Interactions between solid surfaces mediated by polyethylene oxide polymers: effect of polymer concentration

Total internal reflection microscopy: a powerful tool for exploring interactions and dynamics near interfaces

The occurrence of many micro/macrophenomena is closely related to interactions and dynamics near interfaces. Hence, developing powerful tools for characterizing near-interface interactions and dynamics has attached great importance among researchers. In this review, we introduce a noninvasive and ultrasensitive technique called total internal reflection microscopy (TIRM). The principles of TIRM are introduced first, demonstrating the characteristics of this technique. Then, typical measurements with TIRM and the recent development of the technique are reviewed in detail. At the end of the review, we highlight the great progress of TIRM during the past several decades and show its potential to be more influential in measuring interactions and dynamics near interfaces in various research fields.

Modulating transparency and colour of cellulose nanocrystal composite films by varying polymer molecular weight

HYPOTHESIS

Cellulose nanocrystals (CNC) can produce photonic composite films that selectively reflect light based on their periodic cholesteric structure. The hypothesis of this research is that by incorporating water-soluble polymer, photonic properties of CNC composite film can be designed by manipulating the polymer molecular weight.

EXPERIMENTAL

Flexible free-standing composite films of five different poly (ethylene glycol) (PEG) molecular weights were prepared via air drying under a controlled environment, and characterised by reflectance UV-vis spectrometer, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Films with each molecular weight were investigated over a concentration range.

FINDINGS

The colour and transmission haze of the composite films was modified by varying both the PEG molecular weight and concentration. Depending on the molecular weight, the films were able to reflect light from the UV region (242 nm) across the visible spectrum to the near-infrared region (832 nm). Different trends in variation of the reflected light based on the molecular weight was found with increasing PEG concentration and was explained by weak depletion interactions occurring between CNC and PEG, which was reduced with increasing PEG molecular weight.

An enzyme-mediated controlled release system for curcumin based on cyclodextrin/cyclodextrin degrading enzyme

In this study, an enzyme-triggered system based on β-cyclodextrin (β-CD) has been developed to achieve controlled release of hydrophobic drugs in the presence of maltogenic amylase (MAase). The inclusion complex formation of curcumin (CUR), as a model anticancer compound, with β-CD was characterized by fluorescence and Fourier transform infrared (FTIR) spectroscopy. CUR was loaded into β-CD with an encapsulation efficiency of approximately 30 %. The in vitro profiles of CUR release from β-CD showed that 100 % of the drug was released after one hour incubation in the presence of MAase with cyclodextrin degrading activity. Fluorescence microscopy images indicate a significantly greater cellular uptake of CUR using β-CD-CUR/MAase system compared to β-CD-CUR inclusion complex without MAase. The β-CD-CUR/MAase system exhibited lower IC₅₀ values and greater anti-proliferative effects in comparison with free CUR and β-CD-CUR in MCF-7 and Huh-7 cancer cells. The results from fluorescence microscopy and flow cytometric assay using the acridine orange/ethidium bromide and Annexin V-PE/7-AAD staining suggest that the β-CD-CUR/MAase system exhibited higher cytotoxic and apoptotic effects on cancer cells compared to other formulations. This triggered release of CUR in the presence of MAase is owing to the β-CD degradation by MAase resulting ring opening and chain scission in β-CD. We demonstrate that this enzyme-mediated controlled release system has a potential application for controlled release of poorly water-soluble drugs or hydrophobic compounds such as CUR.

Stratification of Colloidal Particles on a Surface: Study by a Colloidal Probe Atomic Force Microscopy Combined with a Transform Theory

Colloidal probe atomic force microscopy (CP-AFM) can be used for measuring force curves between the colloidal probe and the substrate in a colloidal suspension. In the experiment, an oscillatory force curve reflecting the layer structure of the colloidal particles on the substrate is usually obtained. However, the force curve is not equivalent to the interfacial structure of the colloidal particles. In this paper, the force curve is transformed into the number density distribution of the colloidal particles as a function of the distance from the substrate surface using our newly developed transform theory. It is found by the transform theory that the interfacial stratification is enhanced by an increase in an absolute value of the surface potential of the colloidal particle, despite a simultaneous increase in a repulsive electrostatic interaction between the substrate and the colloidal particle. To elucidate the mechanism of the stratification, an integral equation theory is employed. It is found that crowding of the colloidal particles in the bulk due to the increase in the absolute value of the surface potential of the colloidal particle leads to pushing out some colloidal particles to the wall. The combined method of CP-AFM and the transform theory (the experimental-theoretical study of the interfacial stratification) is related to colloidal crystallization, glass transition, and aggregation on a surface. Thus, the combined method is important for developments of colloidal nanotechnologies.

DOX-Fe3O4@mSiO2-PO-FA nanocomposite for synergistic chemo- and photothermal therapy

A DOX-Fe₃O₄@mSiO₂-PO-FA nanocomposite based drug delivery system for cancer chemotherapy and photothermal therapy.

Nanophotonic force microscopy: characterizing particle-surface interactions using near-field photonics

Direct measurements of particle-surface interactions are important for characterizing the stability and behavior of colloidal and nanoparticle suspensions. Current techniques are limited in their ability to measure pico-Newton scale interaction forces on submicrometer particles due to signal detection limits and thermal noise. Here we present a new technique for making measurements in this regime, which we refer to as nanophotonic force microscopy. Using a photonic crystal resonator, we generate a strongly localized region of exponentially decaying, near-field light that allows us to confine small particles close to a surface. From the statistical distribution of the light intensity scattered by the particle we are able to map out the potential well of the trap and directly quantify the repulsive force between the nanoparticle and the surface. As shown in this Letter, our technique is not limited by thermal noise, and therefore, we are able to resolve interaction forces smaller than 1 pN on dielectric particles as small as 100 nm in diameter.

An enzyme-responsive controlled release system of mesoporous silica coated with Konjac oligosaccharide

A simple and green method to fabricate an ingenious enzyme-responsive drug controlled release system was presented. Mesoporous silica material (mSiO2) 100 nm in size was used as the host, and Konjac oligosaccharide (KOGC) was employed to seal the nanopores of mSiO2 to inhibit the drug release. Rhodamine B was used as the model cargo to reveal the release behavior of the system. The KOGC-modified mSiO2 (mSiO2@KOGC) retains the drug until it reaches the colonic environment where bacteria secrete enzymes (β-mannanase) can degrade KOGC and make drug release. The amount of KOGC and enzyme can be used to adjust the release performance. And all the release behaviors fit the two-step Higuchi model, which predominate by KOGC degradation and mesoporous structure, respectively. With well bioactivity and selectivity, the system has potential application as an oral medicine carrier for treating intestinal disease.

Direct measurements of particle–surface interactions in aqueous solutions with total internal reflection microscopy

This feature article reviews the experimental studies of the interactions between designed colloidal surfaces in the presence or absence of macromolecules/nanoparticles including depletion attraction, steric repulsion, bridging flocculation, and specific interactions by using Total Internal Reflection Microscopy.