Polymer Brush/Metal Nanoparticle Hybrids for Optical Sensor Applications: from Self-Assembly to Tailored Functions and Nanoengineering

This review article summarizes the progress of research in the field ofpolymer brush/metal nanoparticle hybrid materials. We will discuss the mutualinfluence of polymer brush matrix and particles. Self-assembly of particles withinpolymer brushes, and ways to control the loading and location of nanoparticlesinside polymer brushes will be described, as well as the possibility to use thebrush templates as nanoreactors to generate metal nanoparticles. The combination of stimuli-responsive polymer brushes and nanoparticles exhibiting surface plasmon resonance, such as gold or silver, enables the design of opticalsensors based on reversible variations of the brush conformation. Sensing devices are capable of detecting avariety of extrinsic variations in their surrounding enviroments. The progress in the development of such optical sensors usingbrush/particle hybrids will be discussed in more detail

Engineered Ovalbumin Nanoparticles for Cancer Immunotherapy

Ovalbumin (OVA) is a protein antigen that is widely used for eliciting cellular and humoral immune responses in cancer immunotherapy. As an alternative to solute OVA, engineering approach is developed herein towards protein nanoparticles (pNPs) based on reactive electrospraying. The resulting pNPs are comprised of polymerized OVA, where individual OVA molecules are chemically linked via poly(ethylene glycol) (PEG) units. Controlling the PEG/OVA ratio allows for fine‐tuning of critical physical properties, such as particle size, elasticity, and, at the molecular level, mesh size. As the PEG/OVA ratio decreased, OVA pNPs are more effectively processed by dendritic cells, resulting in higher OT‐I CD8+ cells proliferation in vitro. Moreover, pNPs with lower PEG/OVA ratios elicit enhanced lymphatic drainage in vivo and increased uptake by lymph node macrophages, dendritic cells, and B cells, while 500 nm OVA pNPs show poor draining lymph nodes delivery. In addition, pNPs with lower PEG/OVA ratios result in higher anti‐OVA antibody titers in vivo, suggesting improved humoral immune responses. Importantly, OVA pNPs result in significantly increased median survival relative to solute OVA antigen in a mouse model of B16F10‐OVA melanoma. This work demonstrates that precisely engineered OVA pNPs can improve the overall anti‐tumor response compared to solute antigen.As an alternative to solute antigens for cancer immunotherapy, protein nanoparticles (pNPs) comprised of polymerized antigen linked by poly(ethylene glycol) units are developed based on reactive electrospraying. This engineering approach allows fine tuning the physico‐chemical properties of pNPs such as particle size, elasticity, and mesh size. These properties are related to pNPs enhanced antigen‐specific immune responses and improved anti‐tumor efficacy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163384/3/adtp202000100-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163384/2/adtp202000100.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163384/1/adtp202000100_am.pd

Smart Hybrid Materials With Tailored Functions: Incorporation of Gold Nanoparticles Into Stimuli-Responsive Polymer Brushes

Diese Dissertation befasst sich mit der Verteilung von Gold-Nanopartikeln (AuNPs) in stimuli-sensitiven Polymerbürsten, die an planare Oberflächen gebunden sind. Die Farbänderung solcher Bürsten/AuNP Hybride hängt von der Partikelbeladung und deren Abstand zueinander ab. Folglich, eine Kontrolle der Partikelverteilung in der Bürste ermöglicht eine Steuerung der Farbe des Hybrids für Anwendungen in der Sensorik. Wie in dieser Arbeit dargelegt, wird die AuNP Verteilung durch viele Faktoren wie Bürstendicke, Ankerdichte, Polymerstruktur, Oberflächenfunktionalisierung der Partikel, Partikelgrösse sowie Partikelform beeinflusst. Oberflächengebundene poly((N,N-dimethylamino ethyl)methacrylat) (PDMAEMA) and poly(N-isopropylacrylamid) (PNIPAM) Bürsten wurden mittels "Atom transfer radical polymerization" (ATRP) synthetisiert; die Beladung mit AuNPs erfolgte durch einen Inkubationsprozess. Beide Polymere weisen eine untere kritische Mischungstemperatur (LCST) auf, oberhalb derer die Polymerketten reversibles Schrumpfen zeigen. In dieser Dissertation werden X-ray und Neutronenreflektometrie, UV/vis Spektroskopie, Rasterelektronenmikroskopie und Ellipsometrie kombiniert, um die Partikelverteilung und die optischen Eigenschaften der Hybride zu untersuchen. Nach Verringern der Ankerdichte konnten Beladungsdichte und Eindringung der Partikel erhöht werden. Wenn PNIPAM als Bürstenmatrix genutzt wurde, konnte die Effizienz der Partikeleindringung für hohe Ankerdichten erhöht werden. Farbänderungen der PNIPAM/AuNP Hybride konnten einerseits durch Variieren der Temperatur, als auch durch Erhöhen des Salzgehaltes hervorgerufen werden; Struktur und Farbänderung von PNIPAM/AuNP hingen stark vom verwendeten Salz ab. Des Weiteren konnte die Partikelverteilung kontrolliert werden, indem zwei Arten an AuNPs in die PNIPAM-Bürste immobilisiert wurden, citratstabilisierte AuNPs, sowie AuNPs funktionalisiert mit 12-Mercaptododecansäure Liganden. Die Farbänderung, die durch das thermisch hervorgerufene Schrumpfen der PNIPAM-Bürsten induziert wurde, hing von der Art der immobilisierten Partikel ab. Abschliessend wurden Oberflächengradienten in Ankerdichte und Quaternisierungsgrad verwendet, um die dominierenden Faktoren der Verteilung anisotropischer Gold-Nanostäbe in PDMAEMA-Bürsten zu untersuchen

Intelligente Hybridmaterialien mit steuerbaren Funktionen : Einlagerung von Goldnanopartikeln in stimuli-sensitive Polymerbürsten

Diese Dissertation befasst sich mit der Verteilung von Gold-Nanopartikeln (AuNPs) in stimuli-sensitiven Polymerbürsten, die an planare Oberflächen gebunden sind. Die Farbänderung solcher Bürsten/AuNP Hybride hängt von der Partikelbeladung und deren Abstand zueinander ab. Folglich, eine Kontrolle der Partikelverteilung in der Bürste ermöglicht eine Steuerung der Farbe des Hybrids für Anwendungen in der Sensorik. Wie in dieser Arbeit dargelegt, wird die AuNP Verteilung durch viele Faktoren wie Bürstendicke, Ankerdichte, Polymerstruktur, Oberflächenfunktionalisierung der Partikel, Partikelgrösse sowie Partikelform beeinflusst. Oberflächengebundene poly((N,N-dimethylamino ethyl)methacrylat) (PDMAEMA) and poly(N-isopropylacrylamid) (PNIPAM) Bürsten wurden mittels "Atom transfer radical polymerization" (ATRP) synthetisiert; die Beladung mit AuNPs erfolgte durch einen Inkubationsprozess. Beide Polymere weisen eine untere kritische Mischungstemperatur (LCST) auf, oberhalb derer die Polymerketten reversibles Schrumpfen zeigen. In dieser Dissertation werden X-ray und Neutronenreflektometrie, UV/vis Spektroskopie, Rasterelektronenmikroskopie und Ellipsometrie kombiniert, um die Partikelverteilung und die optischen Eigenschaften der Hybride zu untersuchen. Nach Verringern der Ankerdichte konnten Beladungsdichte und Eindringung der Partikel erhöht werden. Wenn PNIPAM als Bürstenmatrix genutzt wurde, konnte die Effizienz der Partikeleindringung für hohe Ankerdichten erhöht werden. Farbänderungen der PNIPAM/AuNP Hybride konnten einerseits durch Variieren der Temperatur, als auch durch Erhöhen des Salzgehaltes hervorgerufen werden; Struktur und Farbänderung von PNIPAM/AuNP hingen stark vom verwendeten Salz ab. Des Weiteren konnte die Partikelverteilung kontrolliert werden, indem zwei Arten an AuNPs in die PNIPAM-Bürste immobilisiert wurden, citratstabilisierte AuNPs, sowie AuNPs funktionalisiert mit 12-Mercaptododecansäure Liganden. Die Farbänderung, die durch das thermisch hervorgerufene Schrumpfen der PNIPAM-Bürsten induziert wurde, hing von der Art der immobilisierten Partikel ab. Abschliessend wurden Oberflächengradienten in Ankerdichte und Quaternisierungsgrad verwendet, um die dominierenden Faktoren der Verteilung anisotropischer Gold-Nanostäbe in PDMAEMA-Bürsten zu untersuchen.This Ph.D. thesis aims to study the assembly of gold nanoparticles (AuNPs) within stimuli-responsive polymer brushes that are grafted from planar surfaces. The apparent color of such brush/AuNP hybrids depends on the particle loading and vicinity. Thus, controlling the particle assembly inside the polymer brush matrix allows tuning the color of brush/AuNP hybrids to optimize them for sensor applications. As discussed in this Ph.D. thesis, the particle assembly in polymer brush matrices is influenced by many parameters such as brush thickness, brush grafting density, polymer chemistry, as well as particle surface functionalization, size, and shape. Surface-grafted poly((N,N-dimethylamino ethyl)methacrylate) (PDMAEMA) and poly(N-isopropylacrylamide) (PNIPAM) brushes were prepared by atom transfer radical polymerization (ATRP) and loaded with AuNPs by a dipping process. Both polymers exhibit a lower critical solution temperature (LCST), above which the polymer chains undergo reversible shrinking. In this Ph.D thesis, X-ray and neutron reflectivity, UV/vis spectroscopy, scanning electron microscopy and ellipsometry are combined to study the AuNP assembly and optical properties of the prepared brush/AuNP hybrids. The uptake and penetration of AuNPs could be increased after decreasing the grafting density of the surface-anchored polymers. At high grafting density, the AuNPs penetrated more effectively when PNIPAM was used as the brush matrix. Color changes of PNIPAM/AuNP hybrids could be induced by either varying the temperature or increasing the salinity; the structure of PNIPAM/AuNP and the apparent color strongly depended on the type of salt. The assembly of AuNPs could be controlled by immobilizing two different particle types into the PNIPAM brush matrices, namely citrate-coated AuNPs and AuNPs stabilized with 12-mercaptododecanoic acid ligands, into PNIPAM brushes. The color change associated with the thermoinduced collapse of the PNIPAM brushes depended on the particle type. Finally, surface-bound grafting density gradients and gradients in quaternization degree were employed to determine the dominating factors that govern the assembly of anisotropic gold nanorods in PDMAEMA brushes

Stimuli-Responsive Polyelectrolyte Brushes As a Matrix for the Attachment of Gold Nanoparticles: The Effect of Brush Thickness on Particle Distribution

The effect of brush thickness on the loading of gold nanoparticles (AuNPs) within stimuli-responsive poly-(N,N-(dimethylamino ethyl) methacrylate) (PDMAEMA) polyelectrolyte brushes is reported. Atom transfer radical polymerization (ATRP) was used to grow polymer brushes via a “grafting from” approach. The brush thickness was tuned by varying the polymerization time. Using a new type of sealed reactor, thick brushes were synthesized. A systematic study was performed by varying a single parameter (brush thickness), while keeping all other parameters constant. AuNPs of 13 nm in diameter were attached by incubation. X-ray reflectivity, electron scanning microscopy and ellipsometry were used to study the particle loading, particle distribution and interpenetration of the particles within the brush matrix. A model for the structure of the brush/particle hybrids was derived. The particle number densities of attached AuNPs depend on the brush thickness, as do the optical properties of the hybrids. An increasing particle number density was found for increasing brush thickness, due to an increased surface roughness

Charge Density Gradients of Polymer Thin Film by Gaseous Phase Quaternization

We report on the rapid formation of charge density gradients in polymer films by exposing poly([2-dimethylaminoethyl] methacrylate) (PDMAEMA) films resting on flat silica substrates to methyl iodide (i.e., MI, also known as iodomethane) vapors. We adjust the charge gradient by varying the MI concentration in solution and the process time. The thickness of the parent PDMAEMA film does not affect the diffusion of MI through and the reaction kinetics in the films. Instead, the diffusion of MI through the gaseous phase constitutes the limiting step in the overall process

Uptake of pH-Sensitive Gold Nanoparticles in Strong Polyelectrolyte Brushes

The impact of electrostatic attraction on the uptake of gold nanoparticles (AuNPs) into positively charged strong poly-[2-(Methacryloyloxy) ethyl] trimethylammonium chloride (PMETAC) polyelectrolyte brushes was investigated. In this work, PMETAC brushes were synthesized via surface-initiated atom transfer radical polymerization (Si-ATRP). PMETAC/AuNP composite materials were prepared by incubation of the polymer brush coated samples into 3-mercaptopropionic acid-capped AuNP (5 nm in diameter) suspension. The electrostatic interactions were tuned by changing the surface charge of the AuNPs through variations in pH value, while the charge of the PMETAC brush was not affected. Atomic-force microscopy (AFM), ellipsometry, UV/Vis spectroscopy, gravimetric analysis and transmission electron microscopy (TEM) were employed to study the loading and penetration into the polymer brush. The results show that the number density of attached AuNPs depends on the pH value and increases with increasing pH value. There is also strong evidence that the particle assembly is dependent on the pH value of the AuNP suspension. Incubation of PMETAC brushes in AuNP suspension at pH 4 led to the formation of a surface layer on top of the brush (2D assembly) due to sterical hindrance of the clustered AuNPs, while incubation in AuNP suspension at pH 8 led to deeper particle penetration into the brush (3D assembly). The straightforward control of particle uptake and assembly by tuning the charge density of the nanoparticle surface is a valuable tool for the development of materials for colorimetric sensor applications

Salt-Induced Aggregation of Negatively Charged Gold Nanoparticles Confined in a Polymer Brush Matrix

We report on the salt-induced aggregation of citrate-coated gold nanoparticles (AuNPs) confined within poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) brushes grafted from flat substrates. Compared to highly dispersed AuNPs, a red-shift and broadening of the surface plasmon (SP) band is observed when the AuNPs are confined by the PNIPAM brush matrix due to their close vicinity. Additional red-shifting and broadening occur upon immersion in aqueous salt solutions (1 M NaF, NaCl, NaBr, and KCl). Nanoparticle assemblies are established due to salt-induced aggregation of AuNPs and are dependent on the type of salt. In the presence of KCl, nanoparticle assemblies are built up that result in the formation a second plasmon peak at ∼700 nm. The color change of PNIPAM/AuNP is associated with (1) the collapse of the PNIPAM brushes in the presence of salt and (2) nanoparticle aggregation due to electrostatic screening of the negative charges around the AuNPs by the salt ions. Ion specificity is related to ion-pair association energies and adsorption behavior of ions at the AuNP surface. In addition, we perform a neutron reflectivity experiment to resolve the internal structure of swollen PNIPAM/AuNP hybrids and find that penetrated AuNPs cause PNIPAM chain stretching due to electrostatic repulsion between charged particles in the brush