Inorganic Janus particles for biomedical applications

Abstract

Based on recent developments regarding the synthesis and design of Janus nanoparticles, they have attracted increased scientific interest due to their outstanding properties. There are several combinations of multicomponent hetero-nanostructures including either purely organic or inorganic, as well as composite organic-inorganic compounds. Janus particles are interconnected by solid state interfaces and, therefore, are distinguished by two physically or chemically distinct surfaces. They may be, for instance, hydrophilic on one side and hydrophobic on the other, thus, creating giant amphiphiles revealing the endeavor of self-assembly. Novel optical, electronic, magnetic, and superficial properties emerge in inorganic Janus particles from their dimensions and unique morphology at the nanoscale. As a result, inorganic Janus nanoparticles are highly versatile nanomaterials with great potential in different scientific and technological fields. In this paper, we highlight some advances in the synthesis of inorganic Janus nanoparticles, focusing on the heterogeneous nucleation technique and characteristics of the resulting high quality nanoparticles. The properties emphasized in this review range from the monodispersity and size-tunability and, therefore, precise control over size-dependent features, to the biomedical application as theranostic agents. Hence, we show their optical properties based on plasmonic resonance, the two-photon activity, the magnetic properties, as well as their biocompatibility and interaction with human blood serum.

Keywords: Janus particles; MRI; Multi-photon); bioimaging (CT; hetero-nanoparticles; protein corona; synthesis.

Figure 1

Illustrations of the transition from isotropic to anisotropic particles.

Figure 2

a) Evolution of the PL-peak position, b) schematic representation, and c) evolution of the PL-quantum yield for several core-shell quantum dots starting with a CdSe core. Adapted with permission from [13]. Copyright 2005 American Chemical Society.

Figure 3

Summary of synthetic routes towards organic Janus particles. (a) Directed functionalization after immobilization, (b) ellipsoidal complex core coacervate micelle with an inter-polyelectrolyte complex core (IPEC), (c) classical Pickering emulsion technique, (d) different topologies of Janus particles: snowman-, acorn-, and dumbbell-like nanoparticles (top to bottom), (e) microfluidic photo-polymerization system, and (f) electrospinning technique with a bi-phasic nozzle. Reproduced with permission from [29]. Copyright 2008 The Royal Society of Chemistry.

Figure 4

(a) Schematic representation of bimetallic Janus particles at the hexane–water interface (gold: gold part with surfactant; gray: iron oxide part). (b) Interfacial tension vs time as measured by pendant drop tensiometry (NP: homogeneous nanoparticles; JP: Janus particles). The gold domains were functionalized using 1-dodecanethiol (DDT) or 1-octadecanethiol (ODT). Adapted with permission from [32]. Copyright 2006 American Chemical Society.

Figure 5

(A) SEM top view image of a typical kaolinite platelet (left), schematic picture of kaolinite platelets (centre), and crystal structure of three kaolinite lamellae with the specific chemical functions at the basal TS and OS (right). (B) Schematic picture of a) pristine kaolinite, b) modified with PDPS on the tetrahedral surface (TS), c) further modified with PCM on the opposite octahedral surface (OS), and d) embedding of the final hybrid particle at the interface in a PS-PMMA blend. Reprinted with permission from [34]. Copyright 2013 Elsevier.

Figure 6

a) Proposed photocatalytic process for efficient hydrogen generation using the Janus Au@TiO₂ nanostructures, based on excitation of the LSPR under visible-light irradiation [50]. b) Volume of hydrogen generated (V_H2) under visible-light irradiation from a tungsten halogen lamp using Janus and core-shell Au_50nm@TiO₂ nanostructures, as well as amorphous TiO₂ and bare gold particles [50]. c) Schematic illustration of plasmonic dye-sensitized solar cells (DSSCs) with tailor-designed Au–TiO₂ nanostructures integrated into the photoanode representing the increased photocurrent by LSPR and scattering effects [51]. (a, b) Adapted with permission from [50]. Copyright 2012 WILEY-VCH. (c, d) Reproduced with permission from [51]. Copyright 2014 The Royal Society of Chemistry.

Figure 7

a) UV–vis spectra of Au@Fe₃O₄ nanoparticles corresponding to schematic representations in b). The scheme illustrates the shape evolution of the particles during heating (Au: dark gray, Fe₃O₄: bright gray). Reproduced with permission from [72]. Copyright 2008 WILEY-VCH.

Figure 8

TEM bright field images of Au nanoparticles with different diameters (a) 4 nm, (b) 8 nm, and (c) 15 nm; (d) 2D superlattice of 8 nm Au nanoparticles.

Figure 9

TEM bright field images of Au@MnO and Au@Fe₃O₄ heterodimer-nanoparticles: (a) 9@18 nm Au@MnO, (b) 4@22 nm Au@MnO, (c) 9@15 nm Au@Fe₃O₄, and (d) 7@20 nm Au@Fe₃O₄.

Figure 10

Domain size dependency of absorption maximum of Au@MnO nanoparticles determined by UV–vis spectroscopy in comparison to pristine Au nanoparticles.

Figure 11

UV–vis spectra of Au (solid), Au@MnO (dashed), and Au@Fe₃O₄ (dotted) nanoparticles normalized to the absorption at 800 nm.

Figure 12

Schematic representation of the formation of Cu@Fe₃O₄ heterodimers with different morphologies based on the use of solvents of various polarity (top) and corresponding (HR-)TEM images of (a, b) cube-shape, (c, d) cloverleaf-shape Cu@Fe₃O₄ heterodimerparticles (bottom). Reproduced with permission from [57]. Copyright 2011 The Royal Society of Chemistry.

Figure 13

Synthetic protocol of the synthesis of Co@Fe₂O₃ heterodimer and phase pure CoFe₂O₄ nanoparticles (top) and corresponding (HR-)TEM images of (a,b) heterodimer particles and (c,d) isotropic CoFe₂O₄ nanoparticles. Reproduced with permission from [59]. Copyright 2011 The Royal Society of Chemistry.

Figure 14

CLSM images of HeLa cells co-incubated with Au@MnO@SiO₂-Atto495 Janus particles (green) for 24 h at 37 °C (c(Mn²⁺) = 100 µg/mL). a) λ_ex = 488 nm, cell nuclei were stained using DAPI, b) two-photon image of the same sample, λ_ex(2P) = 970 nm. Scale: 10 µm. Adapted with permission from [39]. Copyright 2014 American Chemical Society.

Scheme 1

Seed-mediated synthesis of Au@MO_x heterodimers, subsequent encapsulation with silica and functionalization of the SiO₂-shell. Adapted with permission from [39]. Copyright 2014 American Chemical Society.

Figure 15

TEM micrographs of silica encapsulated Janus particles; (a,b) Au@MnO@SiO₂ (10@20 nm), and (c,d) Au@Fe₃O₄@SiO₂ (9@15 nm).

Figure 16

Dynamic light scattering results of Au (red dots), Au@Fe₃O₄ (blue dots) dispersed in n-heptane, and Au@Fe₃O₄@SiO₂ (black dots) in water (λ = 632.8 nm, T = 293 K, viscosity η: 0.41 cP n-heptane, 1.005 cP water). a) Universally scaled autocorrelation functions measured at scattering angle θ = 30° together with biexponential fitting function lines and corresponding residues. b) Apparent diffusion coefficients as a function of the scattering vector q² in the range of scattering angle 30° ≤ θ ≤ 150°.

Figure 17

(a) Time-resolved fluorescence spectra of Au nanoparticles (green), Atto495 (orange), MnO@SiO₂ (red), and Au@MnO@SiO₂-Atto495 (blue) after excitation at λ = 400 nm by a 100 fs pulse indicating the absence of electron transfer between Au and MnO respectively Atto495 encapsulated within the SiO₂ shell; (b) respective photoluminescence dynamics tracked at 500–550 nm.

Figure 18

Labelfree LC-MS Analysis of the hard protein corona of Fe₃O₄@SiO₂, MnO@SiO₂, and Au@MnO@SiO₂ nanoparticles showing a dependence on composition, morphology, as well as incubation time.