Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials

Abstract

Chemical sensors respond to the presence of a specific analyte in a variety of ways. One of the most convenient is a change in optical properties, and in particular a visually perceptible colour change. Here we report the preparation of a material that changes colour in response to a chemical signal by means of a change in diffraction (rather than absorption) properties. Our material is a crystalline colloidal array of polymer spheres (roughly 100 nm diameter) polymerized within a hydrogel that swells and shrinks reversibly in the presence of certain analytes (here metal ions and glucose). The crystalline colloidal array diffracts light at (visible) wavelengths determined by the lattice spacing, which gives rise to an intense colour. The hydrogel contains either a molecular-recognition group that binds the analyte selectively (crown ethers for metal ions), or a molecular-recognition agent that reacts with the analyte selectively. These recognition events cause the gel to swell owing to an increased osmotic pressure, which increases the mean separation between the colloidal spheres and so shifts the Bragg peak of the diffracted light to longer wavelengths. We anticipate that this strategy can be used to prepare 'intelligent' materials responsive to a wide range of analytes, including viruses.

Polymer Gel Nanoparticle Networks

“…In 1D, a film was deposited between two reflecting layers to obtain an optical microcavity with efficient, narrow-linewidth emission. [9] In 2D, a film was patterned with a periodic array of holes to obtain a novel cavity-less organic laser. [10] These successes clearly show the power of this approach.…”

“…[22] To overcome this shortcoming, such arrays are usually embedded into a gel matrix. [9,22] With our method, the colloidal crystal array could be stabilized by directly linking nanoparticles through chemical bonds without introducing another gel matrix.…”

Crystallization of Mesoscopic Colloids into 3D Opaline Lattices in Packing Cells Fabricated by Replica Molding

“…For example, three-dimensional (3D) arrays have been successfully demonstrated as precursors to high-strength ceramics; [1] as templates to generate porous materials (or inverse opals); [2] and as periodic structures to fabricate new types of optical sensors, [3] diffractive devices, [4] and photonic bandgap crystals. [5] A range of approaches have been demonstrated for assembling mesoscopic, spherical colloids into 3D crystalline lattices, and notable examples include sedimentation, [6] self-organization of highly charged colloids through electrostatic interactions, [7] and crystallization through attractive capillary forces.…”

Photo-Reversible Regulation of Optical Stop Bands

“…[7] The control of the spatial structure was also realized by taking advantage of the volume phase transition of hydrogels. [2,3,8] The photonic band structures have been tuned by controlling the temperature, pH, and the ionic state. Recently the control of photonic band structure has also been realized by utilizing the phase transition of colloidal crystals in solution, where the stop band can be tuned by light.…”