Engineering nanocarbon interfaces for electron transfer

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 131-141).Electron-transfer reactions at nanometer-scale interfaces, such as those presented by single-walled carbon nanotubes (SWCNTs), are important for emerging optoelectronic and photovoltaic technologies. Electron transfer also governs a primary means by which these interfaces are chemically functionalized and subsequently manipulated. This thesis explores several chemical approaches to understanding and controlling charge transfer at nanocarbon interfaces. In the first part of this thesis, we explore ground-state electron transfer via the chemical reaction of SWCNTs with selected diazonium salts as a means of controlling the number of moieties attached to a given nanotube. We initially explore this reaction theoretically using a kinetic Monte Carlo simulation, with rate parameters evaluated using Gerischer-Marcus theory, in order to examine the extent to which these reactions can be controlled stoichiometrically. These modeling results indicate that heterogeneities in SWCNT chiral population result in a large variance in the number of covalent defects, even at low conversions, thereby limiting the ability to control these reactions through stoichiometry. We then experimentally examine the ability to impart an additional degree of control over these reactions through utilization of the adsorbed surfactant layer. Surfactants are commonly employed in the processing of nanoparticles to impart colloidal stability to otherwise unstable dispersions. We find that the chemical and physical properties of adsorbed surfactants influence the diazonium reaction with SWCNT in several ways. Surfactants can impose electrostatic attraction or repulsion, steric exclusion, and direct chemical modification of the reactant. Electrostatic effects are most pronounced in the cases of anionic sodium dodecyl sulfate and cationic cetyltrimethylammonium bromide, where differences in surfactant charge can significantly affect the ability of the diazonium ion to access the SWCNT surface. For bile salt surfactants, with the exception of sodium cholate, we find that the surfactant wraps tightly enough that exclusion effects are dominant. Here, sodium taurocholate exhibits almost no reactivity under the explored reaction conditions, while for sodium deoxycholate and sodium taurodeoxycholate, we show that the greatest extent of reaction is observed among a small population of nanotube species, with diameters between 0.88 and 0.92nm. The anomalous reaction of nanotubes in this diameter range implies that the surfactant is less effective at coating these species, resulting in a reduced surface coverage on the nanotube. Contrary to the other bile salts studied, sodium cholate enables high selectivity toward metallic species and small band-gap semiconductors, which is attributed to surfactant-diazonium coupling to form highly reactive diazoesters. We subsequently move on to examine excited-state electron transfer events between SWCNTs and fullerenes. This electron transfer system is distinct from the diazonium system since it does not result in the formation of a covalent bond between the donor and acceptor species. To study this interface, we synthesized a series of methanofullerene amphiphiles, including derivatives of C60 , C70, and C84, and investigated their electron transfer with SWCNT of specific chirality, generating a structure/reactivity relationship. In the cases of lipid-C61-PEG and lipid-C 71-PEG, which are predicted to similar surfactant surface coverages, band-gap dependent, incomplete quenching was observed across all semiconducting species, indicating that the driving force for electron transfer from SWCNT is small. This is further supported by a Marcus theory model, which predicts that the energy offsets between the SWCNT conduction bands and the fullerene LUMO levels are less than the exciton binding energy of the SWCNT in these two systems. In contrast, the lipid-C 85-PEG derivative shows complete quenching of all SWCNT species utilized in this work. This enhancement in quenching efficiency is consistent with the fact that the LUMO level of C85 methanofullerene is approximately 0.35eV lower than that of the smaller fullerene adducts, resulting in energy offsets which exceed the exciton binding energy. This result, combined with the fact that C8 5 has much higher photo-stability than C61 and C71, makes this larger fullerene adduct a promising candidate for SWCNT-based sensors and photovoltaics. Finally, we design and synthesize fullerene derivatives that self-assemble into onedimensional arrays. We find that a dendritic fullerene, which possesses a Boc-L-Ser-L-Ala-OMe dipeptide sequence at its apex, selectively forms S-oriented, helical, one-dimensional nanowires upon cooling from an isotropic state in cyclohexane. These nanowires possess diameters of 3.76 ± 0.52nm, and can be several microns in length. Control molecules, which do not possess the dipeptide sequence, only produce poorly formed aggregates under identical conditions, indicating that dipeptide-dipeptide interactions are integral to assembly. These nanorods open new opportunities in the chiral assembly of novel electron acceptor materials for optoelectronic and photovoltatic applications.by Andrew J. Hilmer.Ph.D

Demonstration of Protein-Based Human Identification Using the Hair Shaft Proteome

YesHuman identification from biological material is largely dependent on the ability to characterize genetic polymorphisms in DNA. Unfortunately, DNA can degrade in the environment, sometimes below the level at which it can be amplified by PCR. Protein however is chemically more robust than DNA and can persist for longer periods. Protein also contains genetic variation in the form of single amino acid polymorphisms. These can be used to infer the status of non-synonymous single nucleotide polymorphism alleles. To demonstrate this, we used mass spectrometry-based shotgun proteomics to characterize hair shaft proteins in 66 European-American subjects. A total of 596 single nucleotide polymorphism alleles were correctly imputed in 32 loci from 22 genes of subjects’ DNA and directly validated using Sanger sequencing. Estimates of the probability of resulting individual non-synonymous single nucleotide polymorphism allelic profiles in the European population, using the product rule, resulted in a maximum power of discrimination of 1 in 12,500. Imputed non-synonymous single nucleotide polymorphism profiles from European–American subjects were considerably less frequent in the African population (maximum likelihood ratio = 11,000). The converse was true for hair shafts collected from an additional 10 subjects with African ancestry, where some profiles were more frequent in the African population. Genetically variant peptides were also identified in hair shaft datasets from six archaeological skeletal remains (up to 260 years old). This study demonstrates that quantifiable measures of identity discrimination and biogeographic background can be obtained from detecting genetically variant peptides in hair shaft protein, including hair from bioarchaeological contexts.The Technology Commercialization Innovation Program (Contracts #121668, #132043) of the Utah Governors Office of Commercial Development, the Scholarship Activitie

Feasibility and reliability of frailty assessment in the critically ill: a systematic review

Background. For healthcare systems, an ageing population poses challenges in the delivery of equitable and effective care. Frailty assessment has the potential to improve care in the intensive care setting, but applying assessment tools in critical illness may be problematic. The aim of this systematic review was to evaluate evidence for the feasibility and reliability of frailty assessment in critical care. Methods. Our primary search was conducted in Medline, Medline In-process, EMBASE, CINAHL, PsycINFO, AMED, Cochrane Database of Systematic Reviews, and Web of Science (January 2001 to October 2017). We included observational studies reporting data on feasibility and reliability of frailty assessment in critical care setting in patients 16 years and older. Feasibility was assessed in terms of timing of evaluation, the background, training and expertise required for assessors, and reliance upon proxy input. Reliability was assessed in terms of inter-rater reliability. Results. Data from 11 study publications are included, representing eight study cohorts and 7761 patients. Proxy involvement in frailty assessment ranged from 58- 100%. Feasibility data were not well-reported overall, but the exclusion rate due to lack of proxy availability ranged from 0 to 45%, the highest rate observed where family involvement was mandatory and the assessment tool relatively complex (Frailty Index, FI). Conventional elements of Frailty Phenotype (FP) assessment required modification prior to use in two studies. Clinical staff tended to use a simple judgement-based tool, the Clinical Frailty Scale (CFS). Inter-rater reliability was reported in one study using the CFS and although a good level of agreement was observed between clinician assessments, this was a small and single centre study. Conclusion. Though of unproven reliability in the critically ill, CFS was the tool used most widely by critical care clinical staff. Conventional FP assessment required modification for general application in critical care, and a FI-based assessment may be difficult to deliver by the critical care team on a routine basis. There is a high reliance on proxies for frailty assessment, and the reliability of frailty assessment tools in critical care needs further evaluation. PROSPERO CRD42016052073

Neurotransmitter Detection Using Corona Phase Molecular Recognition on Fluorescent Single-Walled Carbon Nanotube Sensors

ABSTRACT: Temporal and spatial changes in neurotransmitter concentrations are central to information processing in neural networks. Therefore, biosensors for neurotransmitters are essential tools for neuroscience. In this work, we applied a new technique, corona phase molecular recognition (CoPhMoRe), to identify adsorbed polymer phases on fluorescent single-walled carbon nanotubes (SWCNTs) that allow for the selective detection of specific neurotransmitters, including dopamine. We functionalized and suspended SWCNTs with a library of different polymers (n = 30) containing phospholipids, nucleic acids, and amphiphilic polymers to study how neurotransmitters modulate the resulting band gap, near-infrared (nIR) fluorescence of the SWCNT. We identified several corona phases that enable the selective detection of neurotransmitters. Catecholamines such as dopamine increased the fluorescence of specific single-stranded DNA- and RNA-wrapped SWCNTs by 58−80 % upon addition of 100 μM dopamine depending on the SWCNT chirality (n,m). In solution, the limit of detection was 11 nM [Kd = 433 nM for (GT)15 DNA-wrapped SWCNTs]. Mechanistic studies revealed that this turn-on response is due to an increase in fluorescence quantum yield and not covalent modification of the SWCNT or scavenging o