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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...

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...

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 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.

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.

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.

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.

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.

The relative quantum yields of $I*(^2P_{1/2})$ and $Cl*(^2P_{1/2})$ production, $\phi*(I)$ and $\phi*(Cl)$, respectively, have been measured at four different ultraviolet excitation wavelengths, e.g., 222, 236, 266, and 280 nm in the photodissociation of o-, m-, and p-chloroiodobenzenes. The measured I* and Cl* quantum yields are, with some exceptions, higher than those obtained, respectively, from iodobenzene and chlorobenzene, at the same wavelengths. While at most wavelengths the major fraction of the iodine atoms is produced in the excited state, the opposite is true for the chlorine atoms. Both direct and indirect dissociation pathways are involved in the production of I* atoms whereas Cl* is produced only by indirect pathways since direct excitation of the $\sigma$*$(C-Cl) \leftarrow n(Cl)$ transition is not possible at these wavelengths. The halogen atom in the ortho position is found to be most effective in enhancing the yield of the other spin-orbit excited halogen atom in the photolysis. While the nature of the initial transition, the extent of intersystem crossing in the excited states and the exit channel effects need to be considered in interpreting the quantum yield results, some factors seem to be more effective in influencing the final outcome. Induced dipole-induced dipole and quadrupolequadrupole interactions between the two halogen atoms (I and Cl in this case) seem to play an important role in the exit channel dynamics. These electrostatic interactions facilitate the intersystem transfer in the excited state and subsequent production of the spin-orbit excited halogen atoms.

A new class of ternary copper(II) complexes of formulation $[Cu(L^n)B](ClO_4)$ (1-4), where $HL^n$ is a NSO-donor Schiff base $(HL^1, HL^2)$ and B is a NN-donor heterocyclic base viz. 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmp), are prepared, structurally characterized, and their DNA binding and photocleavage activities studied in the presence of red light. Ternary complex $[Cu(L^3)(phen)](ClO_4)$ (5) containing an ONO-donor Schiff base and a binary complex $[Cu(L^2)_2]$ (6) are also prepared and structurally characterized for mechanistic investigations of the DNA cleavage reactions. While 1-4 have a square pyramidal (4 + 1) $CuN_3OS$ coordination geometry with the Schiff base bonded at the equatorial sites, 5 has a square pyramidal (4 + 1) geometry with $CuN_3O_2$ coordination with the alcoholic oxygen at the axial site, and 6 has a square planar trans-$CuN_2O_2$ geometry. Binding of the complexes 1-4 to calf thymus DNA shows the relative order: phen >> dmp. Mechanistic investigations using distamycin reveal minor groove binding for the complexes. The phen complexes containing the Schiff base with a thiomethyl or thiophenyl moiety show red light induced photocleavage. The dmp complexes are essentially photonuclease inactive. Complexes 5 and 6 are cleavage inactive under similar photolytic conditions. A $10 \mu M$ solution of 1 displays a 72% cleavage of SC DNA $(0.5 \mu g)$ on an exposure of 30 min using a 603 nm Nd:YAG pulsed laser (60 mJ/P) in Tris-HCl buffer (pH 7.2). Significant cleavage of 1 is also observed at 694 nm using a Ruby laser. Complex 1 is cleavage inactive under argon or nitrogen atmosphere. It shows a more enhanced cleavage in pure oxygen than in air. Enhancement of cleavage in $D_2O$ and inhibition with sodium azide addition indicate the possibility of the formation of singlet oxygen as a reactive intermediate leading to DNA cleavage. The d-d band excitation with red light shows significant enhancement of cleavage yield. The results indicate that the phen ligand is necessary for DNA binding of the complex. Both the sulfur-to-copper charge transfer band and copper d-d band excitations helped the DNA cleavage. While the absorption of a red photon induces a metal d-d transition, excitation at shorter visible wavelengths leads to the sulfur-to-copper charge transfer band excitation at the initial step of photocleavage. The excitation energy is subsequently transferred to ground state oxygen molecules to produce singlet oxygen that cleaves the DNA.

Dynamics of I*(P-2(1/2)) formation from CH2ICl dissociation has-been investigated at five different ultraviolet excitation wavelengths, e.g., 222, 236, 266, 280, and similar to304 nm. The quantum yield of I*((2)p(1/2)) production, phi*, has been measured by monitoring nascent I(P-2(3/2)) and I* concentrations using a resonance enhanced multiphoton ionization detection scheme. The measured quantum yield as a function of excitation energy follows the same trend as that of methyl iodide except at 236 run. The photodissociation dynamics of CH2ICl also involves three upper states similar to methyl iodide, and a qualitative correlation diagram has been constructed to account for the observed quantum yield. From the difference in behavior at 236 nm, it appears that the crossing region between the two excited states ((3)Q(0) and (1)Q(1)) is located near the exit valley away from the Franck Condon excitation region. The B- and C-band transitions do not participate in the dynamics, and the perturbation of the methyl iodide states due to Cl-I interaction is relatively weak at the photolysis wavelengths employed in this investigation.