Unsupervised Video Domain Adaptation for Action Recognition: A Disentanglement Perspective

Unsupervised video domain adaptation is a practical yet challenging task. In this work, for the first time, we tackle it from a disentanglement view. Our key idea is to handle the spatial and temporal domain divergence separately through disentanglement. Specifically, we consider the generation of cross-domain videos from two sets of latent factors, one encoding the static information and another encoding the dynamic information. A Transfer Sequential VAE (TranSVAE) framework is then developed to model such generation. To better serve for adaptation, we propose several objectives to constrain the latent factors. With these constraints, the spatial divergence can be readily removed by disentangling the static domain-specific information out, and the temporal divergence is further reduced from both frame- and video-levels through adversarial learning. Extensive experiments on the UCF-HMDB, Jester, and Epic-Kitchens datasets verify the effectiveness and superiority of TranSVAE compared with several state-of-the-art methods. The code with reproducible results is publicly accessible.Comment: 18 pages, 9 figures, 7 tables. Code at https://github.com/ldkong1205/TranSVA

Macromolecular Engineering by Surface-Initiated ATRP: : New Nanomaterials for Bioapplications

The objective of this thesis is to investigate the synthesis of well-defined polymer nanohybrid materials bearing desirable functionality via surface-initiated atom transfer radical polymerization (SI-ATRP) for potential bioapplications.SI-ATRP is an excellent controlled radical polymerization (CRP) method for the synthesis of polymer nanohybrid by growing polymer brushes (chains) from an interface, which allows precise control over polymer composition, topology, and functionality. Polymer brushes have proven to be attractive platforms for applications spanning drug delivery, tissue engineering, biosensors as well as bioseparation.Copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction has been widely applied for the design, fabrication and post-polymerization modification of polymer nanohybrid due to some important features: high reaction yields, benign reaction conditions, and tolerance to diverse functional groups.One aim of this thesis is to grow polymer brushes from inorganic nanoparticles via SI-ATRP in organic solvent followed by post-polymerization functionalization of the polymer brushes via click reaction for different applications. Specifically, thermo-responsive polymer brushes composed of poly(N-isopropylacrylamide) (pNIPAm) and poly(glycidyl methacrylate) (pGMA) were grafted from silica nanoparticles via SI-ATRP. A high amount of boronic acid ligands and iminodiacetate (IDA) ligands were introduced into the polymer brushes through the high-efficiency click reaction for the enrichment of glycoproteins and histidine-tagged proteins, respectively. The polymer nanohybrids were characterized to determine the particle size, morphology, organic content, densities of polymer chains and the affinity ligands via techniques including dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, thermogravimetric analysis (TGA), and gel permission chromatography (GPC). The nanocomposites showed high adsorption capacity and selectivity towards the target proteins due to the dense ligands immobilized on the long and flexible polymer brushes that are able to provide rapid protein transport to binding sites. The synthetic approaches developed in this thesis have a great potential for the development of more efficient adsorbents for biological samples.Another focus of this thesis is to investigate the possibility of growing polymer chains from biological interface via SI-ATRP in an aqueous solvent. Specifically, ATRP initiators were first selectively immobilized on amelogenin (AMEL), which is a pH-responsive protein, followed by growing thermo-responsive pNIPAm chains in an aqueous solution via SI-ATRP, leading to a pH and temperature dually responsive bioconjugate. The bioconjugate was characterized in terms of particle size, molecular weight of polymer, and self-assembly behavior in response to pH and temperature. The bioconjugates may serve as a promising platform for bioapplications such as drug delivery and biosensing

Nanoparticle-supported temperature responsive polymer brushes for affinity separation of histidine-tagged recombinant proteins

We developed a modular approach for the preparation of nanoparticle-supported polymer brushes carrying repeating iminodiacetate units for affinity separation of histidine-tagged recombinant proteins. The nanoparticle-supported polymer brushes were prepared via the combination of surface-initiated atom transfer radical polymerization with Cu(I)-catalyzed azide–alkyne cycloaddition reaction. The nanocomposite materials were characterized to determine the particle size, morphology, organic content, densities of polymer chains and the affinity ligand. Protein binding assay illustrated that the iminodiacetate-rich polymer brushes enable to selectively bind histidine-tagged recombinant proteins in the presence of abundant interfering proteins. More importantly, the protein binding capacity can be tuned by adjusting the environmental temperature. Statement of Significance: The nanoparticle core-polymer brush structure enables selective binding of histidine-tagged recombinant proteins via multiple metal-coordination interactions. The soft and flexible structure of the polymer brushes was found beneficial for lowering the steric hindrance in protein binding. Taking advantage of the conformational changes of the polymer brushes at different temperatures, it is possible to modulate the protein binding on the nanocomposite by adjusting the environmental temperature. In general, the iminodiacetate-rich core-brush nano adsorbents are attractive for purifying histidine-tagged recombinant proteins practically. The synthetic approach reported here may be expanded to develop other advanced functional materials for applications in various biomedical fields ranging from biosensors to drug delivery

Towards detection of glycoproteins using molecularly imprinted nanoparticles and boronic acid-modified fluorescent probe

Glycoproteins represent a group of important biomarkers for cancer and other life-threatening diseases. Selective detection of specific glycoproteins is an important step for early diagnosis. Traditional glycoprotein assays are mostly based on lectins, antibodies, and enzymes, biochemical reagents that are costly and require special cold chain storage and distribution. To address the shortcomings of the existing glycoprotein assays, we propose a new approach using protein-imprinted nanoparticles to replace the traditional lectins and antibodies. Protein-imprinted binding sites were created on the surface of silica nanoparticles by copolymerization of dopamine and aminophenylboronic acid. The imprinted nanoparticles were systematically characterized by dynamic light scattering, scanning and transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and elemental analysis. A boronic acid-modified fluorescent probe was used to detect the target glycoprotein captured by the imprinted nanoparticles. Using horseradish peroxidase as a model glycoprotein, we demonstrated that the proposed method can be applied to detect target protein containing multiple glycosylation sites. Because of their outstanding stability and low cost, imprinted nanoparticles and synthetic probes are attractive replacements of traditional biochemical reagents to develop simpler, faster, and more cost-effective analytical methods for glycoproteins

A paradigm shift design of functional monomers for developing molecularly imprinted polymers

Functional monomers play a key role in preparing molecularly imprinted polymers (MIPs) by forming complex with templates to create recognition sites in the polymers. In this paper, a new strategy was proposed to design functional monomers for efficient MIPs synthesis. This strategy dated from the investigations on previously developed MIPs. In propranolol imprinting process, methacrylic acid has always been used as a functional monomer, due to the efficient hydrogen bonding interactions between the carboxyl group in methacrylic acid and the 2-hydroxylethylamine group in propranolol. Given this, we assumed that a functional monomer having a 2-hydroxylethylamine moiety may be used to imprint carboxylic acid molecules e.g. naproxen. To demonstrate this idea, a new monomer 2-hydroxy-3-(isopropylamino)propyl methacrylate (HIMA) was designed. Computation results, by means of density functional theory method, revealed that HIMA could form a stable complex with naproxen through hydrogen bonding interactions with the carboxylic acid group. HIMA was then used to synthesize naproxen-imprinted polymers via precipitation polymerization. Binding experiments showed that all the MIPs could selectively recognize naproxen, confirming the feasibility of our paradigm shift in functional monomer design. The new functional monomer HIMA is a promising ligand that may be used to imprint other molecules having carboxylic acid or phosphoric acid groups. The paradigm shift in this study thereby opens a new avenue to design functional monomers for developing MIPs

Synthesis of fluorescent molecularly imprinted nanoparticles for turn-on fluorescence assay using one-pot synthetic method and a preliminary microfluidic approach

Fluorescent molecularly imprinted polymers (MIPs) have received considerable attention for their promising applications in sensing, imaging and diagnostics. Different synthetic methods have been reported to prepare fluorescent MIPs. Here, one-pot polymerization method was developed to synthesize fluorescent MIP nanoparticles (NPs) bearing a suitable fluorescent label as the fluorescence acceptor. The MIP NPs can emit strong fluorescence based on fluorescence resonance energy transfer (FRET) when they bind to analytes acting as the fluorescence donor. The one-pot synthetic method is straightforward, less time-consuming and easy to optimize the loading of fluorescence acceptor. Additionally, a preliminary microfluidic reactor was designed for preparing such fluorescent MIP NPs with more uniform size in a continuous process for the first time. The fluorescent MIP NPs can be used for selective detection of the analytical target in a FRET-based turn-on fluorescence assay which is easy to carry out with no tedious separation steps

Temperature and pH Dual-Responsive Core-Brush Nanocomposite for Enrichment of Glycoproteins

In this report, we present a novel modular approach to the immobilization of a high density of boronic acid ligands on thermoresponsive block copolymer brushes for effective enrichment of glycoproteins via their synergistic multiple covalent binding with the immobilized boronic acids. Specifically, a two-step, consecutive surface-initiated atom transfer radical polymerization (SI-ATRP) was employed to graft a flexible block copolymer brush, pNIPAm-<i>b</i>-pGMA, from an initiator-functionalized nanosilica surface, followed by postpolymerization modification of the pGMA moiety with sodium azide. Subsequently, an alkyne-tagged boronic acid (PCAPBA) was conjugated to the polymer brush via a Cu­(I)-catalyzed azide–alkyne cycloaddition (CuAAC) click reaction, leading to a silica-supported polymeric hybrid material, Si@pNIPAm-<i>b</i>-pBA, with a potent glycol binding affinity. The obtained core-brush nanocomposite was systematically characterized with regard to particle size, morphology, organic content, brush density, and number of immobilized boronic acids. We also studied the characteristics of glycoprotein binding of the nanocomposite under different conditions. The nanocomposite showed high binding capacities for ovalbumin (OVA) (98.0 mg g^–1) and horseradish peroxidase (HRP) (26.8 mg g^–1) in a basic buffer (pH 9.0) at 20 °C. More importantly, by adjusting the pH and temperature, the binding capacities of the nanocomposite can be tuned, which is meaningful for the separation of biological molecules. In general, the synthetic approach developed for the fabrication of block copolymer brushes in the nanocomposite opened new opportunities for the design of more functional hybrid materials that will be useful in bioseparation and biomedical applications

Dynamic assembly of molecularly imprinted polymer nanoparticles

Manipulation of specific binding and recycling of materials are two important aspects for practical applications of molecularly imprinted polymers. In this work, we developed a new approach to control the dynamic assembly of molecularly imprinted nanoparticles by surface functionalization. Molecularly imprinted polymer nanoparticles with a well-controlled core-shell structure were synthesized using precipitation polymerization. The specific binding sites were created in the core during the first step imprinting reaction. In the second polymerization step, epoxide groups were introduced into the particle shell to act as an intermediate linker to immobilize phenylboronic acids, as well as to introduce cis-diol structures on surface. The imprinted polymer nanoparticles modified with boronic acid and cis-diol structures maintained high molecular binding specificity, and the nanoparticles could be induced to form dynamic particle aggregation that responded to pH variation and chemical stimuli. The possibility of modulating molecular binding and nanoparticle assembly in a mutually independent fashion can be exploited in a number of applications where repeated use of precious nanoparticles is needed

Nanohybrid polymer brushes on silica for bioseparation

Boronic acid based affinity materials are of great importance for effective enrichment of biomolecules containing a cis-diol structure, for example glycoproteins. In this work, we developed a new pH- and temperature-responsive boronate affinity material for effective separation of glycoproteins. A nanohybrid material composed of silica cores and flexible polymer brushes, denoted as Si@poly(NIPAm-co-GMA)@APBA, was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) in combination with Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The size, morphology and composition of the obtained nanohybrid were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis and thermogravimetric analysis (TGA). The density of polymer brushes on the surface of silica nanoparticles was determined to be 0.7 molecules per nm2. The maximum binding capacities of the nanohybrid Si@poly(NIPAm-co-GMA)@APBA for ovalbumin (OVA) and horseradish peroxidase (HRP) were determined to be 87.6 mg g-1 and 22.8 mg g-1, respectively. Glycoprotein binding on the nanohybrid could be controlled by varying the pH of the binding buffer. By increasing the temperature from 20 °C to 35 °C, glycoprotein binding onto the nanohybrid was decreased. This new pH- and temperature-responsive nanohybrid will be useful for a number of biotechnological and biomedical applications, for example, for protein separation and drug delivery