Cun Zhu

Encoded Porous Beads for Label‐Free Multiplex Detection of Tumor Markers

In recent years, suspension arrays, which use self-encoded microcarriers as elements, are attracting increasing interest in the field of drug discovery, gene-function analysis, clinical diagnosis, and so on. Compared with the conventional microarrays on a plate, suspension arrays may offer greater flexibility in the preparation of new assays, higher diffusional flux of analytes due to the radial diffusion, less consumption of sample and reagents, and higher sensitivity. One of the key techniques of suspension arrays is encoding. Spectrum is a wellused encoding approach, due to its simplicity both in encoding and decoding. Fluorescent dyes and quantum dots are the main spectrum-encoding elements, and the beads encoded by fluorescence have been commercialized by Luminex and other companies. However, fluorescence dyes tend to be quenched or bleached, and the quantum dots are usually biotoxic. Also, the fluorescence of the carriers can interfere with the signal from the labeling molecules, and as a result affect the detection limit. Photonic crystals have been suggested as a new type of spectrum-encoding carrier, whose code is the characteristic reflection peak originated from the stop-band. As the peak position is based on their periodical structure, the code is very stable, and the fluorescent background is low. These properties render photonic crystals suitable for highly sensitive detection. Conventional planar photonic-crystal carriers have to be properly dispersed and correctly orientated to avoid stacking or standing of the flakes during the decoding process. Recently, we found that these problems might be solved with the use of photonic beads with a 3D structure. Unlike planar photonic-crystal carriers, the photonic beads retain their reflection spectra when the crystals are rotated under light impinging on the crystal surface at a fixed incident angle. This indicates the accurate encoding character of photonic beads. Another key technique for using suspension arrays is target analysis, which is generally realized by detecting the labels attached to the biomolecules. In addition to the high cost imposed by reagents and instruments, the labels, or labeling itself, will hinder the interactions and the activity of biomolecules. Therefore, label-free detection is anticipated. In this paper, we proposed the use of inverse-opaline photonic beads as carriers for suspension arrays. The beads showed large encoding capacity by changing their lattice constant. A label-free multiplex detection of tumor markers, Human CA125, CA19-9, and CEA, which showed great significance in early screening and clinical diagnosis of some tumor diseases including colorectal cancer, gastric cancer, and lung cancer, show the flexibility and feasibility of our suspension array in clinical applications. In addition, both the decoding and bioreaction detection were measurements of the characteristic reflection peak, which rendered the detection and the analyzing apparatus extremely simple. Up to now, attention was devoted to the fabrication of inverseopaline photonic films, and only a few reports on the formation of inverse-opaline photonic beads are available. Template replication and spray-drying with colloidal templates are examples of methods that showed the difficulty in preparing beads with smooth edges and long-range-ordering porous surfaces, due to low surface tension and too fast assembly. Herein, we produced inverse-opaline photonic beads by colloidal crystallization in droplet templates. First, an aqueous suspension containing monodisperse polystyrene spheres and ultrafine silica particles was broken into droplets by oil flows in a microfluidic device, and the droplets were taken into a collection container that was also filled with silicon oil. Then, the polystyrene spheres self-assembled into ordered lattices, and the ultrafine silica particles infiltrated into the interstitial sites between the spheres during the evaporation of water in the droplets. After solidification, the hybrid beads were thoroughly washed with hexane to remove silicon oil. Finally, the hybrid beads were calcined, to remove the polystyrene spheres and improve the mechanical strength of the inverseopaline photonic beads. Generally, the long-range ordering of pores on bead surfaces was important for the optical performance of the inverse-opaline photonic beads. To optimize this performance, change of pore arrangement on the bead surface with varying polystyrene spheres to silica particles volume ratios in the droplet template were investigated. Theoretically, when the polystyrene spheres packed closely to a bead in a face-centered cubic arrangement, and the ultrafine silica particles infiltrated all the interstitial sites between the polystyrene spheres, the volume ratio was about 3.85. In our experiment, however, we found that during the evaporation of water the polystyrene spheres escaped more easily from the droplet templates than silica particles; also, after solidification the silica particles could not infiltrate into all the interstitial sites

Hybrid mesoporous colloid photonic crystal array for high performance vapor sensing

A hybrid mesoporous photonic crystal vapor sensing chip was developed by introducing fluorescent dyes into mesoporous colloidal crystals. The sensing chip was capable of discriminating various kinds of vapors, as well as their concentrations, according to their fluorescence and reflective responses to vapor analytes.

A Magnetically Tunable Colloidal Crystal Film for Reflective Display

A general approach to fabricate a magnetic field responsive colloidal crystal film has been developed. This is carried out by depositing monodisperse Fe(3) O(4) /PS composite magnetic nanospheres on the surface of an agarose-gel coated substrate. The optical properties of the resultant film can be easily controlled by an external magnetic field, which is caused by assembly of the magnetic nanospheres and alteration of the interparticle distance. With the help of a designed array of small magnets, both the color and pattern of the film can be conveniently modulated and the tuning range covers almost the whole visible spectrum. This work will be important for the potential application of monodisperse magnetic nanospheres in fabricating novel sensors, displays and optoelectronic devices.

Anisotropic colloidal crystal particles from microfluidics.

Anisotropic colloidal crystal particles (CCPs) have showed their great potential in biotechnology and structural materials due to their anisotropic shapes and tunable optical property. However, their controllable generation is still a challenge. Here, a novel microfluidic approach is developed to generate anisotropic CCPs. The microfluidic device is composed of an injection capillary and a collection capillary with available size and shape. Based on the device, the anisotropic particles with non-close-packed colloidal crystal structures are achieved by photo-polymerizing droplet templates in a confined collection capillary with different shapes and sizes. Moreover, anisotropic close-packed CCPs can be made from non-close-packed CCPs through a thermal process. It is demonstrated that the anisotropic CCPs in different sizes, structural colors and shapes (rods, cuboids and disks) can be generated. These distinguishable features of resultant particles make them ideal barcodes for high-throughput bioassays. In order to prove it, DNA multiplex detection is carried out. The experimental results indicate that achieved particles have a great encoding capacity and are highly practical for multiplex coding bioassays. Therefore, we believe that the anisotropic CCPs would be highly promising barcodes in biomedical applications, including high-throughput bioassays and cell culture research where multiplexing is needed.

Structural Color Patterns by Electrohydrodynamic Jet Printed Photonic Crystals

In this work, we demonstrate the fabrication of photonic crystal patterns with controllable morphologies and structural colors utilizing electrohydrodynamic jet (E-jet) printing with colloidal crystal inks. The final shape of photonic crystal units is controlled by the applied voltage signal and wettability of the substrate. Optical properties of the structural color patterns are tuned by the self-assembly of the silica nanoparticle building blocks. Using this direct printing technique, it is feasible to print customized functional patterns composed of photonic crystal dots or photonic crystal lines according to relevant printing mode and predesigned tracks. This is the first report for E-jet printing with colloidal crystal inks. Our results exhibit promising applications in displays, biosensors, and other functional devices.

Carbon Inverse Opal Rods for Nonenzymatic Cholesterol Detection

Carbon inverse opal rods made from silica photonic crystal rods are used for nonenzymatic cholesterol sensing. The characteristic reflection peak originating from the physical periodic structure works as sensing signals for quantitatively estimating cholesterol concentrations. Carbon inverse opal rods work both in cholesterol standard solutions and human serum. They are suitable for practical use in clinical diagnose.

Preparation of magnetic nanoparticles for photonic crystals

Colloidal crystal is one kind of photonic band gap material which can self-assemble into ordered periodical structure and has the ability to reflect some definite light to make the colloidal crystal brilliant. Especially photonic crystals with magnetic properties have received much attention in recent years because of their good responsibility to the external magnetic field. This novel kind of material has potential applications not only in traditional separation, purification of biomolecules and drug delivery system, but also in optical devices and sensors.