Flower-shaped gold nanoparticles: synthesis, characterization and their application as SERS-active tags inside living cells

A ratiometric SERS sensor with one signal probe for ultrasensitive and quantitative monitoring of serum xanthine

Xanthine can be converted into uric acid, and a high concentration of xanthine in the human body can cause many diseases. Therefore, it is important to develop a sensitive, simple, and reliable approach for measuring xanthine in biological liquids. Hence, a ratiometric surface-enhanced Raman spectroscopy (SERS) sensing strategy with one signal probe was exploited for reliable, sensitive, and quantitative monitoring of serum xanthine. 3-Mercaptophenylboronic acid (3-MPBA) was used as a typical reference with a Raman peak at 996 cm-1. First, 3-MPBA was bound to gold nanoflowers@silica (GNFs@Si) through Au-S bonds. Xanthine oxidase (XOD) catalyzed the oxidation of xanthine into H2O2 on GNFs@Si. Afterward, the obtained H2O2 further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) accompanied by the emergence of a new Raman peak at 883 cm-1. Meanwhile, the Raman intensity at 996 cm-1 remained constant. Therefore, the ratio of I883/I996 increased with the increasing of xanthine concentration, thus realizing quantitative detection of xanthine. As a result, a ratiometric SERS sensor for the detection of xanthine was proposed with a detection limit of 5.7 nM for xanthine. The novel ratiometric SERS sensor provides a new direction for analyzing other biomolecules with high sensitivity and reliability.

Metallic Engineered Nanomaterials and Ocular Toxicity: A Current Perspective

The ocular surface, comprised of the transparent cornea, conjunctiva, and protective tear film, forms a protective barrier defending deeper structures of the eye from particulate matter and mechanical trauma. This barrier is routinely exposed to a multitude of naturally occurring and engineered nanomaterials (ENM). Metallic ENMs are particularly ubiquitous in commercial products with a high risk of ocular exposure, such as cosmetics and sunscreens. Additionally, there are several therapeutic uses for metallic ENMs owing to their attractive magnetic, antimicrobial, and functionalization properties. The increasing commercial and therapeutic applications of metallic ENMs come with a high risk of ocular exposure with poorly understood consequences to the health of the eye. While the toxicity of metallic ENMs exposure has been rigorously studied in other tissues and organs, further studies are necessary to understand the potential for adverse effects and inform product usage for individuals whose ocular health may be compromised by injury, disease, or surgical intervention. This review provides an update of current literature on the ocular toxicity of metallic ENMs in vitro and in vivo, as well as the risks and benefits of therapeutic applications of metallic ENMs in ophthalmology.

Shape-selective one-step synthesis of branched gold nanoparticles on the crystal surface of redox-active PdII-macrocycles

The synthesis of branched gold nanoparticles (AuNPs) with shape- and size-specific optical properties requires effective control of the particle formation mechanism using appropriate reducing agents and protective agents that prevent particle aggregation in solution. In this context, the heterogeneous synthesis of AuNPs using solid surfaces of graphene oxides and metal-organic frameworks has attracted much attention. These materials are characterized by their ability to immobilize and stabilize the particles grown on the surface without the need for additional protective agents. However, the shape- and size-selective synthesis of AuNPs using solid surfaces remains challenging. Herein, we report the shape-selective one-step synthesis of monodisperse branched AuNPs using a metal-macrocycle framework (MMF), a porous molecular crystal of PdII3-tris(phenylenediamine) macrocycle. Konpeito-Shaped branched AuNPs with uniform size were obtained on the surface of MMF by mixing HAuCl₄·4H₂O, L-ascorbic acid and MMF microcrystals. Spectroscopic and microscopic observations confirmed that MMF promoted the reduction of gold by its reductive activity as well as acted as a solid support to electrostatically immobilize the pseudo-seed particles for further growth on the crystal surface. In addition, the MMF also served as a substrate for in situ high-speed AFM imaging due to the effective immobilization of AuNPs on the surface, allowing direct visualization of the particle growth. Since the chemical structural features of MMF allow the growth of branched AuNPs via pseudo-seeding, this approach would provide new synthetic methods for obtaining a variety of gold nanostructures.

Surface-enhanced Raman spectroscopy for bioanalysis and diagnosis

In recent years, bioanalytical surface-enhanced Raman spectroscopy (SERS) has blossomed into a fast-growing research area. Owing to its high sensitivity and outstanding multiplexing ability, SERS is an effective analytical technique that has excellent potential in bioanalysis and diagnosis, as demonstrated by its increasing applications in vivo. SERS allows the rapid detection of molecular species based on direct and indirect strategies. Because it benefits from the tunable surface properties of nanostructures, it finds a broad range of applications with clinical relevance, such as biological sensing, drug delivery and live cell imaging assays. Of particular interest are early-stage-cancer detection and the fast detection of pathogens. Here, we present a comprehensive survey of SERS-based assays, from basic considerations to bioanalytical applications. Our main focus is on SERS-based pathogen detection methods as point-of-care solutions for early bacterial infection detection and chronic disease diagnosis. Additionally, various promising in vivo applications of SERS are surveyed. Furthermore, we provide a brief outlook of recent endeavours and we discuss future prospects and limitations for SERS, as a reliable approach for rapid and sensitive bioanalysis and diagnosis.

Nanoscale delivery systems for microRNAs in cancer therapy

Concomitant with advances in research regarding the role of miRNAs in sustaining carcinogenesis, major concerns about their delivery options for anticancer therapies have been raised. The answer to this problem may come from the world of nanoparticles such as liposomes, exosomes, polymers, dendrimers, mesoporous silica nanoparticles, quantum dots and metal-based nanoparticles which have been proved as versatile and valuable vehicles for many biomolecules including miRNAs. In another train of thoughts, the general scheme of miRNA modulation consists in inhibition of oncomiRNA expression and restoration of tumor suppressor ones. The codelivery of two miRNAs or miRNAs in combination with chemotherapeutics or small molecules was also proposed. The present review presents the latest advancements in miRNA delivery based on nanoparticle-related strategies.

UV Lithography-Assisted Fabrication of Low-Cost Copper Electrodes Modified with Gold Nanostructures for Improved Analyte Detection

An in-house UV lithography setup has been optimized to fabricate low-cost disposable electrochemical sensing Cu electrodes using a copper clad board. In view of the high oxidation probability of copper, the low-cost electrodes were modified using different gold nanostructures and a conducing polymer PEDOT:PSS to attain maximal signal output and improved shelf-life. Zero-dimensional (0D) gold nanoparticles (∼40 nm) and three-dimensional (3D) gold nanoflowers (∼38 nm) mixed with PEDOT:PSS were used as signal-enhancing conductors for the ultrasensitive detection of our model contaminant, methylene blue dye (MB). The bare copper electrode was sensitive to MB, linearly within the range of 4-100 μM, with a limit of detection of 3.49 μM. While for gold nanoparticle-PEDOT:PSS-modified electrode, the sensitivity of the electrode was found to increase linearly in the range of 0.01-0.1 μM, and for gold nanoflowers-PEDOT:PSS, the sensitivity achieved was 0.01-0.1 μM with the LOD as 0.0022 μM. For a PEDOT:PSS-modified Cu electrode, used as a comparative to study the contributing role of gold nanostructures towards improved sensitivity, the linearity was found to be in the range of 0.1-1.9 μM with the LOD as 0.0228 μM. A 6 times improvement in signal sensitivity for the nanoflower-PEDOT:PSS electrode compared to the nanoparticle-PEDOT:PSS-modified electrode indicates the influence of nanoparticle shape on the electrode efficiency. 3D gold nanoflowers with a large surface area-to-volume ratio and a high catalytic activity prove to be a superior choice for electrode modification.

Present and Future of Surface-Enhanced Raman Scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

Tunable broadband circular polarizer based on ultrahigh-order surface plasmonic resonance

Circular polarizers have potential applications in optical communication and liquid crystal display. In this paper, a multilayer twisted nanoring-rod nanostructure is designed. The finite element method is used to explore the surface plasmon of the structure under the excitation of left-handed circularly polarized light and right-handed circularly polarized light. The results show that the structure can be used as a polarizer in the tunable operating bandwidth of 400-1290 nm, and tunability is achieved by changing the filling medium near the structure instead of the geometric parameters of the nanostructures. We qualitatively reveal the physical mechanism of this phenomenon from the perspective of plasmon resonance coupling by plotting the charge distribution at several specific wavelengths.

A SERS aptasensor for sensitive and selective detection of bis(2-ethylhexyl) phthalate

Bis(2-ethylhexyl)phthalate (DEHP) is an endocrine disruptor commonly present in plastic products, such as PVC tubes and water bottles. In this work, a surface enhanced Raman spectroscopy (SERS) based aptasensor was developed and utilized for rapid, easy, sensitive, and specific detection of trace DEHP. A DEHP aptamer was immobilized on magnetic particles. Raman reporter molecule conjugated silver nanoparticles were clustered and coated with silica to provide a stable SERS signal. The SERS silica particle was then functionalized with 1,2,4-benzenetricarboxylic acid 1,2-bis(2-ethylhexyl) ester to increase its affinity to the DEHP aptamer. In the presence of a sample with DEHP, the high-affinity SERS silica particle competes with the DEHP molecule to bind with the aptamer on the magnetic particle. By measuring the signal of free SERS silica particles in the supernatant after magnetic separation, the concentration of DEHP in the sample was quantitatively determined. The developed DEHP aptasensor had a detection range from 0.008 to 182 nM and a limit of detection (LOD) of 8 pM. The aptasensor also showed high selectivity when exposed to interferents with analogous structures. The aptasensor was successfully tested for the detection of DEHP spiked in tap water, bottled water, and a carbonate beverage. The developed SERS-based aptasensor provides a rapid, sensitive, and easy-to-use method for the quantitative detection of DEHP in environmental and food analysis.

This paper reports a SERS aptasensor developed to detect DEHP at relevant ranges with ultrasensitive performance and good selectivity.

Determination of brain injury biomarkers by surface-enhanced Raman scattering using hollow gold nanospheres

The development of rapid, highly sensitive detection methods for neuron-specific enolase (NSE) and S100-β protein is very important as the levels of NSE and S100-β protein in the blood are closely related to brain injury.

Antibody Conjugated, Raman Tagged Hollow Gold-Silver Nanospheres for Specific Targeting and Multimodal Dark-Field/SERS/Two Photon-FLIM Imaging of CD19(+) B Lymphoblasts

In this Research Article, we propose a new class of contrast agents for the detection and multimodal imaging of CD19(+) cancer lymphoblasts. The agents are based on NIR responsive hollow gold-silver nanospheres conjugated with antiCD19 monoclonal antibodies and marked with Nile Blue (NB) SERS active molecules (HNS-NB-PEG-antiCD19). Proof of concept experiments on specificity of the complex for the investigated cells was achieved by transmission electron microscopy (TEM). The microspectroscopic investigations via dark field (DF), surface-enhanced Raman spectroscopy (SERS), and two-photon excited fluorescence lifetime imaging microscopy (TPE-FLIM) corroborate with TEM and demonstrate successful and preferential internalization of the antibody-nanocomplex. The combination of the microspectroscopic techniques enables contrast and sensitivity that competes with more invasive and time demanding cell imaging modalities, while depth sectioning images provide real time localization of the nanoparticles in the whole cytoplasm at the entire depth of the cells. Our findings prove that HNS-NB-PEG-antiCD19 represent a promising type of new contrast agents with great possibility of being detected by multiple, non invasive, rapid and accessible microspectroscopic techniques and real applicability for specific targeting of CD19(+) cancer cells. Such versatile nanocomplexes combine in one single platform the detection and imaging of cancer lymphoblasts by DF, SERS, and TPE-FLIM microspectroscopy.

Surfactant-Free Shape Control of Gold Nanoparticles Enabled by Unified Theoretical Framework of Nanocrystal Synthesis

Gold nanoparticles have unique properties that are highly dependent on their shape and size. Synthetic methods that enable precise control over nanoparticle morphology currently require shape-directing agents such as surfactants or polymers that force growth in a particular direction by adsorbing to specific crystal facets. These auxiliary reagents passivate the nanoparticles' surface, and thus decrease their performance in applications like catalysis and surface-enhanced Raman scattering. Here, a surfactant- and polymer-free approach to achieving high-performance gold nanoparticles is reported. A theoretical framework to elucidate the growth mechanism of nanoparticles in surfactant-free media is developed and it is applied to identify strategies for shape-controlled syntheses. Using the results of the analyses, a simple, green-chemistry synthesis of the four most commonly used morphologies: nanostars, nanospheres, nanorods, and nanoplates is designed. The nanoparticles synthesized by this method outperform analogous particles with surfactant and polymer coatings in both catalysis and surface-enhanced Raman scattering.

Polarization dependence of plasmon enhanced fluorescence on Au nanorod array

The spatial anisotropy of Au nanorod results in two distinct orientational modes by which the polarization orientation dependence of excitation and emission can be studied. In this work, a periodical distributed metallic nanostructure substrate, which contains an array of Au nanorods, is synthesized, and the polarization dependence of the plasmon enhanced fluorescence effect is investigated experimentally and numerically. It is found that the fluorescence emission enhancement of organic probe fluorophores located at the surface of Au nanorods depends on the polarization angle very sensitively. Different polarization orientations of the excitation light result in very different enhancement effects. As a result, the change of the polarization orientation of the excitation light can be a sensitive marker of surface chemistry and other possible practical applications.

Nanomedicine approaches in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the malignancy with the highest incidence amongst children (26% of all cancer cases), being surpassed only by the cancers of the brain and of the nervous system. The most recent research on ALL is focusing on new molecular therapies, like targeting specific biological structures in key points in the cell cycle, or using selective inhibitors for transmembranary proteins involved in cell signalling, and even aiming cell surface receptors with specifically designed antibodies for active targeting. Nanomedicine approaches, especially by the use of nanoparticle-based compounds for the delivery of drugs, cancer diagnosis or therapeutics may represent new and modern ways in the near future anti-cancer therapies. This review offers an overview on the recent role of nanomedicine in the detection and treatment of acute lymphoblastic leukemia as resulting from a thorough literature survey. A short introduction on the basics of ALL is presented followed by the description of the conventional methods used in the ALL detection and treatment. We follow our discussion by introducing some of the general nano-strategies used for cancer detection and treatment. The detailed role of organic and inorganic nanoparticles in ALL applications is further presented, with a special focus on gold nanoparticle-based nanocarriers of antileukemic drugs.

Combination assay of lung cancer associated serum markers using surface-enhanced Raman spectroscopy

A highly sensitive and specific SERS-based combination assay of lung cancer associated serum markers is reported, and the LODs of CEA and NSE in human serum specimens are 1.48 pg mL⁻¹ and 2.04 pg mL⁻¹, respectively.

Optimization of second harmonic generation of gold nanospheres and nanorods in aqueous solution: the dominant role of surface area

Gold nanoparticles display exceptionally strong β values. We demonstrated that the first hyperpolarizability (β) strongly depends on surface area of gold nanoparticles.

Gold nanoflowers with tunable sheet-like petals: facile synthesis, SERS performances and cell imaging

Gold nanoflowers with tunable sheet-like petals were controllably synthesized, and their SERS performances as well as their application in cell imaging were studied.

Particle-on-Film Gap Plasmons on Antireflective ZnO Nanocone Arrays for Molecular-Level Surface-Enhanced Raman Scattering Sensors

When semiconducting nanostructures are combined with noble metals, the surface plasmons of the noble metals, in addition to the charge transfer interactions between the semiconductors and noble metals, can be utilized to provide strong surface plasmon effects. Here, we suggest a particle-film plasmonic system in conjunction with tapered ZnO nanowire arrays for ultrasensitive SERS chemical sensors. In this design, the gap plasmons between the metal nanoparticles and the metal films provide significantly improved surface-enhanced Raman spectroscopy (SERS) effects compared to those of interparticle surface plasmons. Furthermore, 3D tapered metal nanostructures with particle-film plasmonic systems enable efficient light trapping and waveguiding effects. To study the effects of various morphologies of ZnO nanostructures on the light trapping and thus the SERS enhancements, we compare the performance of three different ZnO morphologies: ZnO nanocones (NCs), nanonails (NNs), and nanorods (NRs). Finally, we demonstrate that our SERS chemical sensors enable a molecular level of detection capability of benzenethiol (100 zeptomole), rhodamine 6G (10 attomole), and adenine (10 attomole) molecules. This work presents a new design platform based on the 3D antireflective metal/semiconductor heterojunction nanostructures, which will play a critical role in the study of plasmonics and SERS chemical sensors.

Facile synthesis of hydrangea flower-like hierarchical gold nanostructures with tunable surface topographies for single-particle surface-enhanced Raman scattering

The physicochemical properties of noble metal nanocrystals depend strongly on their size and shape, and it is becoming clear that the design and facile synthesis of particular nanostructures with tailored shape and size is especially important. Herein a novel class of hydrangea flower-like hierarchical gold nanostructures with tunable surface topographies and optical properties are prepared for the first time by a facile, one-pot, seedless synthesis using ascorbic acid (AA) to reduce hydrogen tetrachloroaurate (HAuCl4) in the presence of (1-hexadecyl)trimethylammonium chloride (CTAC). The morphologies of the synthesized gold nanoflowers are controlled and fine-tuned by varying the synthetic conditions such as the concentration of reagents and the growth temperature. Due to their unique hierarchical three-dimensional (3D) structures with rich hot spots, these gold nanoflowers exhibit an efficient performance in single-particle surface-enhanced Raman scattering (SERS). The work stands out as an interesting approach for anisotropic particle synthesis and morphological control, and the proposed novel, hierarchical gold nanoflowers have a number of exciting potential applications in SERS-based sensors.

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.

Copolymer and platinum ion assisted growth of functionalized gold nanonests

Novel Au nanonests with high yield and uniformity were successfully synthesized using P123 as a soft template and a reductant in an ice water bath with and without the presence of the second metallic source of Pt ions.

Synthesis of novel gold mesoflowers as SERS tags for immunoassay with improved sensitivity

A new class of flowerlike gold mesostructure in high yield is successfully synthesized through a facile one-step route using ascorbic acid as a reducing agent of gold salt with cetyltrimethylammonium chloride (CTAC) as surfactant. The as-prepared Au particles have spherical profiles with an averaged diameter of 770 ± 50 nm, but showing a highly rough surface consisting of many irregular and randomly arranged protrusions. The Au mesoflowers exhibit strong surface-enhanced effects and near-infrared absorption which were utilized in the design of efficient surface-enhanced Raman scattering (SERS) tags as immunosensors for immunoassay with improved sensitivity. The experimental results indicate that a good linear relationship is found between the peak intensity at 1071 cm(-1) and the logarithm of H-IgG concentration in the range between 1 ng/mL and 1 fg/mL, and the limit of detection (LOD) is 1 fg/mL.

Green synthesis of asymmetrically textured silver meso-flowers (AgMFs) as highly sensitive SERS substrates

Highly asymmetrical "flower-like" micron silver particles, so-called hierarchical silver meso-flowers (AgMFs), were facilely synthesized using ascorbic acid at room temperature in the presence of chitosan biopolymer. The time-evolution of TEM images and XRD analysis confirmed the anisotropic growth of AgMFs with single crystalline phase of which the formation mechanism was described in detail. The morphology and size of as-prepared AgMFs were tunable simply by changing the concentration of chitosan biopolymer and/or AgNO3 precursor under otherwise identical conditions. The asymmetrically textured AgMFs dramatically enhanced Raman signals of probe molecules (2-chlorothiophenol, 4-aminothiophenol) even at a single particle level because of their surface morphologies consisting of numerous nanoedges and crevices.

Detection of Hepatitis B virus antigen from human blood: SERS immunoassay in a microfluidic system

A highly sensitive immunoassay utilizing surface-enhanced Raman scattering (SERS) has been developed with a new Raman reporter and a unique SERS-active substrate incorporated into a microfluidic device. An appropriately designed Raman reporter, basic fuchsin (FC), gives strong SERS enhancement and has the ability to bind both the antibody and gold nanostructures. The fuchsin-labeled immuno-Au nanoflowers can form a sandwich structure with the antigen and the antibody immobilized on the SERS-active substrate based on Au-Ag coated GaN. Our experimental results indicate that this SERS-active substrate with its strong surface-enhancement factor, high stability and reproducibility plays a crucial role in improving the efficiency of SERS immunoassay. This SERS assay was applied to the detection of Hepatitis B virus antigen (HBsAg) in human blood plasma. A calibration curve was obtained by plotting the intensity of SERS signal of FC band at 1178cm(-1) versus the concentration of antigen. The low detection limit for Hepatitis B virus antigen was estimated to be 0.01IU/mL. The average relative standard deviation (RSD) of this method is less than 10%. This SERS immunoassay gives exact results over a broad linear range, reflecting clinically relevant HBsAg concentrations. It also exhibits high biological specificity for the detection of Hepatitis B virus antigen.

Simple control of surface topography of gold nanoshells by a surfactant-less seeded-growth method

We report the synthesis of branched gold nanoshells (BGNS) through a seeded-growth surfactant-less method. This was achieved by decorating chitosan-Pluronic F127 stabilized poly(lactic-co-gycolic) acid nanoparticles (NPs) with Au seeds (NP-seed), using chitosan as an electrostatic self-assembling agent. Branched shells with different degrees of anisotropy and optical response were obtained by modulating the ratios of HAuCl4/K2CO3 growth solution, ascorbic acid (AA) and NP-seed precursor. Chitosan and AA were crucial in determining the BGNS size and structure, acting both as coreductants and structure directing growth agents. Preliminary cytotoxicity experiments point to the biocompatibility of the obtained BGNS, allowing their potential use in biomedical applications. In particular, these nanostructures with "hybrid" compositions, which combine the features of gold nanoshells and nanostars showed a better performance as surface enhanced Raman spectroscopy probes in detecting intracellular cell components than classical smoother nanoshells.

Nanopharmacology in translational hematology and oncology

Nanoparticles have displayed considerable promise for safely delivering therapeutic agents with miscellaneous therapeutic properties. Current progress in nanotechnology has put forward, in the last few years, several therapeutic strategies that could be integrated into clinical use by using constructs for molecular diagnosis, disease detection, cytostatic drug delivery, and nanoscale immunotherapy. In the hope of bringing the concept of nanopharmacology toward a viable and feasible clinical reality in a cancer center, the present report attempts to present the grounds for the use of cell-free nanoscale structures for molecular therapy in experimental hematology and oncology.

Reliable plasmonic substrates for bioanalytical SERS applications easily prepared by convective assembly of gold nanocolloids

The ability to easily prepare Surface Enhanced Raman Scattering (SERS) substrates by the assembly of chemically synthesized gold nanocolloids is of great interest for the advancement of SERS-based optical detection and identification of molecular species of biological or chemical interest, pollutants or warfare agents. In this work we employ three very simple strategies, which can be implemented in any laboratory without the need for specialized equipment, to prepare assemblies of citrate-stabilized spherical gold colloids: (i) drop-coating, which induces the assembly of colloids in so-called coffee rings; (ii) a simplified variant of convective self-assembly (CSA), based on water evaporation in a constrained geometry, which yields highly uniform strips of nanoparticles (NP); (iii) assembly onto chemically functionalized glass surfaces which yields randomly assembled colloids and colloidal clusters. The SERS properties of the resulting colloidal assemblies are comparatively evaluated under multiple excitation lines with p-aminothiophenol (pATP) as a model Raman scatterer. The NP strips obtained by CSA prove to be SERS-active both in the visible and NIR and possess a highly uniform SERS response as demonstrated by spectra at individually selected sites and by confocal SERS mapping. Further it is shown that these NP strips are effective for the detection of cytosine, a DNA component, and for multi-analyte SERS detection. These results, showing how an efficient SERS substrate can be obtained by a very simple assembly method from easy-to-synthesize colloidal gold NP, can have an impact on the development of analytical SERS applications.

Controlled Synthesis of Gold Nanoparticles UsingAspergillus terreusIF0 and Its Antibacterial Potential against Gram Negative Pathogenic Bacteria

Biosynthesis of monodispersed nanoparticles, along with determination of potential responsible biomolecules, is the major bottleneck in the area of bionanotechnology research. The present study focuses on an ecofriendly, ambient temperature protocol for size controlled synthesis of gold nanoparticles, using the fungusAspergillus terreusIF0. Gold nanoparticles were formed immediately, with the addition of chloroauric acid to the aqueous fungal extract. Synthesized nanoparticles were characterized by UV-Vis spectroscopy, TEM-EDX, and XRD analysis. Particle diameter and dispersity of nanoparticles were controlled by varying the pH of the fungal extract. At pH 10, the average size of the synthesized particles was in the range of 10–19 nm. Dialysis to obtain high and low molecular weight fraction followed by FTIR analysis revealed that biomolecules larger than 12 kDa and having –CH, –NH, and –SH functional groups were responsible for bioreduction and stabilization. In addition, the synthesized gold nanoparticles were found to be selectively bactericidal against the pathogenic gram negative bacteria,Escherichia coli.

Electrospun polymer mat as a SERS platform for the immobilization and detection of bacteria from fluids

A new class of SERS substrates is presented that allows for the simultaneous filtration of bacteria from any solution (blood, urine, water, or milk), immobilization of bacteria on the SERS platform, and enhancing the Raman signal of bacteria.

Folic acid-conjugated, SERS-labeled silver nanotriangles for multimodal detection and targeted photothermal treatment on human ovarian cancer cells

The effectiveness of a therapeutic agent for cancer stands in its ability to reduce and eliminate tumors without harming the healthy tissue nearby. Nanoparticles peripherally conjugated with targeting moieties offer major improvements in therapeutics through site specificity. In this study we demonstrate this approach by targeting the folate receptor of NIH:OVCAR-3 human ovary cancer cell line. Herein we used silver nanotriangles which were biocompatibilized with chitosan (bio)polymer, labeled with para-aminothiophenol (pATP) Raman reporter molecule, and conjugated with folic acid. The nanoparticles conjugation and efficient labeling was investigated by localized surface plasmon resonance (LSPR), zeta potential, and surface-enhanced Raman scattering (SERS) measurements. Conjugated particles were proven to be highly stable in aqueous and cellular medium. The targeted uptake of conjugated nanoparticles by human ovary cancer cells was confirmed by dark field microscopy and scattering spectra of the particles inside cells. Comparative studies revealed specific internalization of the conjugated nanoparticles in comparison with similar bare nanoparticles. Moreover, the SERS identity of the particles was proven to be highly conserved inside cells. Targeted cancer cell treatment conducted by irradiating the nanoparticle-treated cells with a continuous wave-nearinfrared (cw-NIR) laser in resonance with their plasmonic band proved an efficient therapeutic response. By integrating the advantages of multimodal optical imaging and SERS detection with hyperthermia capabilities through site specificity, these nanoparticles can represent a real candidate for personalized medicine.

Chitosan-coated triangular silver nanoparticles as a novel class of biocompatible, highly sensitive plasmonic platforms for intracellular SERS sensing and imaging

There is a need for new strategies for noninvasive imaging of pathological conditions within the human body. The approach of combining the unique physical properties of noble-metal nanoparticles with their chemical specificity and an easy way of conjugation open up new routes toward building bio-nano-objects for biomedical tracking and imaging. This work reports the design and assessment of a novel class of biocompatible, highly sensitive SERS nanotags based on chitosan-coated silver nanotriangles (Chit-AgNTs) labeled with para-aminothiophenol (p-ATP). The triangular nanoparticles are used as Raman scattering enhancers and have proved to yield a reproducible and strong SERS signal. When tested inside lung cancer cells (A549) this class of SERS nanotags presents low in vitro toxicity, without interfering with cell proliferation. Easily internalized by the cells, as demonstrated by imaging using both reflected bright-light optical microscopy and SERS spectroscopy, the particles are proved to be detectable inside cells under a wide window of excitation wavelengths, ranging from visible to near infrared (NIR). Their high sensitivity and NIR availability make this class of SERS nanotags a promising candidate for noninvasive imaging of cancer cells.

Hybrid polymer-metal nanospheres based on highly branched gold nanoparticles for potential medical applications

Hybrid polymer-metal nanospheres are potential nano-sized medical devices that can provide multi-functions such as medical imaging and drug/biomolecule delivery. Gold nanoparticle-based hybrid nanospheres are particularly attractive owing to the unique optical and electronic properties that they possess. The polymer in hybrid nanospheres can be tasked for cancer cell targeting, DNA delivering etc. In the current investigation, a simple one-pot synthesis method was developed for producing folic acid-chitosan-capped gold (Au@CS-FA) nanospheres. These nanospheres consisted of a flower-like gold nanoparticle core and a cross-linked folic acid (FA)-conjugated chitosan shell. During the synthesis of Au@CS-FA nanospheres, FA-conjugated chitosan molecules acted as a reductant for gold and also as a structure-directing agent for the formation of highly branched gold nanoparticles. The evolution of Au@CS-FA nanospheres during their manufacture was studied using various analytical techniques and the mechanism of formation and growth was proposed. The Au@CS-FA nanospheres exhibited high-surface-enhanced Raman scattering which could be utilised for imaging at the single molecule level. The biopolymer shell was functionalised with -NH(2) and -COOH groups, which could be readily conjugated with macromolecules, peptides, nucleotides etc. for potentially wide applications of Au@CS-FA nanospheres in the medical field.

Quantitative surface-enhanced resonant Raman scattering multiplexing of biocompatible gold nanostars for in vitro and ex vivo detection

Surface-enhanced Raman scattering (SERS)-active plasmonic nanomaterials have become a promising agent for molecular imaging and multiplex detection. To produce strong SERS intensity while retaining the nonaggregated state and biocompatibility needed for bioapplications, we integrated near-infrared (NIR) responsive plasmonic gold nanostars with resonant dyes for resonant SERS (SERRS). The SERRS on nanostars was several orders of magnitude greater than signals from SERRS on nanospheres and nonresonant SERS on nanostars. For the first time, we demonstrated quantitative multiplex detection using four unique nanostar SERRS probes in both in vitro solutions and ex vivo tissue samples under NIR excitation. With further optimization, in vivo tracking of multiple SERRS probes is possible.

Gelatin-nanogold bioconjugates as effective plasmonic platforms for SERS detection and tagging

It is well known that standard citrate-reduced gold nanoparticles (AuNPs) are unstable at high ionic strength solution, which limits their applications in the biomedical field. In this work we present an environmentally friendly approach for the stabilization of citrate-reduced AuNPs in aqueous solution. Specifically, the stability of the AuNPs against salt-induced aggregation was greatly improved in the presence of gelatin biopolymer and stabilization of individual or small assemblies of nanoparticles can be controlled by the amount of gelatin. Furthermore, the gelatin-nanogold bioconjugates were demonstrated to be operational as highly sensitive surface-enhanced Raman scattering (SERS) active substrate for the detection of Rose Bengal fluorophore in solution at very low concentration. The results suggest that such bioconjugates can be successfully employed not only for detection of analytes, but more interestingly for building SERS-active tags in view of imaging purpose. The stabilization of bioconjugates was analyzed by localized surface plasmon resonance spectroscopy (LSPR), transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta-potential, and the chemical interaction of gelatin with AuNPs was inferred from Fourier transform infrared spectroscopy (FT-IR).