Polyanion cluster patterning on polymer surface through microemulsion approach for selective adsorption of proteins

https://doi.org/10.1016/j.jcis.2013.08.004Get rights and content

Highlights

  • Quick preparation of patterned film is developed by reverse microemulsion method.

  • Additives can selectively anchor into patterned cavities while pattern formation.

  • The inorganic cluster-modified polymer film exhibits selective protein adsorption.

  • The protein-modified polymer film is applicable for further patterned immunoassay.

Abstract

A facile method to fabricate honeycomb-patterned polymer films bearing cavities that are locally decorated with inorganic component is developed in this study. By mixing poly(methyl methacrylate) dichloromethane solution containing P123 with polyoxometalate (POM) aqueous solution through shaking, a reversed hybrid microemulsion is obtained. The evaporation of solvent in the microemulsion on solid surface yields an ordered porous film accompanied by the accumulation of P123 and POMs on the inner surface of the cavities. The formation of patterned structure is proved to be independent from the type of POMs, but the size of the cavities can be adjusted to some extent by changing the concentration of surfactant and polymer, and the volume ratio of water and dichloromethane in the solution used for casting. The locally anchored POMs can be readily applied for the selective recognition of proteins. BSA and hemoglobin patterns are then fabricated through their electrostatic interactions with POMs. At lower pH, POM pattern could prior recognize hemoglobin from its mixed solution of BSA, generating a characteristic pattern. The reported work creates an efficient way of patterning organically incompatible components, such as water-soluble molecules and nanoparticles, on porous polymer films for the fabrication of multi-functional hybrid surface structures.

Introduction

Surface-ordered porous polymer materials have attracted extensive attention over recent years due to their potential applications in the fields such as catalysis [1], photonics [2], [3], optoelectronic devices [4], and membrane science [5]. In addition to various physical approaches, a series of self-assembled methods including colloidal crystals [6], emulsions [7], microphase-separation of block copolymer, have been developed [8], [9]. Among them, the breath figure method that uses condensed water droplets derived from humid flow and rapid cooling induced by solvent evaporation as the template has been widely investigated owing to its fast and easy operation features [10], [11], [12]. A variety of materials such as titanium dioxide microparticles [13], proteins [14], carbon nanotubes [15], polystyrene microspheres [16], silica particles [17], and graphenes [18], [19], have been incorporated into porous matrices to perform the functional properties at localized position. Other than the preparation of patterned surface on polymer films, the functionalization of the formed cavities is also of special significance for the formation of applicable porous materials. However, one of the intrinsic disadvantages of breath figure method is that it is hard to carry out the chemical modification on the patterned cavities during the pattern formation. It is often unavoidable to induce multi-step procedures and non-selective modifications in treatments [14], [20]. Due to the merit in dispersing incompatible components in one solution, some attempts based on emulsion templates were reported in which water droplets were directly introduced into organic phase via a suitable emulsification procedure [21], [22], [23], [24]. But, so far, the porous films prepared through the emulsion approach have not yet directed to a satisfactorily ordered porous structure with even pore size in a larger scale, though some improvements, such as adjusting humidity, water content [25], [26], solvent [27], adding tetrahydrofuran as surfactant [28], and so forth, have been adopted. In this context, developing a new strategy that the chemical modification of cavity, especially the modifier insoluble in organic solvents, can be applied into the inner of cavities in one step, is of great interest in facile chemical and biologic detection purposes.

Polyoxometalates (POMs) as a kind of nanosized inorganic clusters possess diverse functional properties in catalysis [29], optics [30], semiconductivity [31], magnetics [32], energy storage [33] and other materials characteristics. By encapsulating POMs with dimethyl dioctadecylammonium, the formed POM complexes have been applied to construct honeycomb-patterned structures via breath figure [34], and it has been found out that the corresponding results could be extended to other type of POM complexes [35] or mixture containing POM complexes and polymers [36]. The ordered honeycomb films are also fabricated by mixing POMs with surfactants via solvent-evaporation on air/water interface [37]. However, among the aforementioned studies, POMs are simply used as spreading materials throughout the patterned films, and thus, it is difficult to anchor the POMs onto the patterned cavities to perform their functions which are important for fabricating POM-based film materials. More importantly, bare POMs, as a kind of typical inorganic polyanion clusters, are insoluble in weak polar organic solvents, limiting their applications on patterned surface through simple breath figure. Hence, it is necessary to create a different route for self-assemblies of general water-soluble inorganic particles.

Since the key procedure in breath figure method is the introduction of water droplet template, our motivation is that the modification to the patterned surface can be realized through the pre-addition of inorganic modifiers into water droplets. Moreover, the water droplets can be mixed with organic solvents through tuning the size of water droplets. Herein, we developed a new method of patterning POMs on porous polymer films through the following approach: An organic solution of polymer and an aqueous solution of POMs were mixed and emulsified, and then cast onto hydrophilic substrates. Consequently, the polymer constructs the frameworks of films and the POMs accumulate in the patterned sites and functionalize the cavities. This approach exhibits obvious advantages. The POMs are locally patterned in the cavities on the polymer surface in one step. The incompatible modifiers assemble together in the patterned form. The method is universally suitable for surface hybridization of patterned polymer films while preserving the intrinsic chemical and physical properties of inorganic additives. Interestingly, the POMs accumulated inside cavities of polymer surface can adsorb proteins electrostatically for local protein assembly and pattern preparation. We believe that the present method provides a facile and efficient route to acquire ordered porous films with multi-component and multi-function surfaces, which reveal potential applications in microreaction, pattern recognition, cell culture and so forth.

Section snippets

Materials

The POMs used in the present study are K13[Eu(SiW11O39)2]⋅28H2O (its anion abbreviated as EuSiW11) [38], Na9[EuW10O36]⋅32H2O (EuW10) [39], K12.5Na1.5[NaP5W30O110]⋅15H2O (NaP5W30) [40], K9CoW12O40 (CoW12) [41], and Na3(H2O)6[Al(OH)6Mo6O18]⋅2H2O (AlMo6) [42], which were freshly prepared according to the procedures in literatures. H3PW12O40·nH2O (HPW12) was purchased from Sinopham Chemical Reagent Co. Ltd. Poly(methyl methacrylate) (PMMA, Mw: 349 kg/mol), Pluronic P123 (PEO20PPO70PEO20, P123),

Preparation and structural characterization of EuSiW11/PMMA porous films

As a typical procedure, the microemulsion samples of PMMA dichloromethane solution bearing P123 are prepared by simply mixing with the aqueous solution of EuSiW11 clusters and following a short sonication or a gentle shaking, which makes the reversed microemulsion droplets disperse in the organic solution evenly. The microemulsion droplets in such a solution can maintain the preliminary state up to 10 h. After spreading the sample solution onto a solid substrate and evaporating solvent, the

Conclusions

In conclusion, we develop a new general method for the preparation and functionalization of POM-patterned porous film through phase separation self-assembly of reversed microemulsion droplets in polymer solution, which perform as the template of cavities. The present route is much simpler and more facile for fabricating chemically modified cavities on the polymer surface during the pattern formation. Because the POMs are water soluble and can be incorporated into the reversed microemulsion

Acknowledgments

The authors acknowledge the financial support from the National Natural Science Foundation of China (21074046 and 91227110), National 973 Program (2013CB834503), Ministry of Education of China (20120061110047), and Open Project of State Key Laboratory of Polymer Physics and Chemistry of CAS.

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