Antimicrobial peptides are vital to the innate immune system and serve as a safe alternative to traditional antibiotics for bacterial infections. However, their effectiveness is limited by the need for high concentrations to disrupt bacterial membranes and the challenge of protecting them from proteases that degrade them before reaching their target. Intending to improve the delivery of anoplin (ANP) to bacterial cells, we prepared ANP-coated gold nanoparticles (Au NPs) with a diameter of about 50 nm, and investigated their effects on the properties of model bacterial membranes using Raman and surface-enhanced Raman spectroscopy (SERS). Prepared as a mixture of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (PE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho(1'-rac-glycerol) sodium salt (PG) at a ratio PE/PG 3/1, lipid membranes were measured in the absence/presence of pure ANP, Au NPs (coated only with citrate), and Au NPs coated with ANP and at two different temperatures, 10 °C and 26 °C, at which the lipids are found in the gel/fluid and fluid/fluid phases, respectively. In addition to serving as indicators of the disorder caused by the phase change in pure PE/PG bilayers, the bands of skeletal vibrations (νC-Ctrans/gauche) proved to be sensitive enough to detect the increased disorder resulting from the adsorption of ANP and of ANP-coated Au NPs. Since the disorder caused by the adsorption of the latter is significantly greater than that caused by ANP itself, we believe that this study could pave new ways in the research and use of Au NPs (as well as other metal NPs) as targeted and effective delivery of therapeutics.

Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool for the observation, the detection and the identification of chemical or biological species at low concentrations due to its high sensitivity, specific fingerprinting capability and real-time detection. However, a key challenge lies in establishing a suitable and reliable measurement protocol to ensure both reproducibility and repeatability when SERS is used as a sensing nanoplatform. In this paper, we propose a specific methodology to investigate the performance of SERS substrates, with a particular focus on their reproducibility and repeatability. Furthermore, we validate our approach on one commercial SERS Hamamatsu substrate from Hamamatsu Photonics by using diluted solution of 4-mercaptobenzoic acid (MBA) at an excitation wavelength of 633 nm. This proposed protocol consists in recording 25 SERS maps equally distributed on the whole surface substrate. For each map, 16 spectra have been acquired and averaged to provide a representative SERS signal. In total, 400 spectra have been collected and analyzed by using the integrated intensities of characteristic MBA bands to determine both reproducibility and repeatability. This approach enables us to quantify signal variations, at the micrometer scale, as well as across the entire substrate. We demonstrated that while the SERS response is highly reproducible locally, it becomes less consistent when evaluated across the full surface. However, the SERS signal is not repeatable at the local scale but it can be repeatable at the whole substrate scale as the average SERS intensity is identical for both SERS measurements. Furthermore, we demonstrated that this method can also be applied to DNA strands thereby demonstrating its effectiveness in evaluating biosensors. Finally, the proposed methodology and protocol can then be used as a standard to precisely evaluate the sensing performances of other substrates.

Aptamers are single-stranded DNA or RNA oligonucleotides with a unique secondary structure. Target binding induces conformational changes in the secondary structure. Conformation-induced changes in some characteristic Raman bands of DNA aptamer, upon binding to aflatoxin B1 (AFB1), were probed using surface enhanced Raman spectroscopy (SERS). The self-assembled monolayers of thiol-linked DNA aptamer on gold nanoparticles (AuNPs) surface provided a direct, label-free detection method through three adenine bases close to the surface of an AuNPs SERS substrate. The spectra of the DNA aptamer were dominated by the adenine ring breathing mode at 734 cm-1. Upon binding to AFB1 and conformational changes of the aptamer, the 5'-end of the aptamer with three adenine bases moved away from the surface of AuNPs, resulting in the decreased Raman intensity of the adenine band at 734 cm-1 (I734). In addition to the adenine band, the deoxyribose phosphate backbone (O-P-O) band at 1004 cm-1 (I1004) was decreased after aptamer binding to AFB1. The change of I734, corresponding to the AFB1 concentration, was employed for quantitative measurement of AFB1 in the range of 0.1-5000 pg mL-1. The aptamer-based SERS assay exhibited high sensitivity with a limit of detection (LOD) of 0.24 pg mL-1 for I734 calibration curve.

This study demonstrates the highly sensitive detection of DNA hybridization using commercially available Surface-Enhanced Raman Spectroscopy (SERS) substrates. We functionalized the gold nanostructures with thiolated single-stranded adenine (polyA) DNA of various lengths (5-20 bases) and investigated their hybridization with complementary thymine (polyT) strands across different concentrations. DNA hybridization was confirmed by significant spectral changes in the adenine ring breathing mode at 735 cm-1, highlighting its potential as a key marker for hybridization detection. Finite-difference time-domain (FDTD) simulations were used to visualize the distribution of the electromagnetic field at the gold surface. In parallel, principal component analysis (PCA) successfully identified spectral changes resulting from DNA hybridization. By combining experimental SERS measurements with computational modeling, we present a highly sensitive and specific method for monitoring DNA hybridization. These results support the development of advanced nucleic acid detection techniques and offer a reliable platform for investigating biomolecular interactions.

In this article we study the structure and the orientation of DNA strands by Surface Enhanced Raman Scattering (SERS). We study the influence of two parameters on the structure of strands containing 20 adenines: the hybridization with the complementary strand and the presence of mismatch within the sequence. By varying the concentration of complementary strands, we show that hybridisation induces a change in strand orientation and loss of flexibility, indicating that the formation of the double helix freezes the conformation of DNA strand. The introduction of a mismatch has the same effects on strand orientation and flexibility but also induces hybridisation defects in the formation of the double helix. We therefore highlight the presence of non-hybridized adenine bases, this effect being all the more visible when the mismatch is close to the centre of the strand. We also highlight spectral markers of these structural changes and of the evolution of hybridisation. For example, we observe the main band shift of the adenine from 734 to 747 cm-1 indicating a reorientation of the base during hybridisation from a perpendicular configuration to a configuration parallel to the surface.

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for the observation, the detection and the identification of chemical or biological species at low concentrations due to it’s high sensitivity, specific fingerprinting spectra and real-time detection. However, an important task is to define a suitable and reliabale protocol to ensure the reproducibility and repeatability of the SERS measurements in teh framework of SERS sensors. In this paper , a special protocol of measurement have been applied to a commercial SERS Hamamatsu substrate from Hamamatsu Photonics by using diluted solution of 4-mercaptobenzoic acid (MBA) at excitation wavelengths 633nm. This protocol consists in recording 25 SERS maps equally distributed on the whole surface substrate. For each map, 16 spectra have been measure to calculate an average SERS signal of the map. A large set of recorded data for a total of 400 spectra have been collected and analyzed by using the integrated intensities of MBA bands to determine the reproducibility and repeatability of the substrate. This protocol could be applied to other substrates and to precisely evaluate their sensing performances.

Here, we investigate the correlation between the heat generated by gold nanoparticles, in particular nanospheres and nanobipyramids, and their plasmonic response manifested by the presence of Localized Surface Plasmon Resonances (LSPRs). Using a tunable laser and a thermal camera, we measure the temperature increase induced by colloidal nanoparticles in an aqueous solution as a function of the excitation wavelength in the optical regime. We demonstrate that the photothermal performances of the nanoparticles are strongly related not only to their plasmonic properties but also to the size and shape of the nanoparticles. The contribution of the longitudinal and transversal modes in gold nanobipyramids is also analyzed in terms of heat generation. These results will guide us to design appropriate nanoparticles to act as efficient heat nanosources.

Spherical structures built from uni- and multilamellar lipid bilayers (LUV and MLV) are nowadays considered not just as nanocarriers of various kinds of therapeutics, but also as the vehicles that, when coupled with gold (Au) nanoparticles (NPs), can also serve as a tool for imaging and discriminating healthy and diseased tissues. Since the presence of Au NPs or their aggregates may affect the properties of the drug delivery vehicle, we investigated how the shape and position of Au NP aggregates adsorbed on the surface of MLV affect the arrangement and conformation of lipid molecules. By preparing MLVs constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in the presence of uncoated Au NP aggregates found i) both within liposome core and on the surface of the outer lipid bilayer, or ii) adsorbed on the outer lipid bilayer surface only, we demonstrated the maintenance of lipid bilayer integrity by microscopic techniques (cryo-TEM, and AFM). The employment of SERS and FTIR-ATR techniques enabled us not only to elucidate the lipid interaction pattern and their orientation in regards to Au NP aggregates but also unequivocally confirmed the impact of Au NP aggregates on the persistence/breaking of van der Waals interactions between hydrocarbon chains of DPPC.

As the plasmonic properties of metallic nanoparticles and nano- structures are related to their size and shape, experimental investigations to determine their optical and structural properties have been implemented. These techniques have been applied to study the morphology and structure of the plasmonic materials at the sub-nanometer scale.

A plasmon is an optical characteristic of a metal resulting from the excitation of free electrons by their interaction with photons or electrons [1, 2]. As these free electrons are weakly bounded to the metal atom, the plasmon corresponds to a collective oscillation of the charge density, named "plasma oscillation." It occurs when photons or electrons transfer their energy to the free electrons of the metal since their momentum is the same as that of the plasmon. Depending on the geometrical dimensions of the metallic materials, plasmons can be defined and classified as follows: Volume plasmon (3D plasmon): The plasmon is excited in the material volume. Delocalized surface plasmon (DSP), also known as surface plasmon polariton (SPP) (2D plasmon): The plasmon is formed at the interface between a dielectric and a metal. Having an evanescent character, it can only propagate along the surface. Localized surface plasmon (LSP) (0D plasmon): The plasmon is confined inside a nanostructure. It can be seen as an eigen mode of oscillation of the free electrons inside a limited volume. Different plasmon modes can be excited depending on the size, shape, and chemical nature of the nanostructure.

The rise of the populations of antibiotic resistant bacteria represents an increasing threat to human health. In addition to the synthesis of new antibiotics, which is an extremely expensive and time-consuming process, one of the ways to combat bacterial infections is the use of gold nanoparticles (Au NPs) as the vehicles for targeted delivery of therapeutic drugs. Since such a strategy requires the investigation of the effect of Au NPs (with and without drugs) on both bacterial and human cells, we investigated how the presence of coating-free Au NPs affects the physicochemical properties of lipid membranes that model prokaryotic (PRO) and eukaryotic (EU) cells. PRO/EU systems prepared as multilamellar liposomes (MLVs) and hybrid structures (HSs) from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylglycerol (DPPG)/1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS) in the absence (MLVs)/presence (HSs) of differently distributed Au NPs (sizes ∼20 nm) reported stabilization of the gel phase of PRO systems in comparison with EU one (DSC data of PRO/EU were Tm(MLVs) ≈ 41.8 °C/42.0 °C, Tm¯ (HSs) ≈ 43.1 °C/42.4 °C, whereas UV-Vis response Tm(MLVs) ≈ 41.5 °C/42.0 °C, Tm¯ (HSs) ≈ 42.9 °C/41.1 °C). Vibrational spectroscopic data unraveled a substantial impact of Au NPs on the non-polar part of lipid bilayers, emphasizing the increase of kink and gauche conformers of the hydrocarbon chain. By interpreting the latter as Au NPs-induced defects, which exert the greatest effect when Au NPs are found exclusively outside the lipid membrane, these findings suggested that Au NPs reduced the compactness of EU-based lipid bilayers much more than in analogous PRO systems. Since the uncoated Au NPs manifested adverse effects when applied as antimicrobials, the results obtained in this work contribute towards recognizing AuNP functionalization as a strategy in tuning and reversing this effect.

The most limiting aspect of Raman spectroscopy as a generally applicable analytical technique is the extremely low cross section (dσ/dΩ = 10−31 to 10−28 cm−2 sr−1 ) of the Raman scattering process compared with the much higher probability of other optical processes, for example fluorescence, which already meets the sensitivity requirements for single-molecule detection (Fig. 5.1). Thus, powerful exciting sources, sensitive detectors, and a large number of scattering molecules are normally needed to record a Raman spectrum. The last constraint would make Raman spectroscopy rather uninformative for catalytic studies at surfaces, usually dealing with a small number of adsorbed molecules, down to the (sub) monolayer level.

Microplastics (MPs) are ubiquitous in the environment and humans are inevitably exposed to them. However, the effects of MPs in the human digestive environment are largely unknown. The aim of our study was to investigate the impact of repeated exposure to polyethylene (PE) MPs on the human gut microbiota and intestinal barrier using, under adult conditions, the Mucosal Artificial Colon (M-ARCOL) model, coupled with a co-culture of intestinal epithelial and mucus-secreting cells. The composition of the luminal and mucosal gut microbiota was determined by 16S metabarcoding and microbial activities were characterized by gas, short chain fatty acid, volatolomic and AhR activity analyses. Gut barrier integrity was assessed via intestinal permeability, inflammation and mucin synthesis. First, exposure to PE MPs induced donor-dependent effects. Second, an increase in abundances of potentially harmful pathobionts, Desulfovibrionaceae and Enterobacteriaceae, and a decrease in beneficial bacteria such as Christensenellaceae and Akkermansiaceae were observed. These bacterial shifts were associated with changes in volatile organic compounds profiles, notably characterized by increased indole 3-methyl- production. Finally, no significant impact of PE MPs mediated by changes in gut microbial metabolites was reported on the intestinal barrier. Given these adverse effects of repeated ingestion of PE MPs on the human gut microbiota, studying at-risk populations like infants would be a valuable advance.

Time-domain Brillouin scattering (TDBS) is a developing technique for imaging/evaluation of materials, currently used in material science and biology. Three-dimensional imaging and characterization of polycrystalline materials has been recently reported, demonstrating evaluation of inclined material boundaries. Here, the TDBS technique is applied to monitor the destruction of a lithium niobate single crystal upon non-hydrostatic compression in a diamond anvil cell. The 3D TDBS experiments reveal, among others, modifications of the single crystal plate with initially plane-parallel surfaces, caused by non-hydrostatic compression, the laterally inhomogeneous variations of the plate thickness and relative inclination of opposite surfaces. Our experimental observations, supported by theoretical interpretation, indicate that TDBS enables the evaluation of materials interface orientation/inclination locally, from single point measurements, avoiding interface profilometry. A variety of observations reported in this paper paves the way to further expansion of the TDBS imaging use to analyze fascinating processes/phenomena occurring when materials are subjected to destruction.

DNA identification is possible by detecting its components through vibrational spectroscopy. Conventional Raman, Surface-enhanced Raman spectroscopy (SERS) and Tip-enhanced Raman spectroscopy (TERS) have shown a high capacity for the exploration of different molecules and materials (semi-conducting material, carbon nanotubes and biologicals molecules as DNA, proteins). Their applications extended to biological systems and brought significant information to this field. This review summarizes a high number of studies and research conducted with conventional Raman, SERS and TERS on every DNA component starting from the four different nucleic acids in their different forms (nucleosides, deoxyribonucleosides, deoxyribonucleotides) to their biological interaction to form one and double DNA strands. As SERS has an advantage on conventional Raman by exploiting the optical properties of metallic nanostructures to detect very small quantities of molecules, it also clarifies the DNA structure's orientation in addition to its composition. It also clarifies the influence of different parameters, such as the presence of a spacer or a mutation in the strand on the hybridization process. TERS was shown as a relevant tool to scan DNA chemically and to provide information on its sequence.

A label-free surface-enhanced Raman scattering (SERS) was designed for sensitive detection of interleukin-6 (IL6). The sensing element composed of anti-IL-6 antibodies adsorbed on the surface of spherical gold nanoparticles (AuNPs) as SERS-active surface. The principle of detection was probing antibody conformational changes using its intrinsic SERS fingerprint after binding to IL-6. Comparison of SERS spectra of antibody before and after binding to IL-6 showed that secondary structure of antibody does not change upon binding to IL-6. Vibrational information from disulfide bonds nu(S-S) in antibody structure indicated some changes of geometry around S-S bridges as a consequence of the immunocomplex formation. Transmission electron microscopy (TEM) and UV-Vis spectroscopy were used to confirm AuNPs conjugation with antibody as well as IL-6 binding to antibody on the surface of AuNPs. The SERS-based immunoassay showed a wide linear range (2.0-1000 pg mL-1) and a high sensitivity with a limit of detection (LOD) as low as 0.91 pg mL-1 (0.04 pM) without using any extrinsic Raman label. UV-Vis spectroscopy was employed as a conventional method for IL-6 detection based on observation of any change in the position of localized surface plasmon resonance (LSPR) band of AuNPs-antibody conjugates with LOD of 10 ng mL-1.

Infants are characterized by an immaturity of the gut ecosystem and a high exposure to microplastics (MPs) through diet, dust and suckling. However, the bidirectional interactions between MPs and the immature infant intestinal microbiota remain unknown. Our study aims to investigate the impact of chronic exposure to polyethylene (PE) MPs on the gut microbiota and intestinal barrier of infants, using the new Toddler mucosal Artificial Colon coupled with a co-culture of epithelial and mucus-secreting cells. Gut microbiota composition was determined by 16S metabarcoding and microbial activities were evaluated by gas, short chain fatty acid and volatolomics analyses. Gut barrier integrity was assessed via evaluation of intestinal permeability, inflammation and mucus synthesis. Exposure to PE MPs induced gut microbial shifts increasing α-diversity and abundance of potentially harmful pathobionts, such as Dethiosulfovibrionaceae and Enterobacteriaceae. Those changes were associated to butyrate production decrease and major changes in volatile organic compounds profiles. In contrast, no significant impact of PE MPs on the gut barrier, as mediated by microbial metabolites, was reported. For the first time, this study indicates that ingestion of PE MPs can induce perturbations in the gut microbiome of infants. Next step would be to further investigate the potential vector effect of MPs.

In this article, we study the influence of the symmetry breaking in nanocylinder gratings on the plasmonic properties and its impact on surface enhanced Raman scattering (SERS) performances. We modify the symmetry by changing the grating period in one direction from a square grating to rectangular grating that induces a modification of the symmetry group from C4v to C2v. We then observe a redshift and a narrowing of the plasmon resonance when the symmetry is reduced due to a coupling of the plasmon with a diffraction order of the grating. Remarkably, we demonstrate that such a coupling occurs whatever the polarization direction. We also demonstrate that the SERS efficiency of such plasmonic substrates is higher for the grating with a reduced symmetry due to a reduced width (full width half maximum) and a higher quality factor of the surface plasmon resonance.

Since the discovery of Surface Enhanced Raman Spectroscopy (SERS) and the proven ability for this technique to detect molecules at trace level, numerous techniques have been reported for fabricating substrates that ensure reliable and reproducible SERS signal on its whole surface. In this paper we studied the capabilities and sensing performances of three commercial SERS substrates (RAM-SERS-SP from Ocean Optics, QSERS from Nanova Inc. and Hamamatsu from Hamamatsu Photonics) by using diluted solution of 4-mercaptobenzoic acid (MBA) at two different excitation wavelengths (633 and 785 nm). Large datasets were obtained through Raman mappings collected randomly on different areas on the substrate surface. The averaged SERS signals for one specific vibrational band of the MBA were used to compare limit of detection (LOD), limit of quantification (LOQ) and sensitivity of the three substrates. LOD and LOQ between 1 mu M and 10 mu M were calculated with a range of use of only one or two orders of magnitude. The best sensing performances were reached by the Hamamatsu substrate for an excitation wavelength of 633 nm. (C) 2021 Elsevier B.V. All rights reserved.

We report the calculation of Raman modes of thiophenol molecules adsorbed on a real gold surface. The calculated Raman spectra strongly depend on the absorption configuration of the molecule on the metallic surface, a feature that should be carefully taken into account in the interpretation of the surface enhanced Raman spectra (SERS). The calculated Raman spectra are compared with experimental SERS measurements, the best accordance being obtained for a tilted configuration of the absorbed molecule. The present study supports the necessary combination of computational approaches with SERS measurements to predict the type of molecular adsorption configurations on metallic surfaces.