Light Scattering in Solids

Surface-enhanced resonance Raman scattering (SERRS) studies of cytochrome c (cyt c) have demonstrated that the native integrity of this heme-containing protein is preserved in the presence of citrate-reduced sols. Cyt c SERRS spectra exhibit similar spin and oxidation markers as the resonance Raman scattering (RRS) signals displayed by the native protein solution. Previous SERRS investigations of cyt c showed that the protein denatures at the substrate surface. This hemoprotein denaturation was attributed to an electrostatic interaction between the porphyrin and the SERRS-active substrate. The results presented in this study suggest that the citrate ions prevent the biomolecule from directly interacting with the silver-sol surface. The native state of cyt c is also retained with the addition of phosphatidylcholine and/or phosphate buffer. Although the SERRS bandshifts correlate with the RRS spectra, the relative intensities of specific cyt c frequencies change in the presence of adsorbed citrate, phosphate buffer, and phosphatidylcholine. These compounds may influence the orientation of the protein at the substrate surface, which would account for the spectral intensity differences. In order to study the orientation effects further, additional studies of cyt c adsorbed onto silver electrodes and thin silver films were conducted. A comparison of the SERRS relative band intensities and frequency bandshifts shows that the spectra of the protein adsorbed onto phospholipid-coated substrates closely correspond to the RRS cyt c solution spectra. In contrast to the behavior exhibited by cyt c, cytochrome P-450 (cyt P-450) adsorbed onto a phosphatidylcholine silver-sol substrate leads to a low to high spin-state conversion. The shifts in the spin-state markers are ascribed to a strong interaction of the cyt P-450 with the phospholipid coating.

Excitation profiles of SERS (surface-enhanced Raman scattering) and/or SERRS (surface-enhanced resonance Raman scattering) spectral bands of two forms of a Ag-bpy (bpy = 2,2'-bipyridine) surface complex and of [Ru(bpy)3]2+ on Ag nanoparticle (hydrosol) surfaces were determined from the spectra excited in the 458-600 nm region and are reported together with the FT-SERS spectra of the Ag-bpy surface complex and FT Raman spectra of [Ru(bpy)3] Cl2. Seven of the observed 11 fundamentals as well as their first overtones and combination bands are selectively enhanced in SERS of the Ag-bpy surface complex formed in the Ag colloid/HCl/bpy system. The profiles of these bands show a common maximum at approximately 540 nm. The selectively enhanced bands of the Ag-bpy surface complex have nearly the same wavenumbers as those enhanced in the SERRS and resonance Raman spectra of [Ru(bpy)3]2+ upon excitation close to the 453 nm maximum of its MLCT absorption band. Moreover, the intensity patterns of the bpy vibrations of the two species match both in resonance (541 nm excitation for Ag-bpy, 458 nm for [Ru(bpy)3]2+) and in off-resonance (458 and 1064 nm for Ag-bpy, 1064 nm for [Ru(bpy)3]2+). The distinct band shapes of the excitation profiles of the selectively enhanced vibrational modes of the Ag-bpy surface complex, as well as the observation of overtones and combination bands in the SERS spectra upon excitation into this "band", are interpreted in terms of a charge-transfer resonance contribution to the overall SERS enhancement. In view of the near-coincidence of the vibrational modes coupled to the resonant electronic transition of Ag-bpy with those coupled to the MLCT transition of [Ru(bpy)3]2+, the resonant electronic transition is tentatively assigned to a Ag metal to bpy (pi*) CT transition.

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.

Applications of Raman-based techniques to on-site and in-vivo analysis

Η φασματοσκοπία Raman θεωρείται αξιόπιστη μέθοδος χαρακτηρισμού της μοριακής δομής της ύλης. Τελευταία δε καταβάλλεται μεγάλη προσπάθεια να αναδειχθεί και ως μη επεμβατική τεχνική ανίχνευσης ουσιών φαρμακευτικού και βιολογικού ενδιαφέροντος. Επειδή όμως το φαινόμενο Raman είναι ασθενές και τα όρια ανίχνευσης των ουσιών αυτών ιδιαίτερα χαμηλά, η συμβατική φασματοσκοπία Raman ανταποκρίνεται με μεγάλη δυσκολία στις απαιτήσεις μιας μη επεμβατικής τεχνικής. Τα τελευταία χρόνια με την ανακάλυψη της επιφανειακής ενίσχυσης της σκέδασης Raman (Surface Enhanced Raman Scattering) και την ανάπτυξη της ομώνυμης τεχνικής SERS αυξήθηκε η πιθανότητα του φαινομένου κατά τάξεις μεγέθους. Στο πλαίσιο αυτό, έχουν αναφερθεί και μελέτες SERS με ανίχνευση σκέδασης Raman ακόμη και από ένα μόνο μόριο (single molecule detection).Προϋπόθεση όμως ανάπτυξης φαινομένου SERS είναι η γειτνίαση της εξεταζόμενης ουσίας με νανοσωματίδια αργύρου (Ag) ή χρυσού (Au). Τα νανοσωματίδια αυτά χρησιμοποιούνται κυρίως είτε υπό μορφή κολλοειδών διαλυμάτων είτε υπό την μορφή νανοδομημένων επιφανειών. Μια επιπλέον παράμετρος που πρέπει να συνυπολογισθεί ώστε η μέθοδος αυτή να χαρακτηριστεί αναλυτική είναι η δυνατότητα πραγματοποίησης με SERS ποσοτικών μετρήσεων. Στην παρούσα εργασία ως “υπόστρωμα” εμφάνισης του φαινομένου SERS χρησιμοποιήθηκαν κολλοειδή διαλύματα Au και Ag (~2 mL), στα οποία προστίθεντο 25-100 μL διαλύματος της προς ανίχνευσης ουσίας. Η χρησιμοποίηση της γεωμετρίας σκέδασης 90ο, της πλέον ενδεδειγμένης για λήψη φασμάτων Raman από υγρά και κολλοειδή διαλύματα νανομετρικής κλίμακας (10-100 nm), έδωσε τη δυνατότητα ανίχνευσης συγκεντρώσεων ουσιών-στόχων ακόμη και της τάξης των fg/mL. Επιπλέον, η χρησιμοποίηση μιας κυψελίδας με συνεχή ταλάντωση σε κάθετη ως προς το επίπεδο σκέδασης διεύθυνση (oscillating or shaking cell), επέτρεψε την πραγματοποίηση ποσοτικών μετρήσεων SERS σε συγκεντρώσεις της τάξης των (sub)-ng & (sub)-pg/mL. Η διάταξη αυτή φωταψίας δείγματος και συλλογής σκεδαζόμενης ακτινοβολίας εφαρμόστηκε σε αντικαρκινικά φάρμακα (Novantrone® & Doxorubicin), αντιβιοτικό (Ciproxin®) και βάσεις του DNA. Στην περίπτωση του αντιβιοτικού με ενεργή ουσία το Ciprofloxacin ελήφθησαν ποσοτικά αποτελέσματα σε διαλύματα τεχνητών δακρύων της τάξης των ng/mL, κάτω από την συνολική κλίμακα της μέσης ανασταλτικής πυκνότητας (minimum inhibitory concentration range) του φαρμάκου. Στόχος και φιλοδοξία είναι η τεχνική αυτή να αναδειχθεί ως μια ταχεία μη επεμβατική αναλυτική μέθοδος μέτρησης φαρμακευτικών ή/και βιολογικών ουσιών σε σωματικά υγρά (π.χ. σίελος, δάκρυα, …), για την μελέτη της φαρμακοκινητικής, την έγκαιρη διάγνωση ασθενειών καθώς και τη μελέτη ελεγχόμενης αποδέσμευσης ενεργών ουσιών από πολυμερικές μήτρες σε πολύ μικρές συγκεντρώσεις. Επιπλέον, έγινε προσπάθεια μελέτης/ανίχνευσης μορίων Ε18 primary rat cortical cells με την χρήση του SERS σε συνθήκες προσομοίωσης ηλεκτροχημικού εμφυτεύματος. Για τον λόγο αυτό σχεδιάστηκε και αναπτύχθηκε ένας μικρο-επωαστής (micro-incubator) που επιτρέπει αφ’ ενός μεν τη συντήρηση των κυττάρων σε περιβάλλον κατάλληλο για τη μελέτη τους (layer of Neurobasal-culture medium with a 95% air & 5% CO₂ gas flow at 37°C), αφ’ ετέρου δε την προσαρμογή του σε χώρο υποδοχής δείγματος ενός φασματοφωτόμετρου μικρο-Raman για τη λήψη φασματοηλεκτροχημικών μετρήσεων Raman/SERS. Το κύριο σημείο ενδιαφέροντος στο οποίο εστιάσαμε στην παρούσα εργασία αναφέρεται στην διερεύνηση ανίχνευσης βασικών/θεμελιωδών μορίων των κυττάρων στo θρεπτικό υγρό του πειράματος για την ταχεία εκτίμηση ενδεχόμενης αποδέσμευσης DNA που θα αντικατόπτριζε την κατάσταση των κυττάρων.

Well defined gold nanostructures of various sizes are fabricated on glass substrates using high-resolution electron-beam lithography/lift-off techniques and detailed surface-enhanced Raman scattering (SERS) properties of crystal violet molecules are studied in order to elucidate electromagnetic (EM) field enhancement effects on the fabricated structures. SERS measurements are performed with high reproducibility using in situ Raman microspectroscopy in aqueous solution. An analysis based on EM theory is performed using field-enhancement factors obtained from finite-difference time-domain (FDTD) simulations and the analysis reproduces experimental results very well. It is noteworthy, furthermore, that the proposed analytic method of EM effects on SERS allows the estimate of the ideal local temperature of gold nanostructures by canceling out the difference in EM field factors at Stokes and anti-Stokes Raman scattering wavelengths. Thus, these experimental results demonstrate that quantitative analysis based on EM theory can be obtained using highly controlled gold nanostructures for SERS measurements with high reproducibility, a result that is promising for the construction of a SERS analysis chip. Although no SERS chip reported so far has been usable for quantitative analysis, this study opens the door for construction of a quantitative SERS chip.

Raman scattering signals can be enhanced by several orders of magnitude on surface‐enhanced Raman scattering (SERS) substrates made from noble metal nanostructures. Some SERS substrates are even able to detect single‐molecule Raman signals. A novel silver nanobud (AgNB) substrate with superior SERS activity was fabricated with a solid‐state ionics method. The AgNB substrate was formed by tightly collocated unidirectional 100 nm size silver buds, presenting a highly rough surface topography. Distinct SERS signals of single λ‐DNA molecules in water were detected on AgNB substrates. AgNB substrates were compared with disordered silver nanowire (AgNW) substrates manufactured by the same method through the SERS detection of λ‐DNA solutions. This original AgNB substrate provides a reliable approach towards trace analysis of biomacromolecules and promotes the utilization of the SERS technique in biomedical research.

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.

Surface-enhanced Raman scattering (SERS) has garnered substantial attention due to its ability to achieve single-molecule sensitivity by utilizing metallic nanostructures to amplify the exceedingly weak Raman scattering process. However, the introduction of metal nanostructures can induce a background continuum which can reduce the ultimate sensitivity of SERS in ways that are not yet well understood. Here, we investigate the impact of laser irradiation on both Raman scattering and backgrounds from self-assembled monolayers within nanoparticle-on-mirror plasmonic nanocavities with variable geometry. We find that laser irradiation can reduce the height of the monolayer by inducing an irreversible change in molecular conformation. The resulting increased plasmon confinement in the nanocavities not only enhances the SERS signal, but also provides momentum conservation in the inelastic light scattering of electrons, contributing to the enhancement of the background continuum. The plasmon confinement can be modified by changing the size and the geometry of nanoparticles, resulting in a nanoparticle geometry-dependent background continuum in SERS. Our work provides new routes for further modifying the geometry of plasmonic nanostructures to improve SERS sensitivity.

Single-molecule surface-enhanced (resonance) Raman scattering (SM-SE(R)RS) studies have applications beyond analytical chemistry. For instance, SM-SERS spectra carry information about the molecule interaction with the hotspots (regions of strong electric field enhancement due to surface plasmon resonance). The analysis of the time- (or spatial-) dependent fluctuations in SM-SERS spectra permits, for instance, the study of resonance contributions from the local electric field to imbalances in the anti-Stokes to Stokes intensity ratios (IAS/IS). This analysis is a tool for the characterization of the resonance energies of the hotspots. In the case of colloidal samples, the structures of the hotspots and their properties are dependent upon the colloidal aggregation state. The analysis of the IAS/IS ratios in such a system can be a useful characterization tool to infer the hotspot structures for different aggregation states. In this work, the distributions of IAS/IS ratio for crystal violet (CV) adsorbed in Ag colloids at different aggregation states was studied under SM-SERS conditions. The experimental results were interpreted in terms of the generalized Mie theory (GMT) simulations.

Ph-Negative Myeloproliferative Neoplasms Exhibit Some Features Of Warburg Effect

In this study, we developed a simple surface-enhanced Raman Scattering (SERS) composite substrate, composed of an all-metal metasurface and on-surface random distributing silver nanoparticles (AgNPs), to enhance the performance of SERS sensing. The metasurface is made up of gold (Au) nanopillars array on aluminum (Al), it can localize the electromagnetic field energy with a resonant absorption peak near the 630 nm wavelength, which contributes to the SERS performance of AgNPs deposited into the structure. The composite substrate can significantly improve the sensing performance, and the SERS Enhancement Factor (EF) reaches 2.81 × 106. The substrate also has good stability and reproducibility. The research is based on the combination of Localized Surface Plasmon Resonance (LSPR) and SERS effects, providing a method and idea for improving the sensitivity of SERS detection, and achieving the trace detection of Rhodamine 6G (R6G) and Thiram at 10−10 M, respectively.

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.

Shape-controlled synthesis of metal nanostructures has opened many new possibilities to design ideal building blocks for future nanodevices. In this work, new types of monodisperse silver nanoplates with complex shapes, namely, a disklike shape and flowerlike shapes, were controllably synthesized in high yield by reducing [Ag(NH3)2]+ with ascorbic acid in the presence of silver seed at room temperature. Unlike previous methods for synthesizing the silver nanoplates in the presence of cetyltrimethylammonium bromide (CTAB) micelles, the use of the precursor [Ag(NH3)2]+, other than Ag+, provides a flexible strategy to control the procession of the reduction reaction in a mild way. These silver nanoplates with shapes of disk and flower were shown to possess surface plasmon resonance (SPR) that directly relates to their geometric shapes. As a result of their high anisotropy in shape, the flowerlike silver nanoplates exhibit excellent surface-enhanced Raman scattering (SERS) enhancement ability relative to sphe...

A review of Surface Enhanced Raman Scattering (SERS) and Surface Enhanced Resonance Raman Scattering (SERRS) from biomolecules adsorbed on a metal surface is given. Advantages and applications of these new vibration spectroscopic methods particularly in characterize in-situ the chemical identity, structure, orientation, chemical and electrochemical reactions of biological specimens adsorbed at charged surfaces are discussed. The technical aspects of the instrumentation and procedure as also the fundamentals of the SERS theory are exposed. Different applications show that SERS-and SERRS spectroscopy are powerful in-situ methods to study the interfacial behaviour of biomolecules. Moreover, the high enhancement factor of the Raman scattering intensity creates a new technique for obtaining high resolution vibrational spectra of biomolecules from rather diluted aqueous solutions down to 10−8 M.