Showing papers by "Thalappil Pradeep published in 2014"
TL;DR: Sub-nanometer-sized metal clusters, having dimensions between metal atoms and nanoparticles, have attracted tremendous attention in the recent past due to their unique physical and chemical properties. as discussed by the authors provides an account of the recent advances in their applications in areas such as environment, energy, and biology.
Abstract: Sub-nanometer-sized metal clusters, having dimensions between metal atoms and nanoparticles, have attracted tremendous attention in the recent past due to their unique physical and chemical properties. As properties of such materials depend strongly on size, development of synthetic routes that allows precise tuning of the cluster cores with high monodispersity and purity is an area of intense research. Such materials are also interesting owing to their wide variety of applications. Novel sensing strategies based on these materials are emerging. Owing to their extremely small size, low toxicity, and biocompatibility, they are widely studied for biomedical applications. Primary focus of this review is to provide an account of the recent advances in their applications in areas such as environment, energy, and biology. With further experimental and theoretical advances aimed at understanding their novel properties and solving challenges in their synthesis, an almost unlimited field of applications can be foreseen.
282 citations
TL;DR: Ambient ionization is achieved by spraying from a carbon nanotube (CNT)-impregnated paper surface under the influence of small voltages (≥3 V), and organic molecules give simple high-quality mass spectra without fragmentation in the positive or negative ion modes.
Abstract: Ambient ionization is achieved by spraying from a carbon nanotube (CNT)-impregnated paper surface under the influence of small voltages (≥3 V). Organic molecules give simple high-quality mass spectra without fragmentation in the positive or negative ion modes. Conventional field ionization is ruled out, and it appears that field emission of microdroplets occurs. Microscopic examination of the CNT paper confirms that the nanoscale features at the paper surface are responsible for the high electric fields. Raman spectra imply substantial current flows in the nanotubes. The performance of this analytical method was demonstrated for a range of volatile and nonvolatile compounds and a variety of matrices.
95 citations
TL;DR: Apart from the inherent biocompatibility of the CD-protected Au clusters, additional capabilities acquired by the supramolecular functionalization make such modified clusters preferred materials for applications, including those in biology.
Abstract: We present a versatile approach for tuning the surface functionality of an atomically precise 25 atom gold cluster using specific host–guest interactions between β-cyclodextrin (CD) and the ligand anchored on the cluster. The supramolecular interaction between the Au25 cluster protected by 4-(t-butyl)benzyl mercaptan, labeled Au25SBB18, and CD yielding Au25SBB18∩CDn (n = 1, 2, 3, and 4) has been probed experimentally using various spectroscopic techniques and was further analyzed by density functional theory calculations and molecular modeling. The viability of our method in modifying the properties of differently functionalized Au25 clusters is demonstrated. Besides modifying their optoelectronic properties, the CD moieties present on the cluster surface provide enhanced stability and optical responses which are crucial in view of the potential applications of these systems. Here, the CD molecules act as an umbrella which protects the fragile cluster core from the direct interaction with many destabilizi...
89 citations
TL;DR: This work presents the first separation of metal clusters by thin-layer chromatography (TLC), which is simple yet surprisingly efficient and enabled the challenging separation of a multicomponent mixture of mixed-monolayer-protected Au25 clusters with closely similar chemical ligand compositions.
Abstract: There is an urgent need for accessible purification and separation strategies of atomically precise metal clusters in order to promote the study of their fundamental properties. Although the separation of mixtures of atomically precise gold clusters Au25L18, where L are thiolates, has been demonstrated by advanced separation techniques, we present here the first separation of metal clusters by thin-layer chromatography (TLC), which is simple yet surprisingly efficient. This method was successfully applied to a binary mixture of Au25L18 with different ligands, as well as to a binary mixture of different cluster cores, Au25 and Au144, protected with the same ligand. Importantly, TLC even enabled the challenging separation of a multicomponent mixture of mixed-monolayer-protected Au25 clusters with closely similar chemical ligand compositions. We anticipate that the realization of such simple yet efficient separation technique will progress the detailed investigation of cluster properties.
66 citations
TL;DR: Electrolytic spray deposition was used to pattern surfaces with 2D metallic nanostructures that contain silver nanoparticles (AgNP) and their aggregates can be used for surface-enhanced Raman spectroscopy (SERS).
Abstract: Electrolytic spray deposition was used to pattern surfaces with 2D metallic nanostructures. Spots that contain silver nanoparticles (AgNP) were created by landing solvated silver ions at desired locations using electrically floated masks to focus the metal ions to an area as little as 20 mm in diameter. The AgNPs formed are unprotected and their aggregates can be used for surface-enhanced Raman spectroscopy (SERS). The morphology and SERS activity of the NP structures were controlled by the surface coverage of landed silver ions. The NP structures created could be used as substrates onto which SERS samples were deposited or prepared directly on top of predeposited samples of interest. The evenly distributed hot spots in the micron-sized aggregates had an average SERS enhancement factor of 10 8 . The surfaces showed SERS activity when using lasers of different wavelengths (532, 633, and 785 nm) and were stable in air. Metallic nanoparticles have attractive properties in catal- ysis, photonics, and chemical sensing. (1) Raman spectroscopy is a powerful nondestructive technique, (2) the sensitivity of which can be significantly improved through surface- enhanced or tip-enhanced methods. (3) The enhancement arises from the proximity of the analytes to intense localized fields created by nanoscale objects. (4) The capability to modify, coat, and pattern surfaces with nanostructures is important for SERS and also for a wider range of nanomaterials applications. (5) Conventionally, modified surfaces are con-
58 citations
TL;DR: In this paper, a red-luminescent silver cluster with the molecular formula, Ag11(SG)7 (SG: glutathionate) via reduction of silver ions by sodium borohydride in the presence of the tripeptide, glutathione (GSH).
Abstract: We report a one-step and high yield synthesis of a red-luminescent silver cluster with the molecular formula, Ag11(SG)7 (SG: glutathionate) via reduction of silver ions by sodium borohydride in the presence of the tripeptide, glutathione (GSH). The as-prepared cluster shows prominent absorption features at 485 and 625 nm in its UV–vis absorption spectrum. Aging of the as-prepared cluster solution led to the disappearance of the 625 nm peak, followed by broadening of the 485 nm peak to give three maxima at ∼487, 437, and 393 nm in its absorption spectrum. These peaks remain unchanged even after polyacrylamide gel electrophoresis (PAGE), where a single band was observed confirming high purity of the cluster formed. Electrospray ionization mass spectrometry (ESI MS) reveal the composition of the cluster to be Ag11(SG)7 with multiple sodium attachments to the ligand to give −3 and −2 charged species. These compositions match well with their calculated isotope patterns. Extensive MS/MS was performed to underst...
54 citations
TL;DR: The systematic appearance of a plasmon-like optical absorption feature in silver clusters protected with 2-phenylethanethiol, 4-flurothiophenol and BBS suggests that the 'emergence of metallicity' is independent of the functionality of the thiol ligand.
Abstract: We report the systematic appearance of a plasmon-like optical absorption feature in silver clusters protected with 2-phenylethanethiol (PET), 4-flurothiophenol (4-FTP) and (4-(t-butyl)benzenethiol (BBS) as a function of cluster size. A wide range of clusters, namely, Ag44(4-FTP)30, Ag55(PET)31, ∼Ag75(PET)40, ∼Ag114(PET)46, Ag152(PET)60, ∼Ag202(BBS)70, ∼Ag423(PET)105, and ∼Ag530(PET)100 were prepared. The UV/Vis spectra show multiple features up to ∼Ag114; and thereafter, from Ag152 onwards, the plasmonic feature corresponding to a single peak at ∼460 nm evolves, which points to the emergence of metallicity in clusters composed of ∼150 metal atoms. A minor blue shift in the plasmonic peak was observed as cluster sizes increased and merged with the spectrum of plasmonic nanoparticles of 4.8 nm diameter protected with PET. Clusters with different ligands, such as 4-FTP and BBS, also show this behavior, which suggests that the ‘emergence of metallicity’ is independent of the functionality of the thiol ligand.
52 citations
TL;DR: A new methodology has been demonstrated for ultratrace detection of Hg(2+), working at the limit of a few tens of metal ions, and adaptation of such sensors to pH paper-like test-strips would make affordable water quality sensors at ultralow concentrations a reality.
Abstract: A new methodology has been demonstrated for ultratrace detection of Hg2+, working at the limit of a few tens of metal ions. Bright, red luminescent atomically precise gold clusters, Au@BSA (BSA, bovine serum albumin), coated on Nylon-6 nanofibers were used for these measurements. A green emitting fluorophore, FITC (fluorescein isothiocyanate), whose luminescence is insensitive to Hg2+ was precoated on the fiber. Exposure to mercury quenched the red emission completely, and the green emission of the fiber appeared which was observed under dark field fluorescence microscopy. For the sensing experiment at the limit of sensitivity, we have used individual nanofibers. Quenching due to Hg2+ ions was fast and uniform. Adaptation of such sensors to pH paper-like test-strips would make affordable water quality sensors at ultralow concentrations a reality.
36 citations
TL;DR: The density functional-based tight binding calculations show additional dependence of chirality and diameter of nanotubes on the epoxide binding energies, which is in agreement with the Raman spectroscopic results and suggests a possible mechanism of unzipping determined by combined effects of the structural characteristics of SWNTs and applied field.
Abstract: We report an in situ Raman spectroscopic and microscopic investigation of the electro- chemicalunzippingofsingle-walledcarbonnanotubes(SWNTs).Observationsoftheradialbreathingmodes (RBMs) using Raman spectral mapping reveal that metallic SWNTs are opened up rapidly followed by gradual unzipping of semiconducting SWNTs. Consideration of the resonant Raman scattering theory suggests that two metallic SWNTs with chiralities (10, 4) and (12, 0) get unzipped first at a lower electrode potential (0.36 V) followed by the gradual unzipping of another two metallic tubes, (9, 3) and (10, 1), at a relativelyhigher potential (1.16V). The semiconducting SWNTs withchiralities (11, 7) and (12, 5),however, get open up gradually at (1.66 V. A rapid decrease followed by a subsequent gradual decrease in the metallicityoftheSWNTensembleasrevealedfromaremarkablevariationofthepeakwidthoftheGbandcomplieswellwiththevariationsofRBM.Cyclic voltammetry also gives direct evidence for unzipping in terms of improved capacitance after oxidation followed by more important removal of oxygen functionalitiesduringthereductionstep,asreflectedinsubtlechangesofthemorphologyconfirmingtheformationofgraphenenanoribbons.Thedensity functional-basedtightbindingcalculationsshowadditionaldependenceofchiralityanddiameterofnanotubesontheepoxidebindingenergies,whichisin agreement with the Raman spectroscopic results and suggests a possible mechanism of unzipping determined by combined effects of the structural characteristics of SWNTs and applied field.
36 citations
TL;DR: A simple one-pot procedure is demonstrated to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities, resulting in clusters carrying one to eight calixarene moieties.
Abstract: Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]arenes to the Au25 cluster surface with two or four thiolates per moiety.
33 citations
TL;DR: In this paper, the acid-base protolysis and surface complexation constants for fluoride and thermally activated nanogibbsite were investigated for the first time, and it was shown that an immense increase in surface area was obtained from 50 to 399 m2/g by the heat activation.
TL;DR: The synthesis and characterization of novel iron clusters in the hemoglobin matrix that are highly luminescent (quantum yield 10% at 565 nm) are reported.
Abstract: Metal clusters, composed of a few atoms at the core, exhibit unique properties and have potential applications. Although atomically precise clusters of noble metals have been synthesized, analogous systems of reactive metals, such as iron, have not been realized in solution due to high reactivity. Here we report the synthesis and characterization of novel iron clusters in the hemoglobin matrix that are highly luminescent (quantum yield 10% at 565 nm). The super-paramagnetic iron clusters, after successful ligand exchange from protein and phase transfer from water to chloroform using tri-octylphosphineoxide (TOPO), were detected as [Fe₁₀(TOPO)₃(H₂O)₃](+), [Fe₁₃(TOPO)₂(H₂O)](+) and [Fe₈(TOPO)(H₂O)₂](+) by mass spectrometry. This study lays the groundwork for exploiting unique properties of soluble iron clusters.
TL;DR: A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized and is highly stable and compatible with many organic solvents.
Abstract: A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents.
TL;DR: In this paper, a tunable metallophilic interaction between monolayer-protected quantum clusters and a closed-shell metal ion was reported, and it was shown that the tunability of luminescence quenching is achieved by the systematic variation of the metheophilic interactions between the AuI ions of the alloy cluster and CuI ions formed by the reduction of CuII ions by the cluster core.
Abstract: Luminescent AgAu alloy quantum clusters are synthesized by a simple method that utilizes the galvanic reduction of polydisperse plasmonic silver nanoparticles. The clusters are characterized by ultraviolet–visible (UV/Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). Selective and tunable quenching of cluster luminescence by CuII ions is observed and depends highly on the solvent as well as the protecting ligands. Metal-ion selectivity is exclusively caused by metallophilic interactions with the cluster core, and the tunability depends on the nature of the protecting ligands as well as solvent effects. Detailed XPS and time-resolved luminescence measurements reveal that the tunability of luminescence quenching is achieved by the systematic variation of the metallophilic interactions between the AuI ions of the alloy cluster and CuI ions formed by the reduction of CuII ions by the cluster core. This is the first report of tunable metallophilic interactions between monolayer-protected quantum clusters and a closed-shell metal ion. We hope that these results will draw more attention to the field of quantum cluster–metal ion interactions and provide useful insights into the stability of these clusters, origin of their intense luminescence, mechanisms of metal-ion sensing, and also help in the development of methods for tuning their properties.
TL;DR: In this article, the reaction of two different nanosystems of silver, namely nanoparticles and atomically precise clusters, toward 1D tellurium nanowires (NWs) was probed and compared with reaction of silver ions.
Abstract: Reactivity of two different nanosystems of silver, namely nanoparticles and atomically precise clusters, toward 1D tellurium nanowires (NWs) was probed and compared with the reaction of silver ions. While the reaction of nanoparticles and ions led to silver telluride nanowires, a different reactivity was exhibited by clusters which resulted in silver islands at different positions on the Te NWs. These hybrid Ag nodule-decorated Te NWs are sensitive to temperature, and they transform to dumbbell-shaped silver-tipped Te NWs upon solution phase annealing. Differences in chemical reactivity of nanoparticles of two different size regimes with nanowires are demonstrated. Synthetic methods of this kind will be useful in creating complex nanostructures which are difficult to be made in the solution phase.
TL;DR: A selenolate-protected Ag-Pd alloy cluster was synthesized using a one-pot solution-phase route and is found to be highly stable, with a molecular peak centered at m/z 2839 having an exact match with the corresponding calculated spectrum.
Abstract: A selenolate-protected Ag-Pd alloy cluster was synthesized using a one-pot solution-phase route. The crude product upon chromatographic analyses under optimized conditions gave three distinct clusters with unique optical features. One of these exhibits a molecular peak centered at m/z 2839, in its negative ion mass spectrum assigned to Ag5Pd4(SePh)12(-), having an exact match with the corresponding calculated spectrum. Tandem mass spectrometry of the molecular ion peak up to MS(9) was performed. Complex isotope distributions in each of the mass peaks confirmed the alloy composition. We find the Ag3Pd3(-) core to be highly stable. The composition was further supported by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy.
TL;DR: A stable, Ag55 cluster protected with 4-(tert-butyl)benzyl mercaptan (BBSH) was synthesized which exhibits two prominent absorption bands with maxima at 2.25 and 2.81 eV which proves the amenability of this cluster and the synthetic methodology to other ligands.
Abstract: A stable, Ag55 cluster protected with 4-(tert-butyl)benzyl mercaptan (BBSH) was synthesized which exhibits two prominent absorption bands with maxima at 2.25 and 2.81 eV. A molecular ion peak at m/z 11 500 ± 20 in matrix assisted laser desorption ionization mass spectrum (MALDI MS), assigned to Ag55(BBS)31 was observed. Electrospray ionization (ESI MS) shows a prominent trication along with higher charged species. An analogous Ag55(PET)31 (PET = 2-phenylethanethiol, in the thiolate form) was also synthesized under optimized conditions which proves the amenability of this cluster and the synthetic methodology to other ligands.
TL;DR: The cover image shows a schematic phase diagram of the three-component solvent system used for preparing monolayer-protected silver clusters as mentioned in this paper, where different clusters obtained by keeping the reactants the same but adjusting the solvent system by moving to different regions of the phase diagram are shown in different colors.
Abstract: Invited for the cover of this issue is Thalappil Pradeep at the Indian Institute of Technology Madras, India. The cover image shows a schematic phase diagram of the three-component solvent system used for preparing monolayer-protected silver clusters. The different clusters obtained by keeping the reactants the same but adjusting the solvent system by moving to different regions of the phase diagram are shown in different colors.
TL;DR: A highly optimized low energy ion optical system designed for such studies coupled with reflection absorption infrared and temperature programmed desorption spectroscopies and its initial characterization is combined.
Abstract: Extremely surface specific information, limited to the first atomic layer of molecular surfaces, is essential to understand the chemistry and physics in upper atmospheric and interstellar environments. Ultra low energy ion scattering in the 1–10 eV window with mass selected ions can reveal extremely surface specific information which when coupled with reflection absorption infrared (RAIR) and temperature programmed desorption (TPD) spectroscopies, diverse chemical and physical properties of molecular species at surfaces could be derived. These experiments have to be performed at cryogenic temperatures and at ultra high vacuum conditions without the possibility of collisions of neutrals and background deposition in view of the poor ion intensities and consequent need for longer exposure times. Here we combine a highly optimized low energy ion optical system designed for such studies coupled with RAIR and TPD and its initial characterization. Despite the ultralow collision energies and long ion path lengths...
TL;DR: In this paper, the formation of 35 ± 1 kDa cluster from the parent Au25 is governed by the trapping of smaller clusters in a deep potential well generated at the graphene surface.
Abstract: The interaction of ultrasmall metal clusters with surfaces of graphene is important for developing promising future applications of graphenic materials. In the experiment, chemically synthesized reduced graphene oxide (RGO) in water was mixed with Au25SR18 (where SR, SCH2CH2Ph, is a ligand protecting the cluster core) in tetrahydrofuran, and a completely new cluster, larger in mass, was formed at the liquid–liquid interface. Matrix assisted laser desorption ionization mass spectrometry of the product attached to RGO show that the peak due to Au25SR18 disappears gradually upon reaction and a single sharp peak referred to here as “135 ± 1 kDa cluster” appears. The composition of the new cluster is very close to the well-known magic cluster, Au144SR60 while the peak maximum is at Au135SR57. The formation of 35 ± 1 kDa cluster from the parent Au25 is proposed to be governed by the trapping of smaller clusters in a deep potential well generated at the graphene surface. We theoretically model the active role of...
TL;DR: From several characterization studies such as mass spectrometry, Raman spectroscopy, etc., it has been confirmed that the degraded and as-synthesized selenolates are the same in nature, which leads to the reversible process.
Abstract: The cluster Ag44SePh30, originally prepared from silver selenolate, upon oxidative decomposition by H2O2 gives the same cluster back, in an apparently reversible synthesis. Such an unusual phenomenon was not seen for the corresponding thiolate analogues. From several characterization studies such as mass spectrometry, Raman spectroscopy, etc., it has been confirmed that the degraded and as-synthesized selenolates are the same in nature, which leads to the reversible process. The possibility of making clusters from the degraded material makes cluster synthesis economical. This observation makes one to consider cluster synthesis to be a reversible chemical process, at least for selenolates.
TL;DR: In-situ production and detection of intermediates at graphenic surfaces, especially during alcohol oxidation, are reported, opening up a new pathway for different industrially and energetically important reactions using different metal catalysts and modified substrate.
Patent•
22 Dec 2014TL;DR: In this article, a mass spectrometry probe including a substrate in which a portion of the substrate is coated with a material is protruded from the substrate, a part of which protrudes from a substrate protrusion protrusion.
Abstract: The invention generally relates to mass spectrometry probes and systems for ionizing a sample In certain embodiments, the invention provides a mass spectrometry probe including a substrate in which a portion of the substrate is coated with a material, a portion of which protrudes from the substrate
TL;DR: VUV spectra recorded at higher temperature reveal conformational changes in the ice and phase transitions whilst evidence for dimer production is also presented.
Abstract: Following the recent identification of ethanethiol in the interstellar medium (ISM) we have carried out Vacuum UltraViolet (VUV) spectroscopy studies of ethanethiol (CH3CH2SH) from 10 K until sublimation in an ultrahigh vacuum chamber simulating astrochemical conditions. These results are compared with those of methanethiol (CH3SH), the lower order thiol also reported to be present in the ISM. VUV spectra recorded at higher temperature reveal conformational changes in the ice and phase transitions whilst evidence for dimer production is also presented.
TL;DR: A multiple scattering based physical model is proposed to explain this counterintuitive temperature rise inside tissue and the results show promising future for better understanding and standardizing the protocols for photothermal therapy.
Abstract: Photothermal therapy using (Near Infrared) NIR region of EM spectrum is a fast emerging technology for cancer therapy. Different types of nanoparticles may be used for enhancing the treatment. Though the treatment protocols are developed based on experience driven estimated temperature increase in the tissue, it is not really known what spatiotemporal thermal behavior in the tissue is. In this work, this thermal behavior of tissue models is investigated with and without using nanoparticles. An increased temperature inside tissue compared to surface is observed which is counter intuitive from the present state of knowledge. It is shown from fiber level microstructure that this increased temperature leads to enhanced damage at the deeper parts of biomaterials. Nanoparticles can be utilized to control this temperature increase spatially. A multiple scattering based physical model is proposed to explain this counterintuitive temperature rise inside tissue. The results show promising future for better understanding and standardizing the protocols for photothermal therapy.
14 Aug 2014
TL;DR: In this paper, the structural, photo-physical aspects and applications of this new system are discussed in detail, and several fundamental questions are yet to be answered in this emerging discipline, but we believe that the field will continue to evolve in terms of understanding and will be widely applied in several areas of sensing, catalysis, biology and medicine.
Abstract: Noble metal quantum clusters (NMQCs) are considered to be the bridge between atoms and nanoparticles. They have dimensions comparable to the Fermi wavelength of electrons and have discrete energy levels due to quantum confinement which makes many of them luminescent in the visible region. NMQCs have been synthesized in the solution phase with various ligands, ranging from phosphines over four decades ago, to proteins, in the recent past. Brightly luminescent NMQCs embedded in proteins (NMQCs@proteins) make functional and smart hybrid materials, since proteins are functional soft biological nanomachines. The transdisciplinary and expansive nature of atomic cluster science is once again evident in this new entrant to the cluster family. In this chapter, structural, photo-physical aspects and applications of this new system are discussed in detail. Protein–metal ion adducts act as templates from which atomically precise gas phase clusters have been formed. Looking critically, several fundamental questions are yet to be answered in this emerging discipline, but we believe that the field will continue to evolve in terms of understanding and will be widely applied in several areas of sensing, catalysis, biology and medicine.
TL;DR: In this paper, it was shown that plasmonic chirality in single gold nanorod (GNR) aggregates leads to the rotation of polarization of the scattered light.
Abstract: We show that plasmonic chirality in single gold nanorod (GNR) aggregates leads to the rotation of polarization of the scattered light. 3D glasses in conjunction with linearly polarized dark field scattering microspectroscopy were used to study the chirality of single GNR aggregates. Using this hetero-polarizer setup, we not only detect but also quantify their chirality. A polar mapping strategy was used for providing direct evidence for the emergence of light of different polarization angles when chiral GNR aggregates were excited with circularly polarized light of different handedness. Further, we have developed a methodology to eliminate fluctuations in the scattering intensity by averaging and normalizing the data. This allows calculation of plasmonic circular dichroism scattering spectra with high accuracy.
Patent•
22 Dec 2014TL;DR: In this paper, the authors describe a mass spectrometry probe including a substrate in which a portion of the substrate is coated with a material, a portion protruded from the substrate.
Abstract: The invention generally relates to mass spectrometry probes and systems for ionizing a sample. In certain embodiments, the invention provides a mass spectrometry probe including a substrate in which a portion of the substrate is coated with a material, a portion of which protrudes from the substrate.
01 Jan 2014
TL;DR: It is an established fact that groundwater sources in many parts of the world are heavily contaminated with pesticide residues, but the concentrations are low in comparison to those of other commonly encountered chemicals and the purification technologies have to be efficient for them to be removed at affordable cost.
Abstract: Intensive farming, rapid industrialization, and increasingly sophisticated lifestyles have added artificial chemicals into many water bodies. While pesticide residues in groundwater was unexpected years ago as soil was thought to act as a filter, it is an established fact that groundwater sources in many parts of the world are heavily contaminated with them. Although these levels are significant vis-a-vis the permissible limits, the concentrations are low in comparison to those of other commonly encountered chemicals and the purification technologies have to be efficient for them to be removed at affordable cost. For such a solution to be useful for all strata of the society, it needs to be economically attractive, requiring zero electricity and minimum maintenance. Any novel technology should solve the problem in its entirety and not result in toxic by-products or residuals. These requirements pose numerous challenges to chemistry and engineering, some of which are discussed here.
24 Sep 2014