The multiplexed detection of protein biomarkers in plasma present over a range of clinically relevant concentrations continues to be difficult for surface-based bioaffinity detection platforms such as surface plasmon resonance (SPR). As well as nonspecific adsorption, challenges include quantitative comparison between targets whose concentrations differ by orders of magnitude, regenerating SPR chips after plasma exposure, and the two- or four-channel limitation of many commercial SPR instruments limiting sample throughput. In this article, we explore an approach where two protein biomarkers alpha-1 antitrypsin (AAT) and Tau 381 are detected in tandem within a single SPR channel at micromolar and femtomolar concentrations, respectively. This was achieved by creating a mixed antibody (antiAAT and antiTau) monolayer on the chip surface. After the adsorption of AAT and/or Tau, further specificity was obtained via the adsorption of a DNA aptamer specific to each target. The detection range for each target was controlled via the relative surface density ratio of each antibody type as well as each aptamer concentration. Calibration measurements were performed in both buffer and spiked plasma with the detection of native concentrations of ∼39 fM (Tau) and ∼65 μM (AAT) in a human plasma sample. Finally, tandem measurements of both targets within the same SPR signal channel were demonstrated at these very different concentrations.

In this paper, we report on a new type of self-assembled plasmonic nanostructure, called gold suprashells, which are assembled around superparamagnetic iron oxide nanoparticle (SPION) cores. Gold suprashells have multiple surface plasmon resonances over a broad vis–NIR wavelength range, which makes them useful in applications where broadband absorption is required. For example, suprashells are efficient substrates that enhance surface-enhanced Raman scattering signals across multiple excitation wavelengths. This unique multiresonant character is afforded by the suprashell structure, which comprises anisotropic assemblies of nanoparticles of tunable length. Furthermore, gold suprashells generate more heat when excited with a laser compared to the nanoparticle building blocks, therefore making them promising materials for photothermal applications. The suprashells can potentially be assembled onto any negatively charged core, which opens up multiple possibilities for the development of multifunctional core/suprashell nanoparticle designs. Here, we assemble gold suprashells around dextran-coated SPIONs in order to obtain plasmonic and magnetic nanoparticles. Cells that have internalized the multifunctional nanoparticles can be accumulated with a magnet and killed with a laser through the generation of plasmonic heat. This approach shows promise for the development of therapies aimed at killing circulating tumor cells by utilizing the proposed magnetic and plasmonic nanoparticles.

Surface-enhanced Raman scattering (SERS) is a promising imaging modality for use in a variety of multiplexed tracking and sensing applications in biological environments. However, the uniform production of SERS nanoparticle tags with high yield and brightness still remains a significant challenge. Here, we describe an approach based on the controlled coadsorption of multiple dye species onto gold nanorods to create tags that can be detected across a much wider range of excitation wavelengths (514–1064 nm) compared to conventional approaches that typically focus on a single wavelength. This was achieved without the added complexity of nanoparticle aggregation or growing surrounding metallic shells to further enhance the surface-enhanced resonance Raman scattering (SERRS) signal. Correlated Raman and scanning electron microscopy mapping measurements of individual tags were used to clearly demonstrate that strong and reproducible SERRS signals at high particle yields (>92%) were readily achievable. The polyelectrolyte-wrapped nanorod–dye conjugates were also found to be highly stable as well as noncytotoxic. To demonstrate the use of these universal tags for the multimodal optical imaging of biological specimens, confocal Raman and fluorescence maps of stained immune cells following nanoparticle uptake were acquired at several excitation wavelengths and compared with dark-field images. The ability to colocalize and track individual optically encoded nanoparticles across a wide range of wavelengths simultaneously will enable the use of SERS alongside other imaging techniques for the real-time monitoring of cell–nanoparticle interactions.Keywords: cell imaging; gold nanorod; single nanoparticle imaging and spectroscopy; surface-enhanced Raman

The preparation and characterization of stable and non-aggregated colloidal suspensions of gold nanorod–molecular dye complexes which exhibit very bright surface-enhanced resonance Raman scattering (SERRS) signals is described. A systematic study was performed where both the localized surface plasmon resonance (LSPR) of the nanorod and the molecular resonance of dyes adsorbed onto the rod surface were selectively tuned with respect to the laser excitation wavelengths. Resonance coupling was found to be a significant factor in the overall SERRS enhancement. The polymer stabilized nanorod–dye conjugates were prepared without the added complexity of nanoparticle aggregation as well as having good control over the surface coverage and orientation of the dye molecules. Furthermore, we demonstrate that this new class of Raman nanotags greatly outperforms an approach based on quasi-spherical gold nanoparticles.

The application of biofunctionalized nanoparticles possessing various shapes and sizes for the enhanced surface plasmon resonance (SPR) detection of a protein biomarker at attomolar concentrations is described. Three different gold nanoparticle shapes (cubic cages, rods and quasi-spherical) with each possessing at least one dimension in the 40–50 nm range were systematically compared. Each nanoparticle (NP) was covalently functionalized with an antibody (anti-thrombin) and used as part of a sandwich assay in conjunction with a Au SPR chip modified with a DNA-aptamer probe specific to thrombin. The concentration of each NP-antibody conjugate solution was first optimized prior to establishing that the quasi-spherical nanoparticles resulted in the greatest enhancement in sensitivity with the detection of thrombin at concentrations as low as 1 aM. When nanorod and nanocage antibody conjugates were instead used, the minimum target concentrations detected were 10 aM (rods) and 1 fM (cages). This is a significant improvement (>103) on previous NP-enhanced SPR studies utilizing smaller (∼15 nm) gold NP conjugates and is attributed to the functionalization of both the NP and chip surfaces resulting in low nonspecific adsorption as well as a combination of density increases and plasmonic coupling inducing large shifts in the local refractive index at the chip surface upon nanoparticle adsorption.

The controlled side-by-side assembly of gold nanorods in solution together with Raman reporter dye molecules to create small SERRS-active clusters stabilised by a surrounding polymer layer is demonstrated. This promising new class of nanotags offers several advantages over spherical nanoparticles for bioimaging and is of potential importance for a wide range of plasmon-enhanced spectroscopies and can also serve as building blocks for more complex solution-phase nanostructures.

A novel wide-field approach for the real-time Surface Enhanced Raman Scattering (SERS) imaging of multiple silver nanoparticle clusters suspended in solution is described. This method enables direct correlation of the SERS activity of a single nanoparticle aggregate and its size through measurement of the cluster diffusion coefficient and can also be performed in a high-throughput basis. As a first demonstration, we investigate the salt-induced aggregation of silver nanoparticles in the presence of a reporter tag molecule, which has a high affinity for the nanoparticle surface. In addition to tracking individual particles, direct comparison of Rayleigh and SERS videos of the same colloid solution enabled measurement of the fraction of individual clusters that are SERS active and the dependence of this value on the relative concentration of the tag molecule. Furthermore, given the ability to also rapidly profile any nonuniformity in particle size distributions, we expect this approach will not only provide a new tool for the fundamental understanding of SERS but also significantly contribute to the development of an array of emerging nanoparticle-enhanced biomolecule and imaging detection platforms.

The controlled side-by-side assembly of gold nanorods in solution together with Raman reporter dye molecules to create small SERRS-active clusters stabilised by a surrounding polymer layer is demonstrated. This promising new class of nanotags offers several advantages over spherical nanoparticles for bioimaging and is of potential importance for a wide range of plasmon-enhanced spectroscopies and can also serve as building blocks for more complex solution-phase nanostructures.

The preparation and characterization of stable and non-aggregated colloidal suspensions of gold nanorod–molecular dye complexes which exhibit very bright surface-enhanced resonance Raman scattering (SERRS) signals is described. A systematic study was performed where both the localized surface plasmon resonance (LSPR) of the nanorod and the molecular resonance of dyes adsorbed onto the rod surface were selectively tuned with respect to the laser excitation wavelengths. Resonance coupling was found to be a significant factor in the overall SERRS enhancement. The polymer stabilized nanorod–dye conjugates were prepared without the added complexity of nanoparticle aggregation as well as having good control over the surface coverage and orientation of the dye molecules. Furthermore, we demonstrate that this new class of Raman nanotags greatly outperforms an approach based on quasi-spherical gold nanoparticles.