On the emergence of Raman signals characterizing multicenter nanoscale interactions

Raman scattering is most commonly associated with a change in vibrational state within one molecule, with signals in the corresponding spectrum widely used to identify material structures. When the corresponding theory is developed using quantum electrodynamics, the fundamental scattering process is described by a single photon of one radiation mode being annihilated with the concurrent creation of another photon; the two photon energies differ by an amount corresponding to the transfer of vibrational energy within the system. Here, we consider nanoscale interactions between neighboring molecules to mediate the process, by way of a virtual photon exchange to connect the evolution of the two molecular states. We consider both a single and pair of virtual photon exchanges. Our analysis deploys two realistic assumptions: in each pairwise interaction the two components are considered to be (i) chemically different and (ii) held in a fixed orientation with respect to each other, displaced by an amount equivalent to the near-field region; resulting in higher order dependences on displacement R becoming increasingly significant, and at the limit the short-range R-6 term can even dominate over R-3 dependence. In our investigation one center undergoes a change in vibrational energy; each neighboring molecule returns to the electronic and vibrational state in which it began. For the purposes of providing results, a Stokes transition has been assumed; analogous principles hold for the anti-Stokes counterpart. Experimentally, there is no change to the dependence on the intensity of laser light. However, the various mechanisms presented herein lead to different selection rules applying in each instance. In some cases specifically identifiable mechanisms will be active for a given transition, leading to new and characteristic lines in the Raman spectrum. A thorough investigation of all physically achievable mechanisms will be detailed in this work

HD DVD substrates for surface enhanced Raman spectroscopy analysis : fabrication, theoretical predictions and practical performance

Commercial HD DVDs provide a characteristic structure of encoding pits which were utilized to fabricate cost efficiently large area SERS substrates for chemical analysis. The study targets the simulation of the plasmonic structure of the substrates and presents an easily accessible fabrication process to obtain highly sensitive SERS active substrates. The theoretical simulation predicted the formation of supermodes under optimized illumination conditions, which were verified experimentally. First tests of the developed SERS substrates demonstrated their excellent potential for detecting vitamin A and pro- vitamin A at low concentration levels

Application of molecular SERS nanosensors: where we stand and where we are headed towards?

Molecular specific and highly sensitive detection is the driving force of the surface-enhanced Raman spectroscopy (SERS) community. The technique opens the window to the undisturbed monitoring of cellular processes in situ or to the quantification of small molecular species that do not deliver Raman signals. The smart design of molecular SERS nanosensors makes it possible to indirectly but specifically detect, e.g. reactive oxygen species, carbon monoxide or potentially toxic metal ions. Detection schemes evolved over the years from simple metallic colloidal nanoparticles functionalized with sensing molecules that show uncontrolled aggregation to complex nanostructures with magnetic properties making the analysis of complex environmental samples possible. The present article gives the readership an overview of the present research advancements in the field of molecular SERS sensors, highlighting future trends. © 2020, The Author(s)

Application of molecular SERS nanosensors: where we stand and where we are headed towards?

Abstract Molecular specific and highly sensitive detection is the driving force of the surface-enhanced Raman spectroscopy (SERS) community. The technique opens the window to the undisturbed monitoring of cellular processes in situ or to the quantification of small molecular species that do not deliver Raman signals. The smart design of molecular SERS nanosensors makes it possible to indirectly but specifically detect, e.g. reactive oxygen species, carbon monoxide or potentially toxic metal ions. Detection schemes evolved over the years from simple metallic colloidal nanoparticles functionalized with sensing molecules that show uncontrolled aggregation to complex nanostructures with magnetic properties making the analysis of complex environmental samples possible. The present article gives the readership an overview of the present research advancements in the field of molecular SERS sensors, highlighting future trends

Cyclodextrin-assisted surface-enhanced Raman spectroscopy: a critical review

Numerous approaches have been proposed to overcome the intrinsically low selectivity of surface-enhanced Raman spectroscopy (SERS), and the modification of SERS substrates with diverse recognition molecules is one of such approaches. In contrast to the use of antibodies, aptamers, and molecularly imprinted polymers, application of cyclodextrins (CDs) is still developing with less than 100 papers since 1993. Therefore, the main goal of this review is the critical analysis of all available papers on the use of CDs in SERS analysis, including physicochemical studies of CD complexation and the effect of CD presence on the Raman enhancement. The results of the review reveal that there is controversial information about CD efficiency and further experimental investigations have to be done in order to estimate the real potential of CDs in SERS-based analysis

Selection of ssDNA aptamers and construction of an aptameric electrochemical biosensor for detecting Giardia intestinalis cyst protein †

Giardia intestinalis , an intestinal protozoan parasite, is one of the potentially severe parasitic infections, especially in children. Rapid and simple diagnostic tools are highly desired to prevent the potential outbreak of G. intestinalis infection. The life cycle of Giardia species is quite simple and consists of trophozoite and cystic forms. This report presents the selection of ssDNA aptamers with high binding affinity to a G. intestinalis cyst recombinant protein using the SELEX process (systematic evolution of ligands by exponential enrichment). The process is based on incubating a random DNA library with the targeted protein, and the bound sequences are recovered and amplified by polymerase chain reaction (PCR). The generated pool of aptamer sequences is used in the subsequent selection round. After ten selection cycles, three sequences were isolated with low dissociation constants ( K d ) of 7.98, 21.02, and 21.86 nM. Subsequently, the aptamer with the best affinity was integrated into a label-free electrochemical biosensor to detect G. intestinalis cyst protein. The developed aptasensor accurately detected the G. intestinalis recombinant cyst protein within the range of 0.1 pg mL −1 to 1000 ng mL −1 , and a low detection limit of 0.0026 pg mL −1 . Furthermore, a selectivity study showed insignificant cross-reactivity against other proteins such as bovine serum albumin and globulin, and no reactivity against G. intestinalis trophozoite recombinant protein. Finally, the aptasensor was tested using G. intestinalis -spiked tap water samples and showed good recovery rates

Label-free detection of Phytophthora ramorum using surface-enhanced Raman spectroscopy

In this study, we report on a novel approach for the label-free and species-specific detection of the plant pathogen Phytophthora ramorum from real samples using surface enhanced Raman scattering (SERS). In this context, we consider the entire analysis chain including sample preparation, DNA isolation, amplification and hybridization on SERS substrate-immobilized adenine-free capture probes. Thus, the SERS-based detection of target DNA is verified by the strong spectral feature of adenine which indicates the presence of hybridized target DNA. This property was realized by replacing adenine moieties in the species-specific capture probes with 2-aminopurine. In the case of the matching capture and target sequence, the characteristic adenine peak serves as an indicator for specific DNA hybridization. Altogether, this is the first assay demonstrating the detection of a plant pathogen from an infected plant material by label-free SERS employing DNA hybridization on planar SERS substrates consisting of silver nanoparticles

Detection of Pseudomonas aeruginosa Metabolite Pyocyanin in Water and Saliva by Employing the SERS Technique

Pyocyanin (PYO) is a metabolite specific for Pseudomonas aeruginosa. In the case of immunocompromised patients, it is currently considered a biomarker for life-threating Pseudomonas infections. In the frame of this study it is shown, that PYO can be detected in aqueous solution by employing surface-enhanced Raman spectroscopy (SERS) combined with a microfluidic platform. The achieved limit of detection is 0.5 μM. This is ~2 orders of magnitude below the concentration of PYO found in clinical samples. Furthermore, as proof of principle, the SERS detection of PYO in the saliva of three volunteers was also investigated. This body fluid can be collected in a non-invasive manner and is highly chemically complex, making the detection of the target molecule challenging. Nevertheless, PYO was successfully detected in two saliva samples down to 10 μM and in one sample at a concentration of 25 μM. This indicates that the molecules present in saliva do not inhibit the efficient adsorption of PYO on the surface of the employed SERS active substrates

Label-free detection of Phytophthora ramorum using surface-enhanced Raman spectroscopy †

In this study, we report on a novel approach for the label-free and species-specific detection of the plant pathogen Phytophthora ramorum from real samples using surface enhanced Raman scattering (SERS). In this context, we consider the entire analysis chain including sample preparation, DNA isolation, amplification and hybridization on SERS substrate-immobilized adenine-free capture probes. Thus, the SERS-based detection of target DNA is verified by the strong spectral feature of adenine which indicates the presence of hybridized target DNA. This property was realized by replacing adenine moieties in the species-specific capture probes with 2-aminopurine. In the case of the matching capture and target sequence, the characteristic adenine peak serves as an indicator for specific DNA hybridization. Altogether, this is the first assay demonstrating the detection of a plant pathogen from an infected plant material by label-free SERS employing DNA hybridization on planar SERS substrates consisting of silver nanoparticles