Preparation of diclofenac-imprinted polymer beads for selective molecular separation in water.

Molecular imprinting technique is an attractive strategy to prepare materials for target recognition and rapid separation. In this work, a new type of diclofenac (DFC)-imprinted polymer beads was synthesized by Pickering emulsion polymerization using 2-(dimethylamino)ethyl methacrylate as the functional monomer. The selectivity and capacity of the molecularly imprinted polymers (MIPs) were investigated in aqueous solution. Equilibrium binding results show that the MIPs have a high selectivity to bind DFC in a wide range of pH values. Moreover, in liquid chromatography experiment, the imprinted polymer beads were packed into column to investigate the binding selectivity under nonequilibrium conditions. The retention time of DFC on the MIP column is significantly longer than its structural analogues. Also, retention of DFC on the MIP column was significantly longer than on the nonimprinted polymer column under aqueous condition. As the new MIP beads can be used to achieve direct separation of DFC from water, the synthetic method and the affinity beads developed in this work opened new possibilities for removing toxic chemicals from environmental and drinking water.

A modular approach for assembling turn-on fluorescence sensors using molecularly imprinted nanoparticles.

Combining straightforward molecular imprinting with orthogonal click chemistry and accessible fluorescent dyes, a modular approach has been developed to assemble turn-on optical sensors based on fluorescence resonance energy transfer in molecularly imprinted nanoparticles.

Nanoparticle-enhanced fluorescence emission for non-separation assays of carbohydrates using a boronic acid-alizarin complex.

Addition of crosslinked polymer nanoparticles into a solution of a 3-nitrophenylboronic acid-alizarin complex leads to significant enhancement of fluorescence emission. Using the nanoparticle-enhanced boronic acid-alizarin system has improved greatly the sensitivity and extended the dynamic range of separation-free fluorescence assays for carbohydrates.

Covalent immobilization of molecularly imprinted polymer nanoparticles on a gold surface using carbodiimide coupling for chemical sensing.

One challenging task in building (bio)chemical sensors is the efficient and stable immobilization of receptor on a suitable transducer. Herein, we report a method for covalent immobilization of molecularly imprinted core-shell nanoparticles for construction of robust chemical sensors. The imprinted nanoparticles with a core-shell structure have selective molecular binding sites in the core and multiple amino groups in the shell. The model Au transducer surface is first functionalized with a self-assembled monolayer of 11-mercaptoundecanoic acid. The 11-mercaptoundecanoic acid is activated by treatment with carbodiimide/N-hydroxysuccinimide and then reacted with the core-shell nanoparticles to form amide bonds. We have characterized the process by studying the treated surfaces after each preparation step using atomic force microscopy, scanning electron microscopy, fluorescence microscopy, contact angle measurements and X-ray photoelectron spectroscopy. The microscopy results show the successful immobilization of the imprinted nanoparticles on the surface. The photoelectron spectroscopy results further confirm the success of each functionalization step. Further, the amino groups on the MIP surface were activated by electrostatically adsorbing negatively charged Au colloids. The functionalized surface was shown to be active for surface enhanced Raman scattering detection of propranolol. The particle immobilization and surface enhanced Raman scattering approach described here has a general applicability for constructing chemical sensors in different formats.

Nanohybrid polymer brushes on silica for bioseparation.

Boronic acid based affinity materials are of great importance for effective enrichment of biomolecules containing a cis-diol structure, for example glycoproteins. In this work, we developed a new pH- and temperature-responsive boronate affinity material for effective separation of glycoproteins. A nanohybrid material composed of silica cores and flexible polymer brushes, denoted as Si@poly(NIPAm-co-GMA)@APBA, was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) in combination with Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The size, morphology and composition of the obtained nanohybrid were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis and thermogravimetric analysis (TGA). The density of polymer brushes on the surface of silica nanoparticles was determined to be 0.7 molecules per nm2. The maximum binding capacities of the nanohybrid Si@poly(NIPAm-co-GMA)@APBA for ovalbumin (OVA) and horseradish peroxidase (HRP) were determined to be 87.6 mg g-1 and 22.8 mg g-1, respectively. Glycoprotein binding on the nanohybrid could be controlled by varying the pH of the binding buffer. By increasing the temperature from 20 °C to 35 °C, glycoprotein binding onto the nanohybrid was decreased. This new pH- and temperature-responsive nanohybrid will be useful for a number of biotechnological and biomedical applications, for example, for protein separation and drug delivery.

Photoconjugation of Molecularly Imprinted Polymer Nanoparticles for Surface-Enhanced Raman Detection of Propranolol.

We report a simple and versatile method to covalently immobilize molecularly imprinted polymer (MIP) nanoparticles on a Raman active substrate (Klarite) using a disulfide-derivatized perfluorophenylazide (PFPA-disulfide). Gold-coated Klarite was functionalized with PFPA-disulfide via a gold-sulfur bond. Upon light radiation, the available azido groups were converted to highly reactive singlet perfluorophenyl nitrene that undergoes a CH insertion reaction and form covalent bonds with the MIP nanoparticles. The resulting surfaces were characterized using scanning electron microscopy and surface enhanced Raman spectroscopy to study the morphology and template affinity of the surfaces, respectively. The Raman measurements clearly show a dose-responsive signal when propranolol binds to the MIP surface. Because the MIP particles were covalently attached to the Raman active substrate, the sensing surface was stable and could be reused after regeneration in acetic acid solution. The MIP-based Raman sensor was used successfully to detect propranolol in urine samples (7.7 × 10(-4) M). Our results show that the high selectivity of MIPs and the fingerprint Raman identification can be integrated into a compact sensing unit using high-efficiency photoconjugation. Thus, the method proposed is reliable, efficient and fast for fabricating label-free chemical sensors.

Implementation of molecularly imprinted polymer beads for surface enhanced Raman detection.

Molecularly imprinted polymers (MIPs) have a predesigned molecular recognition capability that can be used to build robust chemical sensors. MIP-based chemical sensors allow label-free detection and are particularly interesting due to their simple operation. In this work we report the use of thiol-terminated MIP microspheres to construct surfaces for detection of a model organic analyte, nicotine, by surface enhanced Raman scattering (SERS). The nicotine-imprinted microspheres are synthesized by RAFT precipitation polymerization and converted into thiol-terminated microspheres through aminolysis. The thiol groups on the MIP surface allow the microspheres to be immobilized on a gold-coated substrate. Three different strategies are investigated to achieve surface enhanced Raman scattering in the vicinity of the imprinted sites: (1) direct sputtering of gold nanoparticles, (2) immobilization of gold colloids through the MIP's thiol groups, and (3) trapping of the MIP microspheres in a patterned SERS substrate. For the first time we show that large MIP microspheres can be turned into selective SERS surfaces through the three different approaches of assembly. The MIP-based sensing surfaces are used to detect nicotine to demonstrate the proof of concept. As synthesis and surface functionalization of MIP microspheres and nanoparticles are well established, the methods reported in this work are handy and efficient for constructing label-free chemical sensors, in particular for those based on SERS detection.

Covalent immobilization of molecularly imprinted polymer nanoparticles using an epoxy silane.

Molecularly imprinted polymers (MIPs) can be used as antibody mimics to develop robust chemical sensors. One challenging problem in using MIPs for sensor development is the lack of reliable conjugation chemistry that allows MIPs to be fixed on transducer surface. In this work, we study the use of epoxy silane to immobilize MIP nanoparticles on model transducer surfaces without impairing the function of the immobilized nanoparticles. The MIP nanoparticles with a core-shell structure have selective molecular binding sites in the core and multiple amino groups in the shell. The model transducer surface is functionalized with a self-assembled monolayer of epoxy silane, which reacts with the core-shell MIP particles to enable straightforward immobilization. The whole process is characterized by studying the treated surfaces after each preparation step using atomic force microscopy, scanning electron microscopy, fluorescence microscopy, contact angle measurements and X-ray photoelectron spectroscopy. The microscopy results show that the MIP particles are immobilized uniformly on surface. The photoelectron spectroscopy results further confirm the action of each functionalization step. The molecular selectivity of the MIP-functionalized surface is verified by radioligand binding analysis. The particle immobilization approach described here has a general applicability for constructing selective chemical sensors in different formats.

Preparation of protein imprinted polymer beads by Pickering emulsion polymerization.

We present a new method for preparation of protein-specific polymer beads based on surface molecular imprinting in Pickering emulsion. In the first step, adult human hemoglobin (Hb) was adsorbed on silica nanoparticles. The protein-coated silica particles were then used to stabilize an oil-in-water emulsion (Pickering emulsion) composed of cross-linking monomer in the oil phase. After free radical polymerization of the oil phase, the protein-silica particles were removed to leave Hb-imprinted sites on the polymer surface. The protein-imprinted polymer microspheres were characterized by scanning electron microscopy and their selectivity was investigated by protein binding analysis. The new synthetic method based on Pickering emulsion polymerization produced easily accessible Hb binding sites on the surface of spherical polymer particles, which are useful for protein separation, purification and analysis.

Bacterial imprinting at Pickering emulsion interfaces.

The tendency of bacteria to assemble at oil-water interfaces can be utilized to create microbial recognition sites on the surface of polymer beads. In this work, two different groups of bacteria were first treated with acryloyl-functionalized chitosan and then used to stabilize an oil-in-water emulsion composed of cross-linking monomers that were dispersed in aqueous buffer. Polymerization of the oil phase followed by removal of the bacterial template resulted in well-defined polymer beads bearing bacterial imprints. Chemical passivation of chitosan and cell displacement assays indicate that the bacterial recognition on the polymer beads was dependent on the nature of the pre-polymer and the target bacteria. The functional materials for microbial recognition show great potential for constructing cell-cell communication networks, biosensors, and new platforms for testing antibiotic drugs.

Breath figure patterns made easy.

In this work, a simple breath figure method was proposed to directly fabricate large-area and ordered honeycomb structures on commercial PMMA substrates or PS Petri dishes without the use of an external polymer solution. The obtained honeycomb structure is indeed part of the substrate, providing the honeycomb layer with enough mechanical stability. The breath figure method in this work for the synthesis of honeycomb structure is extremely simple with scale-up capability to large-area production, which offers new insights into surface engineering with great potential in commercial technologies. For example, using the honeycomb-patterned Petri dishes prepared via this method, cells can be easily separated into divided aggregation, which favors understanding of naturally occurring networks in higher organisms and cell-cell and cell-matrix interactions, and the therapeutic control of genetic circuits.

Fluorescent boronic acid polymer grafted on silica particles for affinity separation of saccharides.

Boronic acid affinity gels are important for effective separation of biological active cis-diols, and are finding applications both in biotech industry and in biomedical research areas. To increase the efficacy of boronate affinity separation, it is interesting to introduce repeating boronic acid units in flexible polymer chains attached on solid materials. In this work, we synthesize polymer brushes containing boronic acid repeating units on silica gels using surface-initiated atom transfer radical polymerization (ATRP). A fluorescent boronic acid monomer is first prepared from an azide-tagged fluorogenic boronic acid and an alkyne-containing acrylate by Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction (the CuAAC click chemistry). The boronic acid monomer is then grafted to the surface of silica gel modified with an ATRP initiator. The obtained composite material contains boronic acid polymer brushes on surface and shows favorable saccharide binding capability under physiological pH conditions, and displays interesting fluorescence intensity change upon binding fructose and glucose. In addition to saccharide binding, the flexible polymer brushes on silica also enable fast separation of a model glycoprotein based on selective boronate affinity interaction. The synthetic approach and the composite functional material developed in this work should open new opportunities for high efficiency detection, separation, and analysis of not only simple saccharides, but also glycopeptides and large glycoproteins.