Correlation between Plasmonic and Thermal Properties of Metallic Nanoparticles.

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.

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.

A Novel Optical Fiber Terahertz Biosensor Based on Anti-Resonance for The Rapid and Nondestructive Detection of Tumor Cells.

The sensitive and accurate detection of tumor cells is essential for successful cancer therapy and improving cancer survival rates. However, current tumor cell detection technologies have some limitations for clinical applications due to their complexity, low specificity, and high cost. Herein, we describe the design of a terahertz anti-resonance hollow core fiber (THz AR-HCF) biosensor that can be used for tumor cell detection. Through simulation and experimental comparisons, the low-loss property of the THz AR-HCF was verified, and the most suitable fiber out of multiple THz AR-HCFs was selected for biosensing applications. By measuring different cell numbers and different types of tumor cells, a good linear relationship between THz transmittance and the numbers of cells between 10 and 106 was found. Meanwhile, different types of tumor cells can be distinguished by comparing THz transmission spectra, indicating that the biosensor has high sensitivity and specificity for tumor cell detection. The biosensor only required a small amount of sample (as low as 100 µL), and it enables label-free and nondestructive quantitative detection. Our flow cytometry results showed that the cell viability was as high as 98.5 ± 0.26% after the whole assay process, and there was no statistically significant difference compared with the negative control. This study demonstrates that the proposed THz AR-HCF biosensor has great potential for the highly sensitive, label-free, and nondestructive detection of circulating tumor cells in clinical samples.

Recent Progresses in Optical Biosensors for Interleukin 6 Detection.

Interleukin 6 (IL-6) is pleiotropic cytokine with pathological pro-inflammatory effects in various acute, chronic and infectious diseases. It is involved in a variety of biological processes including immune regulation, hematopoiesis, tissue repair, inflammation, oncogenesis, metabolic control, and sleep. Due to its important role as a biomarker of many types of diseases, its detection in small amounts and with high selectivity is of particular importance in medical and biological fields. Laboratory methods including enzyme-linked immunoassays (ELISAs) and chemiluminescent immunoassays (CLIAs) are the most common conventional methods for IL-6 detection. However, these techniques suffer from the complexity of the method, the expensiveness, and the time-consuming process of obtaining the results. In recent years, too many attempts have been conducted to provide simple, rapid, economical, and user-friendly analytical approaches to monitor IL-6. In this regard, biosensors are considered desirable tools for IL-6 detection because of their special features such as high sensitivity, rapid detection time, ease of use, and ease of miniaturization. In this review, current progresses in different types of optical biosensors as the most favorable types of biosensors for the detection of IL-6 are discussed, evaluated, and compared.

Correction: CTL-doxorubicin (DOX)-gold complex nanoparticles (DOX-AuGCs): from synthesis to enhancement of therapeutic effect on liver cancer model.

[This corrects the article DOI: 10.1039/D0NA00758G.].

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.

New insight into the aptamer conformation and aptamer/protein interaction by surface-enhanced Raman scattering and multivariate statistical analysis.

We study the interaction between one aptamer and its analyte (the MnSOD protein) by the combination of surface-enhanced Raman scattering and multivariate statistical analysis. We observe the aptamer structure and its evolution during the interaction under different experimental conditions (in air or in buffer). Through the spectral treatment by principal component analysis of a large set of SERS data, we were able to probe the aptamer conformations and orientations relative to the surface assuming that the in-plane nucleoside modes are selectively enhanced. We demonstrate that the aptamer orientation and thus its flexibility rely strongly on the presence of a spacer of 15 thymines and on the experimental conditions with the aptamer lying on the surface in air and standing in the buffer. We reveal for the first time that the interaction with MnSOD induces a large loss of flexibility and freezes the aptamer structure in a single conformation.

Streptavidin-functionalized terahertz metamaterials for attomolar exosomal microRNA assay in pancreatic cancer based on duplex-specific nuclease-triggered rolling circle amplification.

Exosomal microRNA (miRNA) is a promising non-invasive biomarker for liquid biopsies. Herein, we fabricated a terahertz (THz) metamaterial biosensor that comprises an array of gold (Au) discs surrounded by annular grooves for exosomal miRNA assays based on duplex-specific nuclease (DSN)-triggered rolling circle amplification (RCA). In this strategy, the target miRNA is captured by a probe P0 immobilized on magnetic beads (MBs); it then repeatedly releases a primer P1 under the action of DSN, which acts as a highly specific initiator of the subsequent RCA step utilizing biotin-dUTP. After target recycling and nucleic acid amplification, the biotinylated amplification products were captured by the streptavidin (SA)-functionalized THz metamaterials, and further conjugated to SA-modified AuNPs that permit formation of a trimeric complex of SA-biotinylated RCA products-AuNP. The complex population scales with the starting concentration of the target miR-21, resulting in a red shift of the resonance peak of the THz metamaterials. This biosensor can lead to highly specific and sensitive detection with one-base mismatch discrimination and a limit of detection (LOD) down to 84 aM. Significant distinctions are seen in the frequency shifts for exosomal miR-21 quantitation in clinical plasma samples between pancreatic cancer patients and healthy controls. The frequency shifts of the THz metamaterials are consistent versus the reverse transcription-polymerase chain reaction (RT-PCR) results, illustrating the applicability and accuracy of our assay in real clinical samples.

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.

A terahertz metamaterial biosensor for sensitive detection of microRNAs based on gold-nanoparticles and strand displacement amplification.

Terahertz (THz) spectroscopy has drawn great interest for the functional and conformational investigations of nucleic acids, but its intrinsic sensitivity hinders potential bio-sensing applications. Here, a novel THz biosensor was developed for detecting microRNA (miRNA) samples based on metamaterials coupled with nanoparticles and strand displacement amplification (SDA). In this method, the SDA reaction amplifies the target miRNA and generates copious yields of secondary DNA molecules (Trigger DNA), which are subsequently conjugated to metallic nanoparticles that form nanoparticle-Trigger DNA complexes. These complexes produce remarkable frequency shifts of metamaterials when linked to a large refractive index metallic nanoparticle like Au. The dependence of the metamaterial resonance on the nanoparticle diameter and metal type was investigated experimentally and theoretically. Under optimal conditions, the THz metamaterial biosensor presents good detection sensitivity with a limit of detection of 14.54 aM and exhibits a linear response for miRNA-21 at a concentration range from 1 fM to 10 pM. By measuring the miRNA-21 in spiked clinical serum samples, the sample recoveries were determined to be in the range between 90.92% and 107.01%. These findings demonstrate that the novel THz biosensor offers the capability for highly sensitive miRNA detection, with noteworthy potential applications in nucleic acid analysis and cancer diagnosis.

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.

Actuated plasmonic nanohole arrays for sensing and optical spectroscopy applications.

Herein, we report a new approach to rapidly actuate the plasmonic characteristics of thin gold films perforated with nanohole arrays that are coupled with arrays of gold nanoparticles. The near-field interaction between the localized and propagating surface plasmon modes supported by the structure was actively modulated by changing the distance between the nanoholes and nanoparticles and varying the refractive index symmetry of the structure. This approach was applied by using a thin responsive hydrogel cushion, which swelled and collapsed by a temperature stimulus. The detailed experimental study of the changes and interplay of localized and propagating surface plasmons was complemented by numerical simulations. We demonstrate that the interrogation and excitation of the optical resonance to these modes allow the label-free SPR observation of the binding of biomolecules, and is applicable for in situ SERS studies of low molecular weight molecules attached in the gap between the nanoholes and nanoparticles.

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.

CTL-doxorubicin (DOX)-gold complex nanoparticles (DOX-AuGCs): from synthesis to enhancement of therapeutic effect on liver cancer model.

In this work, we bring back a rapid way to conceive doxorubicin (DOX) hybrid gold nanoparticles, in which DOX and Au(iii) ions were complexed with a hydrochloride-lactose-modified chitosan, named CTL and dicarboxylic acid-terminated polyethylene-glycol (PEG), leading to hybrid polymer-sugar-metal nanoparticles (DOX-AuGSs). All formulations were assessed by spectroscopic techniques (Raman and UV-Vis) and transmission electron microscopy (TEM). To estimate the therapeutic effect of DOX-AuGSs in liver cancer, murine HepG2 cells were used to induce a hepatic carcinoma model in nude mice. The survival time of the tumor-bearing mice, body weight and tumor volume were measured and recorded. The cytokines were used to detect the serum inflammatory factors, and the blood cell analyzer was used to determine the blood cell content of different groups of nude mice. The outcomes demonstrate that DOX-AuGCs significantly suppressed the tumor growth derived from human HepG2 injection and reduce the tumor index without affecting the body weight of mice. Moreover, DOX-AuGCs significantly reduced the serum levels of cytokines IL-6, TNF-α and IL-12 P70. Finally, a histological analysis of the heart tissue sections indicated that DOX-AuGCs significantly reduce the chronic myocardial toxicity of DOX during the period of treatment.

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.