Analysis of the SERS Spectrum by Theoretical Methodology: Evaluating a Classical Dipole Model and the Detuning of the Excitation Frequency

Surface-enhanced Raman scattering (SERS) spectroscopy is gaining prominence as one of the most powerful ultradetection techniques. The SERS outcome is essentially a complicated pattern of vibrational bands that allows multiplex analysis but, at the same time, makes difficult the interpretation of unknown analytes or known substances in the presence of complex unknown chemical environments. Herein, we show two computational methods to reproduce the spectral shape of the SERS spectra. The first, based in the modification of the classical dipole model, reproduces with a notable similarity the experimental spectrum excited far to the red of the localized surface plasmon resonance (LSPR). This light and time-efficient model is of great interest to elucidate the orientation of the target on the plasmonic surface or even to accurately identify suspected unknown targets in real samples. However, the experimental SERS spectrum in resonance with the LSPR is also modeled by using a more classical CPHF approach. This method provides also good agreement with the experiment but at the expense of much more computational time

Direct Quantification of DNA Base Composition by Surface-Enhanced Raman Scattering Spectroscopy

Design of ultrasensitive DNA sensors based on the unique physical properties of plasmonic nanostructures has become one of the most exciting areas in nanomedicine. However, despite the vast number of proposed applications, the determination of the base composition in nucleic acids, a fundamental parameter in genomic analyses and taxonomic classification, is still restricted to time-consuming and poorly sensitive conventional methods. Herein, we demonstrate the possibility of determining the base composition in single- and double-stranded DNA by using a simple, low-cost, high-throughput, and label-free surface-enhanced Raman scattering (SERS) method in combination with cationic nanoparticles

Fast Optical Chemical and Structural Classification of RNA

As more biological activities of ribonucleic acids continue to emerge, the development of efficient analytical tools for RNA identification and characterization is necessary to acquire an in-depth understanding of their functions and chemical properties. Herein, we demonstrate the capacity of label-free direct surface-enhanced Raman scattering (SERS) analysis to access highly specific structural information on RNAs at the ultrasensitive level. This includes the recognition of distinctive vibrational features of RNAs organized into a variety of conformations (micro-, fully complementary duplex-, small interfering- and short hairpin-RNAs) or characterized by subtle chemical differences (single-base variances, nucleobase modifications and backbone composition). This method represents a key advance in the ribonucleic acid analysis and will have a direct impact in a wide range of different fields, including medical diagnosis, drug design, and biotechnology, by enabling the rapid, high-throughput, simple, and low-cost identification and classification of structurally similar RNAs

Synthesis and Optical Properties of Homogeneous Nanoshurikens

During the last years the controlled synthesis of Au nanoparticles (NPs) has almost become a reality, and structures such as spheres, cubes, rods, decahedra, or octahedra can be prepared with <i>a la carte</i> dimensions in a very homogeneous manner. However, the fabrication of spiked particles, the most efficient plasmonic NPs, with controllable geometric parameters remains elusive. Here we show how to prepare highly homogeneous spiked nanoparticles composed of a penta-twinned core and five tips. These nanoparticles, reminiscent of ninja nanoshurikens (throwing stars), exhibit the ability to concentrate large electromagnetic fields at the apexes of the tips upon illumination. The apexes also present high affinity for analytes, giving rise to an unprecedented capacity for quantitative optical ultradetection with SERS

From Nano to Micro: Synthesis and Optical Properties of Homogeneous Spheroidal Gold Particles and Their Superlattices

Iodide ions have been used as an additive to fabricate homogeneous gold spheres with a la carte dimensions, ranging from the nano- (50 nm) to the microscale (ca<i>.</i> 1 μm). Due to the high uniformity and surface functionalization of the produced materials, they undergo spontaneous assembly into organized superlattices upon solvent drying. Thus, optical properties of the particles including localized surface plasmon resonances and surface enhanced Raman scattering (SERS) response, both in solution and organized into superlattices, are also reported

Boosting the Quantitative Inorganic Surface-Enhanced Raman Scattering Sensing to the Limit: The Case of Nitrite/Nitrate Detection

A high-performance ionic-sensing platform has been developed by an interdisciplinary approach, combining the classical colorimetric Griess reaction and new concepts of nanotechnology, such as plasmonic coupling of nanoparticles and surface-enhanced Raman scattering (SERS) spectroscopy. This approach exploits the advantages of combined SERS/surface-enhanced resonant Raman Scattering (SERRS) by inducing the formation of homogeneous hot spots and a colored complex in resonance with the laser line, to yield detection limits for nitrite down to the subpicomolar level. The performance of this new method was compared with the classical Griess reaction and ionic chromatography showing detection limits about 6 and 3 orders of magnitude lower, respectively

Universal One-Pot and Scalable Synthesis of SERS Encoded Nanoparticles

Encoded particles are one of the most powerful approaches for multiplex high-throughput screening. Surface-enhanced Raman scattering (SERS) based codification can, in principle, avoid many of the intrinsic limitations due to conventional alternatives, as it decreases the reading time and particle size while allowing for almost unlimited codification. Unfortunately, methods for the synthetic preparation of these particles are tedious; often subjected to limited reproducibility (associated with large fluctuations in the size distributions of the polymers employed in the standard protocols); and to date, limited to a small amount of molecules. Herein, we report a universal, one-pot, inexpensive, and scalable synthetic protocol for the fabrication of SERS-encoded nanoparticles. This synthetic strategy is highly reproducible, independent of the chemical nature and size of the Raman code used (31 different codes were tested) and scalable in the liter range without affecting the final properties of the encoded structures. Furthermore, the SERS efficiency of the fabricated encoded nanoparticles is superior to that of the materials produced by conventional methods, while showing a remarkable reproducibility from batch to batch. This encoding strategy can easily be applied to nanoparticles of different materials and shapes

Highly Sensitive SERS Quantification of the Oncogenic Protein c‑Jun in Cellular Extracts

A surface-enhanced Raman scattering (SERS)-based sensor was developed for the detection of the oncoprotein c-Jun at nanomolar levels. c-Jun is a member of the bZIP (basic zipper) family of dimeric transcriptional activators, and its overexpression has been associated with carcinogenic mechanisms in several human cancers. For our sensing purpose, we exploited the ability of c-Jun to heterodimerize with its native protein partner, c-Fos, and therefore designed a c-Fos peptide receptor chemically modified to incorporate a thiophenol (TP) group at the N-terminal site. The TP functionality anchors the c-Fos protein onto the metal substrate and works as an effective SERS probe to sense the structural rearrangements associated with the c-Fos/c-Jun heterodimerization

Nanoreactors for Simultaneous Remote Thermal Activation and Optical Monitoring of Chemical Reactions

We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermally activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels–Alder cycloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing real-time monitoring of the reaction progress

SERS Detection of Amyloid Oligomers on Metallorganic-Decorated Plasmonic Beads

Protein misfolded proteins are among the most toxic endogenous species of macromolecules. These chemical entities are responsible for neurodegenerative disorders such as Alzheimer’s, Parkinson’s, Creutzfeldt–Jakob’s and different non-neurophatic amyloidosis. Notably, these oligomers show a combination of marked heterogeneity and low abundance in body fluids, which have prevented a reliable detection by immunological methods so far. Herein we exploit the selectivity of proteins to react with metallic ions and the sensitivity of surface-enhanced Raman spectroscopy (SERS) toward small electronic changes in coordination compounds to design and engineer a reliable optical sensor for protein misfolded oligomers. Our strategy relies on the functionalization of Au nanoparticle-decorated polystyrene beads with an effective metallorganic Raman chemoreceptor, composed by Al³⁺ ions coordinated to 4-mercaptobenzoic acid (MBA) with high Raman cross-section, that selectively binds aberrant protein oligomers. The mechanical deformations of the MBA phenyl ring upon complexation with the oligomeric species are registered in its SERS spectrum and can be quantitatively correlated with the concentration of the target biomolecule. The SERS platform used here appears promising for future implementation of diagnostic tools of aberrant species associated with protein deposition diseases, including those with a strong social and economic impact, such as Alzheimer’s and Parkinson’s diseases