Synthesis of CO₂/N₂‑Triggered Reversible Stability-Controllable Poly(2-(diethylamino)ethyl methacrylate)-<i>grafted</i>-AuNPs by Surface-Initiated Atom Transfer Radical Polymerization

CO₂/N₂-triggered stability-controllable gold nanoparticles (AuNPs) grafted with poly­(2-(diethylamino)­ethyl methacrylate) (PDEAEMA) layers (PDEAEMA-<i>g</i>-AuNPs) were synthesized by the surface-initiated atom transfer radical polymerization of DEAEMA with AuNPs bearing the bis­[2-(2-bromoisobutyryloxy)­undecyl] layer (<i>grafting from</i> method). Extension of the PDEAEMA chain length increased the stability of the PDEAEMA-<i>g</i>-AuNPs in CO₂-bubbled water because of the electrosteric repulsion of the protonated PDEAEMA layer. The chain-length-dependent stability of PDEAEMA-<i>g</i>-AuNPs was confirmed by DLS and UV–vis spectra by using the localized surface plasmon resonance property of the AuNPs, where the extinction wavelength was shifted toward shorter wavelength with increasing PDEAEMA chain length. The reversible stability change with the gas stimuli of CO₂/N₂ was also successfully demonstrated. Finally, the transfer across the immiscible interface between water and organic solvent was successfully demonstrated by N₂-triggered insolubilization of PDEAEMA layer on AuNPs in the aqueous phase, leading to the successful collection of AuNPs using organic solvent from the aqueous phase. Our “<i>grafting from</i>” method of reversible stability-controllable AuNPs can be applied to develop advanced materials such as reusable optical AuNP-based nanosensors because the molecular recognition layer can be constructed by two-step polymerization

Localized Surface Plasmon Resonance Nanosensing of C‑Reactive Protein with Poly(2-methacryloyloxyethyl phosphorylcholine)-Grafted Gold Nanoparticles Prepared by Surface-Initiated Atom Transfer Radical Polymerization

Highly sensitive and selective protein nanosensing based on localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) on which polymerized specific ligands were grafted as an artificial protein recognition layer for the target protein were demonstrated. As a model, optical nanosensing for C-reactive protein (CRP), a known biomarker for chronic inflammation that predicts the risk of arteriosclerosis or heart attacks, was achieved by measuring the shift of LSPR spectra derived from the change of permittivity of poly­(2-methacryloyloxyethyl phosphorylcholine)-grafted AuNPs (PMPC-g-AuNPs) upon interacting with CRP, in which the PMPC-g-AuNPs layer were grafted on AuNPs by surface-initiated atom transfer radical polymerization (ATRP). This nanosensing system was effective even for detecting CRP concentrations in a human serum solution diluted to 1% (w/w), at which point a limit of detection was ∼50 ng/mL and nonspecific adsorption of other proteins was negligible. The nanosensing system using specific ligand-grafted AuNPs has several strengths, such as low preparation cost, avoiding the need for expensive instruments, no necessary complex pretreatments, and high stability, because it does not contain biobased molecules. We believe this novel synthetic route for protein nanosensors, composed of AuNPs and a polymerized specific ligand utilizing surface-initiated controlled/living radical polymerization, will provide a foundation for the design and synthesis of nanosensors targeting various other biomarker proteins, paving the way for future advances in the field of biosensing

Post-Cross-Linked Molecular Imprinting with Functional Polymers as a Universal Building Block for Artificial Polymeric Receptors

A post-cross-linked molecular imprinting (PC-MI) technique utilizing a functional polymer (FP) with interacting and post-cross-linking groups was developed to create molecularly imprinted polymeric (MIP) receptors. Molecular recognition cavities were formed in the cross-linked polymer matrix by a posteriori cross-linking of the FP with template molecules using photoirradiation. These cavities could be easily tuned to recognize the target molecules by changing the template using a common FP as a universal building block. Thus, precise chiral recognition cavities were successfully created using PC-MI and optimizing the molar ratio of the functional groups between the FP and the target molecules, which suppressed the nonspecific binding of the off-target molecules. Furthermore, the morphology of the MIPs could be changed from bulk to particles. This study provides a facile and efficient synthetic route for MIPs with tailor-made properties. Thus, PC-MI can be utilized to create molecular recognition elements for purification, hygiene control, disease diagnosis, and sensors

Experimental Evidence and Beneficial Use of Confined Space Effect in Nitroxide-Mediated Radical Microemulsion Polymerization (Microemulsion NMP) of <i>n</i>‑Butyl Acrylate

The confined space effect, which was found by the authors, in nitroxide-mediated radical polymerization (NMP) in a microemulsion system (microemulsion NMP) of <i>n</i>-butyl acrylate (BA) was investigated, where the diameter of micelles (monomer droplets) was 5–10 nm and that of poly­(BA) (PBA) particles at the completion of the polymerization was ∼60 nm. To clarify the importance of diameter of monomer droplets (<i>d</i>_m) in the initial stage of the microemulsion NMP, NMP in a miniemulsion system (miniemulsion NMP) (<i>d</i>_m: ∼60 nm) was carried out as a comparative experiment. The miniemulsion NMP proceeded without molecular weight distribution (MWD) control; on the other hand, in the microemulsion NMP the MWD shifted to higher molecular weight with increasing conversion. The livingnesses of PBAs obtained in the initial stages of the miniemulsion and microemulsion NMPs, which were determined by chain extension test, were 0.01% and 64%, respectively. From these results, it is concluded that the confined space effect in the initial stage of the microemulsion NMP effectively operated and resulted in PBA with predetermined molecular weight and good control of MWD even if the diameter of polymerizing particles increased with conversion

pH-Responsive Capsules Fabricated by Interfacial Photo-Cross-Linking Utilizing the Photoreactivity and pH-Responsiveness of Thymine

pH-responsive capsules are useful materials for various applications, such as drug delivery systems and nano-/microreactors. Herein, we developed pH-responsive capsules through interfacial photo-cross-linking with thymine-functionalized parent polymer particles, where thymine functioned as a photoreactive and pH-responsive group. A sufficient hydrophilicity of the capsule polymers was necessary to achieve the controlled release of encapsulated molecules by utilizing the pH-responsiveness of thymine groups. Based on a series of solubility tests for various polymers derived from 4-vinylbenzyl thymine (VBT), styrene (St), 2-vinylpyridine (2VP), and 4-vinylpyridine (4VP), P(St-2VP-VBT) and P(St-VBT) were suitable for preparing capsule particles by interfacial photo-cross-linking. Release tests revealed that P(St-2VP-VBT), but not P(St-VBT), could release its cargo under basic conditions, where thymine transforms from the nonionic to anionic state. This behavior indicates that the increased hydrophilicity of the polymer shell layer obtained by copolymerization with 2VP is critical for cargo release induced by thymine deprotonation. Furthermore, P(St-2VP-VBT) also responded to acidic pH owing to protonation of the pyridine groups. Finally, we successfully created acidic and alkaline dual pH-responsive capsules via interfacial photo-cross-linking using P(St-2VP-VBT) particles

Synthesis of Monodispersed Submillimeter-Sized Molecularly Imprinted Particles Selective for Human Serum Albumin Using Inverse Suspension Polymerization in Water-in-Oil Emulsion Prepared Using Microfluidics

We synthesized monodispersed submillimeter-sized (100 μm–1 mm) microgels by inverse suspension polymerization of water-soluble monomer species with a photoinitiator in water-in-oil (W/O) droplets formed by the microchannel. After fundamental investigations of the selection of suitable surfactants, surfactant concentration, and flow rate, we successfully prepared monodispersed submillimeter-sized W/O droplets. Because radical polymerization based on thermal initiation was not appropriated based on colloidal stability, we selected photoinitiation, which resulted in the successful synthesis of monodispersed submillimeter-sized microgels with sufficient colloidal stability. The microgel size was controlled by the flow rate of the oil phase, which maintained the monodispersity. In addition, the submillimeter-sized microgels exhibit high affinity and selective binding toward HSA utilizing molecular imprinting. We believe the monodispersed submillimeter-sized molecularly imprinted microgels can be used as affinity column packing materials without any biomolecules, such as antibodies, for sample pretreatment to remove unwanted proteins without a pump system

Dispersion Reversible Chain Transfer Catalyzed Polymerization (Dispersion RTCP) of Methyl Methacrylate in Supercritical Carbon Dioxide: Pushing the Limit of Selectivity of Chain Transfer Agent

We demonstrated a dispersion reversible chain transfer catalyzed polymerization (dispersion RTCP) of methyl methacrylate (MMA) with 1-phenylethyl iodide (PE-I) as chain transfer agent and GeI₄ as catalyst in supercritical carbon dioxide (scCO₂), where the PE-I was known as noneffective chain transfer agent for polymerization of MMA in RTCP. The dispersion RTCP in scCO₂ proceeded with control/livingness. On the other hand, in bulk system (bulk RTCP) and in dispersion iodine transfer polymerization (dispersion ITP) in scCO₂ under the same conditions except for GeI₄, no livingness was maintained. From these results, it was assumed that the reason for the living character in the dispersion RTCP in scCO₂ is based on an accelerated reversible chain transfer reaction in scCO₂. Based on the insight, when the dispersion RTCP of MMA was carried out at higher scCO₂ pressure, poly­(MMA) (PMMA) having a narrower molecular weight distribution was obtained because of the higher degree of PMMA plasticization by scCO₂. Moreover, we advanced the idea to synthesize polystyrene (PS)-<i>b</i>-PMMA, of which synthesis was difficult in homogeneous systems, by seeded dispersion RTCP of MMA with PS-I as macro-chain-transfer agent and GeI₄ as catalyst in scCO₂

Amphiphilic Polymerizable Porphyrins Conjugated to a Polyglycerol Dendron Moiety as Functional Surfactants for Multifunctional Polymer Particles

An amphiphilic polyglycerol dendron (PGD) conjugated porphyrin (PGP) bearing a polymerizable group was successfully synthesized. The PGP was used as an effective surfactant in emulsion and microsuspension polymerization systems to prepare styrene and methacrylate polymer particles, and the use of PGP provided the simple polymer particles with fluorescence derived from the metalloporphyrin and high colloidal stability due to the PGD. Furthermore, based on confocal laser scanning microscopy, we observed that the particles spontaneously formed a core–shell morphology with the PGP localized in the shell region during the polymerization and demonstrated drug loading in the shell region using rhodamine B as a model drug. The results indicate that the use of the functional surfactant PGP led to the preparation of multifunctional polymer particles from simple monomer species, and the resulting particles possessed high colloidal stability, fluorescence, and drug loading capability

Supplementary material from Oriented, Molecularly Imprinted Cavities with Dual Binding Sites for Highly Sensitive and Selective Recognition of Cortisol

Materials, Apparatus, Organic synthesis, Preparation and characterization of the MIPs and the reference polymers, Possible sizes of β-CD complexes with FITC-BPA and TM1, Binding behaviors of FITC-BPA to MIPs, and Binding isotherms of cortisol in fluorescence-based competitive binding assay using the MIPs and the reference polymers for the estimation of apparent binding constants

Molecularly Imprinted Polymer Arrays as Synthetic Protein Chips Prepared by Transcription-type Molecular Imprinting by Use of Protein-Immobilized Dots as Stamps

Molecularly imprinted polymer (MIP) arrays were demonstrated for the recognition of proteins. They were prepared via transcription-type molecular imprinting where patterned dots composed of biotinylated nanoparticles were first immobilized on a glass substrate followed by the immobilization of versatile biotinylated proteins via avidin–biotin interactions, yielding a multiple protein-immobilized stamp as a mold that could be transcribed. MIPs were prepared between the stamp and a methacrylated glass substrate, and after the stamp was peeled off, MIP dots were able to be prepared on the methacrylated glass substrate according to the positions of the immobilized proteins on the stamp. We confirmed that the prepared MIP array showed the expected selective binding toward the corresponding template proteins by conducting competitive binding assays using the fluorescently labeled proteins as corresponding competitors. The binding behaviors were consistent with those obtained by a surface plasmon resonance sensing system. We believe that the proposed platform involving the easily handled nanoparticle-based protein stamps for the preparation of MIP arrays can provide a new type of pattern recognition-based protein chip, which can be adopted as a substitute for the use of conventional protein arrays in various research and industrial fields in the life sciences