Inorganic colloidal nanoparticles are very small, nanoscale objects with inorganic cores that are dispersed in a solvent. Depending on the material they consist of, nanoparticles can possess a number of different properties such as high electron density and strong optical absorption (e.g. metal particles, in particular Au), photoluminescence in the form of fluorescence (semiconductor quantum dots, e.g. CdSe or CdTe) or phosphorescence (doped oxide materials, e.g. Y(2)O(3)), or magnetic moment (e.g. iron oxide or cobalt nanoparticles). Prerequisite for every possible application is the proper surface functionalization of such nanoparticles, which determines their interaction with the environment. These interactions ultimately affect the colloidal stability of the particles, and may yield to a controlled assembly or to the delivery of nanoparticles to a target, e.g. by appropriate functional molecules on the particle surface. This work aims to review different strategies of surface modification and functionalization of inorganic colloidal nanoparticles with a special focus on the material systems gold and semiconductor nanoparticles, such as CdSe/ZnS. However, the discussed strategies are often of general nature and apply in the same way to nanoparticles of other materials.

https://faculty.washington.edu/mzhang/mse599/Surface-modification.full.pdf

Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles

There are only few semiconducting materials that have been shaping the progress of third generation photovoltaic cells as much as perovskites. Although they are deceivingly simple in structure, the archetypal AMX3-type perovskites have built-in potential for complex and surprising discoveries. Since 2009, a small and somewhat exotic class of perovskites, which are quite different from the common rock-solid oxide perovskite, have turned over a new leaf in solar cell research. Highlighted as one of the major scientific breakthroughs of the year 2013, the power conversion efficiency of the title compound hybrid organic–inorganic perovskite has now exceeded 18%, making it competitive with thin-film PV technology. In this minireview, a brief history of perovskite materials for photovoltaic applications is reported, the current state-of-the-art is distilled and the basic working mechanisms have been discussed. By analyzing the attainable photocurrent and photovoltage, realizing perovskite solar cells with 20% efficiency for a single junction, and 30% for a tandem configuration on a c-Si solar cell would be realistic.

Organohalide lead perovskites for photovoltaic applications

Stimuli-responsive interfaces and systems for the control of protein-surface and cell-surface interactions.

Despite multiple research approaches to prevent bacterial colonization on surfaces, device-associated infections are currently responsible for about 50% of nosocomial infections in Europe and signifi cantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly( N -isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin-coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite fi lm morphology reveals a homogeneous distribution of the ZnO NP throughout the fi lm for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confi rmed by UV-vis spectroscopy. The nanocomposite fi lms exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈ 0.74 μ g cm − 2 (1.33 mmol cm − 3 ), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non-cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin fi lms between bacterial and cellular species qualifi es them as promising candidates for novel biomedical device coatings.

Antibacterial Surface Coatings from Zinc Oxide Nanoparticles Embedded in Poly(N-isopropylacrylamide) Hydrogel Surface Layers

Hydrogel materials consisting of water-swollen polymer networks exhibit a large number of specific properties highly attractive for a variety of optical biosensor applications. This properties profile embraces the aqueous swelling medium as the basis of biocompatibility, non-fouling behavior, and being not cell toxic, while providing high optical quality and transparency. The present review focuses on some of the most interesting aspects of surface-attached hydrogel films as active binding matrices in optical biosensors based on surface plasmon resonance and optical waveguide mode spectroscopy. In particular, the chemical nature, specific properties, and applications of such hydrogel surface architectures for highly sensitive affinity biosensors based on evanescent wave optics are discussed. The specific class of responsive hydrogel systems, which can change their physical state in response to externally applied stimuli, have found large interest as sophisticated materials that provide a complex behavior to hydrogel-based sensing devices.

/pdf/thin-hydrogel-films-for-optical-biosensor-applications-25j06u2ziu.pdf

Thin hydrogel films for optical biosensor applications.

The structural features and swelling properties of responsive hydrogel films based on poly(N-isopropylacrylamide) copolymers with a photo-cross-linkable benzophenone unit were investigated by surface plasmon resonance, optical waveguide mode spectroscopy, and atomic force microscopy. The temperature-dependent swelling behavior was studied with respect to the chemical composition of the hydrogel polymers containing either sodium methacrylate or methacrylic acid moieties. In the sodium methacrylate system, a refractive index gradient was found that was not present in the free acid gel. This refractive index gradient, perpendicular to the swollen hydrogel film surface, could be analyzed in detail by application of the reversed Wentzel-Kramers-Brillouin (WKB) approximation to the optical data. This novel approach to analyzing thin-film gradients with the WKB method presents a powerful tool for the characterization of inhomogeneous hydrogels, which would otherwise be very difficult to capture experimentally. In AFM images of the hydrogel layers, a macroscopic pore structure was observed that depended on the polymer composition as well as on the swelling history. This pore structure apparently prevents the often-observed skin barrier effect and leads to a quickly responding hydrogel.

Responsive thin hydrogel layers from photo-cross-linkable poly(N-isopropylacrylamide) terpolymers.

We employ fluorescence correlation spectroscopy to study length dependent dynamics in transient and grafted cross-linked poly(N-isopropylacrylamide) (PNIPAAm) networks at different concentrations and cross-link densities, respectively. For nondilute PNIPAAm solutions, the molecular diffusants appear to sense local dynamics on the length scale of the mesh size obtained from photon correlation spectroscopy, whereas a polymer probe, comparable to the PNIPAAm size, reveals global chain motions. The relation of the tracer Brownian diffusion to the mesh size can be utilized to characterize permanently cross-linked and grafted PNIPAAm networks.

Local and global dynamics of transient polymer networks and swollen gels anchored on solid surfaces

A water solubilization method for hydrophobic CdSe-ZnS quantum dots (QDs) is exhibited in this paper. The thermo-sensitive and photo-cross-linkable poly(N-isopropylacrylamide) (PNiPAm) copolymer is used for extraction of the hydrophobic QDs in dichloromethane and transferring them to water. This was accomplished via a solvent-induced phase separation process based on the amphiphilic nature of PNiPAm and their interactions with the different solvents. In addition, the functional ferrocene-containing PNiPAm is also used for the water solubilization of the hydrophobic QDs and the hydrogel/QDs particles demonstrate the chemical redox-controlled switch on−off property.

Rapid and Highly Efficient Preparation of Water-Soluble Luminescent Quantum Dots via Encapsulation by Thermo- and Redox-Responsive Hydrogels

A novel, easy and high-efficient method is described for transferring hydrophobic magnetic Fe 3 O 4 nanoparticles from organic to aqueous solution by wrapping a thermo-responsive and photocrosslinkable poly(N-isopropylacrylamide) (PNIPAm) terpolymer around the particles. The wrapping procedure is introduced by the co-nonsolvent transition of PNIPAm in the mixing solvent and the polymer can dissolve in water carrying Fe 3 O 4 nanoparticles by noncovalent interaction. The temperature-dependant and magnetic properties of the water-soluble particles are characterized in this paper.

Patrick W. Beines

Papers

Responsive thin hydrogel layers from photo-cross-linkable poly(N-isopropylacrylamide) terpolymers.

Local and global dynamics of transient polymer networks and swollen gels anchored on solid surfaces

Rapid and Highly Efficient Preparation of Water-Soluble Luminescent Quantum Dots via Encapsulation by Thermo- and Redox-Responsive Hydrogels

A facile approach for transferring hydrophobic magnetic nanoparticles into water-soluble particles