Surface-initiated Reversible Addition-fragmentation Chain Transfer Polymerization Research Articles

Chain End-Functionalized Dense Polymer Brushes from an Inimer Coating by SI-RAFT.

Polymer brushes with controllable grafting density are grown on an inimer coating bearing Reversible Addition-Fragmentation Chain Transfer polymerization (RAFT) chain transfer agents (CTAs). The inimer coating is cross-linked on the substrate to provide an initiator layer that is stable during exposure to organic solvents at high temperatures. Surface-initiated RAFT is conducted to grow poly(2-vinylpyridine) (P2VP) brushes on the coating at grafting densities approaching the theoretical limits. This methodology allows facile end-group functionalization using an efficient thiol-ene click chemistry. Chain ends were functionalized with low surface energy groups to modulate the location of the untethered chain ends by thermal annealing. At lower grafting densities, the low surface energy groups segregate to the surface upon annealing. This effect is less pronounced at higher grafting densities. Detailed characterization of the brushes at varying grafting densities using X-ray photoelectron spectroscopy (XPS) is presented. In tandem with experiments, Monte Carlo simulations examine the effect of the chain-end group size and selectivity on the conformation of the polymer brush, providing numerical evidence of laterally non-uniform distributions of functional groups at different locations in the brush. Simulations further predict the existence of morphologies with an interlayer formed by spherical micelles rich in functional end groups, demonstrating the possibility of end-group functionalization for synthetic modulation of both brush conformation and chain-end location.

Hemin-catalyzed SI-RAFT polymerization for thrombin detection

Ultrasensitive protein detection has considerable potential for early diagnosis and screening of diseases. Here, based on Hemin-catalyzed surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization, this work developed an assay for ultrasensitive fluorescent biosensing of proteins and established a thrombin fluorescent sensor. First, the amino-modified aptamer 1 was immobilized on Fe3O4 magnetic beads, and then thrombin was added to form the aptamer 1-thrombin bioaffinity complex. Another thiol-modified aptamer 2 binds to bound thrombin to form a sandwich structure. Fluorescein O-methacrylate was used as the monomer, acetylacetone (ACAC) as the initiator, and Hemin as the catalyst. Through Hemin-catalyzed SI-RAFT polymerization, a large number of thrombin molecules are labeled with fluorescein O-methacrylate, resulting in severalfold amplification of the fluorescent signal. By detecting the fluorescent signal in thrombin from 1.0 fM to 0.1 nM, the proposed super sandwich strategy can detect thrombin at 0.98 fM, which is lower than the detection limit of most other methods.

Synthesis and kinetic analysis of poly(N-acryloylmorpholine) brushes via surface initiated RAFT polymerization.

Polymer brushes are promising many applications as smart materials and biocompatible surfaces. Surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the most effective techniques for synthesis of well-defined polymer brushes. Herein, a biocompatible, uniform and stable poly(N-acryloylmorpholine)-silicon hybrid system was achieved using surface-initiated RAFT polymerization. Evidence of a well-controlled surface-initiated RAFT polymerization was confirmed by a linear increase of number average molecular weight (Mn) with overall monomer conversions. Water contact angle, ellipsometry, X-ray photoelectron spectroscopy and atomic force microscopy verified the presence of poly(N-acryloylmorpholine) (poly(NAM)) on silicon wafers. The grafting density (σ) and the average distance between grafting points (D) were estimated to be 0.58 chains/nm2 and 1.5 nm, respectively. The ratio of D value to radius of gyration (Rg) value is smaller than 1 (D/2Rg < 1), which corresponds to the brush regime of all grafted poly(NAM) films.

Quaternized salicylaldehyde Schiff base side-chain polymer-grafted magnetic Fe3O4 nanoparticles for the removal and detection of Cu2+ ions in water

In this study, quaternized salicylaldehyde Schiff base side-chain polymer grafted magnetic Fe3O4 nanoparticles (Fe3O4@SiO2-PAP) were formed via the surface-initiated reversible addition-fragmentation chain-transfer polymerization of 2-(dimethylamino)ethyl methacrylate, subsequent quaternization with 5-chloromethylsalicylaldehyde and Schiff condensation with 2-aminophenol. The prepared nanohybrid was characterized by scanning and transmission electron microscopes, Fourier transform infrared spectroscopy, X-ray diffractometer, vibrating sample magnetometer and X-ray photoelectron spectroscopy. Fe3O4@SiO2-PAP was found to disperse well in water due to the strong hydrophilicity of the immobilized polymer. Cu2+ ion adsorption by the nanohybrid followed both pseudo-second-order kinetic and Langmuir isotherm models, and a maximum adsorption capacity of 59.98 mg/g was attained, with good repeatability. In addition, the nanohybrid exhibited significant and sensitive fluorescence quenching characteristics after capturing Cu2+ ions in water with good selectivity among the other studied cations. The fluorescence detection linear range was 0.1–2 mg/L, with the lowest detection limit measured as 0.125 μmol/L. Moreover, the nanohybrid exhibited high reusability for Cu2+ ion adsorption and sensing applications. Finally, the interaction of grafted Schiff base ligand with Cu2+ ions was analyzed using theoretical calculations. Consequently, the developed nanohybrid offers a new pathway for the removal and detection of Cu2+ ions in water.

Light-regulated growth of polymer chains from the surface of RAFT agent primed mesoporous silica nanoparticles

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the extensively explored and studied controlled radical polymerization methods. Recently, in comparison to the conventional RAFT polymerization process, visible light-regulated photo-induced electron/energy transfer (PET)-RAFT polymerization has picked up interest. With an ever-increasing desire for greener and more sustainable methods for synthesis, techniques such as PET-RAFT polymerization can be well adapted as an alternative approach for performing a variety of syntheses. Keeping this in mind we step forward with the synthesis of mesoporous silica nanoparticles containing an in-built RAFT agent using a stepwise co-condensation method. Herein, we report a facile synthesis of an organic-inorganic hybrid system in which surface-initiated RAFT polymerization was performed using several monomers (hydrophobic and hydrophilic) from RAFT agent primed mesoporous silica nanoparticles (RAFT-MSNs). The surface-initiated RAFT polymerization was carried through thermally initiated polymerization using AIBN and visible light-regulated PET-RAFT polymerization using Eosin Y as a photocatalyst. The light-regulated PET-RAFT polymerization was carried out smoothly in a shorter time frame as compared to the thermally initiated RAFT polymerization. A variety of characterization methods were used to confirm the successful grafting of polymeric chains from the surface of RAFT-MSNs. Hence, by appropriate polymer functionalization of mesoporous silica nanoparticles with stimuli-responsive polymers or polymers bearing functional groups, these organic-inorganic hybrids can be studied in a wide variety of applications such as drug delivery, catalysis, nanoconfinement, etc.

Cross-Linked Polymer Brushes Containing N-Halamine Groups for Antibacterial Surface Applications.

Microbial contamination is a significant issue in various areas, especially in the food industry. In this study, to overcome microbial contamination, cross-linked polymer brushes containing N-halamine were synthesized, characterized, and investigated for antibacterial properties. The cross-linked polymer brushes with different N-halamine ratios were synthesized by in-situ cross-linking methods with reversible addition−fragmentation chain transfer (RAFT) polymerization using a bifunctional cross-linker. The RAFT agent was immobilized on an amine-terminated silicon wafer surface and utilized in the surface-initiated RAFT polymerization of [N-(2-methyl-1-(4-methyl-2,5-dioxoimidazolidin-4-yl)propane-2-yl)acrylamide] (hydantoin acrylamide, HA), and N-(2-hydroxypropyl)methacrylamide) (HPMA) monomers. Measurement of film thickness, contact angle, and surface morphology of the resulting surfaces were used to confirm the structural characteristics of cross-linked polymer brushes. The chlorine content of the three different surfaces was determined to be approximately 8–31 × 1013 atoms/cm2. At the same time, it was also observed that the activation–deactivation efficiency decreased during the recharge–discharge cycles. However, it was determined that the prepared N-halamine-containing cross-linked polymer brushes inactivated approximately 96% of Escherichia coli and 91% of Staphylococcus aureus. In conclusion, in the framework of this study, high-performance brush gels were produced that can be used on antibacterial surfaces.

Comparison of Long-Term Stability of Initiating Monolayers in Surface-Initiated Controlled Radical Polymerizations.

The reproducibility of polymer brush synthesis via surface-initiated controlled radical polymerization is interrogated. Experiments compare the stability of initiating monolayers for surface-initiated (SI) reversible addition-fragmentation chain transfer polymerization (SI-RAFT) and SI atom transfer radical polymerization (SI-ATRP). Initiator-functionalized substrates are stored under various conditions and grafting densities of the resulting polymer brush films are determined via in situ ellipsometry. Decomposition of one of the examined SI-RAFT initiators results in limited reproducibility for polymer brush surface modification. In contrast, initiators for SI-ATRP show excellent stability and reproducibility. While both techniques bring inherent benefits and limitations, the described findings will help scientists choose the most efficient technique for their goals in chemical and topographical surface modification.

Antimicrobial and antifouling coating constructed using rosin acid-based quaternary ammonium salt and N-vinylpyrrolidone via RAFT polymerization

Biofilm formation of pathogenic bacteria on the surfaces of implantable biomedical devices limit their applications and effective usage. Current antimicrobial coatings for implantable biomedical devices have significant deficiencies including a lack of long-term activity and biocompatibility. Herein, a dual-functional coating (antifouling and antimicrobial) was constructed using a combination of N-vinylpyrrolidone (NVP) and maleopimaric acid quaternary ammonium cation containing a double bond functionality (GMA-MPA-N+) via surface-initiated reversible addition-fragmentation chain-transfer polymerization. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were used to confirm the successful construction of coating. GMA-MPA-N+ endowed the dual-functional coating with excellent broad-spectrum antimicrobial activities against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. The biofilm formation on this coating was inhibited for up to 21 days, and protein adsorption and platelet adhesion decreased significantly compared to those on the pristine substrate surfaces. The cytotoxicity assays demonstrated that the coating displayed excellent biocompatibility with the mammalian cells. Notably, the subcutaneous implantation of samples in the rat assay showed the excellent anti-infective property of the coating in vivo. Thus, the dual-functional antimicrobial coating exhibited long-term anti-biofilm properties as well as excellent biocompatibility, thereby providing insights into the design of implantable biomedical devices with antimicrobial properties.

Ultrasensitive detection of CYFRA 21-1 DNA via SI-RAFT based in-situ metallization signal amplification

Cytokeratin fragment antigen 21-1 (CYFRA 21-1) DNA is a significant biomarker with relation to non-small cell lung cancer. Here, we described an ultrasensitive electrochemical biosensor for detection of CYFRA 21-1 DNA (target DNA, tDNA) via surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization-based DNA metallization signal amplification strategy. Specifically, 5′terminal modified thiol peptide nucleic acid (PNA) probes are immobilized on the gold electrode surface (by Au-S selfassembly) for the identification of specific tDNA sequences. After hybridization, the 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid (CPAD) is tethered to the PNA/DNA duplexes by means of the recognized phosphate-Zr4+-carboxylate chemistry. Subsequently, in the situation of C3H4O as the monomer, SI-RAFT polymerization can bring numerous aldehyde groups sites for the subsequent silver mirror reaction. The acrolein-polymers act as reductant to reduce Ag+ into Ag0, and then the silver particles are deposited on the polymer skeleton, which significantly amplifies the electrochemical signal. Under optimal conditions, the designed sensor for tDNA detection show a wide linear range from 100 aM to 1 nM, and the detection limit is as low as 0.89 aM. Moreover, the proposed biosensor exhibits prominent applicability for analysis of tDNA in serum samples and high selectivity for different mismatched oligonucleotide fragments. Given the proposed biosensor without extra natural enzyme or bio-labels, this method has enormous potential in bioanalysis.

Electrochemical CYFRA21-1 DNA sensor with PCR-like sensitivity based on AgNPs and cascade polymerization.

In this work, a new method of CYFRA21-1 DNA (tDNA) detection based on electrochemically mediated atom transfer radical polymerization (e-ATRP) and surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT) cascade polymerization and AgNP deposition is proposed. Firstly, the peptide nucleic acid (PNA) probe is captured on a gold electrode by Au-S bonds for specific recognition of tDNA. After hybridization, PNA/DNA strands provide high-density phosphate groups for the subsequent ATRP initiator by the identified carboxylate-Zr4+-phosphate chemistry. Then, a large number of monomers are successfully grafted from the DNA through the e-ATRP reaction. After that, the chain transfer agent of SI-RAFT and methacrylic acid (MAA) are connected by recognized carboxylate-Zr4+-carboxylate chemistry. Subsequently, through SI-RAFT, the resulting polymer introduces numerous aldehyde groups, which could deposit many AgNPs on tDNA through silver mirror reaction, causing significant amplification of the electrochemical signal. Under optimal conditions, this designed method exhibits a low detection limit of 0.487aM. Moreover, the method enables us to detect DNA at the level of PCR-like and shows high selectivity and strong anti-interference ability in the presence of serum. It suggests that this new sensing signal amplification technology exhibits excellent potential of application in the early diagnosis of non-small cell lung cancer (NSCLC). Graphical abstract Electrochemical detection principle for CYFRA21-1 DNA based on e-ATRP and SI-RAFT signal amplification technology.

Antibacterial Bionic Surface on Intraocular Lenses to Prevent PCO and Endophthalmitis Through Surface-Initiated RAFT Polymerization

Antifouling and antibacterial intraocular lenses (IOLs) are required to lower the incidence of posterior capsule opacification (PCO) and postoperative endophthalmitis. Bionic zwitterionic polymer such as 2-methacryloyloxyethyl phosphorylcholine (MPC) shows excellent biocompatibility and strong ability to resist nonspecific proteins and bacterial adhesion. In this work, a novel bionic brushes coating containing MPC and N, N, N-trimethyl-2-((4-(2-(4-nonylphenoxy) ethoxy)-4-oxobut-2-enoyl) oxy) ethan-1-aminium chloride (TOEAC), a quaternary ammonium monomer, was prepared onto IOLs using reversible addition-fragmentation chain transfer (RAFT) polymerization method. The success of surface modification was investigated by spectroscopic ellipsometry, water contact angle, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The P(TOEAC-co-MPC) brushes functionalized IOL exhibited excellent antifouling efficiency against bovine serum albumin, Staphylococcus aureus, and human lens epithelial cells. In addition, the P(TOEAC-co-MPC) brushes showed excellent antibacterial and antibiofilm abilities and good biocompatibility. Anin vivo study confirmed that the P(TOEAC-co-MPC) brushes effectively prevented PCO and endophthalmitis. Consequently, the P(TOEAC-co-MPC) bionic brushes are promising for IOLs surface modification to resist postoperative complications for long-term implantation.

A dual signal amplification strategy combining thermally initiated SI-RAFT polymerization and DNA-templated silver nanoparticles for electrochemical determination of DNA.

A highly sensitive method is described for determination ofDNA. It is based on dual signal amplification, viz. (a)DNA-templated metal deposition, and (b) thermally initiated surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization. A peptide nucleic acid (PNA) with a terminal thiol group was grasped onto a gold electrode by self-assembly. The modified electrode serves as a probe to selectively capture target DNA (tDNA). In the next step, Zr(IV) ions are bound to the phosphate groups of the tDNA. A chain-transfer agent (CTA) for thermally initiated SI-RAFT polymerization, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD), was immobilized on tDNA by conjugation of the carboxy group to Zr(IV) ions. Subsequently, numerous monomers of glycosyloxyethyl methacrylate (GEMA) were connected to the CPAD by thermally initiated SI-RAFT polymerization with azobisisobutyronitrile (AIBN) serving as the free-radical thermal initiator. Afterwards, hydroxyl groups of the GEMA were oxidized to aldehyde groups reacting with sodium periodate, and silver nanoparticles were further introduced on the surface of electrode via "silver mirror reaction". This results in a large electrochemical signal amplification. Under optimized conditions, the electrochemical signal (best measured at a working potential of 0V vs. SCE (KCl; 3M)) increases linearly with the logarithm of tDNA concentration in the 10 to 106 aM concentration range. The detection limit is as low as 5.6 aM (~34 molecules in a 10μL sample). This is lower by factors between 2 and 1800 times than detection limits of most other ultra-sensitive electrochemical DNA assays. Graphical abstractSchematic representation of a dual signal amplification strategy combining thermally initiated surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT) and DNA-templated silver nanoparticles for electrochemical determination of DNA.

PH and thermal dual-responsive poly(NIPAM-co-GMA)-coated magnetic nanoparticles via surface-initiated RAFT polymerization for controlled drug delivery.

Herein, a novel type of multifunctional magnetic nanoparticles with dual thermal and pH-responsive behavior was fabricated as the carrier for delivery of doxorubicin (DOX). Fe3O4@SiO2 magnetic nanoparticles, were grafted with polymer brushes consisting of poly (NIPAM-co-GMA) (PNG) chains via surface initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization. The polymer brushes were then modified with hydrazine groups as DOX binding sites. The prepared multifunctional magnetic nanoparticles were characterized by FT-IR, 1H NMR, XPS, TGA, DLS, VSM, GPC, TEM, and XRD analysis. The in vitro drug release of the multifunctional magnetic nanoparticles was examined at 37 °C (above LCST) and 25 °C (below LCST) in different pH media and exhibited excellent pH- and thermo-sensitive behavior. The results show that the Fe3O4@SiO2@PNG-Hy fabricated via SI-RAFT polymerization is a viable candidate material for tumor treatment studies.

Construction of ordered multienzyme systems using multifunctional polymer brush-grafted magnetic nanoparticles as scaffolds

A block copolymer brush based on functional monomers (N-succinimidyl acrylate and N-adamantylacrylamide) successfully grew on the surface of Fe3O4@SiO2 nanoparticles by surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT). According to the multiple recognition mechanisms of this material, horseradish peroxidase (HRP) and β-cyclodextrin-modified glucose oxidase (GOx-CD) were constructed into a multienzyme system with an ordered distribution for the cascade reaction, where multifunctional polymer brush-grafted magnetic nanoparticles were used as the scaffolds. The catalytic activity of GOx-CD was enhanced compared with free GOx. In addition to being easily recycled, this multienzyme system exhibited an outstanding conditional stability compared with the free enzyme system. After being reused 8 times, the activity of multienzyme system retained 67.21% of the initial catalytic activity. This strategy provides a novel idea for reusable ordered enzyme immobilization.

Precise Self-Assembly and Controlled Catalysis of Thermoresponsive Core–Satellite Multicomponent Hybrid Nanoparticles

The construction of multicomponent hybrid nanomaterials with well-controlled architecture, especially bearing an ordered homogeneity and distribution of the subunits with tunable functions, is a key challenge in chemistry and material science. Herein, we reported a versatile and novel strategy to fabricate core-satellite multicomponent nanostructures with tunable interparticle distances and catalysis properties by the combination of surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization and self-assembly. The arrangement and interparticle distance of gold satellites could be precisely tuned by the SI-RAFT polymerization process and the feeding ratio of gold nanoparticles (AuNPs) and the core nanoparticle. It is worthto note that multilayered core-satellite nanostructures have been fabricated by a high-feeding ratio of AuNPs and magnetite NP (MNP)@SiO2-PNIPAm. Notably, the core-satellite MNP@SiO2-PNIPAm-Au nanoparticles exhibited excellent thermoresponsive behaviors with the change of temperature. Furthermore, the catalytic efficiency of MNP@SiO2-PNIPAm-Au nanoparticles via the reduction of 4-nitrophenol to 4-aminophenol can be well modulated by the nanoparticle size, temperature, and polymer feed ratio. This strategy for precise construction of core-satellite nanostructures would open a new pathway to construct multicomponent functionalnanostructures.

Surface-Initiated-Reversible-Addition-Fragmentation-Chain-Transfer Polymerization for Electrochemical DNA Biosensing.

Sensitive detection of biomolecules is integral for biomarker screening and early diagnosis. Herein, surface-initiated reversible-addition-fragmentation-chain-transfer (SI-RAFT) polymerization is exploited as a novel amplification strategy for highly sensitive electrochemical biosensing of DNA. Briefly, thiol-terminated peptide nucleic acid (PNA) probes are first self-assembled onto a gold electrode for the specific capture of target-DNA fragments; the carboxyl-group-containing dithiobenzoate 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD) is then tethered to the hybridized PNA-DNA heteroduplexes by means of the well-established carboxylate-Zr4+-phosphate chemistry and serves as the chain-transfer agent (CTAs) for subsequent SI-RAFT polymerization, which is thermally initiated in the presence of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044) as the free-radical initiator and ferrocenylmethyl methacrylate (FcMMA) as the monomer. Through SI-RAFT polymerization, one target-DNA fragment can be labeled by a large number of electroactive Fc tags, giving rise to significant amplification of the electrochemical signal. The SI-RAFT-polymerization-based strategy does not involve the use of natural enzymes or complex nanomaterials, offering the benefits of low cost and easy operation. Under optimal conditions, the electrochemical signal is linearly related to the logarithm of the concentration of target DNA over the range from 10 aM to 10 pM ( R2 = 0.997), with a detection limit down to 3.2 aM, which is much lower than those of other amplification-by-polymerization-based methods. By virtue of its easy operation, low cost, and high efficiency, the SI-RAFT-polymerization-based amplification strategy is believed to have great application prospects in the sensitive detection of biomolecules.

Preparation of Nano-TiO&lt;sub&gt;2&lt;/sub&gt; Modified Temperature-Responsive Chromatographic Materials for Enrichment of Phosphopeptides

Chromatographic stationary phases with specific capturing phosphoproteins is widely used in biological sample pretreatment. However, when captured protein is released, it is required to change the pH of the mobile phase or to use an eluent. Usually, the mobile phase or eluent are salt solutions with high concentration and extreme pH or toxic organic reagents. In this situation, these reagents will destroy the activity and structure of phosphorylated proteins. In addition, the mobile phase after switching the column takes longer time to restore the balance, reducing the experimental efficiency. In order to solve the these problems, we introduce temperature-reponsive materials into the chromatographic stationary phase to achieve the capture and release of phosphorylated proteins by changing the temperature only, in which we use water as the mobile phase. This approach overcomes the drawbacks of traditional methods, and makes the separation process safe and simple. Based on the surface initiated Reversible Addition Fragmentation Chain Transfer Polymerization (SI-RAFT) method, silica@pNIPAAm-nanoTiO2, a kind of Metal Oxide Affinity Chromatography, was synthesized by the rapid introduction of functional groups. The synthesis of silica@pNIPAAm-nanoTiO2was confirmed by infrared and X-ray photoelectron spectroscopy. The grafting rate and the lowest critical temperature were measured by TG and DSC. The results showed that the material had qualified temperature-sensitive properties. The grafting conformation and mobile phase pH of the material were optimized before testing the properties and found that when the material grafting ratio was 10% -15%, the graft density was 30%, and the mobile phase pH was 6, it had the best separate effect. Finally, the material successfully achieved the capture and release of adenosine triphosphate and casein phosphopeptides.

Crosslinked-Polymer Brushes with Switchable Capture and Release Capabilities.

Crosslinked-polymer brushes give rise to new opportunities for functionalizing, protecting, and structuring both organic and inorganic materials. In this study, pH- and temperature-switchable crosslinked-polymer brushes were easily prepared by combining the in situ method with reversible addition–fragmentation chain transfer (RAFT) polymerization. Initially, the RAFT agent was immobilized on an amine-terminated silicon wafer surface and utilized in the surface-initiated RAFT polymerization of 2-N-morpholinoethyl methacrylate (MEMA) as a monomer, and β-cyclodextrin methacrylate (CDMA) was used as a crosslinker on the silicon substrate. Measurements of film thickness, water contact angle, surface morphology, and structural characteristics of the resulting surfaces confirmed the poly(2-N-morpholinoethyl methacrylate) (PMEMA) brush-gels. Reversible capture and release measurements of methylene blue as a model molecule were also performed by UV–vis analysis. The switchable properties of the PMEMA brush-gels were maintained over five cycles. The results indicate that these PMEMA brush-gels with reversible capture and release properties might have widespread potential applications, including improved diagnostic tools as well as bioseparation.

Surface PEGylation and biological imaging of fluorescent Tb3+-doped layered double hydroxides through the photoinduced RAFT polymerization

Tb3+-doped layered double hydroxides (LDHs) exhibit excellent optical characteristics, uniform size and uniform morphologies when synthesized through a hydrothermal method. However, due to their lack of functional groups and poor dispersibility, applications of these fluorescent Tb3+-doped LDHs have been largely impeded especially in the biomedical fields. In this work, a novel strategy was developed for the surface modification of these fluorescent Tb3+-doped LDHs using photoinduced surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization with hydrophilic poly(ethylene glycol) methacrylate (PEGMA) as the monomer. The final products were obtained via the metal free surface-initiated RAFT polymerization with light irradiation. Successful preparation of these fluorescent LDHs polymer composites (LDH-PEG) was confirmed by a number of analytical technologies, such as transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. In addition, laser scanning confocal microscope was employed to examine the cell uptake behavior of the LDH-PEG composites and evaluate their potential for biomedical applications. We demonstrated that the hydrophilic monomer PEGMA could be facilely grafted on the surface of Tb3+-doped LDHs through metal free photoinduced surface-initiated RAFT polymerization. The resultant LDH-PEG composites displayed high water dispersibility, strong fluorescence, low cytotoxicity and a desirable cell uptake performance. These features of the LDH-PEG composites indicated their great potential for biomedical applications. More importantly, photoinduced RAFT polymerization has the advantages of a conventional controlled living radical polymerization, which could overcome drawbacks such as toxicity, the fluorescence quenching effects of metal catalysts and the complex synthesis of chain transfer agents. Therefore, this method could be an alternative tool for the surface modification of materials and fabrication of multifunctional fluorescent nanomaterials based polymer composites.

Preparation of zwitterionic polymers functionalized fluorescent mesoporous silica nanoparticles through photoinduced surface initiated RAFT polymerization in the presence of oxygen

Abstract Mesoporous silicon nanoparticles (MSNs) have gradually developed into the multi-functional platforms in biomedical fields for their properties of high specific surface areas, regular mesoporous structure, low toxicity, chemical inert and facile functionalization. MSNs based fluorescent nanoprobes have been extensively investigated previously and many effective methods have been devoted to simplify the fabrication process. In this work, the MSNs based fluorescent polymer composites were prepared by a facile and effective reversible addition−fragmentation chain-transfer (RAFT) polymerization with the assistance by visible light irradiation, which could conduct in the presence of oxygen without complicated deoxygenation steps. A series of characterization techniques were employed to determine the successful synthesis of our preconceived MSNs-co-poly(MPC–AcFl) composites. Besides, the bright green fluorescence was observed in live L929 cells through CLSM, and cell viability evaluation was revealed that these as prepared composites were nearly no damage to cells. Combined with all the above results, the as prepared MSNs-co-poly(MPC–AcFl) composites should promising fluorescent nanoprobes for biomedical applications. Owing to the good monomer adoptability, the photoinduced oxygen tolerance RAFT polymerization could also be expanded for surface modification and construction of multifunctional composites.