This PDF file contains the front matter associated with SPIE Proceedings Volume 11978, including the Title Page, Copyright information, and Table of Contents.

Exciting the Raman effect at a wavelength in resonance with the absorption spectrum of the sample, typically in the visible spectral range, can increase the strength of Raman lines by orders of magnitude. Particularly in this case, the lines can be obscured by fluorescence but also by background light. Shifted excitation Raman difference spectroscopy (SERDS) can recover Raman signatures. This method uses an excitation light source with alternating operation of two neighboring, spectrally stabilized, narrow emission wavelengths. Only the Raman lines follow that change in the excitation wavelength and can be separated from the background. Up to now, internally wavelength stabilized dual wavelength diode lasers for the blue and green spectral range are unavailable. Other concepts, as presented in this work, had to be evaluated. First, the combination of two external cavity stabilized GaN diode lasers will be presented. Low reflection coated laser diodes are externally wavelength stabilized using VBGs and their beams are superimposed. Output powers in the 10- mW range for emission wavelengths of 454 nm and 456 nm will be presented. Second, devices based on frequency doubled GaAs diode lasers will be tested. The wavelength shift is realized by thermal tuning of the heat sink or by applying a current to internal heater elements in the GaAs-DBR-RW-lasers. In this case output powers, up to 50 mW at 488 nm or 515 nm were achieved. Third, dual wavelength Y-branch diode lasers at 1064 nm were frequency converted towards 532 nm with output powers in the 10-mW range using customized SHG waveguide crystals.

This work presents Multiphysics COMSOL simulations that help dissect the relative contributions of multiple forces of optical and electrical origin acting on a 20 nm diameter silica nanoparticle trapped by a plasmonic nanopore sensor. Specifically, the nanosensor uses the principle of self-induced back action (SIBA) to trap nanoparticle optically at the center of a double nanohole (DNH) structure integrated on top of a solid-state nanopores (ssNP). This novel SIBA actuated nanopore electrophoresis (SANE) sensor allows simultaneous recording of optical and electrical data features that are generated by the interaction of multiple underlying forces: Plasmonic optical trapping, electroosmosis, electrophoresis, viscous drag and heat conduction forces are all felt by a silica nanoparticle trapped by the sensor. This work aims to simulate these underlying forces in order to help understand how they contribute to the optical-electrical measurements generated by sensor. Furthermore, experimental measurements of 20 nm silica nanoparticles trapped the SANE sensor were compared against computational predictions to test the qualitatively trends seen in experimentally measured signal profiles during the nanoparticle’s approach to the optical trap and its translocation through the plasmonic nanopore, located immediately below the optical trap.

Shifted excitation Raman difference spectroscopy (SERDS) has been successfully applied for on-site soil analysis. Here, a portable SERDS sensor system is developed for in-field investigations. A dual-wavelength diode laser emitting at 785 nm is integrated into an in-house realized turnkey laser system as the excitation source. For our experiments, an operating point for the two laser lines with a spectral distance of 10 cm^-1 and 36 mW excitation power at the sample is selected. The sensor system allows a rapidly alternating operation between the two excitation wavelengths in the millisecond range and thus provides background-free SERDS spectra immediately after the measurement. This enables real-time evaluations, e.g., for quick on-site decisions. On-site soil analysis is carried out with the developed portable sensor system and SERDS extracts Raman signals of soil substances from background interferences with a 15-fold improvement of the signal-to-background-noise ratio. Besides others, closely neighbored Raman signals at 1084 cm-1 of calcite and at 1095 cm^-1 of dolomite are identified and mixtures of both soil carbonates are successfully discriminated by using SERDS. The presented results demonstrate the capability of the portable SERDS sensor system for on-site soil analysis and furthermore show the potential for applications such as geological investigations.

Surface-enhanced Raman spectroscopy (SERS) has wide applications in chemical and biosensing as well as imaging. Raman spectra obtained from SERS exhibit characteristic narrow peaks that allow higher degrees of multiplexing than possible with fluorescence imaging. The nanorattle is a bimetallic nanoparticle which can be loaded with different dyes to produce SERS for multiplexed mRNA detection assays and in vivo imaging. But as multiplexing degree increases, so does spectral complexity, making analysis difficult. Machine learning has been applied for SERS-based chemical recognition and quantification. However, multiplexed, assays using SERS labels or imaging using SERS-labeled materials rarely utilize machine learning. Since the spectral shapes of each multiplexed label is known, analysis is easy when multiplexing <4 dyes given the computational tradeoff. Here we demonstrate and compare the use of spectral decomposition, support vector regression, and convolutional neural network (CNN) for “spectral unmixing” of SERS spectra obtained from a highly multiplexed mixture of 7 SERS-active nanorattles. Training data was simulated by combining individual nanorattle spectra by linear scaling and addition. We show that CNN performed the best in determining relative contributions of each distinct dye-loaded nanorattle.

Surface plasmon resonance (SPR) based sensors have emerged as an excellent analytical technique known for their ultra-high sensitivity capable of detecting even minute refractive index (RI) changes of the surrounding during biomolecular interactions. However, due to their exceptional sensitivity towards RI changes, they are also susceptible to variations to reaction parameters such as temperature, concentration and non-specific adsorption which contributes to its inherent non-specificity. To circumvent these problems, researchers have employed various downstream techniques like chromatographic separations linked with Mass spectroscopy (MS) to ascertain sensor specificity. In an attempt to resolve this issue, we have exploited Surface-enhanced Raman Spectroscopy (SERS) as a secondary tool to validate the specificity of SPR signals. For this purpose, we have utilized a fiber-optic SPR system and gold nanoparticles to create a “metal film-molecule- metal nanoparticle” configuration and have shown that the resultant enhancement in the Raman signal of the molecule can be utilized as a self-validating tool. Accordingly, we have functionalized our FO-SPR with the bifunctional Raman active molecules; 4- aminothiolphenol (4-ATP), which could interact with carboxylated gold nanoparticles to create a “metal film-moleculemetal nanoparticle” configuration. The successful binding of the gold nanoparticles was reflected in ~19 nm SPR shift along with the simultaneous increase in the Raman signals of the 4-ATP molecules sandwiched in-between metal film and gold nanoparticles.

Surface plasmon resonance (SPR) has been widely exploited for label-free molecular detection in various applications. Despite significant advances in SPR technology, most uses are based on the flat device platform, limiting their scopes of applications. This is because plasmonic devices with a finite radius of curvature are difficult to experimentally implement and require heavy computing resources to analyze. In this report, we carried out calculation of SPR characteristics for curved structures by using segmented-wave analysis which enables calculation of curved plasmonic structures efficiently. We conducted calculation of Au thin film on a curved substrate for the curvature radius in a range of 100 to 3000 um for parallel and perpendicular light incidence in which chord length is fixed regardless of the curvature radius. Reflectance spectra by each segment were obtained using the transfer matrix method based on thin-film optics. This is followed by the results expressed as a discrete sum of segmental results. Then we compared the segmented-wave analysis with the finite element method (FEM) model for validation of results and prove the efficiency of the suggested method. The calculation time of segmented-wave analysis took less than 5 seconds on the personal computer whereas FEM took about 25 hours on the workstation. It was found that the results from the segmentation were in excellent agreement, resonance wavelength in particular, while other parameters such as reflectance and resonance width under parallel incidence showed disparity between the two models in the case of the short segmentation.

Alternating current (AC) modulation of command voltage applied across a Self-induced Back Action Actuated Nanopore Electrophoresis (SANE) sensor, a type of plasmonic nanopore sensor that we have developed previously, enables acquisition of new data types that could potentially enhance the characterization of nanoparticles (NPs) and single molecules. In particular, AC voltage frequency response provides insight into the charge and dielectric constant of analytes that are normally obfuscated using DC command voltages. We first analyzed Axopatch 200B data to map the frequency response of the empty SANE sensor in terms of phase shift and amplitude modulation, with and without plasmonic excitation. We then tested the frequency response of 20 nm diameter silica NPs and 20 nm gold NPs trapped optically, which made these particles hover over an underlying 25 nm nanopore at the center of the SANE sensor. By applying a DC command voltage with a superimposed AC frequency sweep while keeping the NPs optically trapped in the vicinity of the nanopores’s entrance, we have found that silica and gold NPs to have distinctly different electrical responses. This pilot work demonstrates the feasibility of performing AC measurements with a plasmonic nanopore, which encourages us to pursue more detailed characterization studies with NPs and single molecules in future work.

Despite the recent progress in creating photothermal agents of various compositions and morphologies, there is a strong need to further develop photothermal transducers that absorb light in the near-infrared region, which corresponds to the biological window, and enhance the local heat generation at the cellular level. One of the major limitations of photothermal therapy is the nonselective and uncontrolled heating of tumor tissues that lead to the heat diffusion in the normal cells. Therefore, we propose to fill these gaps by designing and developing decorated multiwalled carbon nanotubes (MWCNTs) with plasmonic nanoparticles that enhance the light-to-heat conversion in the therapeutic window through the localized surface plasmon resonance on the carbon nanotube surface. These novel hybrid nanostructures used as plasmonic photothermal transducers will provide efficient thermal ablation as well as minimal damage to normal cells compared to the current plasmonic nanostructures. Here, we focus on optimizing the near-infrared optical absorption of multiwalled carbon nanotubes by decorating their surfaces with gold nanorods. First, we present the synthesis process of this hybrid plasmonic nanostructure as well as their characterization employing high-resolution microscopic and spectroscopic tools such as TEM, FTIR, Raman spectroscopy and UV-Vis spectroscopy. Then, we report the numerical evaluation of the optical spectra distribution of decorated multiwall carbon nanotubes in a water environment using COMSOL Multiphysics software. Finally, near infrared photothermal measurements and quantitative analysis (more particularly using a laser wavelength of 808 nm) of this hybrid carbon nanostructure will be discussed.

We have investigated the feasibility of disordered plasmonic nanocomposites for super-resolution imaging. Annealing-based nanocomposite substrate has a great potential in biomedical optical and sensing technology because it can be mass-produced without difficult manufacturing processes. We introduce a new approach for wide-field super-resolution fluorescence imaging based on the nanocomposite island substrates, which we call nanospeckle illumination microscopy (NanoSIM). Near-field speckle patterns produced on disordered nanoisland substrates can help reconstruction of high-resolution fluorescence images with appropriate basis images. We have acquired basis images using azimuthal scanning illumination (ASI). Each ASI produces nonuniform nanoscale near-field speckles which can excite fluorescent dyes within a subdiffraction-limited area. While exploiting the random nature of plasmonic nanocomposite, NanoSIM does not require any specific polarization state to be maintained for ASI. We have tested NanoSIM to obtain super-resolved mages of molecules on the HeLa cell membrane. The full-width-at-half maximum was shown to improve by more than three times over the diffraction-limit with 360 basis images. Reconstructed images of gangliosides distribution on the HeLa cell suggest that fewer basis images may produce almost the same resolution with a shorter computation time. The optical resolution and sensitivity of disordered plasmonic substrate can be further enhanced by controlling the geometrical features of nanoislands structure.

Plant biotechnology and biofuel research is critical in addressing increasing global demands for energy. Further understanding of biomass producing associated metabolic pathways in plants can be used to exploit and increase the production of biomass for energy purposes. In vivo detection of biomarkers associated with plant growth for bioenergy has proved to be limited due to complex sample preparation required by traditional methods. In addition, genetic transformation and biomolecule monitoring inside plant cells is regulated by diameter and size exclusion limits of the plant cell wall (5 - 20 nm). Currently limited methods exist for enabling direct entry into plant cells. Moreover, these methods, such as biolistic particle delivery and electroporation use mechanical force that causes damages to the plant tissue. Nanoparticles could serve as promising platforms for probes to characterize intercellular and intracellular plant biomarkers and pathways. Bi-metallic nanostars are a plasmonics-active nanoplatform capable of high surface-enhanced Raman scattering (SERS) which can enter plant cells and have the future potential for nucleic acid sensing. Imaging technologies such as SERS mapping, confocal imaging, X-ray fluorescence imaging, multi-photon imaging, and transmission electron microscopy have been utilized to determine the compartmentalization and location of the SERS iMS biosensors inside Arabidopsis plants.