Fast pH-assisted functionalization of silver nanoparticles with monothiolated DNA

Attaching monothiolated DNA to silver nanoparticles has been achieved at pH 3.0 in 30 minutes and difficulties associated with DNA attachment to AgNPs at neutral pH have been revealed by studying DNA adsorption kinetics.University of Waterloo || Canadian Foundation for Innovation || Canadian Institutes of Health Research || Natural Sciences and Engineering Research Council || Ontario Ministry of Research and Innovation |

Ultrahigh Nanoparticle Stability against Salt, pH, and Solvent with Retained Surface Accessibility via Depletion Stabilization

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemistry Society copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see Zhang, X., Servos, M. R., & Liu, J. (2012). Ultrahigh Nanoparticle Stability against Salt, pH, and Solvent with Retained Surface Accessibility via Depletion Stabilization. Journal of the American Chemical Society, 134(24), 9910–9913. https://doi.org/10.1021/ja303787eFor many applications, it is desirable to stabilize colloids over a wide range of buffer conditions while still retaining surface accessibility for adsorption and reaction. Commonly used charge or steric stabilization cannot achieve this goal since the former is sensitive to salt and the latter blocks the particle surface. We use depletion stabilization in the presence of high molecular weight polyethylene glycol (PEG) to stabilize a diverse range of nanomaterials, including gold nanoparticles (from 10 to 100 nm), graphene oxide, quantum dots, silica nanoparticles, and liposomes in the presence of Mg2+ (>1.6 M), heavy metal ions, extreme pH (pH 1–13), organic solvents, and adsorbed nucleosides and drugs. At the same time, the particle surface remains accessible for adsorption of both small molecules and macromolecules. Based on this study, high loading of thiolated DNA was achieved in one step with just 2% PEG 20 000 in 2 h.University of Waterloo || Canadian Foundation for Innovation || Ontario Ministry of Research & Innovation || Canadian Institutes of Health Research || Natural Sciences and Engineering Research Council |

Instantaneous and Quantitative Functionalization of Gold Nanoparticles with Thiolated DNA Using a pH-Assisted and Surfactant-Free Route

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see Zhang, X., Servos, M. R., & Liu, J. (2012). Instantaneous and Quantitative Functionalization of Gold Nanoparticles with Thiolated DNA Using a pH-Assisted and Surfactant-Free Route. Journal of the American Chemical Society, 134(17), 7266–7269. https://doi.org/10.1021/ja3014055The attachment of thiolated DNA to gold nanoparticles (AuNPs) has enabled many landmark works in nanobiotechnology. This conjugate chemistry is typically performed using a salt-aging protocol where, in the presence of an excess amount of DNA, NaCl is gradually added to increase DNA loading over 1–2 days. To functionalize large AuNPs, surfactants need to be used, which may generate difficulties for downstream biological applications. We report herein a novel method using a pH 3.0 citrate buffer to complete the attachment process in a few minutes. More importantly, it allows for quantitative DNA adsorption, eliminating the need to quantify the number of adsorbed DNA and allowing the adsorption of multiple DNAs with different sequences at predetermined ratios. The method has been tested for various DNAs over a wide range of AuNP sizes. Our work suggests a synergistic effect between pH and salt in DNA attachment and reveals the fundamental kinetics of AuNP aggregation versus DNA adsorption, providing a novel means to modulate the interactions between DNA and AuNPs.University of Waterloo || Canadian Foundation for Innovation || Ontario Ministry of Research & Innovation || Canadian Institutes of Health Research || Natural Sciences and Engineering Research Council |

Polarity Control for Nonthiolated DNA Adsorption onto Gold Nanoparticles

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see Zhang, X., Liu, B., Servos, M. R., & Liu, J. (2013). Polarity Control for Nonthiolated DNA Adsorption onto Gold Nanoparticles. Langmuir, 29(20), 6091–6098. https://doi.org/10.1021/la400617uGold nanoparticles (AuNPs) functionalized with thiolated DNA have enabled many studies in nanoscience. The strong thiol/gold affinity and the nanoscale curvature of AuNPs allow the attached DNA to adapt an upright conformation favorable for hybridization. Recently, it has been shown that nonthiolated DNA can also be attached via DNA base adsorption. Without a thiol label, both ends of the DNA and even internal bases could be adsorbed, decreasing the specificity of subsequent molecular recognition reactions. In this work, we employed a modular sequence design approach to systematically study the effect of DNA sequence on adsorption polarity. A block of poly adenine (poly-A) could be used to achieve a high density of DNA attachment. When the poly-A block length is short (e.g., below 5–7), the loading was independent of the block length, and the conjugate cannot hybridize to its cDNA effectively, suggesting a random attachment controlled by adsorption kinetics. Increasing the block length leads to reduced capacity but improved hybridization, suggesting that more DNA with the desired conformation was adsorbed due to the thermodynamic effects of poly-A binding. The design can be further improved by including capping sequences rich in T or G. Finally, a more general double-stranded DNA approach was described to be suitable for DNA that cannot satisfy the above-mentioned design requirements.University of Waterloo || Canadian Institutes of Health Research || Canadian Foundation for Innovation || Natural Sciences and Engineering Research Council || Ontario Ministry of Research and Innovation |

Instantaneous Attachment of an Ultrahigh Density of Nonthiolated DNA to Gold Nanoparticles and Its Applications

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see http://dx.doi.org/10.1021/la3035424The last 16 years have witnessed the landmark development of polyvalent thiolated DNA-functionalized gold nanoparticles (AuNP's) possessing striking properties within the emerging field of nanobiotechnology. Many novel properties of this hybrid nanomaterial are attributed to the dense DNA shell. However, the question of whether nonthiolated polyvalent DNA–AuNP could be fabricated with a high DNA density and properties similar to those of its thiolated counterpart has not been explored in detail. Herein, we report that by simply tuning the pH of the DNA–AuNP mixture an ultrahigh capacity of nonthiolated DNA can be conjugated to AuNP's in a few minutes, resulting in polyvalent DNA–AuNP conjugates with cooperative melting behavior, a typical property of polyvalent thiolated DNA-functionalized AuNP's. With this method, large AuNP's (e.g., 50 nm) can be functionalized to achieve the colorimetric detection of sub-nanometer DNA. Furthermore, this fast, stable DNA loading was employed to separate AuNP's of different sizes. We propose that a large fraction of the attached DNAs are adsorbed via one or a few terminal bases to afford the high loading capacity and the ability to hybridize with the complementary DNA. This discovery not only offers a time- and cost-effective way to functionalize AuNP's with a high density of nonthiolated DNA but also provides new insights into the fundamental understanding of how DNA strands with different sequences interact with AuNP's.University of Waterloo || Canadian Foundation for Innovation || Ontario Ministry of Research & Innovation || Canadian Institutes of Health Research || Natural Sciences and Engineering Research Counci

Effects of Polyethylene Glycol on DNA Adsorption and Hybridization on Gold Nanoparticles and Graphene Oxide

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see http://dx.doi.org/10.1021/la302799sUnderstanding the interface between DNA and nanomaterials is crucial for rational design and optimization of biosensors and drug delivery systems. For detection and delivery into cells, where high concentrations of cellular proteins are present, another layer of complexity is added. In this context, we employ polyethylene glycol (PEG) as a model polymer to mimic the excluded volume effect of cellular proteins and to test its effects on DNA adsorption and hybridization on gold nanoparticles (AuNPs) and graphene oxide (GO), both of which show great promise for designing intracellular biosensors and drug delivery systems. We show that PEG 20000 (e.g., 4%) accelerates DNA hybridization to DNA-functionalized AuNPs by 50–100%, but this enhanced hybridization kinetics has not been observed with free DNA. Therefore, this rate enhancement is attributed to the surface blocking effect by PEG instead of the macromolecular crowding effect. On the other hand, DNA adsorption on citrate-capped AuNP surfaces is impeded even in the presence of a trace level (i.e., parts per billion) of PEG, confirming PEG competes with DNA for surface binding sites. Additional insights have been obtained by studying the adsorption of a thiolated DNA and a peptide nucleic acid. In these cases, the steric effects of PEG to impede adsorption are observed. Similar observations have also been made with GO. Therefore, PEG may be used as an effective blocking agent for both hydrophilic AuNP and for GO that also contains hydrophobic domains.University of Waterloo || Canadian Foundation for Innovation || Ontario Ministry of Research & Innovation || Canadian Institutes of Health Research || Natural Sciences and Engineering Research Council |

Adsorption of DNA Oligonucleotides by Titanium Dioxide Nanoparticles

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see http://dx.doi.org/10.1021/la404633pTitanium dioxide (TiO2) or titania shows great promise in detoxification and drug delivery. To reach its full potential, it is important to interface TiO2 with biomolecules to harness their molecular recognition function. To this end, DNA attachment is an important topic. Previous work has mainly focused on long double-stranded DNA or single nucleotides. For biosensor development and targeted drug delivery, it is more important to use single-stranded oligonucleotides. Herein, the interaction between fluorescently labeled oligonucleotides and TiO2 nanoparticles is reported. The point of zero charge (PZC) of TiO2 is around 6 in water or acetate buffer; therefore, the particles are positively charged at lower pH. However, if in phosphate or citrate buffer, the particles are negatively charged, even at pH ∼2, suggesting strong adsorption of buffer anions. DNA adsorption takes place mainly via the phosphate backbone, although the bases might also have moderate contributions. Peptide nucleic acids (PNAs) with an amide backbone cannot be adsorbed. DNA adsorption is strongly affected by inorganic anions, where phosphate and citrate can strongly inhibit DNA adsorption. DNA adsorption is promoted by adding salt or lowering pH. DNA adsorption is accompanied with fluorescence quenching, and double-stranded DNA showed reduced quenching, allowing for the detection of DNA using TiO2 nanoparticles.University of Waterloo || Canadian Foundation for Innovation || Natural Sciences and Engineering Research Council || Canadian Institutes of Health Research || Ontario Ministry of Research and Innovation |

'Werner Buttner's Collages: From A to T (and Back Again)'

Contribution to a monograph on noted German collagist and painter Werner Buttner at Marlborough Contemporary Gallery, London

A 30-Year Study of Impacts, Recovery, and Development of Critical Effect Sizes for Endocrine Disruption in White Sucker (Catostomus commersonii) Exposed to Bleached-Kraft Pulp Mill Effluent at Jackfish Bay, Ontario, Canada

Jackfish Bay is an isolated bay on the north shore of Lake Superior, Canada that has received effluent from a large bleached-kraft pulp mill since the 1940s. Studies conducted in the late 1980s found evidence of reductions in sex steroid hormone levels in multiple fish species living in the Bay, and increased growth, condition and relative liver weights, with a reduction in internal fat storage, reduced gonadal sizes, delayed sexual maturation, and altered levels of circulating sex steroid hormones in white sucker (Catostomus commersonii). These early studies provided some of the first pieces of evidence of endocrine disruption in wild animals. Studies on white sucker have continued at Jackfish Bay, monitoring fish health after the installation of secondary waste treatment (1989), changes in the pulp bleaching process (1990s), during facility maintenance shutdowns and during a series of facility closures associated with changing ownership (2000s), and were carried through to 2019 resulting in a 30-year study of fish health impacts, endocrine disruption, chemical exposure, and ecosystem recovery. The objective of the present study was to summarize and understand more than 75 physiological, endocrine, chemical and whole organism endpoints that have been studied providing important context for the complexity of endocrine responses, species differences, and challenges with extrapolation. Differences in body size, liver size, gonad size and condition persist, although changes in liver and gonad indices are much smaller than in the early years. Population modeling of the initial reproductive alterations predicted a 30% reduction in the population size, however with improvements over the last couple of decades those population impacts improved considerably. Reflection on these 30 years of detailed studies, on environmental conditions, physiological, and whole organism endpoints, gives insight into the complexity of endocrine responses to environmental change and mitigation.Canada Research Chairs||NSERC Discovery grant program||Environment and Climate Change Canada’s Great Lakes Action Plan||University of New Brunswick||Wilfrid Laurier University||University of Calgary||University of Waterlo

Multiple Stressors in the Environment: The Effects of Exposure to an Antidepressant (Venlafaxine) and Increased Temperature on Zebrafish Metabolism

Aquatic organisms are continuously exposed to multiple environmental stressors working cumulatively to alter ecosystems. Wastewater-dominated environments are often riddled by a myriad of stressors, such as chemical and thermal stressors. The objective of this study was to examine the effects of an environmentally relevant concentration of a commonly prescribed antidepressant, venlafaxine (VFX) [1.0 μg/L], in addition to a 5°C increase in water temperature on zebrafish metabolism. Fish were chronically exposed (21 days) to one of four conditions: (i) 0 μg/L VFX at 27°C; (ii) 1.0 μg/L VFX at 27°C; (iii) 0 μg/L VFX at 32°C; (iv) 1.0 μg/L VFX at 32°C. Following exposure, whole-body metabolism was assessed by routine metabolic rate (RMR) measurements, whereas tissue-specific metabolism was assessed by measuring the activities of major metabolic enzymes in addition to glucose levels in muscle. RMR was significantly higher in the multi-stressed group relative to Control. The combination of both stressors resulted in elevated pyruvate kinase activity and glucose levels, while lipid metabolism was depressed, as measured by 3-hydroxyacyl CoA dehydrogenase activity. Citrate synthase activity increased with the onset of temperature, but only in the group treatment without VFX. Catalase activity was also elevated with the onset of the temperature stressor, however, that was not the case for the multi-stressed group, potentially indicating a deleterious effect of VFX on the anti-oxidant defense mechanism. The results of this study highlight the importance of multiple-stressor research, as it able to further bridge the gap between field and laboratory studies, as well as have the potential of yielding surprising results that may have not been predicted using a conventional single-stressor approach.This study was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC: RGPIN-2015-05643) as well as the Canada Foundation for Innovation (CFI 34317)