Yuanjin Zhao

Microfluidic generation of multifunctional quantum dot barcode particles

We develop a new strategy to prepare quantum dot (QD) barcode particles by polymerizing double-emulsion droplets prepared in capillary microfluidic devices. The resultant barcode particles are composed of stable QD-tagged core particles surrounded by hydrogel shells. These particles exhibit uniform spectral characteristics and excellent coding capability, as confirmed by photoluminescence analyses. By using double-emulsion droplets with two inner droplets of distinct phases as templates, we have also fabricated anisotropic magnetic barcode particles with two separate cores or with a Janus core. These particles enable optical encoding and magnetic separation, thus making them excellent functional barcode particles in biomedical applications.

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

Encoded Silica Colloidal Crystal Beads as Supports for Potential Multiplex Immunoassay

We developed a new kind of suspension array for multiplexed immunoassays using silica colloidal crystal beads (SCCBs) as coding carriers. The monodisperse and size-controlled SCCBs were fabricated by a microfluidic device. Calcination was employed to improve the mechanical stability and lower the fluorescent background of the SCCBs. Immobilization of protein molecules on the surface of the SCCBs through chemical bonds was studied, and the modification condition was optimized to increase the detection sensitivity. Results indicated that the SCCBs as supports were more sensitive (0.92 ng/mL IgG) than the glass beads (27 ng/mL IgG) and the planar carriers (140 ng/mL IgG). A multiplex immunoassay showed the flexibility and feasibility of SCCBs array in clinical applications.

Multiplex Label-Free Detection of Biomolecules with an Imprinted Suspension Array†

Multiplex detection of biomolecules has facilitated clinical diagnosis, drug discovery, and environmental testing. Immunoassays using labeled antibodies are the most popular methods for the detection of biomolecules because of their sensitivity and selectivity. However, labeling protocols are time-consuming and expensive, and may alter the form or physicochemical behavior of the antibodies, which could lead to false negative results. In addition, the reagent stability, high cost, and difficulties associated with antibody production, together with the adverse action of toxic compounds or immunosuppressants on the metabolism and the immune system during the production of antibodies, are often cited as problems. Therefore, it is highly desirable to carry out multiplex label-free detection of biomolecules without using immunoassay methods. Suspension arrays, which use self-encoded microcarriers as elements, have shown obvious advantages in the multiplex detection of biomolecules. However, few of them can be used for the label-free detection of biomolecules. Moreover, these methods are still based on the use of probe antibodies. In contrast, molecularly imprinted polymers (MIPs) have unique properties as mimics of natural molecular receptors that may make them suitable for revolutionary applications in biotechnology. Recently, many kinds of MIP sensors have been developed for the detection of biomolecules based on physicochemical responses of the MIPs, such as changes in refractive index and volume. However, these sensors could respond only to single analytes, and the detection signals from the physicochemical response of the MIPs were not distinct and were difficult to measure with accuracy. Herein, we report a new type of suspension array for the multiplex label-free detection of biomolecules without using immunoassay methods. The microcarriers of our suspension array are molecularly imprinted polymer beads (MIPBs) with photonic crystal structure, which not only provide diffraction peaks for encoding but also convert the slight physicochemical response signals to the obvious changes of optical signals. This technique combines the advantages of suspension arrays, molecular imprinting, and photonic crystal sensors. As a proof of concept for the multiplex label-free detection of biomolecules not based on immunoassay methods, we constructed an imprinted suspension array with affinity for proteins. For large biomacromolecules, surface imprinting was used for the fabrication of the MIPBs with photonic crystal structure due to the easy removal and rapid rebinding characteristics during assays. Scheme 1 outlines the

Spherical colloidal photonic crystals.

CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be generated by evaporation-induced nanoparticle crystallization or polymerization of ordered nanoparticle crystallization arrays. In particular, because microfluidics was used for the generation of the droplet templates, the development of spherical colloidal PhCs has progressed significantly. These new strategies not only ensure monodispersity, but also increase the structural and functional diversity of the PhC beads, paving the way for the development of advanced optoelectronic devices. In this Account, we present the research progress on spherical colloidal PhCs, including their design, preparation, and potential applications. We outline various types of spherical colloidal PhCs, such as close-packed, non-close-packed, inverse opal, biphasic or multiphasic Janus structured, and core-shell structured geometries. Based on their unique optical properties, applications of the spherical colloidal PhCs for displays, sensors, barcodes, and cell culture microcarriers are presented. Future developments of the spherical colloidal PhC materials are also envisioned.

Bioinspired Multicompartmental Microfibers from Microfluidics

Bioinspired multicompartmental microfibers are generated by novel capillary microfluidics. The resultant microfibers possess multicompartment body-and-shell compositions with specifically designed geometries. Potential use of these microfibers for tissue-engineering applications is demonstrated by creating multifunctional fibers with a spatially controlled encapsulation of cells.

Microfluidic synthesis of barcode particles for multiplex assays.

The increasing use of high-throughput assays in biomedical applications, including drug discovery and clinical diagnostics, demands effective strategies for multiplexing. One promising strategy is the use of barcode particles that encode information about their specific compositions and enable simple identification. Various encoding mechanisms, including spectroscopic, graphical, electronic, and physical encoding, have been proposed for the provision of sufficient identification codes for the barcode particles. These particles are synthesized in various ways. Microfluidics is an effective approach that has created exciting avenues of scientific research in barcode particle synthesis. The resultant particles have found important application in the detection of multiple biological species as they have properties of high flexibility, fast reaction times, less reagent consumption, and good repeatability. In this paper, research progress in the microfluidic synthesis of barcode particles for multiplex assays is discussed. After introducing the general developing strategies of the barcode particles, the focus is on studies of microfluidics, including their design, fabrication, and application in the generation of barcode particles. Applications of the achieved barcode particles in multiplex assays will be described and emphasized. The prospects for future development of these barcode particles are also presented.

Biodegradable Core−Shell Carriers for Simultaneous Encapsulation of Synergistic Actives

Simultaneous encapsulation of multiple active substances in a single carrier is essential for therapeutic applications of synergistic combinations of drugs. However, traditional carrier systems often lack efficient encapsulation and release of incorporated substances, particularly when combinations of drugs must be released in concentrations of a prescribed ratio. We present a novel biodegradable core-shell carrier system fabricated in a one-step, solvent-free process on a microfluidic chip; a hydrophilic active (doxorubicin hydrochloride) is encapsulated in the aqueous core, while a hydrophobic active (paclitaxel) is encapsulated in the solid shell. Particle size and composition can be precisely controlled, and core and shell can be individually loaded with very high efficiency. Drug-loaded particles can be dried and stored as a powder. We demonstrate the efficacy of this system through the simultaneous encapsulation and controlled release of two synergistic anticancer drugs using two cancer-derived cell lines. This solvent-free platform technology is also of high potential value for encapsulation of other active ingredients and chemical reagents.

Photonic Crystal Microcapsules for Label‐free Multiplex Detection

A novel suspension array, which possesses the joint advantages of photonic crystal encoded technology, bioresponsive hydrogels, and photonic crystal sensors with capability of full multiplexing label-free detection is developed.

Emerging Droplet Microfluidics

Droplet microfluidics generates and manipulates discrete droplets through immiscible multiphase flows inside microchannels. Due to its remarkable advantages, droplet microfluidics bears significant value in an extremely wide range of area. In this review, we provide a comprehensive and in-depth insight into droplet microfluidics, covering fundamental research from microfluidic chip fabrication and droplet generation to the applications of droplets in bio(chemical) analysis and materials generation. The purpose of this review is to convey the fundamentals of droplet microfluidics, a critical analysis on its current status and challenges, and opinions on its future development. We believe this review will promote communications among biology, chemistry, physics, and materials science.