Synthesis of Biofunctional Janus Particles

Synthesis of dimpled polymer particles and polymer particles with protrusions - Past, present, and future

Since the development of emulsion polymerization techniques, polymer particles have become the epitome of standard colloids due to the exceptional control over size, size distribution, and composition the synthesis methods allow reaching. The exploration of different variations of the synthesis methods has led to the discovery of more advanced techniques, enabling control over their composition and shape. Many early investigations focused on forming particles with protrusions (with one protrusion, called dumbbell particles) and particles with concavities, also called dimpled particles. This paper reviews the literature covering the synthesis, functionalization, and applications of both types of particles. The focus has been on the rationalization of the various approaches used to prepare such particles and on the discussion of the mechanisms of formation not just from the experimental viewpoint but also from the standpoint of thermodynamics. The primary motivation to combine in a single review the preparation of both types of particles has been the observation of similarities among some of the methods developed to prepare dimpled particles, which sometimes include the formation of particles with protrusions and vice versa. The most common applications of these particles have been discussed as well. By looking at the different approaches developed in the literature under one general perspective, we hope to stimulate a more ample use of these particles and promote the development of even more effective synthetic protocols.

Single Step Assembly of Janus Porous Biomaterial by Sub-Ambient Temperature Electrodeposition

Janus porous biomaterials are gaining increasing attention and there are considerable efforts to develop simple, rapid, and scalable methods capable of tuning micro- and macro-structures. Here, a single-step electro-fabrication method to create a Janus porous film by the electrodeposition of the amino-polysaccharide chitosan is reported. Specifically, a Janus structure emerges spontaneously when electrodeposition is performed at sub-ambient temperature (0-5 °C). Sub-ambient temperature electrodeposition experiments show that: a Janus microstructure emerges (potentially as the result of a subtle alteration of the intermolecular interactions responsible for self-assembly); important microstructural features (pore size, porosity, and thicknesses) can be tuned by conditions; and this method is readily scalable (vs serial printing) and can yield complex tubular structures with Janus faces. In vitro studies demonstrate anisotropic cell guidance, and in vivo studies using a rat calvarial defect model further confirm the beneficial features of such Janus porous film for guided bone regeneration. In summary, these results further demonstrate that electro-fabrication provides a simple and scalable platform technology for the controlled functional structures of soft matter for applications in regenerative medicine.

Application of Janus Particles in Point-of-Care Testing

Janus particles (JPs), named after the two-faced Roman god, are asymmetric particles with different chemical properties or polarities. JPs have been widely used in the biomedical field in recent years, including as drug carriers for targeted controlled drug release and as biosensors for biological imaging and biomarker detection, which is crucial in the early detection and treatment of diseases. In this review, we highlight the most recent advancements made with regard to Janus particles in point-of-care testing (POCT). Firstly, we introduce several commonly used methods for preparing Janus particles. Secondly, we present biomarker detection using JPs based on various detection methods to achieve the goal of POCT. Finally, we discuss the challenges and opportunities for developing Janus particles in POCT. This review will facilitate the development of POCT biosensing devices based on the unique properties of Janus particles.

Synthesis of Shape-Controllable Anisotropic Microparticles and "Walnut-like" Microparticles via Emulsion Interfacial Polymerization

Anisotropic microparticles have plenty of applications for their asymmetric structure and precisely modified surface. In our research, the uniform anisotropic microparticles with benzyl chloride group were synthesized successfully via emulsion interfacial polymerization. By varying the degree of cross-linking and the concentration of slightly hydrophilic monomer 4-vinyl benzyl chloride (VBC), several types of microparticles with different concavities and different shapes of microparticles (hemisphere, bowl-like, egg-like, etc.) were obtained. Nanoporous microparticles with a walnut-like heterostructure were achieved with modified hydrophilic seeds with the same strategy. The potential applications of shape-controllable fluorescent microparticles and surface modification of microparticles by thiol-click reaction were explored. The modified microparticles achieved in this study are very useful in labeling, tracing, protein separation, and other biomedical fields.

Dielectrophoretic Manipulation of Janus Particle in Conductive Media for Biomedical Applications

Janus particles are applied to many fields including biomedical applications. To expand the usability of Janus particles, a technique to manipulate the particle movement is required. A dielectrophoresis (DEP) method can be a promising candidate; however, independent manipulation or separation of Janus particle by DEP is still challenging. Additionally, DEP of Janus particles in conductive media is important especially for biomedical applications where ion-rich media are typically used. Here, the experimental results of DEP-induced transport and separation of the Janus particle in conductive media are presented. To predict the DEP behavior, the Clausius-Mossotti (CM) factors of both Janus and homogeneous particles are calculated, depending on the alternating current (AC) frequency and medium conductivity. The Janus particles show the positive-DEP behavior at the entire AC frequency region tested due to the metal-coated half surface. On the other hand, the homogeneous particles show the negative-DEP behavior at the high AC frequency or in conductive media. Additionally, in the conductive media, an electrohydrodynamic flow hinders the DEP-driven particle transport below MHz AC frequencies. Finally, the separation of the Janus particles from the homogeneous ones is experimentally demonstrated and the separation efficiency is discussed based on the evaluation parameters established in this study.

Organic–inorganic bimetallic hybrid particles with controllable morphology for the catalytic degradation of organic dyes

Amphiphilic bimetallic hybrid Janus nanoparticles with controllable morphology and ability to perform highly efficient catalytic degradation of organic dyes.

Biosensing and Delivery of Nucleic Acids Involving Selected Well-Known and Rising Star Functional Nanomaterials

In the last fifteen years, the nucleic acid biosensors and delivery area has seen a breakthrough due to the interrelation between the recognition of nucleic acid's high specificity, the great sensitivity of electrochemical and optical transduction and the unprecedented opportunities imparted by nanotechnology. Advances in this area have demonstrated that the assembly of nanoscaled materials allows the performance enhancement, particularly in terms of sensitivity and response time, of functional nucleic acids' biosensing and delivery to a level suitable for the construction of point-of-care diagnostic tools. Consequently, this has propelled detection methods using nanomaterials to the vanguard of the biosensing and delivery research fields. This review overviews the striking advancement in functional nanomaterials' assisted biosensing and delivery of nucleic acids. We highlight the advantages demonstrated by selected well-known and rising star functional nanomaterials (metallic, magnetic and Janus nanomaterials) focusing on the literature produced in the past five years.

Magnetic Janus Particles for Static and Dynamic (Bio)Sensing

Magnetic Janus particles bring together the ability of Janus particles to perform two different functions at the same time in a single particle with magnetic properties enabling their remote manipulation, which allows headed movement and orientation. This article reviews the preparation procedures and applications in the (bio)sensing field of static and self-propelled magnetic Janus particles. The main progress in the fabrication procedures and the applicability of these particles are critically discussed, also giving some clues on challenges to be dealt with and future prospects. The promising characteristics of magnetic Janus particles in the (bio)sensing field, providing increased kinetics and sensitivity and decreased times of analysis derived from the use of external magnetic fields in their manipulation, allows foreseeing their great and exciting potential in the medical and environmental remediation fields.

Bifunctional Janus Spheres with Chemically Orthogonal Patches

Bifunctional Janus particles with patches carrying orthogonal surface functionalities that can be independently modified are widely seen as promising building blocks for the bottom-up assembly of functional materials due to their full compositional and geometrical programmability. However, synthesis of these colloids remains an elusive task as current scalable procedures are generally limited to monofunctional particles only. Herein, a scalable bulk wet-chemical synthetic method for fabricating bifunctional Janus particles following a two-step dispersion polymerization is developed. Patch formation on these colloids is driven by the spontaneous phase separation between a brominated outer shell and poly(propargyl acrylate) (p(PA)), formed after the seed particles were swollen with the corresponding monomer. The size ratio between the two patches is readily tunable by controlling the volumetric ratio between the feeding monomers. The distinct patches of these Janus particles carry chemical handles facilitating independent and orthogonal surface modification using Atom Transfer Radical Polymerization (ATRP) and thiol-yne Click chemistry for the brominated and alkyne-containing patches, respectively. The presented route toward bifunctional patchy spheres provides a versatile starting point for the development of bifunctional colloidal particles with tailored directional properties.

One-Step Photochemical Generation of Biofunctionalized Hydrogel Particles via Two-Phase Flow

Biofunctional hydrogel particles have become increasingly popular in medical diagnostics; however, their generation is time-consuming and typically requires several process steps. We report on a new method for the simple, fast, and reproducible one-step generation of monodisperse hydrogel particles equipped with biofunctional molecules such as proteins or DNA. Key to the approach is the simultaneous photo cross-linking of the polymer chains and covalent binding of proteins or DNA through a C,H insertion reaction inside aqueous plug compartments that are produced via microfluidics. The strong performance in biological binding assays of the functionalized particles is demonstrated.

Synthesis of Polystyrene Particles with Precisely Controlled Degree of Concaveness

Shape is an essential property of polymeric particles. Herein, we propose a simple method to synthesize polymeric particles with a well-controlled concave shape. Our method takes advantage of the powerful seeded emulsion polymerization strategy with the well-known principle of "like dissolves like" in solvent chemistry. We first prepared polystyrene (PS) particles with a single dimple by seeded emulsion polymerization. Then the dimpled PS particles were dispersed in a dimethylformamide (DMF) and water mixture. Consequently, the non-crosslinked polymer chains inside the particle were dissolved by DMF, a good solvent for PS, and the PS chains migrated out of the particle, causing buckling of the dimple and enlargement of the concave. By systematic change of the fraction of DMF in the solvent mixture, we changed the amount of the dissolved PS chains, and achieved polymeric particles with precisely tuned degree of concaveness. These concave particles were found to readily self-assemble, driven by polymer-induced depletion interaction. The concave PS particles reported here provide potential building blocks for self-assembled polymeric materials, and new model systems for condensed matter research.

Janus Particles Templated by Janus Emulsions and Application as a Pickering Emulsifier

One-step vibrational mixing has afforded the batch-scale preparation of a Janus emulsion. The fabrication of Janus particles (JPs) templated by Janus emulsions was motivated by the topology and composition of the Janus droplets being highly tunable and controllable. Two immiscible polymerizable monomers were introduced as inner phases of the Janus emulsion. The advanced geometry of the resultant JPs was easily and precisely controlled from "snowman" to "dumbbell" by adjusting the mass ratio of two oils in the initial emulsion. The surface coverage of one lobe to the other was tuned by adjusting the mass ratio of mixed surfactants. Moreover, the size of JPs was able to be extended continuously from hundreds of micrometers to a few hundred nanometers while their morphologies remained within this wide size range. The proposed strategy is a universal technique in the synthesis of a family of composite polymeric JPs with both chemical and shape anisotropy. In addition, the as-generated chemically biphasic JPs were applied as emulsifiers to stabilize Pickering emulsions, and more attractively, emulsion inversion was readily achieved by choosing JPs with different morphologies.

Combined chain- and step-growth dispersion polymerization toward PSt particles with soft, clickable patches

Particles with a hard body and soft, clickable dimple- or bulge-patches are prepared by simple combined chain- and step-growth dispersion polymerization.