6 research outputs found
Mie Resonance Engineering in Meta-Shell Supraparticles for Nanoscale Nonlinear Optics
Supraparticles are coordinated assemblies of discrete nanoscale building blocks into complex and hierarchical colloidal superstructures. Holistic optical responses in such assemblies are not observed in an individual building block or in their bulk counterparts. Furthermore, subwavelength dimensions of the unit building blocks enable engraving optical metamaterials within the supraparticle, which thus far has been beyond the current pool of colloidal engineering. This can lead to effective optical features in a colloidal platform with ability to tune the electromagnetic responses of these particles. Here, we introduce and demonstrate the nanophotonics of meta-shell supraparticle (MSP), an all dielectric colloidal superstructure having an optical nonlinear metamaterial shell conformed onto a spherical core. We show that the metamaterial shell facilitates engineering the Mie resonances in the MSP that enable significant enhancement of the second harmonic generation (SHG). We show several orders of magnitude enhancement of second-harmonic generation in an MSP compared to its building blocks. Furthermore, we show an absolute conversion efficiency as high as 10â»â· far from the damage threshold, setting a benchmark for SHG with low-index colloids. The MSP provides pragmatic solutions for instantaneous wavelength conversions with colloidal platforms that are suitable for chemical and biological applications. Their engineerability and scalability promise a fertile ground for nonlinear nanophotonics in the colloidal platforms with structural and material diversity
Omnidispersible Hedgehog Particles with Multilayer Coatings for Multiplexed Biosensing
Hedgehog particles (HPs) replicating
the spiky geometry of pollen
grains revealed surprisingly high dispersion stability regardless
of whether their hydrophobicity/hydrophilicity matches that of the
media or not. This property designated as omnidispersibility is attributed
to the drastic reduction of van der Waals interactions between particles
coated with stiff nanoscale spikes as compared to particles of the
same dimensions with smooth surfaces. One may hypothesize but it remains
unknown, however, whether HPs modified with polymers or nanoparticles
(NPs) would retain this property. Surface modifications of the spikes
will expand the functionalities of HPs, making possible their utilization
as omnidispersible carriers. Here, we show that HPs carrying dense
conformal coatings made by layer-by-layer (LBL/LbL) assembly maintain
dispersion stability in environments of extreme polarity and ionic
strength. HPs, surface-modified by multilayers of polymers and gold
NPs, are capable of surface-enhanced Raman scattering (SERS) and overcome
the limited colloidal stability of other SERS probes. The agglomeration
resilience of HPs leads to a greater than one order of magnitude increase
of SERS intensity as compared to colloids with smooth surfaces and
enables simultaneous detection of several targets in complex media
with high ionic strength. Omnidispersible optically active colloids
open the door for rapid multiplexed SERS analysis in biological fluids
and other applications
Scattering Properties of Individual Hedgehog Particles
âHedgehogâ
particles (HPs) possess a micrometer-sized
dielectric spherical core which is densely coated with nanoscale metal
oxide spikes. This unique surface topography, resembling the appearance
of a hedgehog, provides the particles with the exclusive physiochemical
property to stably disperse in both polar and nonpolar solvents without
the necessity of changing the surface chemistry. Optical extinction
measurements of HP ensembles in aqueous solution indicate a broad
spectral response in the visible range. However, there remains a dearth
of fundamental knowledge about the cause of the broad optical resonance,
as it can be a consequence of shape polydispersity in the many-particle
system or intrinsic to each individual HP. In this paper, we present
the first experimental study of the dark-field scattering of individual
hydrophilic and hydrophobic HPs. Our measurements disclose that the
expansive optical response in the visible spectral range is truly
characteristic for the far-field scattering of a single HP. Our results
also uncover how intrinsic particle features, such as spike length,
as well as environmental changes affect the scattering of individual
HPs. In particular, by changing the atmosphere around a hydrophilic
HP from air to nitrogen and by completely immersing in water by employing
a 3D optical trap, we discovered that the scattering from a hydrophilic
HP is strongly modulated by excess water in its interstitial shell