This PDF file contains the front matter associated with SPIE Proceedings Volume 10080, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Near-infrared (NIR) absorption spectroscopy in the 1-2.5 μm wavelength range can provide chemical information based on the overtones and combination bands of fundamental vibrational modes in the infrared (IR) wavelength range. NIR absorption features are significantly broader and weaker due to the fact that the underlying processes are quantum mechanically forbidden. However, substantially lower water absorption allows NIR spectroscopy to be performed on samples with high water content, e.g., biological specimen and other in situ measurements, which otherwise restricts the use of IR light. However, small NIR absorption cross-section results in less sensitivity compared to measuring the IR fundamentals. In addition, NIR measurements are more challenging compared to in other spectral regions because of the lack of high-sensitivity detectors. To overcome these barriers, we propose the use of plasmonic nanostructures.

Nanoporous gold nanoparticle (NPG-NP) array chip showcases tunable pore and ligament sizes ranging from nanometers to microns. The nanoporous structure and sub-wavelength nanoparticle shape contribute to its unique LSPR properties. NPG-NP features large specific surface area and high-density plasmonic field enhancement known as “hot-spots”. Hence, NPG-NP has found many applications in nanoplasmonic sensor development. In our recent studies, we have shown that NPG-NP array chip can be utilized for high-sensitivity detection by various enhanced spectroscopic modalities, as photothermal agents, and for disease biomarker detection. In this paper, we show the first experimental demonstration of effective and robust surface-enhanced near-infrared absorption (SENIRA) on NPG-NP array chip.

Raman scattering spectroscopy is a unique tool to probe vibrational, rotational, and other low-frequency modes of a molecular system and therefore could be utilized to identify chemistry and quantity of molecules. However, the ultralow efficient Raman scattering, which is only 1/10⁹ ~ 1/10¹⁴ of the excitation light due to the small Raman scattering cross-sections of molecules, have significantly hindered its development in practical sensing applications. The discovery of surface-enhanced Raman scattering (SERS) in the 1970s and the significant progress in nanofabrication technique, provide a promising solution to overcome the inherent issues of Raman spectroscopy. It is found that In the vicinity of nanoparticles and their junctions, the Raman signals of molecules can be significantly improved by an enhancement factor as high as 10¹⁰, due to the ultrahigh electric field generated by the localized surface plasmons resonance (LSPR), where the intensity of Raman scattering is proportional to the |E|⁴. In this work, we propose and demonstrate a new approach combining LSPR from nanocapsules with densely assembled silver nanoparticles (NC-AgNPs) and guidemode- resonance (GMR) from dielectric photonic crystal slabs (PCSs) for SERS substrates with robustly high performance.

It has been shown that surface enhanced Raman spectroscopy (SERS) has many promising applications in ultrasensitive detection of Raman signal of substances. However, optimizing the enhancement in SERS signal for different applications typically requires several levels of fabrication of active plasmonic SERS substrates. In this paper, we report the enhancement of SERS signal of a single layer of graphene located on a plasmonic nano-Lycurgus cup array after placing water droplets on it. The experimental data shows that addition of water droplets can enhance the SERS signal of the single layer of graphene about 10 times without requiring any modifications to the nano-Lycurgus cup array. Using fullwave electromagnetic simulations, we show that addition of water droplets enhances the local electric field at the graphene layer, resulting in stronger light-graphene interaction at the excitation pump laser wavelength. We also show that the addition of water droplets on the graphene layer enables us to modify the band diagram of the structure, in order to enhance the local density of optical states at the Raman emission wavelengths of the graphene layer. Numerical calculations of both the excitation field enhancement at the location of the graphene layer, and the emission enhancement due to enhanced local density of optical states, support the experimental results. Our results demonstrate an approach to boost the SERS signal of a target material by controlling the band diagram of the active nanostructured SERS substrate through the use of fluidic dielectrics. These results could find potential applications in biomedical and environmental technologies.

Nanoplasmonic sensor has become a recent research focus due to its significant signal enhancement and robust signal transduction measured by various techniques. However, since the native gold surface does not have the capability to selectively bind target biomolecules, high molecular specificity has been a challenge. Nanoporous gold nanoparticle (NPG-NP) array chip showcases large specific surface area and high-density plasmonic field enhancement known as “hot-spots”. In this paper, we discuss strategies to enhance molecular specificity by functionalizing NPG-NP with unique bio-recognition elements towards both high sensitivity and specificity. A few examples will be given using existing and novel bio-recognition elements.

The development of sensitive and selective biosensing techniques is of great interest for clinical diagnostics. Here, we describe the development and application of a surface enhanced Raman scattering (SERS) sensing technology, referred to as "inverse Molecular Sentinel (iMS)" nanoprobes, for the detection of nucleic acid biomarkers in biological samples. This iMS nanoprobe involves the use of plasmonic-active nanostars as the sensing platform for a homogenous assay for multiplexed detection of nucleic acid biomarkers, including DNA, RNA and microRNA (miRNA). The "OFF-to-ON" signal switch is based on a non-enzymatic strand-displacement process and the conformational change of stem-loop (hairpin) oligonucleotide probes upon target binding. Here, we demonstrate the development of iMS nanoprobes for the detection of DNA sequences as well as a modified design of the nanoprobe for the detection of short (22-nt) microRNA sequences. The application of iMS nanoprobes to detect miRNAs in real biological samples was performed with total small RNA extracted from breast cancer cell lines. The multiplex capability of the iMS technique was demonstrated using a mixture of the two differently labeled nanoprobes to detect miR-21 and miR-34a miRNA biomarkers for breast cancer. The results of this study demonstrate the feasibility of applying the iMS technique for multiplexed detection of nucleic acid biomarkers, including short miRNAs molecules.

To establish detection schemes in life science applications, specific and sensitive methods allowing for fast detection times are required. Due to the interaction of molecules with strong electromagnetic fields excited at metallic nanostructures, the molecular fingerprint specific Raman spectrum is increased by several orders of magnitude. This effect is described as surface-enhanced Raman spectroscopy (SERS) and became a very powerful analytical tool in many fields of application. Within this presentation, we will introduce innovative bottom-up strategies to prepare SERS-active nanostructures coated with a lipophilic sensor layer. To do so, the food colorant Sudan III, an indirect carcinogen substance found in chili powder, palm oil or spice mixtures, is detected quantitatively in the background of the competitor riboflavin as well as paprika powder extracts. The SERS-based detection of azorubine (E122) in commercial available beverages with different complexity (e.g. sugar content, alcohol concentration) illustrates the strong potential of SERS as a qualitative as well as semiquantitative prescan method in food analytics. Here, a good agreement between the estimated concentration employing SERS as well as the gold standard technique HPLC, a highly laborious method, is found. Finally, SERS is applied to detect vitamin B2 and B12 in cereals as well as the estimate the ratio of lycopene and β-carotene in tomatoes.

Acknowledgement: Funding the projects “QuantiSERS” and “Jenaer Biochip Initiative 2.0” within the framework “InnoProfile Transfer – Unternehmen Region“ the Federal Ministry of Education and Research, Germany (BMBF) is gratefully acknowledged.

The development of rapid, easy-to-use, cost-effective, high accuracy, and high sensitive DNA detection methods for molecular diagnostics has been receiving increasing interest. Over the last five years, our laboratory has developed several chip-based DNA detection techniques including the molecular sentinel-on-chip (MSC), the multiplex MSC, and the inverse molecular sentinel-on-chip (iMS-on-Chip). In these techniques, plasmonic surface-enhanced Raman scattering (SERS) Nanowave chips were functionalized with DNA probes for single-step DNA detection. Sensing mechanisms were based on hybridization of target sequences and DNA probes, resulting in a distance change between SERS reporters and the Nanowave chip’s gold surface. This distance change resulted in change in SERS intensity, thus indicating the presence and capture of the target sequences. Our techniques were single-step DNA detection techniques. Target sequences were detected by simple delivery of sample solutions onto DNA probe-functionalized Nanowave chips and SERS signals were measured after 1h - 2h incubation. Target sequence labeling or washing to remove unreacted components was not required, making the techniques simple, easy-to-use, and cost effective. The usefulness of the techniques for medical diagnostics was illustrated by the detection of genetic biomarkers for respiratory viral infection and of dengue virus 4 DNA.

Plasmonic metamaterials for biosensing were designed as artificial materials, composed of gold/silver nanostructured blocks forming a nanolattice, which can provide improved sensing response in optical transduction compared to classical materials and additional sensing functionalities. 2D plasmonic nanoperiodic structures, including nanohole and nanodot arrays are prominent examples of such metamaterials, which can offer a series of novel functionalities, including size selectivity, spectral tuneability, drastical field enhancement etc., although spectral sensitivity of these structures is limited by spatial periodicity related to diffraction nature of plasmon coupling. Here, we consider metamaterials based on 3D plasmonic crystals and show the possibility of a delocalized plasmon mode, which can provide a drastic gain in spectral sensitivity (> 2600 nm/RIU compared to 200-400 nm/RIU for 2D structures). Combined with larger surface for bioimmobilization provided by the 3D matrix, the proposed metamaterial structure promises the advancement of plasmonic biosensing technology.

In this work, we report a novel substrate for surface enhanced Raman spectroscopy (SERS) composed of silver nanoparticles protected by small nitrogen-doped Graphene Quantum Dots, i.e. Ag NPs-N-GQDs, synthesized under mild experimental conditions, which can preserve the SERS performance in normal indoor environment for up to 30 days. The field emission scanning electronic microscope (FESEM) images confirm that the N-GQDs play a significant role in the control of metallic nanoparticles morphology. The X-ray photoelectron spectroscopy (XPS) result clearly indicates the N-GQDs was successfully immobilized on the surface of silver nanoparticles (Ag NPs). Ag NPs-N-GQDs demonstrated Raman enhancement stronger than pure Ag NPs likely due to an increase in the number of the “hotspots” formed by coupled nanostructures. N-GQD protected Ag NPs were evaluated in SERS measurements of R6G when they were made fresh and have been stored in normal indoors condition for up to 30 days. Then Ag NPs-N-GQDs were used as a SERS substrate for glucose detection. The linearity range of glucose was found to be ranged from 1 μM to 1 M with a detection limit of 0.1 μM in glucose solutions. It was also applied successfully for glucose detection in rat blood samples. The present study demonstrates that the novel Ag NPs−N-GQDs nanostructure has great potential to be used as a cost effective sustained SERS substrate, which can be extremely useful in the wide adoption of SERS based sensors.

We have studied fluorescence cellular imaging with randomly distributed localized near-field induced by silver nano-islands. For the fabrication of nano-islands, a 10-nm silver thin film evaporated on a BK7 glass substrate with an adhesion layer of 2-nm thick chromium. Micrometer sized silver square pattern was defined using e-beam lithography and then the film was annealed at ~ 200°C. Raw images were restored using electric field distribution produced on the surface of random nano-islands. Nano-islands were modeled from SEM images. 488-nm p-polarized light source was set to be incident at 60°. Simulation results show that localized electric fields were created among nano-islands and that their average size was found to be ~135 nm. The feasibility was tested using conventional total internal reflection fluorescence microscopy while the angle of incidence was adjusted to maximize field enhancement. Mouse microphage cells were cultured on nano-islands, and actin filaments were selectively stained with FITC-conjugated phalloidin. Acquired images were deconvolved based on linear imaging theory, in which molecular distribution was sampled by randomly distributed localized near-field and blurred by point spread function of far-field optics. The optimum fluorophore distribution was probabilistically estimated by repetitively matching a raw image. The deconvolved images are estimated to have a resolution in the range of 100-150 nm largely determined by the size of localized near-fields. We also discuss and compare the results with images acquired with periodic nano-aperture arrays in various optical configurations to excite localized plasmonic fields and to produce super-resolved molecular images.

Surface plasmon resonance depends on the dielectric medium at the vicinity and makes it a quasi-universal detector. Therefore, and due to the label-free nature, SPR is a widely used sensing tool for real‐time monitoring molecular interactions of various analytes. However, detection of highly diluted analytes and small molecules (< 400 Da) is still challenging. Gold nanohole arrays provide plasmonic hotspots with improved surface sensitivity and 2D carbon nanomaterials enable binding near the surface. Both effects together are promising in the development of SPR sensors for the efficient determination of small molecules. Graphene is known for efficient binding of molecules with delocalized aromatic π-systems. Additionally, the electromagnetic field is locally enhanced and modulated by the interaction of graphene photonics with the plasmonics of metal nanostructures. The advantages of chemical vapor deposition (CVD) graphene over reduced graphene oxide (rGO) is illustrated by a proof of concept study. In comparison to substrates consisting of a continuous film the surface sensitivity is enhanced for a nanohole arrays and further improved for CVD graphene functionalization in contrast to rGO. The feasibility of the sensor was demonstrated for the detection of adenine down to a concentration of 0.9 μM.

For optical manipulation, a nano-optical conveyor belt consisting of an array of gold plasmonic non-concentric nano-rings (PNNRs) is demonstrated for the realization of trapping and unidirectional transportation of nanoparticles by polarization rotation of excitation beam. These hot spots of an asymmetric plasmonic nanostructure are polarization dependent, therefore, one can use the incident polarization state to manipulate the trapped targets. Trapped particles could be transferred between adjacent PNNRs in a given direction just by rotating the polarization of incident beam due to unbalanced potential. The angular dependent distribution of electric field around PNNR has been solved using the three- dimensional finite-difference time-domain (FDTD) technique. For optical enhanced catalytic activity, the spectral properties of dimers of Au nanorod-Au nanorod nanostructures under the excitation of 532nm photons have been investigated. With a super-resolution catalytic mapping technique, we identified the existence of "hot spot" in terms of catalytic reactivity at the gap region within the twined plasmonic nanostructure. Also, FDTD calculation has revealed an intrinsic correlation between hot electron transfer.

Infrared spectroscopy enables the label-free detection of structure specific fingerprints of analytes. The sensitivity of corresponding methods can strongly be enhanced by attaching analytes on plasmonic active surfaces.

We introduce a slit array metamaterial perfect absorber (SAMPA) ^[1] consisting of a dielectric layer sandwiched between two Au layers of which the upper layer is perforated with a periodic array of slits. This structure combines the principle of Extraordinary Optical Transmission (more light is transmitted through a hole than is incident on its surface) with that of Perfect Absorption (reflectance and transmittance are virtually zero). Accordingly, within the slights the electric fields are strongly enhanced and light-matter interaction is correspondingly greatly amplified. Thus, already small concentrations of analytes down to a monolayer can be detected and identified by their spectral fingerprints with a standard mid-infrared spectrometer.

Closely related to the SAMPAs are plasmonic slit absorbers, which simply consist of slit arrays in thin gold layers deposited on a layer of Si₃N₄.^[2] These slit arrays operate like unstructured gold layers if the incident light is polarized parallel to the long slit axes. In contrast, for light polarized perpendicular to the long slit axis, the plasmon is excited. By the introduction of a second slit, which is rotated relative to the first slit, both principal polarization states excite plasmon resonances which can be made to differ in wavelength. As a consequence, the operating wavelength range of this slit array can be tuned by adjusting the polarization state of the incoming light.

[1] Mayerhöfer, T.G., et al.. ACS Photonics, 2015. 2(11): p. 1567-1575.

[2] Knipper, R., et. al., in preparation.

Surface plasmon resonance (SPR) devices have been widely used in label-free biosensing applications due to their convenient surface wave configuration and the capability to optically detect biomolecule surface binding with a high stability and uniformity between different experiments. Meanwhile, integrating SPR nanostructures onto single-mode fiber (SMF) end facets provides unique advantages such as flexible geometry, compact sizes and in vivo monitoring capability. To improve the performance of SMF end facet SPR devices which are usually limited by guided mode diffraction, following our previous work on plasmonic crystal cavities [1], in this work we demonstrate a plasmonic distributed feedback (DFB) cavity with a phase shift section. The DFB structure contains a periodic array of nanoslits in a gold film, which provides a surface plasmon polariton (SPP) bandgap from 865 to 877 nm on the water-gold interface. A phase shift section is embedded at the center of the DFB structure to introduce an SPR defect state within the SPP bandgap. The devices were fabricated onto the fiber end facets by a glue-and-strip transfer process [1]. To demonstrate real biosensing implementations, the reflection spectra of the SMF guided lightwaves were taken in real-time to detect refractive index change, adsorption of bovine serum albumin onto gold surface, and the association and dissociation between human immunoglobulin G (hIgG) and its antibody. [1] X. He, H. Yi, J. Long, X. Zhou, J. Yang and T. Yang, "Plasmonic Crystal Cavity on Single-Mode Optical Fiber End Facet for Label-Free Biosensing," Applied Physics Letters 108, 231105 (2016)

Nanoparticles have been explored extensively as potential biomedical imaging and therapeutic agents. One critical aspect of in vivo nanoparticle use is the characterization of biodistribution profiles. Such studies improve our understanding of particle uptake, specificity, and clearance mechanisms. Currently, the most prevalent nanoparticle biodistribution methods provide either aspatial quantification of whole-organ particle accumulation or nanometerresolution images of uptake in single cells. Few existing techniques are well-suited to study particle uptake on the micron to millimeter scales relevant to sub-tissue physiology. Here we demonstrate a new method called Hyperspectral Microscopy with Adaptive Detection (HSM-AD) that uses machine learning classification of hyperspectral dark-field images to study interactions between tissues and administered nanoparticles. This label-free, non-destructive method enables quantitative particle identification in histological sections and detailed observations of sub-organ accumulation patterns consistent with organ-specific clearance mechanisms, particle size, and the molecular specificity of the nanoparticle surface. Unlike studies with electron microscopy, HSM-AD is readily applied for large fields of view. HSM-AD achieves excellent detection sensitivity (99.4%) and specificity (99.7%) and can identify single nanoparticles. To demonstrate HSM-AD’s potential for novel nanoparticle uptake studies, we collected the first data on the sub-organ localization of large gold nanorods (LGNRs) in mice. We also observed differences in particle accumulation and localization patterns in tumors as a function of conjugated molecular targeting moieties. Thus, HSM-AD affords new degrees of detail for the study of nanoparticle uptake at physiological scales. HSM-AD may offer an auxiliary or alternative approach to study the biodistribution profiles of existing and novel nanoparticles.

The determination of the concentration of xenobiotics in biological matrix followed by the change of the prescribing procedure plays a major role in the transition from general to personalized medicine. For this contribution, human urine samples collected from healthy volunteers and from patients having urinary tract infection were used as biological matrix to assess the potential and limitation of LoC-SERS to detected levofloxacin and nitroxoline. The determination of both antibiotics at clinically relevant concentrations, 1.38 mM ± 0.68 mM for levofloxacin and 10-40 µM for nitroxoline, will be presented. For quantification purposes the standard addition method is combined with LoC-SERS.

Surface plasmon represents oscillations of electrons at the interface between metal and dielectric layers. Surface plasmon resonance (SPR) is influenced by the environment near the surface, which has been the basis for label-free biosensor structure for various applications of molecular detection. An important aspect of SPR biosensing is that its characteristics are affected by the geometrical structure. Yet most research has focused largely on a structure using flat surface. Although flat structure is suitable for typical sensor applications, it may not be appropriate for wearable or in vivo applications. In this study, we analyzed the effects of surface curvature on flexible SPR biosensors. Curved surface was approximated using a segmented model in which each segment is treated as a flat surface with a different incident angle and then optical characteristics of the overall model were calculated by rigorous coupled wave analysis in two different configurations of light incidence. We calculated curvature effects on SPR with curvature radius larger than 255 μm. It was found that regardless of the incident configurations, resonance curves tend to broaden with increased curvature due to larger momentum dispersion. Resonance shifts as a result of DNA immobilization and hybridization decrease with curvature. The analysis was extended to multi-curvature structure and finds significant fluctuation of resonance shift for parallel light incidence. The study can be of profound importance for plasmonic devices using flexible substrates.

The effective confinement of light in a deep-subwavelength volume can be achieved in metallic nanostructures through the electronic resonance, surface plasmons (SPs). There are few ways to enhance the localization of the field such as adopting metallic nanopost or nanowire structures on the precious metallic film. The achieved highly enhanced field localization through SPs can be exploited for surface-enhanced spectroscopy, biosensor, enhancing energy emitter, and enhanced energy generator. Also, many researches have been tried with few-nanometer gap between the metals for achieving large field enhancements. In this paper, by comparing the scattering of gold nanoparticles, the effects of metallic film of substrates were investigated through simulation. In addition, as changing of the gap between gold nanoparticle and metallic surface, different resonance wavelengths were observed in scattering spectra from simulation and practical experiments. We confirmed that the gold film with gold nanoparticles shows the most distinctive scattering spectra. The numerical demonstration was matched with our experimental demonstration, also with the previously introduced papers as well.

The aim of this work is to develop a platform for characterizing extracellular vesicles (EV) by using gold-polymer nanopillar SERS arrays simultaneously circumventing the photoluminescence-related disadvantages of Raman with a time-resolved approach. EVs are rich of biochemical information reporting of, for example, diseased state of the biological system. Currently, straightforward, label-free and fast EV characterization methods with low sample consumption are warranted. In this study, SERS spectra of red blood cell and platelet derived EVs were successfully measured and their biochemical contents analyzed using multivariate data analysis techniques. The developed platform could be conveniently used for EV analytics in general.