Browsing by Author "Wang, Jinghan"

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Adsorption of DNA Oligonucleotides by Self-Assembled Metalloporphyrin Nanomaterials
(American Chemical Society, 2022-03-08) Wang, Jinghan; Wang, Zhen; Huang, Po-Jung Jimmy; Bai, Feng; Liu, Juewen
Porphyrin assemblies have controllable morphology, high biocompatibility, and good optical properties and were widely used in biomedical diagnosis and treatment. With the development of DNA biotechnology, combining DNA with porphyrin assemblies can broaden the biological applications of porphyrins. Porphyrin assemblies can serve as nanocarriers for DNA, although the fundamental interactions between them are not well understood. In this work, zinc meso-tetra(4-pyridyl)porphyrin (ZnTPyP) assemblies were prepared in the presence of various surfactants and at different pH values, yielding a variety of aggregation forms. Among them, the hexagonal stacking form exposes more pyridine substituents, and the hydrogen bonding force between the substituents and the DNA bases allows the DNA to be quickly adsorbed on the surface of the assemblies. The effects of DNA sequence and length were systematically tested. In particular, the adsorption of duplex DNA was less efficient compared to the adsorption of single-stranded DNA. This fundamental study is useful for the further combination of DNA and porphyrin assemblies to prepare new functional hybrid nanomaterials.
Disturbance Vulnerability Analysis and Reduction for Nonlinear Systems using Modes of Instability
(University of Waterloo, 2025-05-08) Wang, Jinghan
Engineered systems naturally experience large disturbances which have the potential to disrupt desired operation because the system may fail to recover to a desired exponentially stable equilibrium point (SEP). It is valuable to determine the mechanism of instability when the system is subject to a particular finite-time disturbance, because this information can be used to improve vulnerability detection, and to design controllers capable of mitigating these disturbances to enhance system resilience and ensure reliable performance, thereby reducing vulnerability. For a large class of nonlinear systems there exists a particular unstable equilibrium point (UEP) on the region of attraction (RoA) boundary of the desired SEP such that the unstable eigenvector of the Jacobian at this UEP represents the mode of instability for the disturbance. Unfortunately, it is challenging to find this mode of instability, especially in high dimensional systems, because it is often computationally intractable to compute this particular UEP for a given disturbance. Consider a particular finite time disturbance applied to a nonlinear system which possesses a SEP representing desired behavior. The system is able to recover from the disturbance if its post disturbance initial condition (IC) lies inside the RoA of the desired SEP. In cases where the system fails to recover, the nonlinear mode of instability for the disturbance represents the subset of system dynamics most responsible for this failure to recover. This thesis develops a novel algorithm for numerically computing the mode of instability for parameter-dependent nonlinear systems without prior knowledge of the particular UEP, resulting in a computationally efficient method. The key idea is to first consider the setting where the system recovers, and to average the Jacobian along the system trajectory from the post-disturbance state up until the Jacobian becomes stable. As the system approaches inability to recover, the averaged Jacobians converge to the Jacobian at the particular UEP, and can be used to extract the unstable eigenvector representing the mode of instability. Convergence guarantees are provided for computing the mode of instability, both for the theoretical setting in continuous time, and for the proposed algorithm which relies on numerical integration. Numerical examples illustrate the successful application of the method to identify the mechanism of instability in power systems subject to temporary short circuits. Then a novel approach to control design for reducing disturbance vulnerability of nonlinear systems using knowledge of the mode of instability is developed. The main idea is to tune controller parameter values so as to drive the post-disturbance IC further inwards away from the RoA boundary by driving it in the direction opposite to the mode of instability. To achieve this, the problem is formulated as a nonconvex optimization problem, and an efficient algorithm is developed to solve it. Local convergence guarantees are provided for this method. Numerical examples illustrate the successful application of the method to reduce the vulnerability of power systems subject to temporary short circuits.
Gold Nanoparticles Synthesized Using Various Reducing Agents and the Effect of Aging for DNA Sensing
(American Chemical Society, 2022-12-28) Ding, Yuzhe; Huang, Po-Jung Jimmy; Zandieh, Mohamad; Wang, Jinghan; Liu, Juewen
Gold nanoparticles (AuNPs) are one of the most commonly used reagents in colloidal science and biosensor technology. In this work, we first compared AuNPs prepared using four different reducing agents including citrate, glucose, ascorbate, and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). At the same absorbance at the surface plasmon peak of 520–530 nm, citrate-AuNPs and glucose-AuNPs adsorbed more DNA and achieved higher affinity to the adsorbed DNA. In addition, citrate-AuNPs had better sensitivity than glucose-AuNPs for label-free DNA detection. Then, using citrate-AuNPs, the effect of aging was studied by incubation of the AuNPs at 22 °C (room temperature) and at 4 °C for up to 6 months. During aging, the colloidal stability and DNA adsorption efficiency gradually decreased. In addition, the DNA sensing sensitivity using a label-free method also dropped around 4-fold after 6 months. Heating at boiling temperature of the aged citrate-AuNPs could not rejuvenate the sensing performance. This study shows that while citrate-AuNPs are initially better than the other three AuNPs in their colloid properties and sensing properties, this edge in performance might gradually decrease due to constantly changing surface properties caused from the aging effect.
Self-assembled manganese phthalocyanine nanoparticles with enhanced peroxidase-like activity for anti-tumor therapy Research Article Published: 29 September 2021
(2021-09-29) Wang, Jinghan; Gao, Shanqing; Wang, Xiao; Zhang, Haozhen; Ren, Xitong; Liu, Juewen; Bai, Feng
The use of functional nanoparticles as peroxidase-like (POD-like) catalyst has recently become a focus of research in cancer therapy. Phthalocyanine is a macrocyclic conjugated metal ligand, which is expected to achieve a high POD-like catalytic activity, generating free radicals and inhibiting the proliferation of cancer cells. In this paper, we synthesized phthalocyanine nanocrystals with different structures through noncovalent self-assembly confined within micro-emulsion droplets, and manganese phthalocyanine (MnPc) possessing a metal-N-C active center was used as the building block. These nano-assemblies exhibit shape-dependent POD-like catalytic activities, because the emulsifier and MnPc co-mixed assembly reduced the close packing between MnPc molecules and exposed more active sites. The assembly had a water-dispersed nanostructure, which is conducive to accumulation at tumor sites through the enhanced permeability and retention effect (EPR). Because of a highly efficient microenvironmental response, the assembly showed higher catalytic activity only emerged under the acidic tumor-like microenvironment, but caused less damage to normal tissues in biomedical applications. In vivo and in vitro catalytic therapy tests showed excellent anti-tumor effects. This work explored a new way for the application of metal-organic macromolecules such as MnPc as nanozymes for catalytic tumor therapy.