Plasmon-enhanced photocatalysis: New horizons in carbon dioxide reduction technologies.

The urgent need for transition to renewable energy is underscored by a nearly 50 % increase in atmospheric carbon dioxide levels over the past century. The combustion of fossil fuels for energy production, transportation, and industrial activities are the main contributors to carbon dioxide emissions in the anthroposphere. Present approaches to reducing carbon emissions are proving inefficient, thereby accentuating the relevance of carbon dioxide photocatalysis in combating climate change - one of the critical issues of public concern. This process uses sunlight to convert carbon dioxide into valuable products, e.g., clean fuels, effectively reducing the carbon footprint and offering a sustainable use of carbon dioxide. In this context, plasmonic nanoparticles such as gold, silver, and copper play a pivotal role due to their proficiency in absorbing a wide range of light spectra, thereby effectively generating the necessary electrons and holes for the degradation of pollutants and surpassing the capabilities of traditional semiconductor catalysts. This review meticulously examines the latest advancements in plasmon-based carbon dioxide photocatalysis, scrutinizing the methodologies, characterizations, and experimental outcomes. The critical evaluation extends to exploring adjustments in the dimensional and morphological aspects of plasmonic nanoparticles, complemented by the incorporation of stabilizing agents, which may offer additional benefits. Furthermore, the review includes a thorough analysis of production rates and quantum yields based on different plasmonic materials and nanoparticle shapes and sizes, enriching the ongoing discourse on effective solutions in the field. Thus, our work emphasizes the pivotal role of plasmon-based photocatalysts in reducing carbon dioxide, investigating both the merits and challenges associated with integrating this emerging technology into climate change mitigation efforts.

The presence of uncoated gold nanoparticle aggregates may alter the phase of phosphatidylcholine lipid as evidenced by vibrational spectroscopies.

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.

Evaluation of classification ability of logistic regression model on SERS data of miRNAs.

Logistic regression (LR) is a supervised multiple linear regression model, which uses linear weighted calculation for input to obtain weight coefficients of model. The surface enhanced Raman spectroscopy (SERS) technology greatly enhances the Raman signal of analyte. LR model was used to analyze the data of seven types of pancreatic cancer-related miRNAs obtained from commercial SERS substrate. The classification ability of the model on such data was observed under the configurations of different key parameters (classification mode, regularization method and loss function optimization way), and the effect of the two types of data formats were also evaluated. The results showed that though LR model used to classify this data did not perform well as expected, miRNA-191 and miRNA-4306 still had high recalls (sensitivity), which laid a theoretical foundation for the purpose of using LR model to identify these two miRNAs to jointly diagnose of pancreatic cancer at miRNA level.

One-step isothermal amplification strategy for microRNA specific and ultrasensitive detection based on nicking-assisted entropy-driven DNA circuit triggered exponential amplification reaction.

Sensitive and specific detection of microRNAs (miRNAs) is of critical significance for early diagnosis of cancers such as pancreatic cancer with atypical initial symptoms and high mortality. Despite exponential amplification reaction (EXPAR) is an attractive isothermal amplification method for detecting miRNAs, it faces the problems of the dependence difference and low specificity. To address such challenges, herein, a nicking-assisted entropy-driven DNA circuit triggered exponential amplification reaction (NAED-EXPAR) was firstly employed for ultrasensitive and specific detection of miRNA in "one-pot" manner at constant temperature. Nicking-assisted entropy-driven DNA circuit can specifically recognize the target miRNA, leading to continuous disassembly of DNA substrates via intramolecular toehold-mediated branch migration. During the reaction, the catalytic circuit can consume excess fuel DNA strands to produce a large number of primers. Then the newly formed primers can trigger EXPAR for highly efficient signal amplification. Mechanism analysis shows that the amplification efficiency of NAED-EXPAR is superior than that of single EXPAR. For miR-21, the detection limit of NAED-EXPAR can reach 100 aM, which is at least five orders of magnitude higher than the standard EXPAR that directly uses the target as primer. NAED-EXPAR shows improved specificity for identifying single nucleotide variations and enables sensitive and accurate analysis of miR-21 in human cancer cell lines. This method is expected to offer a new approach for the reliable quantification of miRNAs in complex biological matrices and provide valuable information for early cancer diagnosis.

Enzyme mediated synthesis of hybrid polyedric gold nanoparticles.

Large protein complexes carry out some of the most complex activities in biology1,2. Such structures are often assembled spontaneously through the process of self-assembly and have characteristic chemical or biological assets in the cellular mechanisms3. Gold-based nanomaterials have attracted much attention in many areas of chemistry, physics and biosciences because of their size- and shape-dependent optic, electric, and catalytic properties. Here we report for the first time a one step synthesis in which Manganese Superoxide Dismutase protein plays a key role in the reduction of gold salts via the use of a Good's buffer (HEPES) to produce gold nanoparticles, compared to other proteins as catalase (CAT) and bovine serum albumin (BSA).We prove that this effect is directly related with the biological activities of the proteins that have an effect on the gold reduction mechanisms. Such synthesis route also induces the integration of proteins directly in the AuNPs that are intrinsically safe by design using a one-step production method. This is an important finding that will have uses in various applications, particularly in the green synthesis of novel nanomaterials.

Gold Nanocylinders on Gold Film as a Multi-spectral SERS Substrate.

The surface enhanced Raman scattering (SERS) efficiency of gold nanocylinders deposited on gold thin film is studied. Exploiting the specific plasmonic properties of such substrates, we determine the influence of the nanocylinder diameter and the film thickness on the SERS signal at three different excitation wavelengths (532, 638 and 785 nm). We demonstrate that the highest signal is reached for the highest diameter of 250 nm due to coupling between the nanocylinders and for the lowest thickness (20 nm) as the excited plasmon is created at the interface between the gold and glass substrate. Moreover, even if we show that the highest SERS efficiency is obtained for an excitation wavelength of 638 nm, a large SERS signal can be obtained at all excitation wavelengths and on a wide spectral range. We demonstrate that it can be related with the nature of the plasmon (propagative plasmon excited through the nanocylinder grating) and with its angular dependence (tuning of the plasmon position with the excitation angle). Such an effect allows the excitation of plasmon on nearly the whole visible range, and paves the way to multispectral SERS substrates.

Indirect surface-enhanced Raman scattering assay of insulin-like growth factor 2 receptor protein by combining the aptamer modified gold substrate and silver nanoprobes.

An indirect aptamer-based SERS assay for insulin-like growth factor 2 receptor (IGF-IIR) protein was developed. The gold substrate and silver nanoparticles (AgNPs) were employed simultaneously to achieve double enhancement for SERS signals. Firstly, the five commercial SERS substrates including Enspectr, Ocean-Au, Ocean-AG, Ocean-SP and Q-SERS substrates were evaluated using 4-mercaptobenzoic acid (4-MBA). The Q-SERS substrate was selected based on low relative standard deviation (RSD, 8.6%) and high enhancement factor (EF, 8.7*105), using a 785 nm laser. The aptamer for IGF-IIR protein was designed to include two sequences: one grafted on gold substrate to specifically capture the IGF-IIR protein and a second one forming a 3' sticky bridge to capture SERS nanotags. The SERS nanotag was composed by AgNPs (20 nm), 4-MBA and DNA probes that can hybridize with the aptamer. Due to the steric-hindrance effect, when the aptamer doesn't combine with IGF-IIR protein, it only can capture the SERS nanotags. Therefore, there was a negative correlation between the concentration of IGF-IIR protein and the intensity of 4-MBA at 1076 cm-1. The detection limit reached to 141.2 fM and linear range was from 10 pM to 1 µM. The SERS aptasensor also exhibits a high reproducibility with an average RSD of 4.5%. The interference test was conducted with other four proteins to verify the accuracy of measuring. The study provides an approach to quantitative determination of proteins based on specific recognition and nucleic acid hybridization of aptamers, to establish sandwich structure for SERS enhancement. Graphical abstractSchematic representation of surface-enhanced Raman scattering (SERS) assay on insulin-like growth factor 2 receptor (IGF-IIR) protein by combining the aptamer modified gold substrate and 4-mercaptobenzoic acid (4-MBA) and DNA probe modified silver nanoparticles.

Towards Reliable and Quantitative Surface-Enhanced Raman Scattering (SERS): From Key Parameters to Good Analytical Practice.

Experimental results obtained in different laboratories world-wide by researchers using surface-enhanced Raman scattering (SERS) can differ significantly. We, an international team of scientists with long-standing expertise in SERS, address this issue from our perspective by presenting considerations on reliable and quantitative SERS. The central idea of this joint effort is to highlight key parameters and pitfalls that are often encountered in the literature. To that end, we provide here a series of recommendations on: a) the characterization of solid and colloidal SERS substrates by correlative electron and optical microscopy and spectroscopy, b) on the determination of the SERS enhancement factor (EF), including suitable Raman reporter/probe molecules, and finally on c) good analytical practice. We hope that both newcomers and specialists will benefit from these recommendations to increase the inter-laboratory comparability of experimental SERS results and further establish SERS as an analytical tool.

Surface-enhanced Raman scattering method for the identification of methicillin-resistant Staphylococcus aureus using positively charged silver nanoparticles.

The article describes a SERS-based method for diagnosis of bacterial infections. Positively charged silver nanoparticles (AgNPs+) were employed for identification of methicillin-resistant Staphylococcus aureus (MRSA). It is found that AgNPs+ undergo self-assembly on the surface of bacteria via electrostatic aggregation. The assembled AgNPs+ are excellent SERS substrates. To prove the capability of SERS to differentiate between S. aureus and other microorganisms, six standard strains including S. aureus 29213, S. aureus 25923, C. albicans, B. cereus, E. coli, and P. aeruginosa were tested. To further demonstrate its applicability for the identification of MRSA in clinical samples, 52 methicillin-sensitive S. aureus (MSSA) isolates and 215 MRSA isolates were detected by SERS. The total measurement time (include incubation) is 45 min when using a 3 µL sample. The method gives a strongly enhanced Raman signal (at 730 cm-1 and 1325 cm-1) with good reproducibility and repeatability. It was successfully applied to the discrimination of the six strain microorganisms. The typical Raman peaks of S. aureus at 730, 1154, 1325, and 1457 cm-1 were observed, which were assigned to the bacterial cell wall components (730 cm-1- adenine, glycosidic ring mode, 1154 cm-1- unsaturated fatty acid, 1325 cm-1- adenine, polyadenine, and 1457 cm-1 for -COO- stretching). S. aureus was completely separated from other species by partial least squares discriminant analysis (PLS-DA). Moreover, 52 MSSA isolates and 215 MRSA isolates from clinical samples were identified by PLS-DA. The accuracy was almost 100% when compared to the standard broth microdilution method. A classification based on latent structure discriminant analysis provided spectral variability directly. Conceivably, the method offers a potent tool for the identification of bacteria and antibiotics resistance, and for studies on antibiotic-resistance in general. Graphical abstract Schematic of the surface-enhanced Raman scattering (SERS) measurements on Staphylococcus aureus (S. aureus) using positively charged silver nanoparticles (AgNPs+). AgNPs+ are adsorbed on the bacterial cell wall by electrostatic attraction. SERS spectra were analyzed by PLS-DA for the identification of Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus aureus (MSSA). MRSA isolates were divided into four groups, including R1, R2, R3, and R4. MSSA just includes group S.

Polyphosphonate ligands: From synthesis to design of hybrid PEGylated nanoparticles toward phototherapy studies.

The use of phosphonate ligands to modify the nanoparticle (NPs) surface has attracted a strong interest in the last years for the design of highly functional hybrid materials. Here, we applied a methodology to synthesize bisphosphonates having functionalized PEG side chains with a specific length in order to design a novel class of hybrid nanomaterials composed by tetraphosphonate-complex-gold COOH-terminated PEG-coated NPs (Bis-PO-PEG-AuNPs). The synthetic approach consist in three steps: (1) Complexation between new phosphonate ligands (Bis PO) and tetrachloroauric acid (HAuCl4) to form gold clusters; (2) adsorption of COOH-terminated PEG molecules (PEG) onto Bis PO-Au complex; (3) reduction of metal ions in that vicinity, growth of gold particles and colloidal stabilization. The obtained snow-shape-like hybrid nanoparticles, have been characterized by ultra-violet/visible, Raman spectroscopies, and electron microscopy imaging, involving their optical properties and photothermal activity in pancreatic adenocarcinoma cancer cells (PDAC).

Investigation of aromatic hydrocarbon inclusion into cyclodextrins by Raman spectroscopy and thermal analysis.

Among various cavitand molecules, cyclodextrins are extensively studied due to their ability to form host-guest complexes with small hydrophobic molecules. Aiming to explore cyclodextrin implementation on the scopes related to the environmental pollution monitoring or remediation, extensive studies for understanding the cyclodextrin-based host-guest complex formation with selected targeted substances are conducted. In this context, two polycyclic aromatic hydrocarbons, naphthalene and fluoranthene as well as toluene as a member of volatile organic compounds, were studied regarding their ability to encapsulate into cyclodextrin cavities. Synthesised complexes were examined by thermogravimetric analysis combined with Raman spectroscopy. The obtained results demonstrated that the size between targeted molecules and the cyclodextrin cavities strongly correlates with its ability to engage in complexation. Thus, this latter parameter plays an important role in the inclusion complex formation as well as in the strength of the interaction between the molecules.

Tunable Design of Gold(III)-Doxorubicin Complex-PEGylated Nanocarrier. The Golden Doxorubicin for Oncological Applications.

To date, the translation of Au (III) complexes into chemotherapeutic agents has been hindered by their low stability under physiological conditions, a crucial parameter in drug development. In this study, we report an innovative four-step synthesis of a stable Au (III)-doxorubicin (DOX) complex, acting as a key constitutive component of doxorubicin-loaded PEG-coated nanoparticles (DOX IN-PEG-AuNPs). For therapeutic purposes, such AuNPs were then functionalized with the anti-Kv11.1 polyclonal antibody (pAb), which specifically recognizes the hERG1 channel that is overexpressed on the membrane of human pancreatic cancer cells. The nature of the interactions between DOX and Au (III) ions was probed by various analytical techniques (Raman spectroscopy, UV-vis, and (1)H NMR), which enabled studying the Au (III)-DOX interactions during AuNPs formation. The theoretical characterization of the vibrational bands and the electronic transitions of the Au (III)-DOX complex calculated through computational studies showed significant qualitative agreement with the experimental observations on AuNPs samples. Stability in physiological conditions and efficient drug loading (up to to 85 w/w %) were achieved, while drug release was strongly dependent on the structure of DOX IN-PEG-AuNPs and on the pH. Furthermore, the interactions among DOX, PEG, and Au (III) ions in DOX IN-PEG-AuNPs differed significantly from those found in polymer-modified AuNPs loaded with DOX by covalent linkage, referred to as DOX ON-PEG-AuNPs. In vitro experiments indeed demonstrated that such differences strongly influenced the therapeutic potential of AuNPs in pancreatic cancer treatment, with a significant increase of the DOX therapeutic index when complexed to Au (III) ions. Collectively, our study demonstrated that Au (III)-DOX complexes as building blocks of PEGylated AuNPs constitutes a promising approach to transform promising Au (III) complexes into real chemotherapeutic drugs for the treatment of pancreatic cancer.

Directional surface enhanced Raman scattering on gold nano-gratings.

Directional plasmon excitation and surface enhanced Raman scattering (SERS) emission were demonstrated for 1D and 2D gold nanostructure arrays deposited on a flat gold layer. The extinction spectrum of both arrays exhibits intense resonance bands that are redshifted when the incident angle is increased. Systematic extinction analysis of different grating periods revealed that this band can be assigned to a propagated surface plasmon of the flat gold surface that fulfills the Bragg condition of the arrays (Bragg mode). Directional SERS measurements demonstrated that the SERS intensity can be improved by one order of magnitude when the Bragg mode positions are matched with either the excitation or the Raman wavelengths. Hybridized numerical calculations with the finite element method and Fourier modal method also proved the presence of the Bragg mode plasmon and illustrated that the enhanced electric field of the Bragg mode is particularly localized on the nanostructures regardless of their size.

Enhanced Vibrational Spectroscopies as Tools for Small Molecule Biosensing.

In this short summary we summarize some of the latest developments in vibrational spectroscopic tools applied for the sensing of (small) molecules and biomolecules in a label-free mode of operation. We first introduce various concepts for the enhancement of InfraRed spectroscopic techniques, including the principles of Attenuated Total Reflection InfraRed (ATR-IR), (phase-modulated) InfraRed Reflection Absorption Spectroscopy (IRRAS/PM-IRRAS), and Surface Enhanced Infrared Reflection Absorption Spectroscopy (SEIRAS). Particular attention is put on the use of novel nanostructured substrates that allow for the excitation of propagating and localized surface plasmon modes aimed at operating additional enhancement mechanisms. This is then be complemented by the description of the latest development in Surface- and Tip-Enhanced Raman Spectroscopies, again with an emphasis on the detection of small molecules or bioanalytes.

Comparative toxicity evaluation of flower-shaped and spherical gold nanoparticles on human endothelial cells.

In this paper, we propose a multi-parametric in vitro study of the cytotoxicity of gold nanoparticles (GNPs) on human endothelial cell (HUVEC). The cytotoxicity is evaluated by incubating cells with six different GNP types which have two different morphologies: spherical and flower-shaped, two sizes (∼15 and ∼50 nm diameter) and two surface chemistries (as prepared form and PEGylated form). Our results showed that by increasing the concentration of GNPs the cell viability decreases with a toxic concentration threshold of 10 pM for spherical GNPs and of 1 pM for flower-shaped GNPs. Dark field images, flow cytometry and spreading test revealed that flower-shaped GNPs have more deleterious effects on the cell mechanisms than spherical GNPs. We demonstrated that the main parameter in the evaluation of the GNPs toxicity is the GNPs roughness and that this effect is independent on the surface chemistry. We assume that this behavior is highly related to the efficiency of the GNPs internalization within the cells and that this effect is enhanced due to the specific geometry of the flower-shaped GNPs.

Soft UV nanoimprint lithography-designed highly sensitive substrates for SERS detection.

We report on the use of soft UV nanoimprint lithography (UV-NIL) for the development of reproducible, millimeter-sized, and sensitive substrates for SERS detection. The used geometry for plasmonic nanostructures is the cylinder. Gold nanocylinders (GNCs) showed to be very sensitive and specific sensing surfaces. Indeed, we demonstrated that less than 4 ×10(6) avidin molecules were detected and contributed to the surface-enhanced Raman scattering (SERS) signal. Thus, the soft UV-NIL technique allows to obtain quickly very sensitive substrates for SERS biosensing on surfaces of 1 mm (2).

Fast and reliable fabrication of gold tips with sub-50 nm radius of curvature for tip-enhanced Raman spectroscopy.

We have developed a new electrochemical etching procedure to fabricate gold tips with sub-50 nm apical radius of curvature with a production yield of 80% and production time lower than 5 min. The technique is based on a two-step self-terminating process in which a gold wire is first quickly (<1 min) pre-etched in an hydrochloric acid (HCl)∕ethanol solution at high voltage (10 VDC), and then slowly (2-4 min) etched at lower voltages (<2.5 VDC). The first step occurs under intense bubbling conditions and allows us to thin rapidly the wire. This reduces the time required by subsequent low-voltage process during which the tips are formed at the liquid∕air interface. A statistical analysis of the surface morphology has been carried out on a set of 60 tips by scanning electron microscopy. The results show that the surface roughness and the sharpness of the final tip are critically influenced by the intrinsic granularity of the gold wires. Moreover, there is a correlation between the tip quality and the time elapse required to complete the low-voltage etching step. Tips featuring smooth surfaces and radii of curvature <50 nm are produced whenever the etching times are lower than 250 s, while etching times larger than 300 s typically yield rough, blunt tips. Such a correlation can be used as a screening criterion to select sharp tips during production with an 80% yield. The high quality of the gold tips produced with such method is confirmed by the electromagnetic field enhancement measured both in tip-enhanced Raman scattering and surface-enhanced Raman scattering on the tip apex experiments.

Localized surface plasmon resonance in arrays of nano-gold cylinders: inverse problem and propagation of uncertainties.

The plasmonic nanostructures are widely used to design sensors with improved capabilities. The position of the localized surface plasmon resonance (LSPR) is part of their characteristics and deserves to be specifically studied, according to its importance in sensor tuning, especially for spectroscopic applications. In the visible and near infra-red domain, the LSPR of an array of nano-gold-cylinders is considered as a function of the diameter, height of cylinders and the thickness of chromium adhesion layer and roughness. A numerical experience plan is used to calculate heuristic laws governing the inverse problem and the propagation of uncertainties. Simple linear formulae are deduced from fitting of discrete dipole approximation (DDA) calculations of spectra and a good agreement with various experimental results is found. The size of cylinders can be deduced from a target position of the LSPR and conversely, the approximate position of the LSPR can be simply deduced from the height and diameter of cylinders. The sensitivity coefficients and the propagation of uncertainties on these parameters are evaluated from the fitting of 15500 computations of the DDA model. The case of a grating of nanodisks and of homothetic cylinders is presented and expected trends in the improvement of the fabrication process are proposed.