pH-responsive Silica Nanoparticles Research Articles

Probing the Interfacial Properties of Oil-Water Interfaces Decorated with Ionizable, pH Responsive Silica Nanoparticles.

Particle-stabilized emulsions (Pickering emulsions) have recently attracted significant attention in scientific studies and for technological applications. The interest stems from the ease of directly assembling the particles at interfaces and modulating the interfacial properties. In this paper, we demonstrate the formation of stable, practical emulsions leveraging the assembly of ionizable, pH responsive silica nanoparticles, surface-functionalized by a mixture of silanes containing amine/ammonium groups, which renders them positively charged. Using pH as the trigger, the assembly and the behavior of the emulsion are controlled by modulating the charges of the functional groups of the nanoparticle and the oil (crude oil). In addition to their tunable charge, the particular combination of silane coupling agents leads to stable particle dispersions, which is critical for practical applications. Atomic force microscopy and interfacial tension (IFT) measurements are used to monitor the assembly, which is controlled by both the electrostatic interactions between the particles and oil and the interparticle interactions, both of which are modulated by pH. Under acidic conditions, when the surfaces of the oil and the nanoparticles (NPs) are positively charged, the NPs are not attracted at the interface and there is no significant reduction in the IFT. In contrast, under basic conditions in which the oil carries a high negative charge and the amine groups on the silica are deprotonated while still positively charged because of the ammonium groups, the NPs assemble at the interface in a closely packed configuration yielding a jammed state with a high dilatational modulus. As a result, two oil droplets do not coalesce even when pushed against each other and the emulsion stability improves significantly. The study provides new insights into the directed assembly of nanoparticles at fluid interfaces relevant to several applications, including environmental remediation, catalysis, drug delivery, food technology, and oil recovery.

Visual detection of the prostate specific antigen via a sandwich immunoassay and by using a superwettable chip coated with pH-responsive silica nanoparticles.

A pH-responsive superwettable chip is described whose surface can switch between superhydrophobic and superhydrophilic. It can be used for the visual detection of the prostate specific antigen (PSA) based on contact angle readout. Magnetic beads were modified with primary antibody against PSA. After immunobinding, gold nanoparticles loaded with secondary antibody labeled with glucose oxidase is added. On addition of glucose, gluconic acid is formed which causes a drop in the local pH value. This results in a wettability switch of the pH-responsive superwettable chip from hydrophobic to hydrophilic. Under the optimized conditions, PSA can be quantified with a 3.2pgmL-1 limit of detection by analyzing the contact angle and the related color that changes from blue via orange to red. The method is applicable to PSA detection in serum samples and for visual classification by cancer patients and healthy persons. It is also suitable for color-blind and color-weak individuals. Conceivably, this kind of assay can be transferred to the determination of various kinds of other bioanalytes including nucleotide, proteins, and even of ions and small organic molecules, and thus is has a wide scope. Graphical abstract Schematic presentation of a pH-responsive superwettable chip coated with silica nanoparticles for the visual detection of prostate specific antigen (PSA) by reading the contact angle. The superwettable chip achieves reliable clinical detection of serum PSA from prostate cancer patients.

Fabrication of doubly responsive polymer functionalized silica nanoparticles via a simple thiol–ene click chemistry

Temperature and pH responsive silica nanoparticles were easily prepared by a simple thiol–ene click chemistry. Well-defined poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) and poly(N-isopropylacrylamide) (PNIPAAm) were first synthesized by a reversible addition–fragmentation chain transfer (RAFT) process. The polymers were then reduced to generate a thiol group at the chain end to react with vinyl groups on the surface of silica nanoparticles via a simple ‘click’ reaction. The ratio of the PDEAEMA and PNIPAAm segments on the silica nanoparticles surface was controlled by adjusting the feed weight ratios of the polymers in the reaction solution. The surface coated silica nanoparticles were characterized by a range of techniques such as thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The functionalized silica nanoparticles showed both pH and temperature responsive behavior and the solution properties were dependent on the ratio of the two polymers on the surface.