@article { ISI:000238220900056, title = {Construction of conductive multilayer films of biogenic triangular gold nanoparticles and their application in chemical vapour sensing}, journal = {Nanotechnology}, volume = {17}, number = {9}, year = {2006}, month = {MAY}, pages = {2399-2405}, publisher = {IOP PUBLISHING LTD}, type = {Article}, address = {DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND}, abstract = {

Metal nanoparticles are interesting building blocks for realizing films for a number of applications that include bio- and chemical sensing. To date, spherical metal nanoparticles have been used to generate functional electrical coatings. In this paper we demonstrate the synthesis of electrically conductive coatings using biologically prepared gold nanotriangles as the building blocks. The gold nanotriangles are prepared by the reduction of aqueous chloroaurate ions using an extract of the lemongrass plant (Cymbopogon flexuosus) which are thereafter assembled onto a variety of substrates by simple solution casting. The conductivity of the film shows a drastic fall upon mild heat treatment, leading to the formation of electrically conductive thin films of nanoparticles. We have also investigated the possibility of using the gold nanotriangle films in vapour sensing. A large fall in film resistance is observed upon exposure to polar molecules such as methanol, while little change occurs upon exposure to weakly polar molecules such as chloroform.

}, issn = {0957-4484}, doi = {10.1088/0957-4484/17/9/055}, author = {Singh, Amit and Chaudhary, Minakshi V. and Sastry, Murali} } @article { ISI:000244909500021, title = {Spider silk as an active scaffold in the assembly of gold nanoparticles and application of the gold-silk bioconjugate in vapor sensing}, journal = {Small}, volume = {3}, number = {3}, year = {2007}, month = {MAR}, pages = {466-473}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {

Spider silk is being viewed with interest by materials scientists due to its excellent resilience and mechanical properties. In this paper we show that spider silk is an excellent scaffold for the one-step synthesis and assembly of gold nanoparticles. Formation of a gold nanoparticle-spider-silk bioconjugate material is accomplished by simple reaction of the fibers with aqueous chloroauric acid. The gold nanoparticles thus formed are strongly bound to the spider-silk fiber surface enabling study of the electrical properties of the nano bioconjugate. Using the well-known contraction/expansion behavior of the fibers in solvents of varying polarity, we show that exposure of the gold nanoparticle-spider silk bioconjugate to vapors of methanol and chloroform leads to changes in electrical transport through the nanoparticles and thus, the possibility of developing a vapor sensor. The bioconjugate shows excellent response time and cycling efficiency to methanol vapors. The activation energy of electron transport from one gold nanoparticle to another in the nanobiocojugate was determined from temperature-dependent electron-transport measurements to be approximately 1.7 eV.

}, keywords = {bioconjugates, Gold, Nanoparticles, sensors, spider silk}, issn = {1613-6810}, doi = {10.1002/smll.200600413}, author = {Singh, Amit and Hede, Shantesh and Sastry, Murali} } @article { ISI:000264897200052, title = {Shape and size selective separation of gold nanoclusters by competitive complexation with octadecylamine monolayers at the air-water interface}, journal = {Journal of Colloid and Interface Science}, volume = {333}, number = {1}, year = {2009}, month = {MAY}, pages = {380-388}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, address = {525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA}, abstract = {

The paper presents a time-dependent study of shape-dependent preferential complexation of gold nanoparticles to the octadecyl amine (ODA) monolayers at the air-water interface. Room temperature reduction of chloroaurate ions using lemon grass leaf extract yields a Mixture of spherical and triangular nanoparticles, which were used for this study. These nanoparticles have a net negative charge on their surface due to the presence of biomolecules from plant extract and thus a strong attractive electrostatic interaction with the positively charged ODA monolayers drives the complexation process. The extent of preferential complexation of the gold nanoparticles to the ODA monolayers is a function of the charge on the particles and the relative mobility of the nanoclusters in the medium. The complexation process has been followed in real time by a host of techniques such as surface pressure-area (pi-A) isotherms, UV-vis-NIR spectroscopy and Brewster angle microscopy. The charge and mobility of the gold nanoparticles was confirmed by measurement of their electrophoretic mobility. Langmuir-Blodgett films of the nanogold-ODA composites have been characterized by UV-vis-NIR spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. These measurements clearly indicate that the cluster mobility and complexation increase with decreasing cluster size. In the competitive complexation process of large and small gold particles, it was observed that some bigger gold particles were also incorporated into the amine matrix even though the cluster mobility is higher for smaller gold particles. (c) 2009 Elsevier Inc. All rights reserved.

}, keywords = {Competitive complexation, gold nanoparticles, Langmuir-Blodgett technique, ODA monolayer}, issn = {0021-9797}, doi = {10.1016/j.jcis.2008.12.076}, author = {Pasricha, Renu and Singh, Amit and Sastry, Murali} } @article { ISI:000303366000001, title = {Polymorphs, salts, and cocrystals: what{\textquoteright}s in a name?}, journal = {Crystal Growth \& Design}, volume = {12}, number = {5}, year = {2012}, month = {MAY}, pages = {2147-2152}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The December 2011 release of a draft United States Food and Drug Administration (FDA) guidance concerning regulatory classification of pharmaceutical cocrystals of active pharmaceutical ingredients (APIs) addressed two matters of topical interest to the crystal engineering and pharmaceutical science communities: (1) a proposed definition of cocrystals; (2) a proposed classification of pharmaceutical cocrystals as dissociable {\textquoteleft}{\textquoteleft}API-excipient{\textquoteright}{\textquoteright} molecular complexes. The Indo U.S. Bilateral Meeting sponsored by the Indo-U.S. Science and Technology Forum titled The Evolving Role of Solid State Chemistry in Pharmaceutical Science was held in Manesar near Delhi, India, from February 2-4, 2012. A session of the meeting was devoted to discussion of the FDA guidance draft. The debate generated strong consensus on the need to define cocrystals more broadly and to classify them like salts. It was also concluded that the diversity of API crystal forms makes it difficult to classify solid forms into three categories that are mutually exclusive. This perspective summarizes the discussion in the Indo-U.S. Bilateral Meeting and includes contributions from researchers who were not participants in the meeting.

}, issn = {1528-7483}, doi = {10.1021/cg3002948}, author = {Aitipamula, Srinivasulu and Banerjee, Rahul and Bansal, Arvind K. and Biradha, Kumar and Cheney, Miranda L. and Choudhury, Angshuman Roy and Desiraju, Gautam R. and Dikundwar, Amol G. and Dubey, Ritesh and Duggirala, Nagakiran and Ghogale, Preetam P. and Ghosh, Soumyajit and Goswami, Pramod Kumar and Goud, N. Rajesh and Jetti, Ram R. K. R. and Karpinski, Piotr and Kaushik, Poonam and Kumar, Dinesh and Kumar, Vineet and Moulton, Brian and Mukherjee, Arijit and Mukherjee, Gargi and Myerson, Allan S. and Puri, Vibha and Ramanan, Arunachalam and Rajamannar, T. and Reddy, C. Malla and Rodriguez-Hornedo, Nair and Rogers, Robin D. and Row, T. N. Guru and Sanphui, Palash and Shan, Ning and Shete, Ganesh and Singh, Amit and Sun, Changquan C. and Swift, Jennifer A. and Thaimattam, Ram and Thakur, Tejender S. and Thaper, Rajesh Kumar and Thomas, Sajesh P. and Tothadi, Srinu and Vangala, Venu R. and Variankaval, Narayan and Vishweshwar, Peddy and Weyna, David R. and Zaworotko, Michael J.} } @article { ISI:000306942300059, title = {Polymorphs, salts and cocrystals: what{\textquoteright}s in a name? (vol 12, pg 2147, 2012)}, journal = {Crystal Growth \& Design}, volume = {12}, number = {8}, year = {2012}, month = {AUG}, pages = {4290-4291}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, issn = {1528-7483}, doi = {10.1021/cg300704b}, author = {Aitipamula, Srinivasulu and Banerjee, Rahul and Bansal, Arvind K. and Biradha, Kumar and Cheney, Miranda L. and Choudhury, Angshuman Roy and Desiraju, Gautam R. and Dikundwar, Amol G. and Dubey, Ritesh and Duggirala, Nagakiran and Ghogale, Preetam P. and Ghosh, Soumyajit and Goswami, Pramod Kumar and Goud, N. Rajesh and Jetti, Ram R. K. R. and Karpinski, Piotr and Kaushik, Poonam and Kumar, Dinesh and Kumar, Vineet and Moulton, Brian and Mukherjee, Arijit and Mukherjee, Gargi and Myerson, Allan S. and Puri, Vibha and Ramanan, Arunachalam and Rajamannar, T. and Reddy, C. Malla and Rodriguez-Hornedo, Nair and Rogers, Robin D. and Row, T. N. Guru and Sanphui, Palash and Shan, Ning and Shete, Ganesh and Singh, Amit and Sun, Changquan C. and Swift, Jennifer A. and Thaimattam, Ram and Thakur, Tejender S. and Thaper, Rajesh Kumar and Thomas, Sajesh P. and Tothadi, Srinu and Vangala, Venu R. and Vishweshwar, Peddy and Weyna, David R. and Zaworotko, Michael J.} } @article { ISI:000304913100024, title = {Ultra-low level optical detection of mercuric ions using biogenic gold nanotriangles}, journal = {Analyst}, volume = {137}, number = {13}, year = {2012}, month = {APR}, pages = {3083-3090}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Mercury is a serious environmental pollutant known to have detrimental health effects in all life forms. Here, we report the use of biologically synthesized aqueous gold nanotriangles for sensitive and selective optical detection of femto-molar levels of mercury ions by exploiting the high amalgamation tendency of mercury metal towards gold. Aqueous chloroaurate ions were reduced using lemongrass (Cymbopogon flexuosus) leaf extract at room temperature to form gold nanotriangles. Mercuric (Hg2+) ions were reduced in the presence of these triangles to facilitate amalgamation and the optical properties were monitored. We observe a significant change in the longitudinal plasmon absorption band of the nanotriangles even at femto-molar concentrations of mercuric ions. High-resolution transmission electron microscopy confirms changes in particle morphology at such low concentrations. This protocol shows no sensitivity to other environmentally relevant metal ions, including Pb2+, Zn2+, Cd2+, Fe2+, Ni2+, Sr2+, Ca2+, Mn2+, and Cu2+, confirming further that change in the optical properties of gold nanotriangles in the presence of reduced mercuric ions is solely due to the strong amalgamation tendency of mercury metal.

}, issn = {0003-2654}, doi = {10.1039/c2an35162e}, author = {Singh, Amit and Pasrichax, Renu and Sastry, Murali} }