Colloidal Self-Assembly of Silver Nanoparticle Clusters for Optical Metasurfaces.

Optical metasurfaces are two-dimensional assemblies of nanoscale optical resonators and could constitute the next generation of ultrathin optical components. The development of methods to manufacture these nanostructures on a large scale is still a challenge, while most performance demonstrations were obtained with lithographically fabricated metasurfaces that are restricted to small scales. Self-assembly fabrication routes are promising alternatives and have been used to produce original nanoresonators. Reports of self-assembled metasurface fabrication, however, are still scarce. Here, we show that an emulsion-based formulation approach can be used both for the fabrication of complex colloidal resonators, presenting a strong interaction with light, in particular due to simultaneous magnetic and electric modes of resonance, and for their deposition in homogeneous films. This fabrication technique involves emulsification of an aqueous suspension of silver nanoparticles in an oil phase, followed by controlled drying of the emulsion, and produces silver colloidal clusters. We show that the drying process can be controlled in a liquid emulsion, producing a metafluid, as well as in a sedimented emulsion, producing a metasurface. The structural control of the synthesized colloidal clusters is demonstrated with electron microscopy and X-ray scattering techniques. Using a polarization-resolved multiangle light scattering setup in the visible wavelength range, we conduct a comprehensive angular and spectroscopic study of the optical resonant scattering of the nanoresonators in a metafluid and show that they present strong optical magnetic resonances and directional forward-scattering patterns, with scattering efficiencies of up to 4. The metasurfaces consist of homogeneous films, of variable surface density, of colloidal clusters that have the same extinction properties on the surface and in the fluid. This experimental approach allows for large-scale production of metasurfaces.

Characterization of ovarian cancer-derived extracellular vesicles by surface-enhanced Raman spectroscopy.

Ovarian cancer is the most lethal gynecological malignancy, owing to the fact that most cases are diagnosed at a late stage. To improve prognosis and reduce mortality, we must develop methods for the early diagnosis of ovarian cancer. A step towards early and non-invasive cancer diagnosis is through the utilization of extracellular vesicles (EVs), which are nanoscale, membrane-bound vesicles that contain proteins and genetic material reflective of their parent cell. Thus, EVs secreted by cancer cells can be thought of as cancer biomarkers. In this paper, we present gold nanohole arrays for the capture of ovarian cancer (OvCa)-derived EVs and their characterization by surface-enhanced Raman spectroscopy (SERS). For the first time, we have characterized EVs isolated from two established OvCa cell lines (OV-90, OVCAR3), two primary OvCa cell lines (EOC6, EOC18), and one human immortalized ovarian surface epithelial cell line (hIOSE) by SERS. We subsequently determined their main compositional differences by principal component analysis and were able to discriminate the groups by a logistic regression-based machine learning method with ∼99% accuracy, sensitivity, and specificity. The results presented here are a great step towards quick, facile, and non-invasive cancer diagnosis.

Characterization of extracellular vesicles derived from mesenchymal stromal cells by surface-enhanced Raman spectroscopy.

Extracellular vesicles (EVs) are secreted by all cells into bodily fluids and play an important role in intercellular communication through the transfer of proteins and RNA. There is evidence that EVs specifically released from mesenchymal stromal cells (MSCs) are potent cell-free regenerative agents. However, for MSC EVs to be used in therapeutic practices, there must be a standardized and reproducible method for their characterization. The detection and characterization of EVs are a challenge due to their nanoscale size as well as their molecular heterogeneity. To address this challenge, we have fabricated gold nanohole arrays of varying sizes and shapes by electron beam lithography. These platforms have the dual purpose of trapping single EVs and enhancing their vibrational signature in surface-enhanced Raman spectroscopy (SERS). In this paper, we report SERS spectra for MSC EVs derived from pancreatic tissue (Panc-MSC) and bone marrow (BM-MSC). Using principal component analysis (PCA), we determined that the main compositional differences between these two groups are found at 1236, 761, and 1528 cm-1, corresponding to amide III, tryptophan, and an in-plane -C=C- vibration, respectively. We additionally explored several machine learning approaches to distinguish between BM- and Panc-MSC EVs and achieved 89 % accuracy, 89 % sensitivity, and 88 % specificity using logistic regression.

Investigation of Au SAMs Photoclick Derivatization by PM-IRRAS.

In this work, we present a clean one-step process for modifying headgroups of self-assembled monolayers (SAMs) on gold using photo-enabled click chemistry. A thiolated, cyclopropenone-caged strained alkyne precursor was first functionalized onto a flat gold substrate through self-assembly. Exposure of the cyclopropenone SAM to UVA light initiated the efficient photochemical decarbonylation of the cyclopropenone moiety, revealing the strained alkyne capable of undergoing the interfacial strain-promoted alkyne-azide cycloaddition (SPAAC). Irradiated SAMs were derivatized with a series of model azides with varied hydrophobicity to demonstrate the generality of this chemical system for the modification and fine-tuning of the surface chemistry on gold substrates. SAMs were characterized at each step with polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to confirm the successful functionalization and reactivity. Furthermore, to showcase the compatibility of this approach with biochemical applications, cyclopropenone SAMs were irradiated and modified with azide-bearing cell adhesion peptides to promote human fibroblast cell adhesion, and then imaged by live-cell fluorescence microscopy. Thus, the "photoclick" methodology reported here represents an improved, versatile, catalyst-free protocol that allows for a high degree of control over the modification of material surfaces, with applicability in materials science as well as biochemistry.

Deciphering tip-enhanced Raman imaging of carbon nanotubes with deep learning neural networks.

Recent release of open-source machine learning libraries presents opportunities to unify machine learning with nanoscale research, thus improving effectiveness of research methods and characterization protocols. This paper outlines and demonstrates the effectiveness of such a synergy with artificial neural networks to provide for an accelerated and enhanced characterization of individual carbon nanotubes deposited over a surface. Our algorithms provide a rapid diagnosis and analysis of tip-enhanced Raman spectroscopy mappings and the results show an improved spectral assignment of spectral features and spatial contrast of the collected images. Using several examples, we demonstrate the robustness and versatility of our deep learning neural network models. We highlight the use of machine learning and data science in tandem with tip-enhanced Raman spectroscopy technique enables a fast and accurate understanding of experimental data, thus leading to a powerful and comprehensive imaging analysis applied to spectroscopic measurements.

Probing mid-infrared plasmon resonances in extended radial fractal structures.

Infrared (IR) antennas made of metallic nanostructures are widely tunable from the near- to the far-IR range. They can be utilized for a variety of applications such as light harvesting and photonic filters, and their structural linear or circular anisotropy can be exploited to further enhance the sensitivity of spectroscopic measurements. Here gold dendritic fractal structures that were optimized to exhibit multiple resonances in the mid-IR range were characterized using a scattering-type scanning near-field optical IR microscope. The spatially resolved IR maps associated with the individual modes serve as a basis to understand the mode evolution between each fractal generation.

Optoelectronic, Aggregation, and Redox Properties of Double-Rotor Boron Difluoride Hydrazone Dyes.

We develop the chemistry of boron difluoride hydrazone dyes (BODIHYs) bearing two aryl substituents and explore their properties. The low-energy absorption bands (λmax =427-464 nm) of these dyes depend on the nature of the N-aryl groups appended to the BODIHY framework. Electron-donating and extended π-conjugated groups cause a redshift, whereas electron-withdrawing groups result in a blueshift. The title compounds were weakly photoluminescent in solution and strongly photoluminescent as thin films (λPL =525-578 nm) with quantum yields of up to 18 % and lifetimes of 1.1-1.7 ns, consistent with the dominant radiative decay through fluorescence. Addition of water to THF solutions of the BODIHYs studied causes molecular aggregation which restricts intramolecular motion and thereby enhances photoluminescence. The observed photoluminescence of BODIHY thin films is likely facilitated by a similar molecular packing effect. Finally, cyclic voltammetry studies confirmed that BODIHY derivatives bearing para-substituted N-aryl groups could be reversibly oxidized (Eox1 =0.62-1.02 V vs. Fc/Fc+ ) to their radical cation forms. Chemical oxidation studies confirmed that para-substituents at the N-aryl groups are required to circumvent radical decomposition pathways. Our findings provide new opportunities and guiding principles for the design of sought-after multifunctional boron difluoride complexes that are photoluminescent in the solid state.

Advancements in fractal plasmonics: structures, optical properties, and applications.

The structural characteristics of plasmonic nanostructures directly influence their plasmonic properties, and therefore, their potential role in applications ranging from sensing and catalysis to light- and energy-harvesting. For a structure to be compatible with a selected application, it is critical to accurately tune the plasmonic properties over a specific spectral range. Fabricating structures that meet these stringent requirements remains a significant challenge as plasmon resonances are generally narrow with respect to the considered selected spectral range. Adapted from their well-established role in GHz applications, plasmonic fractal structures have emerged as architectures of interest due to their ability to support multiple tunable resonances over broad spectral domains. Here, we review the advancements that have been made in the growing field of fractal plasmonics. Iterative and space-filling geometries that can be prepared by advanced nanofabrication techniques, notably electron-beam lithography, are presented along with the optical properties of such structures and metasurfaces. The distributions of electromagnetic enhancement for some of these fractals is shown, along with how the resonances can be mapped experimentally. This review also explores how fractal structures can be used for applications in solar cell and plasmon-based sensing applications. Finally, the future areas of physical and analytical science that could benefit from fractal plasmonics are discussed.

Luminescent CdSe Superstructures: A Nanocluster Superlattice and a Nanoporous Crystal.

Superstructures, combining nanoscopic constituents into micrometer-size assemblies, have a great potential for utilization of the size-dependent quantum-confinement properties in multifunctional electronic and optoelectronic devices. Two diverse superstructures of nanoscopic CdSe were prepared using solvothermal conversion of the same cadmium selenophenolate precursor (Me4N)2[Cd(SePh)4]: the first is a superlattice of monodisperse [Cd54Se32(SePh)48(dmf)4]4- nanoclusters; the second is a unique porous CdSe crystal. Nanoclusters were crystallized as cubic crystals (≤0.5 mm in size) after solvothermal treatment at 200 °C in DMF. UV-vis absorption and PLE spectra of the reported nanoclusters are consistent with previously established trends for the known families of tetrahedral CdSe frameworks. In contrast to these, results of PL spectra are rather unexpected, as distinct room temperature emission is observed both in solution and in the solid state. The porous CdSe crystals were isolated as red hexagonal prisms (≤70 µm in size) via solvothermal treatment under similar conditions but with the addition of an alkylammonium salt. The presence of a three-dimensional CdSe network having a coherent crystalline structure inside hexagonal prisms was concluded based on powder X-ray diffraction, selected area electron diffraction and electron microscopy imaging. Self-assembly via oriented attachment of crystalline nanoparticles is discussed as the most probable mechanism of formation.

Tip-enhanced Raman spectroscopy of amyloid ß at neuronal spines.

The early stages of Alzheimer's disease pathogenesis are thought to occur at the synapse level, since synapse loss can be directly correlated with memory dysfunction. Considerable evidence has suggested that amyloid beta (Aß), a secreted proteolytic derivative of amyloid precursor protein, appears to be a critical factor in the early 'synaptic failure' that is observed in Alzheimer's disease pathogenesis. The identification of Aß at neuronal spines with high spatial resolution and high surface specificity would facilitate unraveling the intricate effect of Aß on synapse loss and its effect on neighboring neuronal connections. Here, tip-enhanced Raman spectroscopy was used to map the presence of Aß aggregations in the vicinity of the spines exposed to Aß preformed in vitro. Exposure to Aß was of 1 and 6 hours. The intensity variation of selected vibrational modes of Aß was mapped by TERS for different exposure times to Aß. Of interest, we discuss the distinct contributions of the amide modes from Aß that are enhanced by the TERS process and in particular the suppression of the amide I mode in the context of recently reported observations in the literature.

Tip-enhanced Raman spectroscopy: plasmid-free vs. plasmid-embedded DNA.

Tip-enhanced Raman spectroscopy (TERS) provides greatly enhanced Raman signals along with ultra-high lateral spatial resolutions and has been demonstrated to be a technique of choice to study a variety of biochemical specimens such as DNA and RNA at the single chain level. However, the sensitivity of TERS to demonstrate the influence of the nanoscale environment on DNA properties has not been investigated. Herein, we used a gap-mode TERS as an ultra-sensitive label-free technique to investigate the influence of the local plasmid on the DNA properties of a ß2-adrenergic receptor (ß2AR). Remarkable lateral spatial resolutions down to 8 nm were also acquired for the collected Raman signals under ambient conditions. This approach offers not only a tool to examine the influence of the local nanoscale environment surrounding the DNA structure, but also the localization of the majority of nucleic acid base(s) present in selected regions on the DNA strand.

A nanoaggregate-on-mirror platform for molecular and biomolecular detection by surface-enhanced Raman spectroscopy.

A nanoaggregate-on-mirror (NAOM) structure has been developed for molecular and biomolecular detection using surface-enhanced Raman spectroscopy (SERS). The smooth surface of the gold mirror allows for simple and homogeneous functionalization, while the introduction of the nanoaggregates enhances the Raman signal of the molecule(s) in the vicinity of the aggregate-mirror junction. This is evidenced by functionalizing the gold mirror with 4-nitrothiophenol, and the further addition of gold nanoaggregates promotes local SERS activity only in the areas with the nanoaggregates. The application of the NAOM platform for biomolecular detection is highlighted using glucose and H2O2 as molecules of interest. In both cases, the gold mirror is functionalized with 4-mercaptophenylboronic acid (4-MPBA). Upon exposure to glucose, the boronic acid moiety of 4-MPBA forms a cyclic boronate ester. Once the nanoaggregates are added to the surface, detection of glucose is possible without the use of an enzyme. This method of indirect detection provides a limit of detection of 0.05 mM, along with a linear range of detection from 0.1 to 15 mM for glucose, encompassing the physiological range of blood glucose concentration. The detection of H2O2 is achieved with optical inspection and SERS. The H2O2 interferes with the coating of the gold mirror, enabling qualitative detection by visual inspection. Simultaneously, the H2O2 reacts with the boronic acid to form a phenol, a change that is detected by SERS.

Second harmonic generation from gold meta-molecules with three-fold symmetry.

The unique optical properties of arrays of metallic nanoparticles are of great interest for many applications such as in optical data storage, sensing applications, optoelectronic devices or as platforms to increase the detection limit in spectroscopic measurements. Nonlinear optical phenomena can also be altered by metallic nanostructures opening new possible applications. In this work, arrays composed of non-centrosymmetric individual structures with three fold axial symmetry made of gold are designed and fabricated using electron beam lithography. The nonlinear optical properties of these structures are investigated using second-harmonic generation microscopy (SHGM) with a femtosecond excitation source set near the plasmon resonance frequency. Modeling of the electromagnetic field distribution around the metallic structures is performed using the Finite Difference Time Domain (FDTD) method, highlighting the confinement of the SHG signal and its polarization dependence. Polarization-resolved measurements are conducted to correlate the SHG signal with the structure and symmetry of the individual nanostructures. Since both two-photon induced photoluminescence (TPPL) and SHG signals are produced upon excitation of these structures, lifetime measurements are performed to further evaluate the magnitude of these two effects.

Enhanced Rates of Photoinduced Molecular Orientation in a Series of Molecular Glassy Thin Films.

Photoinduced orientation in a series of molecular glasses made of small push-pull azo derivatives is dynamically investigated for the first time. Birefringence measurements at 632.8 nm are conducted with a temporal resolution of 100 ms to probe the fast rate of the azo orientation induced under polarized light and its temporal stability over several consecutive cycles. To better evaluate the influence of the azo chemical substituents and their electronic properties on the orientation of the whole molecule, a series of push-pull azo derivatives involving a triphenylaminoazo core substituted with distinct electron-withdrawing moieties is studied. All resulting thin films are probed using polarization modulation infrared spectroscopy that yields dynamical linear dichroism measurements during a cycle of orientation followed by relaxation. We show here in particular that the orientation rates of small molecule-based azo materials are systematically increased up to 7-fold compared to those of a reference polymer counterpart. For specific compounds, the percentage of remnant orientation is also higher, which makes these materials of great interest and promising alternatives to azobenzene-containing polymers for a variety of applications requiring a fast response and absolute control over the molecular weight.

Gold nanosponges (AuNS): a versatile nanostructure for surface-enhanced Raman spectroscopic detection of small molecules and biomolecules.

Prepared by simple pour and mix chemistry, gold nanosponges (AuNS) are versatile structures for surface-enhanced Raman spectroscopy (SERS). An investigation into the enhancement is performed by relating the nanostructure's morphology to the SERS signal. The potential of the AuNS in SERS-based molecular and biomolecular detection is introduced.

Tip-enhanced Raman spectroscopy of graphene-like and graphitic platelets on ultraflat gold nanoplates.

In this study, tip-enhanced Raman spectroscopy (TERS) is used to characterize graphene-like and graphitic platelets composed of a few layers of graphene. Specifically, gap-mode TERS geometry provides a larger enhancement of the local electromagnetic field at the junction formed by a gold sharp tip and a gold substrate. Graphene-like platelets are deposited onto ultra-flat thin gold nanoplates using a surfactant-assisted method. Au-coated atomic force microscopy (AFM) tips are used to probe specific substrate regions coated by the platelets. TERS spectra are collected on distinctive points on the graphene-like layers and surrounding substrate using radially or linearly polarized light, with an excitation wavelength of 632.8 nm. The position, width and intensity of G, D, and 2D Raman-active modes of graphene are discussed as a function of the incident light polarization and for distinct positions on the graphene layer. We report here on the nature of the collected TERS spectra focusing in particular on the edges of the graphene platelets.

On the absorption and electromagnetic field spectral shifts in plasmonic nanotriangle arrays.

The behavior of the electromagnetic field interaction with gold nanotriangles organized in bow-tie arrays is investigated. A side-by-side comparison between the measured absorbance of the array and the modelled integrated electric field resonances confined around the gold structures is presented and discussed to explain the spectral shift between both parameters. Finite difference time domain calculations and Raman measurements of gold triangles of different sizes and periodicity are systematically performed. Numerical calculations show that the spectral maximum of the electric field varies in distinct areas over the metallic structures.

Nanoparticle organization through photoinduced bulk mass transfer.

A series of dipolar triphenylaminoazo derivatives, with largely distinct charge transfer and glass transition temperatures, has been synthesized. Their photomigration capability in the solid state to form surface relief gratings (SRGs) under interferential illumination has been investigated with respect to their photochromic properties and showed a prevailing influence of the bulkiness of the azo substituent. The azo mass transfer was utilized to efficiently photoalign 200 nm polystyrene nanoparticles along the SRG crests, which were initially deposited on nonirradiated azo surfaces. In contrast, nanoparticles spin cast on prestructured surface relief gratings were localized in the troughs of the periodic structures. These distinct locations point out the ability of isotropic and amorphous photochromic thin films to collectively move and organize nano-objects in an ordered fashion through the use of polarized illumination. This versatile approach opens the path to optically aligned ensembles of individual nano-objects over large areas, which can be further combined with metallic conductive or magnetic coating to create novel functional nanostructures.

Targeted proteomics of plasma extracellular vesicles uncovers MUC1 as combinatorial biomarker for the early detection of high-grade serous ovarian cancer.

BACKGROUND: The five-year prognosis for patients with late-stage high-grade serous carcinoma (HGSC) remains dismal, underscoring the critical need for identifying early-stage biomarkers. This study explores the potential of extracellular vesicles (EVs) circulating in blood, which are believed to harbor proteomic cargo reflective of the HGSC microenvironment, as a source for biomarker discovery. RESULTS: We conducted a comprehensive proteomic profiling of EVs isolated from blood plasma, ascites, and cell lines of patients, employing both data-dependent (DDA) and data-independent acquisition (DIA) methods to construct a spectral library tailored for targeted proteomics. Our investigation aimed at uncovering novel biomarkers for the early detection of HGSC by comparing the proteomic signatures of EVs from women with HGSC to those with benign gynecological conditions. The initial cohort, comprising 19 donors, utilized DDA proteomics for spectral library development. The subsequent cohort, involving 30 HGSC patients and 30 control subjects, employed DIA proteomics for a similar purpose. Support vector machine (SVM) classification was applied in both cohorts to identify combinatorial biomarkers with high specificity and sensitivity (ROC-AUC > 0.90). Notably, MUC1 emerged as a significant biomarker in both cohorts when used in combination with additional biomarkers. Validation through an ELISA assay on a subset of benign (n = 18), Stage I (n = 9), and stage II (n = 9) plasma samples corroborated the diagnostic utility of MUC1 in the early-stage detection of HGSC. CONCLUSIONS: This study highlights the value of EV-based proteomic analysis in the discovery of combinatorial biomarkers for early ovarian cancer detection.

Tandem SERS and MS/MS Profiling of Plasma Extracellular Vesicles for Early Ovarian Cancer Biomarker Discovery.

Extracellular vesicles (EVs) are vectors of biomolecular cargo that play essential roles in intercellular communication across a range of cells. Protein, lipid, and nucleic acid cargo harbored within EVs may serve as biomarkers at all stages of disease; however, the choice of methodology may challenge the specificity and reproducibility of discovery. To address these challenges, the integration of rigorous EV purification methods, cutting-edge spectroscopic technologies, and data analysis are critical to uncover diagnostic signatures of disease. Herein, we demonstrate an EV isolation and analysis pipeline using surface-enhanced Raman spectroscopy (SERS) and mass spectrometry (MS) techniques on plasma samples obtained from umbilical cord blood, healthy donor (HD) plasma, and plasma from women with early stage high-grade serous carcinoma (HGSC). Plasma EVs were purified by size exclusion chromatography and analyzed by surface-enhanced Raman spectroscopy (SERS), mass spectrometry (MS), and atomic force microscopy. After determining the fraction of highest EV purity, SERS and MS were used to characterize EVs from HDs, pooled donors with noncancerous gynecological ailments (n = 6), and donors with early stage [FIGO (I/II)] with HGSC. SERS spectra were subjected to different machine learning algorithms such as PCA, logistic regression, support vector machine, naïve Bayes, random forest, neural network, and k nearest neighbors to differentiate healthy, benign, and HGSC EVs. Collectively, we demonstrate a reproducible workflow with the potential to serve as a diagnostic platform for HGSC.