaces were prepared and characterized. The SAMs were then immersed into either phosphate buffered saline (PBS) or calf serum. The SAM samples were emmersed and investigated using several analytical techniques at numerous points over the next 35 days. Contact angles and current densities in voltammetry changed dramatically for the PBS samples over the time period, particularly after 21 days. Results indicate substantial loss of the integrity of the SAM. Similar alterations with time were observed for the calf serum samples in both contact angle and voltammetry measurements. X-ray photoelectron spectroscopy indicates that the likely origin is desorption of the alkanethiol moiety as evidenced by appreciable loss of the S 2p signal after 35 days. Additionally, this work may serve as a starting point for further studies of surface chemical modification methods for moderate to long-term minimization of biofouling for in vivo applications.by Thanh-Nga T. Tran.Ph.D

Secular trend, seasonality and effects of a community-based intervention on neonatal mortality: follow-up of a cluster-randomised trial in Quang Ninh province, Vietnam.

BACKGROUND: Little is know about whether the effects of community engagement interventions for child survival in low-income and middle-income settings are sustained. Seasonal variation and secular trend may blur the data. Neonatal mortality was reduced in a cluster-randomised trial in Vietnam where laywomen facilitated groups composed of local stakeholders employing a problem-solving approach for 3 years. In this analysis, we aim at disentangling the secular trend, the seasonal variation and the effect of the intervention on neonatal mortality during and after the trial. METHODS: In Quang Ninh province, 44 communes were allocated to intervention and 46 to control. Births and neonatal deaths were assessed in a baseline survey in 2005, monitored during the trial in 2008-2011 and followed up by a survey in 2014. Time series analyses were performed on monthly neonatal mortality data. RESULTS: There were 30 187 live births and 480 neonatal deaths. The intervention reduced the neonatal mortality from 19.1 to 11.6 per 1000 live births. The reduction was sustained 3 years after the trial. The control areas reached a similar level at the time of follow-up. Time series decomposition analysis revealed a downward trend in the intervention areas during the trial that was not found in the control areas. Neonatal mortality peaked in the hot and wet summers. CONCLUSIONS: A community engagement intervention resulted in a lower neonatal mortality rate that was sustained but not further reduced after the end of the trial. When decomposing time series of neonatal mortality, a clear downward trend was demonstrated in intervention but not in control areas. TRIAL REGISTRATION NUMBER: ISRCTN44599712, Post-results

Enzyme-linked immunoassay for dengue virus IgM and IgG antibodies in serum and filter paper blood

BACKGROUND: The reproducibilty of dengue IgM and IgG ELISA was studied in serum and filter paper blood spots from Vietnamese febrile patients. METHODS: 781 pairs of acute (t0) and convalescent sera, obtained after three weeks (t3) and 161 corresponding pairs of filter paper blood spots were tested with ELISA for dengue IgG and IgM. 74 serum pairs were tested again in another laboratory with similar methods, after a mean of 252 days. RESULTS: Cases were classified as no dengue (10 %), past dengue (55%) acute primary (7%) or secondary (28%) dengue. Significant differences between the two laboratories' results were found leading to different diagnostic classification (kappa 0.46, p < 0.001). Filter paper results correlated poorly to serum values, being more variable and lower with a mean (95% CI) difference of 0.82 (0.36 to 1.28) for IgMt3, 0.94 (0.51 to 1.37) for IgGt0 and 0.26 (-0.20 to 0.71) for IgGt3. This also led to differences in diagnostic classification (kappa value 0.44, p < 0.001) The duration of storage of frozen serum and dried filter papers, sealed in nylon bags in an air-conditioned room, had no significant effect on the ELISA results. CONCLUSION: Dengue virus IgG antibodies in serum and filter papers was not affected by duration of storage, but was subject to inter-laboratory variability. Dengue virus IgM antibodies measured in serum reconstituted from blood spots on filter papers were lower than in serum, in particular in the acute phase of disease. Therefore this method limits its value for diagnostic confirmation of individual patients with dengue virus infections. However the detection of dengue virus IgG antibodies eluted from filter paper can be used for sero-prevalence cross sectional studies

YY1 Regulates Melanocyte Development and Function by Cooperating with MITF

Studies of coat color mutants have greatly contributed to the discovery of genes that regulate melanocyte development and function. Here, we generated Yy1 conditional knockout mice in the melanocyte-lineage and observed profound melanocyte deficiency and premature gray hair, similar to the loss of melanocytes in human piebaldism and Waardenburg syndrome. Although YY1 is a ubiquitous transcription factor, YY1 interacts with M-MITF, the Waardenburg Syndrome IIA gene and a master transcriptional regulator of melanocytes. YY1 cooperates with M-MITF in regulating the expression of piebaldism gene KIT and multiple additional pigmentation genes. Moreover, ChIP–seq identified genome-wide YY1 targets in the melanocyte lineage. These studies mechanistically link genes implicated in human conditions of melanocyte deficiency and reveal how a ubiquitous factor (YY1) gains lineage-specific functions by co-regulating gene expression with a lineage-restricted factor (M-MITF)—a general mechanism which may confer tissue-specific gene expression in multiple lineages

The Sudden Dominance of blaCTX–M Harbouring Plasmids in Shigella spp. Circulating in Southern Vietnam

Shigellosis is a disease caused by bacteria belonging to Shigella spp. and is a leading cause of bacterial gastrointestinal infections in infants in unindustrialized countries. The Shigellae are dynamic and capable of rapid change when placed under selective pressure in a human population. Extended spectrum beta lactamases (ESBLs) are enzymes capable of degrading cephalosporins (a group of antimicrobial agents) and the genes that encode them are common in pathogenic E. coli and other related organisms in industrialized countries. In southern Vietnam, we have isolated multiple cephalosporin-resistant Shigella that express ESBLs. Furthermore, over two years these strains have replaced strains isolated from patients with shigellosis that cannot express ESBLs. Our work describes the genes responsible for this characteristic and we investigate one of the elements carrying one of these genes. These finding have implications for treatment of shigellosis and support the growing necessity for vaccine development. Our findings also may be pertinent for other countries undergoing a similar economic transition to Vietnam's and the corresponding effect on bacterial populations

Micronutrient Deficits Are Still Public Health Issues among Women and Young Children in Vietnam

Background: The 2000 Vietnamese National Nutrition Survey showed that the population’s dietary intake had improved since 1987. However, inequalities were found in food consumption between socioeconomic groups. As no national data exist on the prevalence of micronutrient deficiencies, a survey was conducted in 2010 to assess the micronutrient status of randomly selected 1526 women of reproductive age and 586 children aged 6–75 mo. Principal Findings: In women, according to international thresholds, prevalence of zinc deficiency (ZnD, 67.262.6%) and vitamin B12 deficiency (11.761.7%) represented public health problems, whereas prevalence of anemia (11.661.0%) and iron deficiency (ID, 13.761.1%) were considered low, and folate (,3%) and vitamin A (VAD,,2%) deficiencies were considered negligible. However, many women had marginal folate (25.1%) and vitamin A status (13.6%). Moreover, overweight (BMI$23 kg/m 2 for Asian population) or underweight occurred in 20 % of women respectively highlighting the double burden of malnutrition. In children, a similar pattern was observed for ZnD (51.963.5%), anemia (9.161.4%) and ID (12.961.5%) whereas prevalence of marginal vitamin A status was also high (47.362.2%). There was a significant effect of age on anemia and ID prevalence, with the youngest age group (6–17 mo) having the highest risk for anemia, ID, ZnD and marginal vitamin A status as compared to other groups. Moreover, the poorest groups of population had a higher risk for zinc, anemia and ID

Socializing One Health: an innovative strategy to investigate social and behavioral risks of emerging viral threats

In an effort to strengthen global capacity to prevent, detect, and control infectious diseases in animals and people, the United States Agency for International Development’s (USAID) Emerging Pandemic Threats (EPT) PREDICT project funded development of regional, national, and local One Health capacities for early disease detection, rapid response, disease control, and risk reduction. From the outset, the EPT approach was inclusive of social science research methods designed to understand the contexts and behaviors of communities living and working at human-animal-environment interfaces considered high-risk for virus emergence. Using qualitative and quantitative approaches, PREDICT behavioral research aimed to identify and assess a range of socio-cultural behaviors that could be influential in zoonotic disease emergence, amplification, and transmission. This broad approach to behavioral risk characterization enabled us to identify and characterize human activities that could be linked to the transmission dynamics of new and emerging viruses. This paper provides a discussion of implementation of a social science approach within a zoonotic surveillance framework. We conducted in-depth ethnographic interviews and focus groups to better understand the individual- and community-level knowledge, attitudes, and practices that potentially put participants at risk for zoonotic disease transmission from the animals they live and work with, across 6 interface domains. When we asked highly-exposed individuals (ie. bushmeat hunters, wildlife or guano farmers) about the risk they perceived in their occupational activities, most did not perceive it to be risky, whether because it was normalized by years (or generations) of doing such an activity, or due to lack of information about potential risks. Integrating the social sciences allows investigations of the specific human activities that are hypothesized to drive disease emergence, amplification, and transmission, in order to better substantiate behavioral disease drivers, along with the social dimensions of infection and transmission dynamics. Understanding these dynamics is critical to achieving health security--the protection from threats to health-- which requires investments in both collective and individual health security. Involving behavioral sciences into zoonotic disease surveillance allowed us to push toward fuller community integration and engagement and toward dialogue and implementation of recommendations for disease prevention and improved health security

Phylogeographical analysis of the dominant multidrug-resistant H58 clade of Salmonella Typhi identifies inter- and intracontinental transmission events.

The emergence of multidrug-resistant (MDR) typhoid is a major global health threat affecting many countries where the disease is endemic. Here whole-genome sequence analysis of 1,832 Salmonella enterica serovar Typhi (S. Typhi) identifies a single dominant MDR lineage, H58, that has emerged and spread throughout Asia and Africa over the last 30 years. Our analysis identifies numerous transmissions of H58, including multiple transfers from Asia to Africa and an ongoing, unrecognized MDR epidemic within Africa itself. Notably, our analysis indicates that H58 lineages are displacing antibiotic-sensitive isolates, transforming the global population structure of this pathogen. H58 isolates can harbor a complex MDR element residing either on transmissible IncHI1 plasmids or within multiple chromosomal integration sites. We also identify new mutations that define the H58 lineage. This phylogeographical analysis provides a framework to facilitate global management of MDR typhoid and is applicable to similar MDR lineages emerging in other bacterial species

Socializing One Health: an innovative strategy to investigate social and behavioral risks of emerging viral threats

In an effort to strengthen global capacity to prevent, detect, and control infectious diseases in animals and people, the United States Agency for International Development’s (USAID) Emerging Pandemic Threats (EPT) PREDICT project funded development of regional, national, and local One Health capacities for early disease detection, rapid response, disease control, and risk reduction. From the outset, the EPT approach was inclusive of social science research methods designed to understand the contexts and behaviors of communities living and working at human-animal-environment interfaces considered high-risk for virus emergence. Using qualitative and quantitative approaches, PREDICT behavioral research aimed to identify and assess a range of socio-cultural behaviors that could be influential in zoonotic disease emergence, amplification, and transmission. This broad approach to behavioral risk characterization enabled us to identify and characterize human activities that could be linked to the transmission dynamics of new and emerging viruses. This paper provides a discussion of implementation of a social science approach within a zoonotic surveillance framework. We conducted in-depth ethnographic interviews and focus groups to better understand the individual- and community-level knowledge, attitudes, and practices that potentially put participants at risk for zoonotic disease transmission from the animals they live and work with, across 6 interface domains. When we asked highly-exposed individuals (ie. bushmeat hunters, wildlife or guano farmers) about the risk they perceived in their occupational activities, most did not perceive it to be risky, whether because it was normalized by years (or generations) of doing such an activity, or due to lack of information about potential risks. Integrating the social sciences allows investigations of the specific human activities that are hypothesized to drive disease emergence, amplification, and transmission, in order to better substantiate behavioral disease drivers, along with the social dimensions of infection and transmission dynamics. Understanding these dynamics is critical to achieving health security--the protection from threats to health-- which requires investments in both collective and individual health security. Involving behavioral sciences into zoonotic disease surveillance allowed us to push toward fuller community integration and engagement and toward dialogue and implementation of recommendations for disease prevention and improved health security