High-speed fabrication of patterned colloidal photonic structures in centrifugal microfluidic chips

Van der Waals Colloidal Crystals

A general guiding principle for colloidal crystallization is to tame the attractive enthalpy such that it slightly overwhelms the repulsive interaction. As-synthesized colloids are generally designed to retain a strong repulsive potential for the high stability of suspensions, encoding appropriate attractive potentials into colloids has been key to their crystallization. Despite the myriad of interparticle attractions for colloidal crystallization, the van der Waals (vdW) force remains unexplored. Here, it is shown that the implementation of gold cores into silica colloids and the resulting vdW force can reconfigure the pair potential well depth to the optimal range between -1 and -4 kB T at tens of nanometer-scale colloidal distances. As such, colloidal crystals with a distinct liquid gap can be formed, which is evidenced by photonic bandgap-based diffractive colorization.

Microfluidic-LAMP chip for the point-of-care detection of gene-deleted and wild-type African swine fever viruses and other four swine pathogens

Introduction

Different pathogens causing mixed infection are now threatening the pig industry in the context of the African Swine Fever (ASF) circulating especially in China, and it is crucial to achieving the early diagnosis of these pathogens for disease control and prevention.

Methods

Here we report the development of a rapid, portable, sensitive, high-throughput, and accurate microfluidic-LAMP chip detection system for simultaneous detection and differentiation of gene-deleted type and wild-type African swine fever virus (ASFV), pseudorabie virus (PRV), porcine parvovirus (PPV), porcine circovirus type 2 (PCV2), and porcine reproductive and respiratory syndrome (PRRSV).

Results and discussion

The newly developed system was shown to be sensitive with detection limits of 101 copies/μl for ASFV-MGF505-2R/P72, PPV, and PCV2, 102 copies/μl for ASFV-CD2v, PRV, and PRRSV. The system was highly specific (100%) and stable (C.V.s < 5%) in its ability to detect different pathogens. A total 213 clinical samples and 15 ASFV nucleic acid samples were collected to assess the performance of the detection system, showing highly effective diagnosis. Altogether, the developed microfluidic-LAMP chip system provides a rapid, sensitive, high-throughput and portable diagnostic tool for the accurate detection of multiple swine pathogens.

Advanced "lab-on-a-chip" to detect viruses - Current challenges and future perspectives

Massive viral outbreaks draw attention to viruses that have not been thoroughly studied or understood. In recent decades, microfluidic chips, known as "lab-on-a-chip", appears as a promising tool for the detection of viruses. Here, we review the development of microfluidic chips that could be used in response to viral detection, specifically for viruses involved in more recent outbreaks. The advantages as well as the disadvantages of microfluidic systems are discussed and analyzed. We also propose ideas for future development of these microfluidic chips and we expect this advanced technology to be used in the future for viral outbreaks.

Heterogeneity of dynamics in a modulated colloidal liquid

We study the dynamics of a system of two dimensional colloidal particles subjected to a spatially periodic external potential using Brownian dynamics simulations. We characterize the dynamics in the system by the mean square displacements and the self-van Hove function. The static density plots suggest that system gets into modulated liquid phase in presence of the external potential. We find that diffusion coefficients, obtained from long time mean sqaure displacements, decay exponentially with increasing potential strength. The self-van Hove functions computed from the distribution of particle displacemets in a given time interval show non-gaussian behaviour in directions both parallel and transverse to the external modulation. This suggests heterogeneous dynamics and is supported by particle mobilities and residence times.

Colloidal Crystals from Microfluidics

Colloidal crystals are of great interest to researchers because of their excellent optical properties and broad applications in barcodes, sensors, displays, drug delivery, and other fields. Therefore, the preparation of high quality colloidal crystals in large quantities with high speed is worth investigating. After decades of development, microfluidics have been developed that provide new choices for many fields, especially for the generation of functional materials in microscale. Through the design of microfluidic chips, colloidal crystals can be prepared controllably with the advantages of fast speed and low cost. In this Review, research progress on colloidal crystals from microfluidics is discussed. After summarizing the classifications, the generation of colloidal crystals from microfluidics is discussed, including basic colloidal particles preparation, and their assembly inside or outside of microfluidic devices. Then, applications of the achieved colloidal crystals from microfluidics are illustrated. Finally, the future development and prospects of microfluidic-based colloidal crystals are summarized.

Designing Structural-Color Patterns Composed of Colloidal Arrays

Structural coloration provides a great potential for various applications due to unique optical properties distinguished from conventional pigment colors. Structural colors are nonfading, iridescent, and tunable, which is difficult to achieve with pigments. In addition, structural color is potentially less toxic than pigments. However, it is challenging to develop structural colors because elaborate nanostructures are a prerequisite for the coloration. Furthermore, it is highly suggested the nanostructures be patterned at various length scales on a large area to provide practical formats. There have been intensive studies to develop pragmatic methods for producing structural-color patterns in a controlled manner using either colloidal crystals or glasses. This article reviews the current state of the art in the structural-color patterning based on the colloidal arrays. We first discuss common and different features between colloidal crystals and glasses. We then categorize colloidal arrays into six distinct structures of 3D opals, inverse opals, non-close-packed arrays, 2D colloidal crystals, 1D colloidal strings, and 3D amorphous arrays and study various methods to make them patterned from recent key contributions. Finally, we outline the current challenges and future perspectives of the structural-color patterns.

Centrifugal microfluidic platforms: advanced unit operations and applications

Review on miniaturization, integration, and automation of laboratory processes within centrifugal microfluidic platforms. For efficient implementation of applications, building blocks are categorized into unit operations and process chains.

Creating sub-50 nm nanofluidic junctions in a PDMS microchip via self-assembly process of colloidal silica beads for electrokinetic concentration of biomolecules

In this work we describe a novel and simple self-assembly process of colloidal silica beads to create a nanofluidic junction between two microchannels. The nanoporous membrane was used to induce ion concentration polarization inside the microchannel and this electrokinetic preconcentration system allowed rapid concentration of DNA samples by ~1700 times and of protein samples by ~100 times within 5 minutes.

Electrokinetically driven reversible banding of colloidal particles near the wall

Polystyrene microparticles of 0.5 μm diameter form long-lived streamwise bands within 1 μm of the wall in the combined steady electroosmotic (EO) and Poiseuille flow of a dilute particle suspension through fused-silica microchannels. The bands disappear when the electric field driving the EO flow is turned off, and the band characteristics can be changed by adjusting the flow parameters. To our knowledge, these are the first observations of near-wall particle self-assembly due to shear and steady electric fields.

Controlled fabrication of hexagonally close-packed Langmuir-Blodgett silica particulate monolayers from binary surfactant and solvent systems

We describe a controllable method to fabricate hexagonally close-packed Langmuir-Blodgett (LB) monolayers with stearic acid (SA) as co-surfactant and methanol as co-solvent. The optimal SA concentrations and volume ratios of chloroform to methanol are 0.8 mg/mL and 3:1 for particles of 140 nm, 0.50 mg/mL and 4:1 for particles of 300 nm, and 0.05 mg/mL and 5:1 for particles of 550 nm, respectively. Additionally, SEM detections of the monolayers transferred at different surface pressures indicate that the monolayers deposited from the binary systems are more compressible. The experimental results indicate that the interparticle repulsions and particle-water interactions can be enhanced without decreasing the particle hydrophobicity by adding SA and methanol; thus, particulate monolayers with large hexagonally close-packed domains composed of small silica particles can be successfully fabricated using LB technique. We propose that the enhanced interparticle repulsion is attributed to the Columbic repulsion resulting from the attachment of SA molecules to the CTAB modified particles around the three phase contact line.

Microfluidic generation of droplets with a high loading of nanoparticles

Microfluidic approaches for controlled generation of colloidal clusters, for example, via encapsulation of colloidal particles in droplets, have been used for the synthesis of functional materials including drug delivery carriers. Most of the studies, however, use a low concentration of an original colloidal suspension (<10 wt %). Here we demonstrate microfluidic approaches for directly making droplets with moderate (10-25 wt %) and high (>60 wt %) particle concentrations. Three types of microfluidic devices, PDMS flow-focusing, PDMS T-junction, and microcapillary devices, are investigated for direct encapsulation of a high concentration of polystyrene (PS) nanoparticles in droplets. In particular, it is shown that PDMS devices fabricated by soft lithography can generate droplets from a 25 wt % PS suspension, whereas microcapillary devices made from glass capillary tubes are able to produce droplets from a 67 wt % PS nanoparticle suspension. When the PS concentration is between 0.6 and 25 wt %, the size of the droplets is found to change with the oil-to-water flow rate ratio and is independent of the concentration of particles in the initial suspensions. Drop sizes from ~12 to 40 μm are made using flow rate ratios Q(oil)/Q(water) from 20 to 1, respectively, with either of the PDMS devices. However, clogging occurs in PDMS devices at high PS concentrations (>25 wt %) arising from interactions between the PS colloids and the surface of PDMS devices. Glass microcapillary devices, on the other hand, are resistant to clogging and can produce droplets continuously even when the concentration of PS nanoparticles reaches 67 wt %. We believe that our findings indicate useful approaches and guidelines for the controlled generation of emulsions filled with a high loading of nanoparticles, which are useful for drug delivery applications.

Patterning organic/inorganic hybrid Bragg stacks by integrating one-dimensional photonic crystals and macrocavities through photolithography: toward tunable colorful patterns as highly selective sensors

Herein, we report a simple method to fabricate patterned organic/inorganic hybrid 1DPCs by top-down assisted photolithography. Versatile colorful pattern with different size and shape can be produced by selectively exposing the 1DPCs under UV light with predesigned photomask directly. The period change, especially the thickness variation of the top polymer layer, is the main reason for the colorful pattern generation. Because of the swelling property of the polymer layers, the pattern color can be modulated by introducing or taking off organic solvents, leading the as-prepared patterned 1DPCs to be effective sensors with high selectivity.

Electrophoretic separation of neurotransmitters on a polystyrene nano-sphere∕polystyrene sulphonate coated poly(dimethylsiloxane) microchannel

In this paper, a poly(dimethylsiloxane) microchip with amperometric detector was developed for the electrophoretic separation and determination of neurotransmitters. For increasing the separation efficiency, the microchannel is modified by polystyrene sulphonate∕polystyrene nano-sphere self-assembly coating. A stable electro-osmotic flow (EOF) and higher separation efficiency are obtained in proposed modified microchannel. Under optimized conditions, dopamine, epinephrine, catechol, and serotonin are acceptably baseline separated in this 3.5 cm length separation channel with the theoretical plate number from 4.6 × 10(4) to 2.1 × 10(5) per meter and resolution from 1.29 to 12.5. The practicability of proposed microchip is validated by the recovery test with cerebrospinal fluid as real sample which resulted from 91.7% to 106.5%.

Microfluidics in inorganic chemistry

The application of microfluidics in chemistry has gained significant importance in the recent years. Miniaturized chemistry platforms provide controlled fluid transport, rapid chemical reactions, and cost-saving advantages over conventional reactors. The advantages of microfluidics have been clearly established in the field of analytical and bioanalytical sciences and in the field of organic synthesis. It is less true in the field of inorganic chemistry and materials science; however in inorganic chemistry it has mostly been used for the separation and selective extraction of metal ions. Microfluidics has been used in materials science mainly for the improvement of nanoparticle synthesis, namely metal, metal oxide, and semiconductor nanoparticles. Microfluidic devices can also be used for the formulation of more advanced and sophisticated inorganic materials or hybrids.

Magnetic assembly of nonmagnetic particles into photonic crystal structures

We report the rapid formation of photonic crystal structures by assembly of uniform nonmagnetic colloidal particles in ferrofluids using external magnetic fields. Magnetic manipulation of nonmagnetic particles with size down to a few hundred nanometers, suitable building blocks for producing photonic crystals with band gaps located in the visible regime, has been difficult due to their weak magnetic dipole moment. Increasing the dipole moment of magnetic holes has been limited by the instability of ferrofluids toward aggregation at high concentration or under strong magnetic field. By taking advantage of the superior stability of highly surface-charged magnetite nanocrystal-based ferrofluids, in this paper we have been able to successfully assemble 185 nm nonmagnetic polymer beads into photonic crystal structures, from 1D chains to 3D assemblies as determined by the interplay of magnetic dipole force and packing force. In a strong magnetic field with large field gradient, 3D photonic crystals with high reflectance (83%) in the visible range can be rapidly produced within several minutes, making this general strategy promising for fast creation of large-area photonic crystals using nonmagnetic particles as building blocks.

Centrifugal deposition of microgels for the rapid assembly of nonfouling thin films

Thin films assembled from microgel building blocks have been constructed using a simple, high-throughput, and reproducible centrifugation (or "active") deposition technique. When compared to a common passive adsorption method (e.g., dip coating), microgels that are actively deposited onto a surface have smaller footprints and are more closely packed. Under both active and passive deposition conditions, the microgel footprint areas decrease during deposition. However, under active deposition, the microgel footprint appears to decrease continually and to a greater degree over the course of the deposition, forming a tightly packed, homogeneous film. Taking advantage of the rapid and uniform assembly of these films, we demonstrate the use of active deposition toward the fabrication of polyelectrolyte multilayers containing anionic microgels and a cationic linear polymer. Microgel multilayers successfully demonstrated effective blocking of the underlying substrate toward macrophage adhesion, which is a highly sought-after property for modulating the inflammatory response to an implanted biomaterial.

Invited Review Article: Review of centrifugal microfluidic and bio-optical disks

Spinning biodisks have advantages that make them attractive for specialized biochip applications. The two main classes of spinning biodisks are microfluidic disks and bio-optical compact disks (BioCD). Microfluidic biodisks take advantage of noninertial pumping for lab-on-a-chip devices using noninertial valves and switches under centrifugal and Coriolis forces to distribute fluids about the disks. BioCDs use spinning-disk interferometry, under the condition of common-path phase quadrature, to perform interferometric label-free detection of molecular recognition and binding. The optical detection of bound molecules on a disk is facilitated by rapid spinning that enables high-speed repetitive sampling to eliminate 1/f noise through common-mode rejection of intensity fluctuations and extensive signal averaging. Multiple quadrature classes have been developed, such as microdiffraction, in-line, phase contrast, and holographic adaptive optics. Thin molecular films are detected through the surface dipole density with a surface height sensitivity for the detection of protein spots that is approximately 1 pm. This sensitivity easily resolves a submonolayer of solid-support immobilized antibodies and their antigen targets. Fluorescence and light scattering provide additional optical detection techniques on spinning disks. Immunoassays have been applied to haptoglobin using protein A/G immobilization of antibodies and to prostate specific antigen. Small protein spots enable scalability to many spots per disk for high-throughput and highly multiplexed immonoassays.

Colloid-templated multisectional porous polymeric fibers

A fabrication method for porous polymeric fibers (PPFs) is reported. We show that a multisectional colloidal crystal can be assembled within a microcapillary by alternating dipping into colloidal solutions of varying size. Subsequent infiltration with curable polymer and washing with suitable solvents results in porous fibers with a cylindrical cross section. Along the length of the fiber, alternating sections of controlled length, pore size, and pore size distribution exist. These fibers present interesting materials for neural scaffolding, catalysis, and possibly photonics if produced with a high degree of crystallinity. The surface pores and bulk porosity of the fibers are characterized by variable-pressure scanning electron microscopy (vp-SEM). Careful analysis shows that the surface pores vary with the colloidal template diameter and polymer infiltration time.

Submicron scale patterning in sintered silica colloidal crystal films using a focused ion beam

Focused ion beam milling is used to fabricate micron and submicron scale patterns in sintered silica colloidal crystal films. Rectangular cavities with both solid and porous boundaries, fluidic channels, and isolation of a small number of packed spheres are patterned. The ion beam can pattern sintered films of individual submicron size spheres and create patterns that cover up to 40 mum in less than 15 min. The experiments in this work indicate that the amount of redeposited material on the surface of a milled cavity determines whether the surface will be porous or solid. FIB direct patterning has applications in colloidal crystal based lithography, integrated photonic devices, optofluidic devices, and micrototal-analytical systems.

Holographic fabrication of photonic nanostructures for optofluidic integration

Holographic lithography in combination with photo-lithography provides a novel optofluidic platform through incorporation of periodic photonic units inside the microfluidic chips in a highly compatible and facile way.