Search

The ionization state of amino acids on the outer surface of a virus regulates its physicochemical properties toward the sorbent surface. Serologically different strain of dengue virus (DENV) shows different extents of infectivity depending upon their interactions with a receptor on the host cell. To understand the structural dependence of E-protein protonation over its sequence dependence, we have followed E-protein titration kinetics both experimentally and theoretically for two differentially infected dengue serotypes, namely DENV-2 and DENV-4. We have performed an E-protein protonation titration-induced single particle chemical force spectroscopy using an atomic force microscope (AFM) to measure the surface chemistry of DENV in physiological aqueous solutions not only to understand the charge distribution dynamics on virus surface but also to estimate the isoelectric point (pI) accurately for infectious dengue viruses. Cryo-EM structure-based theoretical pI calculations of DENV-2 surface protein were shown to be consistent with the evaluated pI value from force spectroscopy measurements. This is a comprehensive study to understand how the cumulative charge distribution on the outer surface of a specific serotype of DENV regulates a prominent role of infectivity over minute changes at the genetic level.

Cancer cells secrete extracellular vesicles (EVs) covered with a carbohydrate polymer, hyaluronan (HA), linked to tumor malignancy. Herein, we have unravelled the contour lengths of HA on a single cancer cell-derived EV surface using single-molecule force spectroscopy (SMFS), which divulges the presence of low molecular weight HA (LMW-HA200 kDa). We also discovered that these LMW-HA-EVs are significantly more elastic than the normal cell-derived EVs. This intrinsic elasticity of cancer EVs could be directly allied to the LMW-HA abundance and associated labile water network on EV surface as revealed by correlative SMFS, hydration dynamics with fluorescence spectroscopy, and molecular dynamics simulations. This method emerges as a molecular biosensor of the cancer microenvironment.

This report quantitatively investigates the role of grain-boundary and grain size in the excellent electrocatalytic activity of our recently synthesized shape-engineered (bud-shaped AuNP50 to bloom...

Spherical gold nanoseed (∼5–6 nm)-induced (but not seed-mediated) silver nanorods (Hy-Au@AgNRs) of variable lengths have been synthesized by a new methodology that shows enhancement in catalytic ac...

Swept-source optical coherence tomography (SSOCT) is a noncontact, noninvasive bioimaging tool that uses various probes to obtain high contrast images. Rare-earth based upconversion particles (UCPs...

Bimetallic Au–Ag hollow nanoprisms (HNPrs) with variable effective surface areas, dynamic atomic compositions (Au:Ag), and distinct stepped surfaces between the central porous region and crystallin...

Polyvinylpyrrolidone (PVP)-based silver nanoprisms (AgNPrs) show an initial stacking geometry because of their low zeta potential and electrostatic interaction between face-to-face energetically stable {111} surface-bound pyrrolidone groups through the Na+-ion-induced cation−π interaction. Congested interplanar space between AgNPrs allows As(III) to react differentially with silver atoms from facial {111} and peripheral {110} facets to result in smaller stackings and finally nanoseeds. Above this critical concentration of As(III), PVP leached out from nanoparticles to form nanoseed-engulfed emulsions and induced controlled aggregation. This entire morphological transition has been decoded by recording their surface plasmon and surface-enhanced Raman scattering tuning and confirmed by the transmission electron microscopy study. Strong affinity and selectivity of As(III) toward the Ag atom (verified and estimated by the HF/3-21g* level of density functional theory calculation) coupled with low-cost colorime...

Aggregation of intrinsically disordered as well as the ordered proteins under certain premises or physiological conditions leads to pathological disorder. Here we have presented a detailed investigation on the effect of a porous metallic (Au) and a non-metallic (Si) nanomaterial on the formation of ordered (fiber-like/amyloid) and disordered (amorphous) aggregates of proteins. Porous nanogold (PNG) was found to reduce the amyloid aggregation of insulin but does not have much impact on the lag phase in the aggregation kinetics, whereas porous nano-silica (PNS) was found both to decrease the amount of aggregation as well as prolong the lag phase of amyloid fiber formation from insulin. On the other hand, both the porous nanoparticles are found to decrease the extent of amorphous aggregation (with slight improvement for PNS) of pathogenic huntingtin (Htt) protein in Huntington's disease cell model. This is a noted direct observation in controlling and understanding protein aggregation diseases which may help us to formulate nanotherapeutic drugs for future clinical applications.

Extracellular vesicles (EVs), naturally occurring nanosized vesicles secreted from cells, are essential for intercellular communication. They carry unique biomolecules on the surface or interior that are of great interest as biomarkers for various pathological conditions such as cancer. In this work, we use high-resolution atomic force microscopy (AFM) and spectroscopy (AFS) techniques to demonstrate differences between EVs derived from colon cancer cells and colon epithelial cells at the single-vesicle level. We observe that EV populations are significantly increased in the cancer cell media compared to the normal cell EVs. We show that both EVs display an EV marker, CD9, while EVs derived from the cancer cells are slightly higher in density. Hyaluronan (HA) is a nonsulfated glycosaminoglycan linked to malignant tumor growth according to recent reports. Interestingly, at the single-vesicle level, colon cancer EVs exhibit significantly increased HA surface densities compared to the normal EVs. Spectroscopic measurements such as Fourier transform infrared (FT-IR), circular dichroism (CD), and Raman spectroscopy unequivocally support the AFM and AFS measurements. To our knowledge, it represents the first report of detecting HA-coated EVs as a potential colon cancer biomarker. Taken together, this sensitive approach will be useful in identifying biomarkers in the early stages of detection and evaluation of cancer.

The role of microscopic elasticity of nano-carriers in cellular uptake is an important aspect in biomedical research. Herein we have used AFM nano-indentation force spectroscopy and Forster resonance energy transfer (FRET) measurements to probe microelastic properties of three novel cationic liposomes based on di-alkyl dihydroxy ethyl ammonium chloride based lipids having asymmetry in their hydrophobic chains (Lip1818, Lip1814 and Lip1810). AFM data reveals that symmetry in hydrophobic chains of a cationic lipid (Lip1818) imparts higher rigidity to the resulting liposomes than those based on asymmetric lipids (Lip1814 and Lip1810). The stiffness of the cationic liposomes is found to decrease with increasing asymmetry in the hydrophobic lipid chains in the order of Lip1818 > Lip1814 > lip1810. FRET measurements between Coumarin 500 (Donor) and Merocyanine 540 (Acceptor) have revealed that full width at half-maxima (hw) of the probability distribution (P(r)) of donor-acceptor distance (r), increases in an order Lip1818 < Lip1814 < Lip1810 with increasing asymmetry of the hydrophobic lipid chains. This increase in width (hw) of the donor-acceptor distance distributions is reflective of increasing flexibility of the liposomes with increasing asymmetry of their constituent lipids. Thus, the results from AFM and FRET studies are complementary to each other and indicates that an increase in asymmetry of the hydrophobic lipid chains increases elasticity and or flexibility of the corresponding liposomes. Cell biology experiments confirm that liposomal flexibility or rigidity directly influences their cellular transfection efficiency, where Lip1814 is found to be superior than the other two liposomes manifesting that a critical balance between flexibility and rigidity of the cationic liposomes is key to efficient cellular uptake. Taken together, our studies reveal how asymmetry in the molecular architecture of the hydrophobic lipid chains influences the microelastic properties of the liposomes, and hence, their cellular uptake efficiency.

The actin cytoskeleton is required for the maintenance of the cell shape and viability of bacteria. It remains unknown to which extent nanoparticles (NPs) can orchestrate the mechanical instability by disrupting the cytoskeletal network in bacterial cells. Our work demonstrates that Au–Ag NPs disrupt the bacterial actin cytoskeleton specifically, fluidize the inner membrane and lead to killing of bacterial cells. In this study, we have tried to emphasize on the key parameters important for NP–cell interactions and found that the shape, specific elemental surface localization and enhanced electrostatic interaction developed due to the acquired partial positive charge by silver atoms in the aggregated NPs are some of the major factors contributing towards better NP interactions and subsequent cell death. In vivo studies in bacterial cells showed that the NPs exerted a mild perturbation of the membrane potential. However, its most striking effect was on the actin cytoskeleton MreB resulting in morphological changes in the bacterial cell shape from rods to predominantly spheres. Exposure to NPs resulted in the delocalization of MreB patches from the membrane but not the tubulin homologue FtsZ. Concomitant with the redistribution of MreB localization, a dramatic increase of membrane fluid regions was observed. Our studies reveal for the first time that Au–Ag NPs can mediate bacterial killing and disrupt the actin cytoskeletal functions in bacteria.

We report an effective method to produce surface-enhanced Raman scattering (SERS) substrates with improved enhancement efficiency, high uniformity, greater chemical and physical stability, and absolute synthetic reproducibility. Nanobipyramidal gold (Au) core and silver (Ag) shell nanorods (NRs) with variable length were prepared simply by varying the Ag precursor amount during growth, and we successfully prepared NRs of lengths from 200 to 1200 nm and studied their formation mechanism and morphology using transmission electron microscopy (TEM) and their optical properties by using UV–vis–near-IR (NIR) and Raman spectroscopy. Here we have utilized the properties of both Au and Ag nanoparticles by synthesizing Au@Ag core–shell NRs for high SERS enhancement. NRs have stronger absorption and large scattering cross sections for electromagnetic radiation, and variation of the aspect ratios of these NRs leads to a broad-band surface plasmon tuning in the vis–NIR region. The relative SERS enhancement efficiencie...

The role of the single-domain ferrimagnetic nanostructure and the associated surface for many fold magnetic-field-induced surface enhanced transient spin-trajectory modulation is a new venture in m...

Formulated mesoporous silica nanoparticle (MSN) systems offer the best possible drug delivery system through the release of drug molecules from the accessible pores. In the present investigation, steady state and time resolved fluorescence techniques along with the fluorescence imaging were applied to investigate the interactions of dye loaded MSN with fluorescent unilamellar vesicles and live cells. Here 1,2-dimyristoyl-sn-glycero-3-phospocholine (DMPC) was used to prepare Small Unilamellar Vesicles (SUVs) as the model membrane with fluorescent 1,6-diphenyl-1,3,5-hexatriene (DPH) molecule incorporated inside the lipid bilayer. The interaction of DPH incorporated DMPC membrane with Fluorescein loaded MSN lead to the release of Fluorescein (Fl) dye from the interior pores of MSN systems. The extent of release of Fl and spatial distribution of the DPH molecule has been explored by monitoring steady-state fluorescence intensity and fluorescence lifetime at physiological condition. To investigate the fate of drug molecule released from MSN, fluorescence anisotropy has been used. The drug delivery efficiency of the MSN as a carrier for doxorubicin (DOX), a fluorescent chemotherapeutic drug, has also been investigated at physiological conditions. The study gives a definite confirmation for high uptake and steady release of DOX in primary oral mucosal non-keratinized squamous cells in comparison to naked DOX treatment.

An efficient nanobioconjugate has been developed as electrode coating material by self-assembling our newly reported porous Au-seeded Ag nanorod networks (Hy-Au@AgNR840-Ass) with a thiol modified DNA aptamer (HS-Apt) for the early-stage specific detection and quantification of Dengue virus (serotype 2). Characterization of the precursors (Hy-Au@AgNR840 and Hy-Au@AgNR840-Ass) for effective fabrication of the bioconjugate (Hy-Au@AgNR840-Ass-S-Apt) was performed by using microscopic (TEM and AFM), spectroscopic (Absorbance, XPS, and SERS), scattering (DLS) and diffractometric (XRD) techniques and has been detailed in our previous publication whereas the binding affinity between the bioconjugate and different serotypes of dengue is studied here using low cost electrochemical impedimetric spectroscopy (EIS). Despite the structural similarity between virion particles of different dengue serotypes, we can detect the most prevalent DENV-2 specifically by using our nonenzymatic nanobioconjugate assay for the first time through the impedimetric technique. The cross-reactivity is checked in presence of closely related serotypes like DENV-1 & DENV-3. The key achievement of this study lies in its ability in the direct detection of DENV-2 serotype without the aid of an enzyme or antibody in dengue-infected blood up to ~ 100 infectious units per mL.

In this study, new types of nanogold labels for lateral flow immunoassay of model antigen procalcitonin based on photometric and surface-enhanced Raman scattering methods of detection were obtained. The linear range of procalcitonin determination applying gold nanoflowers as a label was between 0.5 and 10 ng/mL. The limit of photometric detection was achieved at 0.1 ng/mL that was five times lower than the sensitivity of traditional lateral flow immunoassay with spherical gold nanoparticles as a label. In addition, the conjugate of polyclonal antibodies against procalcitonin with spherical gold nanoparticles labeled with 4-mercaptobenzoic acid as Raman reporter molecule was prepared and used as an immunoprobe in lateral flow immunoassay based on surface-enhanced Raman spectroscopy to improve assay sensitivity.

Applying Le Chatelier's principle, a one-pot synthesis method is reported that generates highly anisotropic hedgehog gold nanoparticles (HHogGNPs), undemanding of a preformed seed or surfactant. These non-toxic HHogGNPs are potent candidates for nanomedicinal applications owing to their broad-band plasmon tunability, gigantic Raman enhancement and remarkable retention in a highly salted physiological environment.

Triplet-triplet (T-T) absorption spectroscopy has been used successfully as a molecular ruler to understand the actual release process of sanguinarine as a drug molecule from a gold nanoparticle surface in the presence of cell components, that is, DNA and chromatin. The obtained results have been verified by fluorescence and surface-enhanced Raman spectroscopy (SERS), and a plausible explanation has been put forward to describe the underestimation and overestimation of the percentage (%) of the release of drug molecules measured by fluorescence- and SERS-based techniques, respectively, over the highlighted T-T absorption spectroscopy. Because of the intrinsic nature of absorption, the reported T-T absorption spectroscopic assay overpowers fluorescence- and SERS-based assays, which are limited by the long-range interaction and nonlinear dependence of the concentration of analytes, respectively.

The complete unzipping of DNA double helix by small size gold nanoparticles having weakly positive surface charge has been monitored using ensemble and single molecule fluorescence resonance energy transfer (smFRET) techniques. We believe, as the gold nanoparticles have positive charge on the surface, the DNA and nanoparticles were pulled together to form two single strands. The positively charged ligands on the nanoparticles attached to the DNA, and the hydrophobic ligands of the nanoparticles became tangled with each other, pulling the nanoparticles into clusters. At the same time, the nanoparticles pulled the DNA apart. The conformational changes followed by unzipping have been investigated for long DNA (calf thymus DNA) as well as for short DNA (∼40 base pair) using ensemble methods like circular dichroism (CD) spectroscopy, fluorescence intercalation assay, viscometric method, and single molecule FRET imaging. This observation not only reveals a new aspect in the field of nano-bio interface but also provides additional information about DNA dynamics.

The ‘green’ synthetic aspects of functionally potent and biologically relevant nanomaterials are a crucial research objective. Pursuing this concept, we have investigated a green synthetic scheme for the sunlight-mediated generation of luminescent silver nanoparticles, which become stabilized via a supramolecular hydrogel (SHGel) network, as already reported by our group. In vitro and in vivo toxicity studies confirm the biologically relevant nature of SHGel-capped Ag NPs. Nontoxic SHGel-capped Ag NPs were intelligently used for the transport of drugs, including antifilarial and antibiotic agents, into cells. Apart from this activity, SHGel-capped Ag NPs and our previously reported nontoxic DNA hydrogel-capped Ag NPs are potent against pathogens and parasites. Most interestingly, the nanostructural patterns of SHGel- and DNA hydrogel-capped Ag NPs have been transformed into cotyledon- and flower bud-shaped forms of nanosilver, respectively, during their chemotherapeutic action against a particular bacterium, Bacillus subtilis. Transmission electron microscopy was used for the visualization of several patterns of nanosilver and the incorporation of Ag NPs into macrophages.

A plausible explanation based on real-time direct experimental observation has been put forward to explain the formation of common salt (NaF, NaCl, NaBr, and NaI) induced aspect ratio tunable Pentagonal Faceted Pyramidal Tipped (PFPT) silver-nanowires by considering the solubility product of the in situ generated silver halides, binding affinity of the added halides at the {111} facets on the growing front, and the free energy associated with the crystallographic planes (obtained from HRTEM study) as the driving forces. Aspect ratio dependent Raman activity was verified by using 4-mercaptobenzoic acid (4-MBA) as a Raman tag and due to the preferential binding of Hg2+ on the pyramidal tip of the silver-nanowire [i.e., {111} facet], as all the {100} facets are blocked by insoluble silver halides, controlled leaching of the nanowires offers the best-possible Raman platform for the ultra sensitive detection of Hg2+ contamination (up to 50 ppt) from ground water.

Here we report a simple low-cost method to produce surface-enhanced Raman scattering (SERS) substrates with improved efficiency and high sensitivity towards uric acid and ascorbic acid sensing using non-enzymatic amperometric electrochemical method. Trisoctahedral gold (Au) core-silver (Ag) shell cubical shaped nanoparticles were synthesized simply by varying the surfactant in the reaction medium, and afterwards we made them hollow by galvanic displacement reaction. Spherical core-shell nanoparticles (both solid and hollow) were also prepared to compare results with cubical one. We have performed transmission electron microscopy (TEM) studies to understand the morphology of these nanoparticles and UV–vis–NIR and Raman spectroscopy studies to understand optical properties. We have obtained a huge SERS enhancement (~109) for hollow Au@Ag nanocube using 4-mercapto benzoic acid (4-MBA) as analyte. Because of the very thin Ag shell wall, both core Au and shell Ag interacts with the incoming electromagnetic wave, and also due to the presence of multiple sharp edges and corners in both core and shell part of the nanoparticles there is a large enhancement of the electromagnetic field. We have performed cyclic voltammetry study using the nanoparticles as electrode to understand how interfacial charge transfer and electron accumulation is happening in between an electrode and electrolyte interface and we have obtained a very high current response for hollow core-shell nanocube due to more surface area. High current response with voltage enable us to use hollow core-shell nanocubes as non-enzymatic electrochemical sensor for sensing uric acid (UA) and ascorbic acid (AA). We found a good sensitivity (1.509 μAmM−1cm−2 and 209.027 μAmM−1cm−2 for UA and AA, respectively) and very low detection limit (0.36 μM and 0.019 μM for UA and AA, respectively) towards sensing, which allows us to use Au@Ag hollow nanocube as a good UA and AA sensors.

Understanding and exploring the decisive factors responsible for superlative catalytic efficiency is necessary to formulate active electrode materials for improved electrocatalysis and high-throughput sensing. This research demonstrates the ability of bud-shaped gold nanoflowers (AuNFs), intermediates in the bud-to-blossom gold nanoflower synthesis, to offer remarkable electrocatalytic efficiency in the oxidation of ascorbic acid (AA) at nanomolar concentrations. Multicomponent sensing in a single potential sweep is measured using differential pulse voltammetry while the kinetic parameters are estimated using electrochemical impedance spectroscopy. The outstanding catalytic activity of bud-structured AuNF [iAuNFp(Bud)/iGCp ≅ 100] compared with other bud-to-blossom intermediate nanostructures is explained by studying their structural transitions, charge distributions, crystalline patterns, and intrinsic irregularities/defects. Detailed microscopic analysis shows that density of crystal defects, such as edges, terraces, steps, ledges, kinks, and dislocation, plays a major role in producing the high catalytic efficiency. An associated ab initio simulation provides necessary support for the projected role of different crystal facets as selective catalytic sites. Density functional theory corroborates the appearance of inter- and intra-molecular hydrogen bonding within AA molecules to control the resultant fingerprint peak potentials at variable concentrations. Bud-structured AuNF facilitates AA detection at nanomolar levels in a multicomponent pathological sample.

Decoupling of different plasmon resonance modes (in-plane, and out-of-plane dipole and quadrupole resonances) by tuning nanoparticle’s size and shape offers a new field of plasmonics as colorimetric assay-based optical-ruler for ultra-trace sensing. Driven by its low cost, easy to perform and efficient way to measure trace level (up to 30 ppt in presence of common mining elements in natural gold ore) abundance, this study develops a highly selective and ultrasensitive turn-on colorimetric sensor to detect gold-ion from environmental samples. Different level of gold-ion tracer makes size variable spherical- and disc-shaped silver nanoparticles when added to a ‘growth solution’ which results decoupling of in-plane dipole resonance from in-plane quadrupole and out-of-plane dipole resonances with a wide range of in-plane dipole plasmon tunability to generate different colors. This color-coded sensing of gold-ion shows high selectivity and ultrasensitivity over other metal ions in the ppt level with an impurity aberration limit of 1 ppm. A plausible explanation explains the possible role of catalytic gold-ion to initiate unfavorable silver ion (Ag+) reduction by ascorbic acid to generate silver nanoparticles. Proposed technology has been applied in real mining sample (Bugunda Gold Deposit, Tajikistan) to detect gold concentration from ores to find potential application in mining technology.

The electrocatalytic performance of noble metal nanoparticles depends upon their size, shape, composition, and crystalline facets. Here we demonstrate the shape-dependent electrocatalytic activity of Au nanoparticles toward ascorbic acid oxidation in acidic medium, wherein the catalysis is strongly influenced by the shape of the nanoparticles. The synthesis of (popcorn, tetrapod, and bipod shaped) Au nanoparticles was carried out using a systematic variation of the surfactant concentrations based on the seed-mediated growth technique at room temperature. Due to the facile electrostatic interaction of the positively charged Au nanoparticles with glassy carbon electrode, the modification of the surface with variable-shaped Au nanoparticles is accomplished without involving any binding agents. Among variable-shaped face-centered cubic (fcc) crystalline AuNPs, bipod-shaped Au nanoparticles (GNBipd) exhibit a superior electrocatalytic performance over tetrapod-shaped (GNTepd) and popcorn-shaped (GNPop) nanoparticles as inferred from the differential pulse voltammetry and electrochemical impedance spectroscopy. The results have been explained by invoking the relative surface free energy (?) with preferentially exposed crystal planes, relative surface area (A), zeta potential (?), and the curvature-induced charge density (?q) at the apex for individual variable-shaped gold nanoparticles. � 2015 American Chemical Society.

A novel hydrogel has been synthesized using 2′,4′,6′-tri(4-pyridyl)pyridine in an acidic water medium. TEM analyses along with rheological experiments explore the supramolecular features of the hydrogel. In vitro and in vivo toxicity studies depict the non-toxic and bio-relevant nature of the pure supramolecular hydrogel and its aqueous solution. This bio-compatible supramolecular hydrogel is used for the synthesis of a DNA-hydrogel with calf thymus DNA. The DNA-hydrogel is intriguing for the effective stabilization of photochemically synthesized silver nanoparticles from Ag(I) under the direct exposure of sunrays. DNA-hydrogel capped Ag-NPs are also bio-compatible. The luminous features of the 2′,4′,6′-tri(4-pyridyl)pyridine based supramolecular hydrogel, DNA-hydrogel and DNA-hydrogel capped Ag-NPs and their aqueous solutions are explored through fluorescence microscopy and spectral analyses, respectively.

We report here, the first experimental realization on the selective excitation of two closely lying tips from the same spherical core of a multitipped gold nanoparticle with flower-like morphology. This gives strong multipeaked resonance in the near-infrared region of the far-field emission spectra showing a clear signature of tip to tip coupling. The cathodoluminescence (CL) technique in a scanning electron microscope (SEM) combined with finite-difference time-domain (FDTD) simulation has helped us to identify the coupled plasmon modes to be originated from the interaction between two closely spaced tips with a narrow angular separation. Our analysis further estimates a range of angular separation between the tips that triggers the onset of the intertip coupling.

A novel nano-templating method with a unique nanocrystal growth mechanism has been introduced for the single-pot production of variable-size (110–360 nm), intrinsically monodispersed, single-shaped, tunable plasmonic (580–1300 nm) gold nanomaterials showing a man-made replica of nature's bud-to-blossom steps associated with the gigantic SERS activity. In the first growth step, we synthesized 45 ± 3 nm gold nano-popcorns (GNPops) from 4.3 ± 1.4 nm spherical gold nano-seeds, and in the second growth step, we used GNPops as templates for controlled overgrowth and to produce bigger gold nano-flowers (GNFs) simply by controlling the viscosity of the surfactant. TEM-based electron tomography (ET) of highly structured GNFs provides their actual morphology with no Bragg diffraction artefacts. Due to their broad plasmon tunability throughout the Vis-NIR region and extraordinarily high Raman activity, these materials are suitable for applications in tunable Plasmon spectroscopy, high-throughput Raman sensing and efficient photothermal therapy in the biological window.

This paper describes the role of ascorbic acid in synthesizing bimetallic core–shell nanorings at room temperature. Using two-dimensional (2D) triangular silver nanoparticles as templates, we first synthesized 2D triangular gold (Au) nanorings via the galvanic replacement reaction and then overgrown Ag on Au nanorings via an epitaxial growth process. Transmission Electron Microscopy (TEM) and associated techniques were used for in-depth characterization. The TEM study revealed that single crystalline Ag nanoparticles led to the formation of continuous Au nanorings with single crystalline walls, and the void spaces which corroborate with the template shapes only when ascorbic acid was added to the growth solution. Both the silver nanoplates and gold nanorings have (111) planes as the basal planes. Subsequently we synthesized Au-core–Ag-shell nanorings using the previously synthesized Au nanorings as templates. Energy dispersive X-ray (EDX) line profile spectra and imaging, along with high-angle annular dark field scanning/transmission electron microscopy (STEM-HAADF), were used extensively for compositional studies in addition to energy filtered TEM (EFTEM) imaging.

Cancer is the greatest challenge in human healthcare today. Cancer causes 7.6 million deaths and economic losses of around 1 trillion dollars every year. Early diagnosis and effective treatment of cancer are crucial for saving lives. Driven by these needs, we report the development of a multifunctional plasmonic shell–magnetic core nanotechnology-driven approach for the targeted diagnosis, isolation, and photothermal destruction of cancer cells. Experimental data show that aptamer-conjugated plasmonic/magnetic nanoparticles can be used for targeted imaging and magnetic separation of a particular kind of cell from a mixture of different cancer cells. A targeted photothermal experiment using 670-nm light at 2.5 W/cm2 for 10 minutes resulted selective irreparable cellular damage to most of the cancer cells. We also showed that the aptamer-conjugated magnetic/plasmonic nanoparticle-based photothermal destruction of cancer cells is highly selective. We discuss the possible mechanism and operating principle for the targeted imaging, separation, and photothermal destruction using magnetic/plasmonic nanotechnology.

The detection of illegally transported explosives materials has become important for assuring safety at airports and air travel. Trinitrotoluene (TNT) is also one of the most commonly used nitroaromatic explosives for landmines of military and terrorist activities. As a result, there is an urgent need for rapid and reliable methods for the detection of trace amount of TNT for screening in airport, analyzing forensic samples, and environmental analysis. Driven by the need to detect trace amounts of TNT from environmental samples, this paper demonstrates a label-free ultrasensitive and highly selective two-photon scattering (TPS) assay using aminothiophenol-modified gold nanoparticle for TNT recognition in 120 picomolar (pM) level from environmental sample. Our experimental results show that TNT can be detected quickly and accurately in pM level with excellent discrimination against other nitro compounds from environmental sample. A detailed mechanism for significant TPS intensity change has been discussed.

Using solution-based method, silver quantum clusters of different sizes (Ag 20 , Ag 140 and Ag 980 ) have been synthesized and their first hyper-polarizabilities were measured using hyper-Rayleigh scattering technique. We have shown that nonlinear optical properties of silver quantum cluster are highly dependent on the size of quantum cluster. Time-dependent density functional theory calculations using the Amsterdam Density Functional (ADF) program package are used to evaluate linear and nonlinear optical properties of silver tetrahedral Ag n ( n = 10, 20, 35, 56) clusters. Both theoretical and experimental data have shown that nonlinear as well as linear optical properties are highly dependent on the size of silver quantum cluster.

Surface-enhanced Raman spectroscopy (SERS) has been shown as one of the most powerful analytical tool with high sensitivity. In this manuscript, we report the chemical design of SERS substrate, based on gold nanoparticles of different shapes-decorated with carbon nanotube with an enhancement factor of 7.5 × 10 10 . Shape dependent result shows that popcorn shape gold nanoparticle decorated SWCNT is the best choice for SERS substrate due to the existence of ‘lightning rod effect’ through several sharp edges or corners. Our results provide a good approach to develop highly sensitive SERS substrates and can help to improve the fundamental understanding of SERS phenomena.

We report the growth mechanisms for the formation of 40 nm star shape gold nanocrystals using real time TEM and in situ two-photon scattering technique. The overall process consists of several intermediate steps and these are: the nucleation process for the formation and accumulation of nanoseeds, Ostwald ripening process for the formation of nanoflower and intraparticle ripening process for the formation of the star sharp nanoparticles via nanocrowns. We demonstrates that the real time shape evolution of intermediate colloidal nanoparticles and their number density change can be fully accessed during the synthesis of star shaped gold nanoparticles using time dependent in situ TPS experiment.

Possible terrorist threats on water supplies are causes for concern given the easy availability of numerous biological and chemical toxins that could be used by a terrorist organization. In this article, we report gold-nanoparticle-based two-photon light-scattering (TPS) assay, for the label-free detection of arsenic and Salmonella bacteria separately, with excellent detection limit and selectivity over other analytes. Our experimental results show that arsenic can be detected quickly and accurately without any tagging, in 100-ppt level with excellent discrimination against other heavy metals. We have demonstrated that our TPS assay is capable of measuring the amount of arsenic in Bangladesh, West Bengal, and Nevada well water as well as in Mississippi river water. We have also shown that gold-nanoparticle-based TPS assay are capable for label-free detection of Salmonella typhimurium (S. typhimurium) with excellent detection limit (103 bacteria/mL) and high selectivity over other pathogens. The mechanism of TPS assay working principle has been discussed. Our results demonstrate the potential for a broad application of nanotechnology in practical defense applications.

Salmonella bacteria are the major cause for the infection of 16 million people worldwide with typhoid fever each year. Antibiotic-resistant Salmonella strains have been isolated from various food products. As a result, the development of ultrasensitive sensing technology for detection and new approaches for the treatment of infectious bacterial pathogens that do not rely on traditional therapeutic regimes is very urgent for public health, food safety, and the world economy. Driven by this need, we report herein a nanotechnology-driven approach that uses antibody-conjugated oval-shaped gold nanoparticles to selectively target and destroy pathogenic bacteria. Our experiments have shown the use of a simple colorimetric assay, with an anti-salmonella antibody conjugated to oval-shaped gold nanoparticles, for the label-free detection of S. typhimurium with an excellent detection limit (10(4) bacteria per mL) and high selectivity over other pathogens. When bacteria conjugated to oval-shaped gold nanoparticles were exposed to near-infrared radiation, a highly significant reduction in bacterial cell viability was observed due to photothermal lysis. Ideally, this nanotechnology-based assay would have enormous potential for rapid, on-site pathogen detection to avoid the distribution of contaminated foods.

Breast cancer is the most common cancer among women, and it is the second leading cause of cancer deaths in women today. The key to the effective and ultimately successful treatment of diseases such as cancer is early and accurate diagnosis. Driven by the need, in this article, we report for the first time a simple colorimetric and highly sensitive two-photon scattering assay for highly selective and sensitive detection of breast cancer SK-BR-3 cell lines at a 100 cells/mL level using a multifunctional (monoclonal anti-HER2/c-erb-2 antibody and S6 RNA aptamer-conjugated) oval-shaped gold-nanoparticle-based nanoconjugate. When multifunctional oval-shaped gold nanoparticles are mixed with the breast cancer SK-BR-3 cell line, a distinct color change occurs and two-photon scattering intensity increases by about 13 times. Experimental data with the HaCaT noncancerous cell line, as well as with MDA-MB-231 breast cancer cell line, clearly demonstrated that our assay was highly sensitive to SK-BR-3 and it was able to distinguish from other breast cancer cell lines that express low levels of HER2. The mechanism of selectivity and the assay's response change have been discussed. Our experimental results reported here open up a new possibility of rapid, easy, and reliable diagnosis of cancer cell lines by monitoring the colorimetric change and measuring TPS intensity from multifunctional gold nanosystems.

In this Letter, we report synthesis protocol for the creation of multi shaped nanocrystals based on a seeded-growth approach. We report real time monitoring of the shape evaluation during synthesis for understanding the growth mechanisms. Our results show that by varying the concentration of cetyltrimethylammonium bromide, one can control the shape of branched gold nanomaterials. Growth mechanisms on how the shape control works for gold anisotropic nanocrystals have been discussed.

Understanding and exploring the decisive factors responsible for superlative catalytic efficiency is necessary to formulate active electrode materials for improved electrocatalysis and high-throughput sensing. This research demonstrates the ability of bud-shaped gold nanoflowers (AuNFs), intermediates in the bud-to-blossom gold nanoflower synthesis, to offer remarkable electrocatalytic efficiency in the oxidation of ascorbic acid (AA) at nanomolar concentrations. Multicomponent sensing in a single potential sweep is measured using differential pulse voltammetry while the kinetic parameters are estimated using electrochemical impedance spectroscopy. The outstanding catalytic activity of bud-structured AuNF [iAuNFp(Bud)/iGCp ≅ 100] compared with other bud-to-blossom intermediate nanostructures is explained by studying their structural transitions, charge distributions, crystalline patterns, and intrinsic irregularities/defects. Detailed microscopic analysis shows that density of crystal defects, such as edges, terraces, steps, ledges, kinks, and dislocation, plays a major role in producing the high catalytic efficiency. An associated ab initio simulation provides necessary support for the projected role of different crystal facets as selective catalytic sites. Density functional theory corroborates the appearance of inter- and intra-molecular hydrogen bonding within AA molecules to control the resultant fingerprint peak potentials at variable concentrations. Bud-structured AuNF facilitates AA detection at nanomolar levels in a multicomponent pathological sample.

Size-controlled synthesis of metal nanostructures has opened many new possibilities to design ideal building blocks for future nanodevices. By solution-based method, silver triangular nanoprisms of different sizes (edge length) have been synthesized. First hyper-polarizabilities of silver triangular nanomaterials were measured using hyper-Rayleigh scattering technique. We have shown that both linear and nonlinear optical properties are highly dependent on the size of silver triangular nanoprism. We provide experimental evidence for higher multipolar contribution to NLO response of silver nanoprism.

Alzheimer’s disease (AD) is a progressive mental disorder disease, which affects 26.6 million people in worldwide and estimated increments can be 100 millions by 2050. Since there is no cure at present, early diagnosis of AD is crucial for the current drugs treatments. Driven by the need, here we demonstrate for the first time that monoclonal ani-tau antibody coated gold nanoparticle based two-photon scattering assay can be used for the detection of Alzheimer’s tau protein in 1 pg/mL level which is about two orders of magnitude lower than cut-off values (195 pg/mL) for tau protein in CSF (cerebrospinal fluid). We have shown that when ani-tau antibody coated gold nanoparticle were mixed with 20 ng/ml of tau protein, two-photon Rayleigh scattering intensity (TPRS) increases by about 16 times. The mechanism of TPRS intensity change has been discussed. Our data demonstrated that our TPRS assay is highly sensitive to Tau protein and it can distinguish from BSA, which is one of the most abundant protein components in CSF. Our results demonstrate the potential for a broad application of this type of nano-bionanotechnology in practical biomedical applications.

We report the photodissociation dynamics of ortho-iodobenzyl chloride $(o-C_6H_4I(CH_2Cl))$ in the ultraviolet. The gas phase dissociation dynamics of o-iodobenzyl chloride at 222, 236, 266, 280, and $\sim304 nm$ was monitored by probing the quantum yields of $I^* \hspace {2mm} (^2P_{1/2})$ as well as $Cl^* \hspace {2mm}(^2P_{1/2})$ production using suitable resonance enhanced multiphoton ionization detection schemes. We find that only iodine atoms in the ground $(I (^2P_{3/2}))$ as well as excited $(I^*)$ states are produced in the dissociation. No $Cl (^2P_{3/2})$ or $Cl^*$ atoms were detected. This accidental bond selective dissociation in o-iodobenzyl chloride is perhaps due to weak coupling among various chromophores present in the molecule and inefficient interchromophore energy transfer among them.

Dynamics of $Cl^*(^2P_{1/2})$ production from chloroiodomethane dissociation has been investigated in the near ultraviolet $(222\leq\lambda_ex\leq304 nm)$. The quantum yield of $Cl^*(^2P_{1/2)}$ production, $\phi^*(Cl),$ has been measured by monitoring nascent $Cl(^2P_{3/2})$ and $Cl^*$ concentrations and compared with the quantum yield of $I^*(^2P_{1/2})$ production at the same excitation wavelengths. In the near ultraviolet where most of the transition strength is carried by the $\sigma^*(C–I)\leftarrown(I)$ transition, the measured $Cl^*$ quantum yield decreases as a function of increasing photolysis wavelength. An interchromophore energy transfer mechanism between the C–I and C–Cl chromophores has been proposed to rationalize $Cl^*$ production since the direct excitation of the $\sigma^*(C–Cl)\leftarrown(Cl)$ transition is less likely at wavelengths $\sim$100 nm away from the peak of the C–Cl absorption band.