Robert Lupitskyy

Single Nanoparticle Plasmonic Devices by the “Grafting to” Method

Hierarchically organized single-nanoparticle structures synthesized in this work consisted of a 200 nm silica core and a pH-responsive poly(2-vinylpyridine) shell decorated with 15 nm gold nanoparticles. pH changes in the range of 3-6 back and forth results in a swelling-shrinking polymer brush shell and, thus, in the tuning distance between noble nanoparticles. A change in the interparticle distance is accompanied by a very pronounced shift in the maximum wavelength of the surface plasmon absorption peak. The dispersion of the resulting composite nanoparticles reversibly changed color from red to purple-blue as the pH changed from 2.5 to 6. Such hierarchically assembled nanostructures can be used as free-standing single-particle sensors in various miniaturized analytical systems.

Stimuli-responsive hydrogel hollow capsules by material efficient and robust cross-linking-precipitation synthesis revisited.

Monodisperse stimuli-responsive hydrogel capsules were synthesized in the 100-nm-diameter to 10-μm-diameter range from poly(4-vinylpyridine) (P4VP) and poly(ethyleneimine) (PEI) through a simple, efficient two-step cross-linking-precipitation template method under conditions of a good solvent. In this method, the core-shell particles were obtained by the deposition (heterocoagulation mechanism) of the cross-linked P4VP, PEI, or their mixtures on the surfaces of the template colloidal silica particles in nitromethane (for PEI) or a nitromethane-acetone mixture (for P4VP and P4VP-PEI mixtures) in the presence of cross-linker 1,4-diiodobutane. The cross-linked polymeric shell swollen in a good solvent stabilized the core-shell colloids. This mechanism provided the conditions for the synthesis of core-shell colloids in a submicrometer range of dimensions with an easily adjusted shell thickness (wall of the capsules) ranging from a few to hundreds of nanometers. The chemical composition of the shell was tuned by varying the ratio of co-cross-linked shell-forming polymers (P4VP and PEI). In the second step, the hollow capsules were obtained by etching the silica core in HF solutions. In this step, the colloidal stability of the hollow capsules was provided by ionized P4VP and PEI cross-linked shells. The hollow capsules demonstrate that the pH- and ionic-strength-triggered swelling and shrinking result in size-selective uptake and release properties. Cross-linked via quaternized functional groups, P4VP capsules undergo swelling and shrinking transitions at a physiologically relevant pH of around 6. The 200-nm-diameter hollow capsule with 25-nm-thick walls demonstrated a factor of 2 greater capacity to accommodate cargo molecules than the core-shell particles of the same dimensions because of an internal compartment and a combination of radial and a circumferential swelling modes in the capsules.

Robust synthesis of nanogel particles by an aggregation-crosslinking method

A simple and robust method for fabricating polyethyleneimine (PEI) nanogel particles has been developed. The particles were synthesized by crosslinking PEI with dibromoethane (DBE) in organic solvents (nitromethane or dimethylformamide). Stable colloidal dispersions were obtained at elevated temperature and in solvents which provide the highest rate of the PEI alkylation reaction, steric and electrostatic mechanisms of stabilization of nanoparticles. The size of the particles swollen in water ranges from 125 to 500 nm and can be regulated by the conditions of the synthesis (solvent and concentrations of PEI and DBE). The particles respond to pH changes with a 10–15% change in diameter. Uptake and, triggered by the changes in pH, release of a model anionic dye, Rose Bengal, by the particles was associated with the electrostatic interaction of the dye with the charged gel. The encapsulating capacity of the particles with respect to the Rose Bengal was determined to be 1.56 × 10−4M of the dye per 1 mg of the gel.