Core-satellite assembly of gold nanoshells on solid gold nanoparticles for a color coding plasmonic nanosensor.

We present core-satellite assemblies comprising a solid gold nanoparticle as the core and hollow decahedral gold nanoshells as satellites for tuning the optical properties of the plasmonic structure for sensing. The core-satellite assemblies were fabricated on a substrate the layer-by-layer assembly of nanoparticles linked by DNA. We used finite-difference time-domain simulations to help guide the geometrical design, and characterized the optical properties and morphology of the solid-shell nanoparticle assemblies using darkfield microscopy, single-nanostructure spectroscopy, and scanning electron microscopy.

Sensing Biomarkers with Plasmonics.

The detection of biomarkers is critical for enabling early disease diagnosis, monitoring the progression, and tracking the effectiveness of therapeutic intervention. Plasmonic sensors exhibit a broad range of analytical capabilities, from the rapid generation of colorimetric readouts to single-molecule sensitivity in ultralow sample volumes, which have led to their increased exploration in bioanalysis and point-of-care applications. This perspective presents selected accounts of recent developments on the different types of plasmonic sensing platforms, the pervasive challenges, and outlook on the pathway to translation.

Metabolic mapping with plasmonic nanoparticle assemblies.

A rapid and simple methodology for the biomolecular analysis of single cells and microenvironments via a stick-and-peel plasmonic sensing platform is reported. Substrate-bound assemblies of plasmonic gold nanoparticles linked by reconfigurable oligonucleotides undergo disassembly upon target binding. Changes in the light scattering intensity of thousands of discrete nanoparticle assemblies are extrapolated concomitantly to yield the mapping of local target concentrations.

DNA-Conjugated Gold Nanoparticles as High-Mass Probes in Imaging Mass Cytometry.

We employ imaging mass cytometry (IMC) to investigate in vitro uptake and cellular distribution of DNA-functionalized gold nanoparticles (AuNPs). IMC enables the multiparametric imaging of cell components and allows for the detection of AuNPs in cells with >100 times higher sensitivity than conventional confocal fluorescence imaging, as each nanoparticle contains thousands of atoms for signal amplification. Changes in the accumulation of nanoparticles in cells due to oligonucleotide sequence-dependent interactions are exploited to examine a model biomarker for hypoxia-microRNA-210.

LSPR Tuning from 470 to 800 nm and Improved Stability of Au-Ag Nanoparticles Formed by Gold Deposition and Rebuilding in the Presence of Poly(styrenesulfonate).

Stability and precise control over functional properties of metal nanoparticles remain a challenge for the realization of prospective applications. Our described process of shell formation and rebuilding can address both these challenges. Template silver nanoparticles (AgNPs) stabilized by poly(styrenesulfonate) are first transformed with gold deposition, after which the resulting shell rebuilds with the replaced silver.

Tuning the Sensing Performance of Multilayer Plasmonic Core-Satellite Assemblies for Rapid Detection of Targets from Lysed Cells.

Optical sensors based on discrete plasmonic nanostructures are invaluable for probing biomolecular interactions when applied as plasmonic rulers or reconfigurable multinanoparticle assemblies. However, their adaptation as a versatile sensing platform is limited by the research-grade instrumentation required for single-nanostructure imaging and/or spectroscopy and complex data fitting and analysis. Additionally, the dynamic range is often too narrow for the quantitative analysis of targets of interest in biodiagnostics, food safety, or environmental monitoring.

Electrical Detection of Quantum Dot Hot Electrons Generated via a Mn-Enhanced Auger Process.

An all-solid-state quantum-dot-based photon-to-current conversion device is demonstrated that selectively detects the generation of hot electrons. Photoexcitation of Mn-doped CdS quantum dots embedded in the device is followed by efficient picosecond energy transfer to Mn with a long-lived (millisecond) excited-state lifetime. Electrons injected into the QDs under applied bias then capture this energy via Auger de-excitation, generating hot electrons that possess sufficient energy to escape over a ZnS blocking layer, thereby producing current.

Factors influencing polyelectrolyte-aptamer multilayered films with target-controlled permeability for sensing applications.

Portable, easy-to-use and cost-effective sensing devices are desirable in healthcare, environmental monitoring and food safety. Herein we employ polyelectrolyte-aptamer (PE-aptamer) multilayered films that exhibit target-responsive permeability for colorimetric and electrochemical sensing. We present the quantitative detection of an exemplary small molecule, quinine, and address the potential for detection in complex media by examining interference effects.

Direct detection of microRNA based on plasmon hybridization of nanoparticle dimers.

MicroRNAs (miRNA) are important for regulating a range of biochemical pathways. Abnormal levels of miRNA in cells or secreted into biological fluids have been identified in diseases. MiRNA can therefore be potential biomarkers for early disease diagnosis; however their detection and quantification are challenging.

Morphology-based plasmonic nanoparticle sensors: controlling etching kinetics with target-responsive permeability gate.

We present a sensing platform based on the morphological changes of plasmonic nanoparticles. Detection is achieved by using a stimulus-responsive polyelectrolyte-aptamer thin film to control the rate of diffusion of etchants that alter the shape and size of the nanoparticles. We show that the extent of morphological change and the colorimetric response depends on the amount of analyte bound.

Photoisomerization quantum yield of azobenzene-modified DNA depends on local sequence.

Photoswitch-modified DNA is being studied for applications including light-harvesting molecular motors, photocontrolled drug delivery, gene regulation, and optically mediated assembly of plasmonic metal nanoparticles in DNA-hybridization assays. We study the sequence and hybridization dependence of the photoisomerization quantum yield of azobenzene attached to DNA via the popular d-threoninol linkage. Compared to free azobenzene we find that the quantum yield for photoisomerization from trans to cis form is decreased 3-fold (from 0.

Electron accumulation on metal nanoparticles in plasmon-enhanced organic solar cells.

Plasmonic metal nanoparticles have been used to enhance the performance of thin-film devices such as organic photovoltaics based on polymer/fullerene blends. We show that silver nanoprisms accumulate long-lived negative charges when they are in contact with a photoexcited bulk heterojunction blend composed of poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM). We report both the charge modulation and electroabsorption spectra of silver nanoprisms in solid-state devices and compare these spectra with the photoinduced absorption spectra of P3HT/PCBM blends containing silver nanoprisms.

Photoswitchable oligonucleotide-modified gold nanoparticles: controlling hybridization stringency with photon dose.

We describe a new class of stimulus-responsive DNA-functionalized gold nanoparticles that incorporate azobenzene-modified oligonucleotides. Beyond the classic directed assembly and sensing behaviors associated with oligonucleotide-modified nanoparticles, these particles also exhibit reversible photoswitching of their assembly behavior. Exposure to UV light induces a trans-cis isomerization of the azobenzene which destabilizes the DNA duplex, resulting in dissociation of the nanoparticle assemblies.

Plasmonic nanoparticle dimers for optical sensing of DNA in complex media.

We introduce a new sensing modality based on the actuation of discrete gold nanoparticle dimers. Binding of the target DNA leads to a geometrical extension of the dimer, thereby yielding a spectral blue shift in the hybridized plasmon mode as detected by single nanostructure scattering spectroscopy. The magnitude and opposite direction of this shift enabled us to spectroscopically distinguish the target from nonspecific binding and to detect the target in complex media like serum.

Synergy of slow photon and chemically amplified photochemistry in platinum nanocluster-loaded inverse titania opals.

We show that the photodegradation efficiency of TiO2 has been amplified 4-fold via the cooperativity of slow photons in photonic crystal and the incorporation of Pt nanoclusters. Various loadings of Pt nanoparticles were photodeposited on the surface of TiO2 inverse opals and the photodegradation of adsorbed acid orange was investigated. While slow photons increased the effective path length of light, Pt nanoparticles extended the lifetimes of the UV-excited electrons and holes.

Effect of disorder on the optically amplified photocatalytic efficiency of titania inverse opals.

Optically amplified photochemistry with slow photons has been realized in our previous work when a photoactive material such as TiO(2) was molded into a photonic crystal and the corresponding energy of photonic bands overlapped with the electronic excitation. While numerous applications of photonic crystals have been proposed, the real practicality depends on the extent of structural imperfection that can be tolerated before significant deterioration in the optical response deems it unrealistic to use. As a result, it is important to evaluate the amount of structural disorder that can be tolerated in inverse TiO(2) opals if they are to be used as amplified photocatalysts for photolytic degradation of organics in environmental remediation and water purification.

Block copolymers under periodic, strong three-dimensional confinement.

In this communication we study the influence of strong 3D confinement on the self-assembly of diblock copolymers containing a polyferrocenylsilane metallopolymer segment. Both silica colloidal crystals and silica inverse colloidal crystals, having nanometer-scale interconnected pore networks, are used as molds to direct the self-assembly. Unusual morphologies, such as concentric shells and branched lamellae, result from the interaction of the polymer with the high surface area topologically periodic templates.