Browsing by Author "Li, Jingqiang"
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Item Detecting the Biopolymer Behavior of Graphene Nanoribbons in Aqueous Solution(Springer Nature, 2016) Wijeratne, Sithara S.; Penev, Evgeni S.; Lu, Wei; Li, Jingqiang; Duque, Amanda L.; Yakobson, Boris I.; Tour, James M.; Kiang, Ching-Hwa; Richard E. Smalley Institute for Nanoscale Science & TechnologyGraphene nanoribbons (GNR), can be prepared in bulk quantities for large-area applications by reducing the product from the lengthwise oxidative unzipping of multiwalled carbon nanotubes (MWNT). Recently, the biomaterials application of GNR has been explored, for example, in the pore to be used for DNA sequencing. Therefore, understanding the polymer behavior of GNR in solution is essential in predicting GNR interaction with biomaterials. Here, we report experimental studies of the solution-based mechanical properties of GNR and their parent products, graphene oxide nanoribbons (GONR). We used atomic force microscopy (AFM) to study their mechanical properties in solution and showed that GNR and GONR have similar force-extension behavior as in biopolymers such as proteins and DNA. The rigidity increases with reducing chemical functionalities. The similarities in rigidity and tunability between nanoribbons and biomolecules might enable the design and fabrication of GNR-biomimetic interfaces.Item DNA under Force: Mechanics, Electrostatics, and Hydration(MDPI AG, 2015) Li, Jingqiang; Wijeratne, Sithara S.; Qiu, Xiangyun; Kiang, Ching-HwaQuantifying the basic intra- and inter-molecular forces of DNA has helped us to better understand and further predict the behavior of DNA. Single molecule technique elucidates the mechanics of DNA under applied external forces, sometimes under extreme forces. On the other hand, ensemble studies of DNA molecular force allow us to extend our understanding of DNA molecules under other forces such as electrostatic and hydration forces. Using a variety of techniques, we can have a comprehensive understanding of DNA molecular forces, which is crucial in unraveling the complex DNA functions in living cells as well as in designing a system that utilizes the unique properties of DNA in nanotechnology.Item Forces unveil physics in biological systems via atomic force microscopy: from single molecules to single cells(2018-06-08) Li, Jingqiang; Kiang, Ching-HwaForce plays an essential role in many biological systems at different length. Physical forces, together with chemical signals contribute to the proper functioning of various biological processes. For example, cells sense and transduce environmental physical cues into biochemical signals so as to realize different cellular processes, such as proliferation, migration. and apoptosis. Thus elucidating the details of force involved in various biological systems is thus crucial for a complete understanding of their biological mechanisms such as biomolecule's mechanical properties, dynamic conformations, native structure, and cell's physical properties. The ability of probing and studying the forces in biology has been revolutionized over the past two decades. Atomic force microscopy (AFM), for example, has been proven a powerful technique in measuring forces in piconewton range, relevant in biological scales. In this thesis, I explored the AFM application on different biological systems ranging from single molecule level to single cell level. In the first part, I will show that single molecule manipulation by AFM can reveal the mechanical properties, equilibrium states, and dynamic conformations of proteins and nucleic acids. In the second part, I will extend the application of AFM on single cells and show that the cancer cells adaption to microenvironment can be revealed by force signatures. In addition, I will also demonstrate the investigation of invasiveness of cancer cells via a specific cell line using AFM force studies. Finally, I will discuss future outlooks of AFM cell studies.Item Single molecule force measurements of perlecan/HSPG2: A key component of the osteocyte pericellular matrix(Elsevier, 2016) Wijeratne, Sithara S.; Martinez, Jerahme R.; Grindel, Brian J.; Frey, Eric W.; Li, Jingqiang; Wang, Liyun; Farach-Carson, Mary C.; Kiang, Ching-HwaPerlecan/HSPG2, a large, monomeric heparan sulfate proteoglycan (HSPG), is a key component of the lacunar canalicular system (LCS) of cortical bone, where it is part of the mechanosensing pericellular matrix (PCM) surrounding the osteocytic processes and serves as a tethering element that connects the osteocyte cell body to the bone matrix. Within the pericellular space surrounding the osteocyte cell body, perlecan can experience physiological fluid flow drag force and in that capacity function as a sensor to relay external stimuli to the osteocyte cell membrane. We previously showed that a reduction in perlecan secretion alters the PCM fiber composition and interferes with bone's response to a mechanical loading in vivo. To test our hypothesis that perlecan core protein can sustain tensile forces without unfolding under physiological loading conditions, atomic force microscopy (AFM) was used to capture images of perlecan monomers at nanoscale resolution and to perform single molecule force measurement (SMFMs). We found that the core protein of purified full-length human perlecan is of suitable size to span the pericellular space of the LCS, with a measured end-to-end length of 170 ± 20 nm and a diameter of 2–4 nm. Force pulling revealed a strong protein core that can withstand over 100 pN of tension well over the drag forces that are estimated to be exerted on the individual osteocyte tethers. Data fitting with an extensible worm-like chain model showed that the perlecan protein core has a mean elastic constant of 890 pN and a corresponding Young's modulus of 71 MPa. We conclude that perlecan has physical properties that would allow it to act as a strong but elastic tether in the LCS.Item Single-molecule force measurements of the polymerizing dimeric subunit of von Willebrand factor(American Physical Society, 2016) Wijeratne, Sithara S.; Li, Jingqiang; Yeh, Hui-Chun; Nolasco, Leticia; Zhou, Zhou; Bergeron, Angela; Frey, Eric W.; Moake, Joel L.; Dong, Jing-fei; Kiang, Ching-HwaVon Willebrand factor (VWF) multimers are large adhesive proteins that are essential to the initiation of hemostatic plugs at sites of vascular injury. The binding of VWF multimers to platelets, as well as VWF proteolysis, is regulated by shear stresses that alter VWF multimeric conformation. We used single molecule manipulation with atomic force microscopy (AFM) to investigate the effect of high fluid shear stress on soluble dimeric and multimeric forms of VWF. VWF dimers are the smallest unit that polymerizes to construct large VWF multimers. The resistance to mechanical unfolding with or without exposure to shear stress was used to evaluate VWF conformational forms. Our data indicate that, unlike recombinant VWF multimers (RVWF), recombinant dimeric VWF (RDVWF) unfolding force is not altered by high shear stress (100dynes/cm2 for 3 min at 37∘C). We conclude that under the shear conditions used (100dynes/cm2 for 3 min at 37∘C), VWF dimers do not self-associate into a conformation analogous to that attained by sheared large VWF multimers.