Highly Controlled Surface‐Enhanced Raman Scattering Chips Using Nanoengineered Gold Blocks

Gold nanoparticles (GNPs) exhibit unique optical properties, depending on the particle size, geometrical shape, and medium refractive index and interparticle interactions, etc. Among these optical properties, localized surface plasmon resonance (LSPR) has significant effects on the electromagnetic field around the GNPs. The LSPR-induced electromagnetic field enhancement is beneficial to the surface-enhanced Raman scattering (SERS) and energy transfer processes. This dissertation deals with the effects of LSPR on SERS and energy transfer between CdSe/ZnS quantum dots and GNPs. Specifically, the research aims to gain better understanding of (i) the electromagnetic enhancement induced by charge transfer from GNP to molecules, (ii) the SERS in various shaped gold nanostructures, (iii) the energy transfer from quantum dots (QDs) to GNPs, and (iv) SERS- and energy transfer-based sensing platforms for detection of chemical species and biomolecules.;The SERS of two different types of molecules on GNPs has been investigated. It has been found that the aromatic molecules such as p-mercaptobenzenoic acid (MBA) exhibit stronger SERS activity than the linear-chain molecules such as 3-mercaptopropionic acid (MPA) and L-cysteine (Cys). The difference in the SERS activity is attributed to the distinct electronic structures among these molecules. The electron transfer from GNPs to MBA can occur under laser excitation. The transferred electron can effectively strengthen the electromagnetic field around GNPs, leading to electromagnetic enhancement of SERS.;Furthermore, the SERS in different shaped gold nanostructures (gold nanospheres (GSPs), nanorods (GRDs) and nanostars (GSTs)) has been investigated. GSTs show the highest SERS enhancement. Three-dimensional finite-difference time domain (FDTD) method has been used to simulate the electric field distribution. It is demonstrated that the electric field can be concentrated around two ends of GRDs and these tips of GSTs, and the GSTs show the highest maximum electric field intensity under both excitations of 532 nm and 785 nm. It is suggested that the shape of gold nanostructures governs the SERS difference among GSPs, GRDs and GSTs. In addition, gold malachite green isothiocyanate(MGITC) SiO 2 sandwiched nanostructures have been prepared. SiO2 encapsulation not only improves the colloidal and LSPR stability but also endows excellent reproducibility of SERS signal due to the prevention of MGITC leaking. It is demonstrated that the GST MGITC SiO2 can be used for monitoring of DNA hybridization and for detection of adenosine triphosphate (ATP) with high sensitivity.;Energy transfer between the CdSe/ZnS QDs and GNPs was investigated. The 3 nm GNPs without observable LSPR absorption quench the fluorescence emission of the

Applicable surface enhanced Raman scattering (SERS) active substrates require high enhancement factor (EF), excellent spatial reproducibility, and low-cost fabrication method on a large area. Although several SERS substrates with high EF and relative standard deviation (RSD) of signal less than 5% were reported, reliable fabrication for large area SERS substrates with both high sensitivity and high reproducibility via low-cost routes remains a challenge. Here, we report a facile and cost-effective fabrication process for large-scale SERS substrate with Ag inter-nanoparticle (NP) gaps of 5 nm based on ultrathin alumina mask (UTAM) surface pattern technique. Such closely packed Ag NP arrays with high density of electromagnetic field enhancement ("hot spots") on large area exhibit high SERS activity and excellent reproducibility, simultaneously. Rhodamine 6G molecules with concentration of 1 × 10(-7) M are used to determine the SERS performance, and an EF of ∼10(9) is obtained. It should be noted that we obtain RSDs about 2% from 10 random spots on an area of 1 cm(2), which implies the highly reproducible signals. Finite-difference time-domain simulations further suggest that the enhanced electric field originates from the narrow gap, which agrees well with the experimental results. The low value of RSD and the high EF of SERS signals indicate that the as-prepared substrate may be promising for highly sensitive and uniform SERS detection.

Silver film over nanospheres (AgFoN) as tri-modal plasmonic sensing platform for Surface Plasmon Resonance Spectroscopy, Surface-Enhanced Raman Scattering, and Surface-Enhanced Fluorescence

Section I Hydrodynamic Instabilities and Critical Phenomena.- To Scale or not to Scale? - The Puzzle at the Lambda Point of Liquid 4He.- Transition to Turbulence in Couette-Taylor Flow.- Hydrodynamic Instabilities and Turbulence.- Light from Gels and a Single Polymer Chain near Phase Transitions.- Interferometric Studies of Thick Film Critical Behavior.- Section II Physics in Two Dimensions and Defects.- Melting and Liquid Crystals in Two Dimensions.- Light Studies of Molecular Orientation Fluctuations in Two Dimensions.- Multiphonon Boundary of the Excitation Spectrum.- Raman Spectra of Proustite and Pyrargyrite Crystals in Low Temperature Phases.- Finite Field Local Field Catastrophe - Application to the Spectra of KCNxCl1?x.- The Effect of Long Range Fluctuations in Impurity Potential on the Electron Light in Heavily Doped Semiconductors.- Resonant and Trapping of 29 cm?1 Acoustic Phonons in Ruby Crystals.- Section III Non-Local and Transient Phenomena.- Some Aspects of the Theory of Surface Polaritons.- Recent Developments in Non-Local Optics.- Resonant Brillouin of Exciton Polaritons.- Ultraslow Optical Dephasing of Pr3+:LaF3.- Picosecond Raman Gain Studies of Molecular Vibrations on a Surface.- Section IV Spins and Excitons.- Brillouin-Mandelstam of Light in Antiferromagnetic CoCO3.- Observation of Pure Spin Diffusion Without Charge Transport by Spin Flip Raman Scattering.- Spin-Flip from Photoexcited Excitons in SiC.- The of Light by Spin Waves on Ferromagnetic Surfaces.- Relaxation of Energy and Polarization in the Resonant Secondary Emission Spectra of Semiconductors.- Resonant Raman from Stress-Split Forbidden Excitons in CU2O.- Low Frequency Exciton and Raman Spectra of CoCO3.- Theoretical and Experimental Determinations of Raman Cross Sections in Simple Solids.- Section V Resonance and Charge Excitations.- Resonant Secondary Emission by Impurities in Crystals.- The Raman and Hot Luminescence of Self-Trapping Excitons.- Phenomenological Description of Light and Thermal Radiation.- Raman from Plasmon-Phonon Coupled Modes in GaP.- Interaction Between Localized Carriers in the Accumulation Layer and Extended Bulk LO Phonons in InSb and GaSb: Raman Interference Lineshapes.- Inelastic Light by the Two Dimensional Electrons in Semiconductor Heterojunction Superlattices.- On the Distinction Between Resonant and Hot Luminescence: Application of Theory to Experiment.- Section VI Phase Transitions.- Light Near Structural Phase Transition Points in Pure Crystals and in Crystals Containing Defects.- Raman From Charge Density Waves and Superconducting Gap Excitations in 2H-TaSe2 and 2H-NbSe2.- Quasielastic Light Near Structural Phase Transitions.- High Resolution X-Ray and Light Spectroscopy of Liquid Crystals.- Optics and Electrooptics of Chiral Smectics.- The Size, Shape and Polydisperity of Micelles of Amphiphillic Molecules.- Resonance Raman Studies of Visual Pigments.- A Nanosecond Probe of Hemoglobin Dynamics Using Time Resolved Resonance Raman Scattering.- Section VII Multi-Photon Spectroscopy.- Recent Results in Four-Photon Spectroscopy of Condensed Media.- Recent Progress in Four-Wave Mixing Spectroscopy in Crystals.- Coherent Raman Ellipsometry of Liquid Water: New Data on the Vibrational Stretching Region.- Time Resolved Coherent Anti-Stokes Raman in Weakly Disordered Molecular Crystals.- Intense Light Resonance Scattering: Spectra and Photon Correlations.- Section VIII Resonance and Surface Enhanced Raman Scattering.- Intensity Effects in Resonance Light Scattering.- The Spontaneous Diffraction of Light by Resonance Atoms.- Raman by Molecules Adsorbed on Metals: an Overview.- Raman Spectroscopy of Molecular Monolayers in Inelastic Electron Tunneling Spectroscopy Junctions.- A Theory of Giant Raman Scattering by Adsorbed Molecules on Metal Surfaces.- Concluding Remarks.- Participants.- Author Index.

<p>This thesis focusses on a number of topics in surface enhanced Raman scattering (SERS). The aim of the undertaken research was to deepen the general understanding of the SERS effect and, thereby, to clarify some of the disputed issues, among them: What is the origin of the enhancement? What is the physical or chemical effect of 'salt activation' in SERS systems? Can we observe single-molecules using SERS? Can we determine the absorbate's orientation on the surface? In part one (chapters 1-3), as a general introduction, I start with a short overview of the Raman effect and its relation to other molecular spectroscopic effects (such as fluorescence, Rayleigh scattering, etc... ). Following these basic remarks, the surface enhancementmechanisms underlying SERS are explained (as a largely electromagnetic field enhancement) and are investigated theoretically on the canonicalmodel of a nanoscopic dimer of silver spheres. The second part (chapter 4) reports on the experimental investigation (electron microscopy, in-situ Raman measurements) of a typical real SERS system: Lee & Meisel silver colloids. An emphasis is put on the self-limiting aggregation kinetics which is observed in such systems after salt addition. This is also investigated and rationalised by means of Monte-Carlo simulations which are footed on empiric theoretical considerations for the interaction potential. Part three (chapter 5) contains a discussion of the early attempts on singlemolecule SERS and points out the shortcomings of the previously used ultra-lowconcentration approach. In response, an improved andmore rigorous approach is presented: Bi-Analyte SERS. Examplary applications of the technique are discussed. Within these experiments the capability of the technique to prove/disprove (with statistical soundness) single-molecule sensitivity in any SERS system is demonstrated, and single-molecule enhancement factors are derived. The last part (chapter 6) presents computational studies based on densityfunctional theory and its use in the context of Raman spectroscopy and SERS. Of particular interest here were the Raman tensors, their visual representation appropriate in the SERS case, their relation to the relative intensities of Raman peaks, and their modification when the photon energy approaches the electronic resonance of the molecule. Last, but not least, a conclusion chapter is presented, where I highlight what has contributed by the thesis to the general understanding of the SERS effect.</p>

A simple high-throughput approach is presented in this work to fabricate the Au nanoparticles (NPs)/nanogap/Au NPs structure for surface enhanced Raman scattering (SERS). This plasmonic nanostructure can be prepared feasibly by the combination of rapid thermal annealing (RTA), atomic layer deposition (ALD) and chemical etching process. The nanogap size between Au NPs can be easily and precisely tuned to nanometer scale by adjusting the thickness of sacrificial ALD Al2O3 layer. Finite-difference time-domain (FDTD) simulation data indicate that most of enhanced field locates at Au NPs nanogap area. Moreover, Au NPs/nanogap/Au NPs structure with smaller gap exhibits the larger electromagnetic field. Experimental results agree well with FDTD simulation data, the plasmonic structure with smaller nanogap size has a stronger Raman intensity. There is highly strong plasmonic coupling in the Au nanogap, so that a great SERS effect is obtained when detecting methylene blue (MB) molecules with an enhancement factor (EF) over 107. Furthermore, this plasmonic nanostructure can be designed on large area with high density and high intensity hot spots. This strategy of producing nanoscale metal gap on large area has significant implications for ultrasensitive Raman detection and practical SERS application.

Surface-enhanced Raman scattering (SERS) is a powerful analytical technique that enhances the Raman scattering signal from molecules adsorbed on or in close proximity to the metal surface. It is possible owing to localized surface plasmon resonance occurring in nanostructures metal surfaces. There are two commonly considered mechanisms for SERS, electromagnetic and chemical enhancement. The electromagnetic theory emphasizes that the Raman enhancements for adsorbates on particular surfaces occur because of the enhancement in electric field provided by the surface. When the incident light strikes the surfaces, surface plasmons can be excited by radiation, resulting in enhanced electromagnetic fields close to the surface. The chemical theory is thought to involve the creation of new electronic states and the formation of charge transfer complexes in some special cases between the chemisorbed species and the SERS active substrates, resulting in an enhanced Raman cross section of the molecules. This chapter describes the SERS activities of quinone derivatives by plasmonic silver nanoparticles and pollutant detection using gold nanoparticles. SERS studies of 2-bromo-1,4-naphthoquinone and 2,3-dibromo-1,4-naphthoquinone on prepared nanoparticles are described. SERS analysis of polluted soil is also discussed. The orientation of the above molecules on silver nanoparticles was elucidated from the spectral analysis

Surface-enhanced Raman scattering (SERS) is a unique analytical technique that provides fingerprint spectra, yet facing the obstacle of low collection efficiency. In this study, we demonstrated a simple approach to measure surface plasmon-coupled directional enhanced Raman scattering by means of the reverse Kretschmann configuration (RK-SPCR). Highly directional and p-polarized Raman scattering of 4-aminothiophenol (4-ATP) was observed on a nanoparticle-on-film substrate at 46° through the prism coupler with a sharp angle distribution (full width at half-maximum of ∼3.3°). Because of the improved collection efficiency, the Raman scattering signal was enhanced 30-fold over the conventional SERS mode; this was consistent with finite-difference time-domain simulations. The effect of nanoparticles on the coupling efficiency of propagated surface plasmons was investigated. Possessing straightforward implementation and directional enhancement of Raman scattering, RK-SPCR is anticipated to simplify SERS instruments and to be broadly applicable to biochemical assays.

The electromagnetic enhancement in surface-enhanced Raman scattering (SERS) caused by localized surface plasmon resonance is a near-field effect, often limiting the practicality of SERS in many applications. However, no attempts have been made to investigate field extension through symmetrical refractive index modulation in a SERS-based system. Here, we report the development and characterization of refractive index-matched SERS substrates supporting electric field extension to realize what is termed "long-range SERS" (LR-SERS). Finite-difference time-domain simulations were employed to tune the plasmonic responses and investigate electric field distributions of gold nanohole arrays (NHAs) as a function of the dielectric environment and geometric parameters. SERS substrates supporting long-range behavior were compared against "conventional" substrates without long-range behavior. SERS intensities from rhodamine 6G (R6G) aqueous solutions of 2.0 × 103 and 1.5 × 102 counts s–1 mW–1 were produced by the LR-SERS and conventional substrates, respectively, on the gold surface. Moreover, a signal response of 9.0 × 101 counts s–1 mW–1 was produced by LR-SERS substrates with a 10 nm separation between the R6G solution and NHA, while no signal was observed from the conventional substrate. As a proof of principle study, the results demonstrate the potential to use LR-SERS substrates in applications where the target analyte is located further from the SERS-active surface.

Nonspecificity and low reproducibility are always the main challenges in surface-enhanced Raman scattering (SERS) detection, especially for testing real samples. In this study, we developed a sandwich-like sensor (AuA-pMIP) to detect rhodamine 6G (R6G) by integrating a porous molecularly imprinted polymer (pMIP) with a well-ordered AuNP array (AuA). To form a uniformly distributed hot spot, AuA was fabricated at an oil-water interface and was subsequently fixed between pMIP and a support slide. Finite-difference time-domain simulation indicated that the enhanced electric field covered a distance of ∼2 μm above the AuA, in which the pMIP provided effective mass-transfer channels and sufficient specific binding sites for target molecules. High specificity for AuA-pMIP in R6G detection was demonstrated by comparing the SERS performance of R6G on AuA-pMIP with that of its structural analogues on the same sensor. Remarkably, the stable sandwich-like structure allowed us to achieve a recyclable SERS sensor with high reproducibility. Finally, AuA-pMIP displayed excellent specificity and sensitivity toward R6G in a test based on a real orange juice sample. This study presents a promising method to achieve real sample testing on a SERS platform.

The discovery that Raman scattering from molecules adsorbed on metal surfaces (electrodes, colloids and island films) were enhanced by 105–106 has caused extraordinary interest and excitement in recent years1,2. What is the advantage of this Surface Enhanced Raman Scattering (SERS)? 1. The high enhancement factor of the Raman scattering intensity creates a new technique for obtaining high resolution vibrational spectra of molecules (organic, inorganic, biomolecules) from very dilute solutions down to 10-9 M. 2. SERS investigations have shown that this surface spectroscopy is an extemely powerful in-situ vibrational method of studying the interfacial behavior of biomacromolecules in their natural environment: water2. 3. Combining SERS spectroscopy and high-performance thin-layer chromatography (HPTLC) has permitted in situ analysis of HPTLC spots down to nanogram amounts of substances3. 4. It was also demonstrated that ring breathing SERS bands of nucleic acids bases are conformation sensitive for B → Z transitions in DNA4.

In this research, sensing performance of mono and bimetallic nanophotonics SERS sensors of gold-silver nano-columns for the detection of chlorpyrifos was investigated. For optimum substrates for Gold-silver/nano-column surface-enhanced, Raman scattering (SERS) was achieved with the silicon substrate. By combining the Ag SERS activity with the Au chemical stability and nano-columns Si large field enhancement, the Au-Ag/nano-columns Si substrate revealed perfect reproducibility, homogeneity, sensitivity in addition to chemical stability. The sensors were tested by Atomic force microscope (AFM), field emission scanning electron microscope (FESEM), energy-dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). Findings presented in this research indicated modified distributions and sizes of formed alloy nanoparticles, and the hot spots junctions within the nanophotonics layer after changing the nanoparticles types. The SERS sensors performance displayed an excellent recognition of ultra-low concentrations of chlorpyrifos solutions with an exponential relationship with the Raman signal. The highest enhancement factor (Ef=1.56×106) and minimum limit of detection 0.069 mg/Kg were obtained with Au-Ag sensors.

This paper presents hybrid plasmonic substrates fabricated by a combination of bottom-up and top-down process of fabrication which can be employed as efficient Surface enhanced Raman scattering (SERS) substrates for chemical sensing. The hybrid approach leads to a cost-efficient fabrication with smaller fabrication times than the pure top-down approach and higher degree of control than the pure bottom-up approach. We demonstrate the achievement of sub-20 nm gaps on a large area with this hybrid methodology. These small gaps lead to the formation of electromagnetic hotspots, i.e., regions of high electromagnetic enhancement. The electromagnetic behavior of these substrates is analyzed theoretically using Finite Difference Time Domain modeling. The sub-20 nm gaps lead to the electromagnetic SERS enhancements of the order of ∼108, and a change in the gap size can tune the plasmon resonance wavelength from the visible to the near-IR region of the spectrum. It is thus shown that these SERS substrates offer high SERS enhancement along with a capability of passive tunability of the plasmon resonance wavelength by changing the geometrical parameters in these substrates.

Novel Z-scheme Cu2O@Ag/g-C3N4 heterojunctions: integrating ultrasensitive SERS detection with superior visible-light photocatalysis for tetracycline elimination.

Nanohole arrays in an Ag film were used as a substrate for surface-enhanced Raman scattering in the optical range. Extraordinary optical transmission and local field enhancement in Ag nanohole arrays were theoretically simulated using three-dimensional finite difference time domain method. The periodicity of the holes was adjusted to control the transmission intensity and electric field intensity. The calculation results show that the peak position of transmission red-shifts as the periodicity increases, while the peak intensity decreases linearly. The electric field is localized in a very small region at the edges of the holes, which means the surface-enhanced Raman scattering originates only from a small number of molecules located in the edge regions. The electric field intensity changes with the excitation wavelength in a similar trend to the transmission intensity. Both the electric field intensity and transmission intensity reach their maximum value at the frequency of surface plasmon resonance. The structure that gives resonant transmission provides the maximum surface-enhanced Raman scattering signal. Controllable and predictable surface-enhanced Raman scattering can be produced by using this novel nanostructure. The structure can be optimized to get the maximum surface-enhanced Raman scattering signal at a certain excitation wavelength through numerical simulations.