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.

Poly(L-lactic acid)/poly(ethylene oxide) based composite electrospun fibers loaded with magnesium-aluminum layered double hydroxide nanoparticles.

Two types of MgAl layered double hydroxide nanoparticles, MgAl LDH, at Mg:Al ratio of 2:1 and 3:1were prepared and used as inorganic fillers to improve the mechanical properties of poly(lactic acid)/poly(ethylene oxide) (PLA/PEO) electrospun composite fibers. Their detailed structural characterization was performed using X-ray diffraction (XRD) and transmission electron spectroscopy (TEM) techniques. Spectroscopic, thermal, mechanical, and morphological properties of the electrospun composite fibers, and cell proliferation on their surface, were examined. XRD and TEM analyses showed that the LDH nanoparticles were 50 nm in size and the Mg:Al ratio did not affect the average spacing between crystal layers. Fourier transform infrared (FTIR) and thermal analyses (TA) revealed the compatibility of the filler and the polymer matrix. The nanoparticles considerably improved the mechanical properties of the electrospun mats. The tensile strength and elongation at break values of the composite samples increased from 0.22 MPA to 0.40 MPa and 12.2 % to 45.66 %, respectively, resulting from the interaction between LDH and the polymer matrix. Scanning electron microscopy (SEM) and MTT analyses demonstrated that the electrospun composite fibers supported the SaOS-2 cells attachment and proliferation on the fiber surfaces, along with their suitable cytocompatibility.

Microwave-Assisted Synthesis of Stretchable and Transparent Poly(Ethyleneglycol-Sebacate) Elastomers with Autonomous Self-Healing and Capacitive Properties.

Introducing functional synthetic biomaterials to the literature became quite essential in biomedical technologies. For the growth of novel biomedical engineering approaches, progressive functional properties as well as the robustness of the manufacturing processes are essential. By using acid-induced epoxide ring-opening polymerizations through catalysts, a wide variety of biodegradable and functionalized biomaterials can be synthesized. Sebacic acid (SA) and poly(ethylene glycol) diglycidyl ether (PEGDGE) are amongst the FDA-approved biocompatible materials. In this study, we focused on the rapid synthesis of caffeine-catalyzed self-healable elastomer via a facile microwave-assisted synthesis route. The elastomer prepared can be used in various applications, including tactile sensors, wearable electronics, and soft robotics. SA and PEGDGE were catalyzed in the presence of caffeine under microwave irradiation followed by crosslinking in vacuo, yielding an elastomeric material. The chemical characterizations of the obtained elastomer were carried out. The resulting material is transparent, highly stretchable, and has capacitive and self-healing properties even at room temperature. The material developed can be easily applied for the aforementioned applications.

A novel route to prepare a multilayer system via the combination of interface-mediated catalytic chain transfer polymerization and thiol-ene click chemistry.

Herein, we have designed a novel multilayer system composed of poly(methyl methacrylate) [poly(MMA)] brush, biotin, streptavidin and protein-A on a silicon substrate to attach onanti-immunoglobulin G (anti-IgG). poly(MMA) brush with vinyl end-group was first synthesized by the interface-mediated catalytic chain transfer polymerization. The brush was then modified with cysteamine molecules to generate the polymer chains with amine end-group via a thiol-ene click chemistry. The amine end-groups of poly(MMA) chains were also modified with biotin units to ensure selective connection points for streptavidin molecules. Finally, a multilayer system on the silicon substrate was formed by using streptavidin and protein-A molecules, respectively. This multilayer system was employed to attach anti-IgG molecules in a highly oriented manner and provide anti-IgG molecular functional configuration on the multilayer. High reproducibility of the amount of anti-IgG adsorption and homogeneous anti-IgG adsorption layer on the silicon surface could be provided by this multilayer system. The multilayer system with protein A may be opened the door for designing an efficient immunoassay protein chip.

A new plasmonic device made of gold nanoparticles and temperature responsive polymer brush on a silicon substrate.

This paper reports a general stepwise route assembling interface-mediated RAFT polymerization of 2-methoxyethoxy ethyl methacrylate and conversion of dodecyl trithiocarbonate end groups to thiol groups for gold nanoparticle assemblies. We intended by this way a new plasmonic device made of gold nanoparticles (Au NPs) and temperature responsive [poly((2-methoxyethoxy)ethyl) methacrylate] [poly(MEO2-MA)] brush on a silicon substrate. This polymeric layer replies to temperature changing by conformational variation and is therefore able to change the distance between the Au NPs on the brush layer with 5,5-dithiobis(2-dinitrobenzoic acid) (DTNB). We show that an increment of the external temperature reversibly stimulates a significant increase of the DTNB SERS signal.

Fabrication of a SERS based aptasensor for detection of ricin B toxin.

In this report, we have developed a novel surface-enhanced Raman scattering (SERS) aptasensor for ricin B toxin recognition based on Ag nanoparticles labeled with 4,4'-bipyridyl (Bpy, Raman reporter) and ricin B aptamer. The hybrid silicon substrate was first prepared via surface-mediated RAFT polymerization of N-acryoyl-l-valine in the presence of 2-(butylthio-carbonothioylthio)-2-methylpropionic acid-modified silicon wafer as a RAFT agent and then biofunctionalized with ricin B aptamer. In this novel system, the ricin B aptamer functionalized silicon substrate was used as a scavenger for target ricin B molecules. After ricin B molecules were separated from the matrix, the sandwich assay procedure was applied using Ag nanoparticles labeled with Bpy and ricin B aptamer which act as SERS probes. Meanwhile, to enhance the SERS signal, silver deposition on the sandwich complex was also performed. The correlation between the ricin B concentration and SERS signal was found to be linear within the range of 1.0 fM to 50 pM. The limit of detection for the SERS aptasensor was determined as 0.32 fM. Furthermore, the SERS aptasensor was also evaluated for detecting ricin B in artificially contaminated orange juice, milk, blood and urine. Finally, this method has the potential to be used for the detection of other protein toxins in a complex matrix if a specific aptamer for that protein toxin can be designed.

Extremely sensitive sandwich assay of kanamycin using surface-enhanced Raman scattering of 2-mercaptobenzothiazole labeled gold@silver nanoparticles.

Herein, we report the development of extremely sensitive sandwich assay of kanamycin using a combination of anti-kanamycin functionalized hybrid magnetic (Fe3O4) nanoparticles (MNPs) and 2-mercaptobenzothiazole labeled Au-core@Ag-shell nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) substrate, respectively. The hybrid MNPs were first prepared via surface-mediated RAFT polymerization of N-acryloyl-L-glutamic acid in the presence of 2-(butylsulfanylcarbonylthiolsulfanyl) propionic acid-modified MNPs as a RAFT agent and then biofunctionalized with anti-kanamycin, which are both specific for kanamycin and can be collected via a simple magnet. After separating kanamycin from the sample matrix, they were sandwiched with the SERS substrate. According to our experimental results, the limit of detection (LOD) was determined to be 2pg mL(-1), this value being about 3-7 times more than sensitive than the LOD of previously reported results, which can be explained by the higher SERS activity of silver coated gold nanoparticles. The analysis time took less than 10min, including washing and optical detection steps. Furthermore, the sandwich assay was evaluated for investigating the kanamycin specificity on neomycin, gentamycin and streptomycin and detecting kanamycin in artificially contaminated milk.

Molecularly imprinted superparamagnetic iron oxide nanoparticles for rapid enrichment and separation of cholesterol.

A general protocol to prepare surface molecularly imprinted polymer core-shell superparamagnetic Fe3O4 nanoparticles (Fe3O4@MIP SPNPs), using a surface-mediated RAFT polymerization approach, is described. Cholesterol-imprinted Fe3O4@MIP SPNPs were obtained by oleic acid-stabilized Fe3O4 nanoparticles with a trithiocarbonate agent and subsequently by polymerizing thin molecularly imprinted layers composed of dimethylacrylamide and N,N'-methylene(bis)acrylamide units. The surface-mediated RAFT polymerization approach allows the synthesis of ∼20 nm hybrid composite particles with a ∼6 nm MIP shell, exhibiting superparamagnetic properties (saturation magnetization = 35.4 emu g(-1)) and specific molecular recognition of cholesterol. The Fe3O4@MIP SPNPs show the capability of rapid enriching and separating cholesterol (∼3.1% in weight) and are renewable and cyclically exploited due to their monodispersive and superparamagnetic features. Moreover, under optimal conditions, the Fe3O4@MIP SPNP recoveries of spiked human serum, milk, yolk and beef were 91.6%, 93.6%, 92.4% and 91.2%, respectively. Finally, the method of molecular imprinting on superparamagnetic particles can be extended to a wide range of applications for cell sorting, biomolecule enrichment and separation, and drug delivery.

A SERS-based sandwich assay for ultrasensitive and selective detection of Alzheimer's tau protein.

In this study, a simple and highly selective homogeneous sandwich assay was developed for fast and ultrasensitive detection of the tau protein using a combination of monoclonal antitau functionalized hybrid magnetic nanoparticles and polyclonal antitau immobilized gold nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) component, respectively. The magnetic silica particles were first coated with poly(2-hydroxyethyl methacrylate) via surface-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization and then biofunctionalized with monoclonal antitau, which are both specific for tau and can be collected via a simple magnet. After separating tau from the sample matrix, they were sandwiched with the SERS substrate composed of polyclonal antitau and 5,5-dithiobis(2-dinitrobenzoic acid) on gold nanoparticles. The correlation between the tau concentration and SERS signal was found to be linear within the range of 25 fM to 500 nM. The limit of detection for the sandwich assay is less than 25 fM. Moreover, the sandwich assay was also evaluated for investigating the tau specificity on bovine serum albumin and immunoglobulin G.

RAFT-mediated synthesis of cationic poly[(ar-vinylbenzyl)trimethylammonium chloride] brushes for quantitative DNA immobilization.

The synthesis of cationic poly[(ar-vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes was achieved via reversible addition-fragmentation chain transfer (RAFT) polymerization and used for quantitative DNA immobilization. Initially, silicon surfaces were modified with RAFT chain transfer agent by utilizing an amide reaction involving a silicon wafer modified with allylamine and 4-cyanopentanoic acid dithiobenzoate (CPAD). Poly(VBTAC) brushes were then prepared via RAFT-mediated polymerization from the surface immobilized CPAD. Various characterization techniques including ellipsometry, X-ray photoelectron spectroscopy, grazing angle-Fourier transform infrared spectroscopy, atomic force microscopy and contact-angle goniometer were used to characterize the immobilization of CPAD on the silicon wafer and the subsequent polymer formation. The addition of free CPAD was required for the formation of well-defined polymer brushes, which subsequently resulted in the presence of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Moreover, from atomic force microscopy and ellipsometry measurements, it was also determined that the density of immobilized DNA on the cationic poly(VBTAC) brushes can be quantitatively controlled by adjusting the solution concentration.

Surface chemical conversion of 3-glycidoxypropyldimethylethoxysilane on hydroxylated silicon surface: FT-IR, contact angle and ellipsometry analysis.

The chemical conversion of the top surface of 3-glycidoxypropyldimethylethoxysilane (GPDMES) on hyroxylated silicon surface has been studied as a function of reaction time. A multiple-step procedure was applied in this study. At first, GPDMES molecules were self-assembled on the hydroxylated silicon surface. The second step was the modification of epoxy groups with 3,3'-iminodipropionitrile and the last step was the amidoximation reaction of nitrile groups. Existence of the monolayers covalently attached to silicon surfaces were revealed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FT-IR). Modification, conversion and thickness of surfaces were followed by FT-IR and ellipsometry analysis.

Preparation of a novel polymer-modified si surface for DNA immobilization.

The design of a novel polymer-modified overlayer composed of PPAPE and GPMS on a silicon wafer for immobilization of DNA molecules is described. After hydroxylation of Si(100) surfaces, GPMS molecules were self-assembled onto these surfaces. PPAPE molecules were then covalently attached to the epoxy-terminated surfaces. The incubation time and concentration of PPAPE was found to effect both layer thickness and water CA. The type of organic solvent and the pH were found to change the nature of the PPAPE-modified surface for DNA immobilization. It is concluded that PPAPE-modified surfaces show advantages for DNA immobilization by electrostatic interactions between DNA molecules and positively charged free amino groups of the PPAPE-modified surfaces at the appropriate pH values.

Dependence of protein recognition of temperature-sensitive imprinted hydrogels on preparation temperature.

Temperature-sensitive imprinted and non-imprinted hydrogels composed of N-isopropylacrylamide (NIPA) and 2-acrylamido-2-methyl-propanosulfonic acid (AMPS) have been prepared by free-radical crosslinking copolymerization in aqueous solution at three different temperatures: 10 degrees C (below the lower critical solution temperature, LCST), 33 degrees C (at the LCST), and 40 degrees C (above the LCST). Myoglobin (Mb, MW 17 kDa) is used as the template biomolecule. The effects of the initial concentration and adsorption time over the Mb adsorption capacity of the hydrogels have been analyzed and found to be strongly dependent on the preparation temperature (T(prep)). The maximum Mb adsorption for the imprinted hydrogel prepared at 10 degrees C is 97.40 +/- 2.35 mg Mb x g(-1) dry gel in 0.32 mg x mL(-1) Mb solution at 22 degrees C. Moreover, batch adsorption equilibrium and selectivity studies have been performed using a reference molecule, hemoglobin (Hb, MW 65 kDa). The imprinted hydrogels have a 2.8-3.3 times higher adsorption capacity for Mb than the non-imprinted hydrogels prepared at the same T(prep)s, and also have a 1.8-2.7 times higher selectivity for the imprinted molecule.

Hemoglobin recognition of molecularly imprinted hydrogels prepared at different pHs.

The hemoglobin-imprinted hydrogels were fabricated by using N-t-butylacrylamide (TBA) acrylamide (AAm) and itaconic acid (IA) monomers and hemoglobin (Hb, MW 65 kDa) imprinted molecule in pH buffer solutions (pH 4.0, 6.8 and 8.0). The nonimprinted hydrogels were also prepared at same conditions without Hb imprinting molecule. The effects of pH, initial concentration and adsorption time over the Hb adsorption capacity of both imprinted and nonimprinted hydrogels were analyzed and found to be strongly dependent on the preparation pH (pH(prep)). The maximum Hb adsorption for the imprinted hydrogel prepared at pH 4.0 was found to be 12.4 mg protein g(-1) dry gel in pH 4.0 buffer solution. This behavior was attributed to the formation of more accessible adsorption sites (imprints) because of the non-covalent interactions between the template and network during formation in pH 4.0 buffer solution which is below of the isoelectric point (pI 6.8) of Hb. Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherm. Langmuir analysis showed that an equal class of adsorption was formed in the hydrogels. Moreover, batch adsorption equilibrium and selectivity studies were also performed by using two reference molecules as fibrinogen (Fb, MW 340 kDa) and myoglobin (Mb, MW 17 kDa). The imprinted hydrogels have 1.5-2.2 times higher adsorption capacity for Hb than the nonimprinted hydrogels prepared at the same pHs, and also have 2.0-3.1 times higher selectivity for the imprinted molecule.

pH/temperature - sensitive imprinted ionic poly(N-tert-butylacrylamide-co-acrylamide/maleic acid) hydrogels for bovine serum albumin.

In this study, we have prepared pH/temperature-sensitive imprinted ionic poly(N-tert-butylacrylamide-co-acrylamide/maleic acid) [P(TBA-co-AAm/MA)] hydrogels for bovine serum albumin (BSA) by using molecular imprinting method. BSA adsorption from aqueous BSA solutions was investigated with two types of hydrogel systems prepared by non-imprinted and imprinted methods. Hydrogels imprinted with BSA showed higher adsorption capacity and specificity for BSA than hydrogels prepared by the usual procedure. At all studied conditions, the highest BSA adsorption was observed in the hydrogel imprinted with 8.63 wt.-% BSA. In addition, the imprinted hydrogels exhibited both for good selectivity BSA and high adsorption rate depending on the number of BSA-sized cavities. Adsorption studies showed that other stimuli, such as pH, temperature and initial BSA concentration also influenced the BSA adsorption capacity of both non-imprinted and imprinted hydrogels.