Surface-enhanced Resonance Raman Scattering Signal Research Articles

Resonance Raman and SERRS of fucoxanthin: Prospects for carotenoid quantification in live diatom cells

Fucoxanthin, one of the most abundant carotenoids in brown algae or in unicellular diatoms, plays a crucial role in photosynthetic processes and has a significant contribution to the natural pigments industry and biomedical application as colouring and bioactive agent. Many carotenoids are widely identified using resonance Raman (RR) spectroscopy, however, quantitative estimation of this pigment in solutions and in live cells from RR data is challenging. Here we investigated the concentration dependence resonance Raman and surface-enhanced resonance Raman scattering (SERRS) spectra of fucoxanthin, to prospect the capability of the techniques for quantitative estimation of the carotenoid in live diatom species, Cylindrotheca closterium and Skeletonema costatum. Furthermore, since pools of carotenoids are usually present in live photosynthetic microorganisms, we compared their SERRS signal when exposed to Ag nanoparticles and found distinct SERRS carotenoids signature. Regarding fucoxanthin quantification, we found a nonlinear increase in the resonance Raman intensity of the ν(C=C) mode in the concentration range from 1.190 µM to 3.035 mM and a linear increase in SERRS intensity in the 0.12 to 1.186 µM concentration range, comparable with the signal intensity collected from single diatom cells. Particularly, S. costatum, an opportunistic diatom causing harmful bloom in certain conditions, could provide important information from carotenoids monitoring in relation with its adaptability to various environmental factors, which would certainly consolidate such monitoring approaches relying on Raman spectroscopy techniques.

Efficient AuFeOx Nanoclusters of Laser-Ablated Nanoparticles in Water for Cells Guiding and Surface-Enhanced Resonance Raman Scattering Imaging

Nanoclusters with plasmonic and magnetic properties are obtained with naked gold (AuNP) and iron oxide nanoparticles (FeOxNP) separately synthesized by laser ablation in water and simply assembled by using their opposite surface charges. Controlling the amount of AuNP and FeOxNP, we obtained nanoclusters with both good surface-enhanced resonance Raman scattering (SERRS) signals and superparamagnetic properties. Nanoclusters are incubated with murine macrophage cells which, after mixing with other macrophages, can be magnetically guided in solution by sorting them in less than 10 min. SERRS signals, observed at the single cell level, were recorded for the sorted macrophages, showing that the nanoclusters are active also in a biological environment and allow the identification of the incubated macrophage cells.

Au Nanowire‐on‐Film SERRS Sensor for Ultrasensitive Hg2+ Detection

We report an ultrasensitive and selective single nanowire-on-film (SNOF) surface-enhanced resonance Raman scattering (SERRS) sensor for Hg(2+) detection based on structure-switching double stranded DNAs (dsDNAs). Binding of Hg(2+) induces conformational changes of the dsDNAs and let a Raman reporter get close to the SNOF structure, thereby turning on SERRS signal. The well-defined SNOF structure provides a detection limit of 100 pM with improved accuracy in Hg(2+) detection. This sensor is stable over a considerable amount of time and reusable after simple treatment. Since this SNOF sensor is composed of a single Au NW on a film, development of a multiplex sensor would be possible by employing NWs modified by multiple kinds of aptamers.

DNA Sequence Detection Using Surface-Enhanced Resonance Raman Spectroscopy in a Homogeneous Multiplexed Assay

Detection of specific DNA sequences is central to modern molecular biology and also to molecular diagnostics where identification of a particular disease is based on nucleic acid identification. Many methods exist, and fluorescence spectroscopy dominates the detection technologies employed with different assay formats. This study demonstrates the use of surface-enhanced resonance Raman scattering (SERRS) to detect specific DNA sequences when coupled with modified SERRS-active probes that have been designed to modify the affinity of double- and single-stranded DNA for the surface of silver nanoparticles resulting in discernible differences in the SERRS which can be correlated to the specific DNA hybridization event. The principle of the assay lies on the lack of affinity of double-stranded DNA for silver nanoparticle surfaces; therefore, hybridization of the probe to the target results in a reduction in the SERRS signal. Use of locked nucleic acid (LNA) residues in the DNA probes resulted in greater discrimination between exact match and mismatches when used in comparison to unmodified labeled DNA probes. Polymerase chain reaction (PCR) products were detected using this methodology, and ultimately a multiplex detection of sequences relating to a hospital-acquired infection, namely, methicillin-resistant Staphylococcus aureus (MRSA), demonstrated the versatility and applicability of this approach to real-life situations.

Simultaneous detection of alkaline phosphatase and β-galactosidase activity using SERRS

Surface enhanced resonance Raman scattering (SERRS) is an alternative to fluorescence for use in bioanalysis however due to the different optical mechanism it requires specifically designed reporters. Recently we have reported the use of 8-hydroxyquinolinyl azo dyes and their ester derivatives as reporters of lipase activity using SERRS. Acylation of the 8-hydroxy moiety significantly reduces surface enhancement of the Raman response and subsequent lipase catalysed ester hydrolysis enables the analyte to bind to silver nanoparticles, thus providing surface enhancement and the SERRS signal is ‘switched on’. By following this principle, phosphorylated and galactosylated analogues of 8-hydroxyquinolinylazo dyes were prepared and shown to act as reporters of enzymatic activity for alkaline phosphatase and β-galactosidase respectively when using SERRS.

SERRS and visible extinction spectroscopy of copper chlorophyllin on silver colloids as a function of pH

A study of sodium copper chlorophyllin adsorbed on silver colloids (CuChl/Ag) is conducted using surface-enhanced resonance Raman scattering (SERRS) and visible extinction spectroscopy to examine how the system changes as a function of pH. Initially at basic pH, SERRS signal is not detected even though CuChl is adsorbed onto the silver surface and deprotonated. Upon decreasing the solution pH slightly, colloidal aggregation is induced, evidenced by the broadening of the visible extinction spectra. The larger aggregates possess a surface plasmon that is in resonance with the laser excitation frequency (633-nm) and SERRS signal is detected. As the acid protonates CuChl, the overall negatively-charged surface approaches neutrality which induces more aggregation. Complete protonation of CuChl by pH 4.6 results in colloidal precipitation. However, when aggregation is halted about pH 5, adding NaOH( aq) to the system maintains the extent of aggregation and an intense SERRS signal is detected at basic pH.

Probing strong optical fields in compact aggregates of silver nanoparticles by SERRS of protoporphyrin IX

TEM images and measurements of SERRS (surface-enhanced resonance Raman scattering) spectra as a function of the porphyrin concentrations in systems with unmodified and chloride-modified Ag nanoparticles and protoporphyrin IX (PPIX) are reported. TEM images have shown formation of compact aggregates in systems with chloride modified Ag nanoparticles, as opposed to systems with the unmodified particles constituted by isolated particles. SERRS spectra of PPIX as a function of PPIX concentration were measured and subjected to factor analysis. Two spectral components were identified and tentatively attributed to unperturbed PPIX and to Ag+ -PPIX surface species. Concentration value of the SERRS spectral detection limit of the latter species was determined to be nearly three orders of magnitude lower in the system with the compact aggregates than in the system with separated nanoparticles and achieves the value of 1 x 10(-10) M in a macrosampling Raman experiment. TEM images and SERRS-micro-Raman spectra of single compact aggregates of chloride-modified Ag nanoparticles incorporating PPIX molecules were acquired from a sample prepared by attachment of the aggregates to amine groups of derivatized, SiOx/formvar coated copper grids for TEM. The SERRS signal has shown large temporal fluctuations as well as variations from one aggregate to another. Within the signal fluctuations, a SERRS spectrum showing the characteristic bands of both SERRS spectral forms of PPIX and originating most probably from a few PPIX molecules located in hot spots in the interstices between the Ag nanoparticles, was obtained.

Probing of Porphyrin Surface Chemistry in Systems with Laser-Ablated Ag Nanoparticle Hydrosol: Role of Thiosulfate Anions

The influence of sodium thiosulfate (THS) concentration in Ag colloid/THS/H(2)TMPyP and Ag colloid/H2TMPyP/THS systems (H2TMPyP = 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin) was investigated by a combination of surface-enhanced resonance Raman scattering (SERRS) spectroscopy, surface plasmon extinction (SPE) measurements, and transmission electron microscopy (TEM). THS was found to have a strong impact on Ag nanoparticle surface structure and aggregation state and on interaction with H2TMPyP probe molecules, as evidenced by variations of the SERRS spectrum. In the Ag colloid/THS/H2TMPyP system, when laser-ablated Ag colloid was THS pretreated prior to the porphyrin addition, a critical threshold THS concentration (4 x 10(-5) M) was discovered. At concentrations below the threshold, THS mainly reduces the number of Ag+ adsorption sites. This leads to increased Ag nanoparticle aggregation prior to the porphyrin addition and significant weakening of the overall SERRS signal. Dominant contributions in the SERRS spectrum correspond to free base H2TMPyP and Ag+ containing the AgTMPyP form. At concentrations above the threshold, THS mediates also the formation and stabilization of new adsorption sites, probably Ag(0) sites. This induces a turn in the aggregation state of the pretreated Ag-c/THS system, an increase of the overall SERRS signal, and the appearance of a new spectral form of Ag metalated porphyrin.

Single molecular detection of a perylene dye dispersed in a Langmuir–Blodgett fatty acid monolayer using surface-enhanced resonance Raman scattering

The Langmuir–Blodgett (LB) monolayer technique was used to fabricate single molecule LB monolayer containing bis(phenethylimido)perylene (PhPTCD), a red dye dispersed in arachidic acid (AA) with an average doping of 1 molecule per μm 2. The monolayer was transferred onto Ag island films to obtain spatially resolved surface-enhanced resonance Raman scattering (SERRS) spectra. The mixed LB monolayers were fabricated with a concentration, on average, of 1, 6, 19 and 118 PhPTCD molecules per μm 2 in AA. The AA provides a two-dimensional host matrix whose background signal does not interfere with the detection of the probe molecule's SERRS signal. The properties of the single molecule detection were investigated using micro-Raman with a 514.5-nm laser line. The Ag island surfaces coated with the LB monolayer were mapped with spatial steps of 3 μm and global chemical imaging of the most intense SERRS band in the spectrum was also recorded. The SERRS and surface-enhanced fluorescence (SEF) of the neat and single molecule LB monolayer were recorded in a temperature range from liquid nitrogen to +200°C. Neat PhPTCD LB monolayer spectra served as reference for the identification of characteristic signatures of the single molecule behavior. The spatial resolution of Raman-microscopy experiments, the multiplicative effect of resonance Raman and SERRS, and the high sensitivity of the new dispersive Raman instruments, allow SERRS to be part of the family of single molecular spectroscopies.

Surface enhanced fluorescence and Raman imaging of Langmuir-Blodgett azopolymer films

The spectroscopic properties and surface-enhanced spectra of Langmuir-Blodgett (LB) films of methacrylic homopolymer (HPDR13) are presented. It is shown that LB film displays strong fluorescence attributed to the spatial restrictions imposed by its structure. The emission is observed in conjunction with photoisomerization, a process clearly demonstrated by the formation of surface-relief gratings in the LB film [C.R. Mendonça et al., Macromolecules 32 (1999) 1493]. Surface-enhanced Raman scattering (SERS), Surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF) were observed for LB films of HPDR13 deposited onto silver island films. SERS measurements were also carried out on a sample fabricated with one monolayer LB film deposited onto silver islands followed by one overlayer of silver (LB sandwiched between two layers of silver islands). The polymer interacts very weakly with the metal surface (physisorption), and the enhancement effect is determined by the local electric field enhancement. The strong SERS and SERRS signals were suitable for micro-Raman imaging. Line, area mapping and global images of the LB monolayer on silver island are reported. The transfer ratio in the fabrication of the LB suggests a homogeneous coating of the silver islands, thereby the chemical images show the variation of the SERS intensity due to surface enhancement.