Engineered synthetic polymer nanoparticles as IgG affinity ligands

Design rationale of thermally responsive microgel particle films that reversibly absorb large amounts of CO2: fine tuning the pKa of ammonium ions in the particles

Fine-tuning of pK_a value of ammonium ions at both CO₂ capture and release temperature is found to be crucial for the design of the thermally responsive gel particle films that reversibly capture large amounts of CO₂.

Herein we revealed the design rationale of thermally responsive gel particle (GP) films that reversibly capture and release large amounts of CO₂ over a narrow temperature range (30–75 °C). The pK_a value of ammonium ions in the GPs at both the CO₂ capture temperature (30 °C) and release temperature (75 °C) is found to be the primary factor responsible for the stoichiometry of reversible CO₂ capture by the amines in the GP films. The pK_a values can be tuned by the properties of GPs such as volume phase transition temperature (VPTT), size, swelling ratio, and the imprinted microenvironment surrounding the amines. The optimal GP obtained according to the design rationale showed high capture capacity (68 mL CO₂ per g dry GPs, 3.0 mmol CO₂ per g dry GPs), although the regeneration temperature was as low as 75 °C. We anticipate that GP films that reversibly capture other acidic and basic gases in large amounts can also be achieved by the pK_a tuning procedures.

Measuring melittin uptake into hydrogel nanoparticles with near-infrared single nanoparticle surface plasmon resonance microscopy

This paper describes how changes in the refractive index of single hydrogel nanoparticles (HNPs) detected with near-infrared surface plasmon resonance microscopy (SPRM) can be used to monitor the uptake of therapeutic compounds for potential drug delivery applications. As a first example, SPRM is used to measure the specific uptake of the bioactive peptide melittin into N-isopropylacrylamide (NIPAm)-based HNPs. Point diffraction patterns in sequential real-time SPRM differential reflectivity images are counted to create digital adsorption binding curves of single 220 nm HNPs from picomolar nanoparticle solutions onto hydrophobic alkanethiol-modified gold surfaces. For each digital adsorption binding curve, the average single nanoparticle SPRM reflectivity response, ⟨Δ%R_NP⟩, was measured. The value of ⟨Δ%R_NP⟩ increased linearly from 1.04 ± 0.04 to 2.10 ± 0.10% when the melittin concentration in the HNP solution varied from zero to 2.5 μM. No change in the average HNP size in the presence of melittin is observed with dynamic light scattering measurements, and no increase in ⟨Δ%R_NP⟩ is observed in the presence of either FLAG octapeptide or bovine serum albumin. Additional bulk fluorescence measurements of melittin uptake into HNPs are used to estimate that a 1% increase in ⟨Δ%R_NP⟩ observed in SPRM corresponds to the incorporation of approximately 65000 molecules into each 220 nm HNP, corresponding to roughly 4% of its volume. The lowest detected amount of melittin loading into the 220 nm HNPs was an increase in ⟨Δ%R_NP⟩ of 0.15%, corresponding to the absorption of 10000 molecules.

A synthetic strategy for the preparation of sub-100 nm functional polymer particles of uniform diameter

An amphiphilic block copolymer surfactant is used to impart modifiable surface functionality to polymer nanoparticles synthesized via emulsion polymerization.

Design of multi-functional linear polymers that capture and neutralize a toxic peptide: a comparison with cross-linked nanoparticles

In this paper, a library of multi-functional linear poly-N-isopropylacrylamide (pNIPAm) polymers having a range of molecular weights and functional groups were synthesized and their interaction with the hemolytic peptide, melittin, was examined.

Mimicking nature with synthetic macromolecules capable of recognition

Nature has, through billions of years of evolution, assembled a multitude of polymeric macromolecules capable of exquisite molecular recognition. This functionality arises from the precise control exerted over their biosynthesis that results in key residues being anchored in the appropriate positions to interact with target substrates. Developing 'wholly synthetic' macromolecular analogues that can mimic this behaviour presents a considerable challenge to chemists, who lack the 'biological machinery' used in nature to assemble polymers with such precision. In addressing this challenge, familiar chemical concepts, such as combinatorial methods and supramolecular interactions, have been adapted for application in the macromolecular arena. Working from a limited set of residues, synthetic macromolecules have been produced that display surprisingly high binding affinities towards target proteins, even possessing useful in vivo activities. These observations are all the more surprising when one considers the heterogeneity inherent within these synthetic macromolecular receptors, and provoke intriguing questions regarding our assumptions about the design of receptors.

A high-sensitivity lanthanide nanoparticle reporter for mass cytometry: tests on microgels as a proxy for cells

This paper addresses the question of whether one can use lanthanide nanoparticles (e.g., NaHoF4) to detect surface biomarkers expressed at low levels by mass cytometry. To avoid many of the complications of experiments on live or fixed cells, we carried out proof-of-concept experiments using aqueous microgels with a diameter on the order of 700 nm as a proxy for cells. These microgels were used to test whether nanoparticle (NP) reagents would allow the detection of as few as 100 proteins per "cell" in cell-by-cell assays. Streptavidin (SAv), which served as the model biomarker, was attached to the microgel in two different ways. Covalent coupling to surface carboxyls of the microgel led to large numbers (>10(4)) of proteins per microgel, whereas biotinylation of the microgel followed by exposure to SAv led to much smaller numbers of SAv per microgel. Using mass cytometry, we compared two biotin-containing reagents, which recognized and bound to the SAvs on the microgel. One was a metal chelating polymer (MCP), a biotin end-capped polyaspartamide containing 50 Tb(3+) ions per probe. The other was a biotinylated NaHoF4 NP containing 15 000 Ho atoms per probe. Nonspecific binding was determined with bovine serum albumin (BSA) conjugated microgels. The MCP was effective at detecting and quantifying SAvs on the microgel with covalently bound SAv (20 000 SAvs per microgel) but was unable to give a meaningful signal above that of the BSA-coated microgel for the samples with low levels of SAv. Here the NP reagent gave a signal 2 orders of magnitude stronger than that of the MCP and allowed detection of NPs ranging from 100 to 500 per microgel. Sensitivity was limited by the level of nonspecific adsorption. This proof of concept experiment demonstrates the enhanced sensitivity possible with NP reagents in cell-by-cell assays by mass cytometry.

Temperature-responsive microgel films as reversible carbon dioxide absorbents in wet environment

Hydrogel films composed of temperature-responsive microgel particles (GPs) containing amine groups work as stimuli-responsive carbon dioxide absorbent with a high capacity of approximately 1.7 mmol g(-1). Although the dried films did not show significant absorption, the reversible absorption capacity dramatically increased by adding a small amount of water (1 mL g(-1)). The absorption capacity was independent of the amount of added water beyond 1 mL g(-1), demonstrating that the GP films can readily be used under wet conditions. The amount of CO2 absorbed by the GP films was proportional to their thickness up to 200-300 μm (maximum capacity of about 2 L m(-2) . Furthermore, the films consisting of GPs showed faster and greater absorption and desorption of CO2 than that of monolithic hydrogel films. These results indicated the importance of a fast stimulus response rate of the films that are composed of GPs in order to achieve long-range and fast diffusion of bicarbonate ions. Our study revealed the potential of stimuli-responsive GP films as energy-efficient absorbents to sequester CO2 from high-humidity exhaust gases.

Epitope discovery for a synthetic polymer nanoparticle: a new strategy for developing a peptide tag

We describe a novel epitope discovery strategy for creating an affinity agent/peptide tag pair. A synthetic polymer nanoparticle (NP) was used as the “bait” to catch an affinity peptide tag. Biotinylated peptide tag candidates of varied sequence and length were attached to an avidin platform and screened for affinity against the polymer NP. NP affinity for the avidin/peptide tag complexes was used to provide insight into factors that contribute NP/tag binding. The identified epitope sequence with an optimized length (tMel-tag) was fused to two recombinant proteins. The tagged proteins exhibited higher NP affinity than proteins without tags. The results establish that a fusion peptide tag consisting of optimized 15 amino acid residues can provide strong affinity to an abiotic polymer NP. The affinity and selectivity of NP/tMel-tag interactions were exploited for protein purification in conjunction with immobilized metal ion/His6-tag interactions to prepare highly purified recombinant proteins. This strategy makes available inexpensive, abiotic synthetic polymers as affinity agents for peptide tags and provides alternatives for important applications where more costly affinity agents are used.

A selective artificial enzyme inhibitor based on nanoparticle-enzyme interactions and molecular imprinting

A novel and general strategy is developed to design selective artificial enzyme inhibitor based on nanoparticleenzyme inter actions and molecular imprinting. Due to the creation of specific binding cavities, the resulting artificial inhibitor has high inhibition efficiency for the target enzyme, and shows great target-selectivity over other enzymes of similar function and proteins of compaable mole cular weight.