How low can you go? The visual detection of 2,4,6-trinitrotoluene and Hg2+ at the sub-zeptomole level is demonstrated. This was achieved using a hybrid material that allowed for the development of a single-particle, single-molecule detection technique, which may be the ultimate in ultra-trace sensitivity with selectivity. Copyright © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Pradeep Thalappil

Department Of Chemistry

Ammu Mathew

Panikkanvalappil Ravindranathan Sajanlal

2 ,4 ,6-TRINITROTOLUENE

MESOFLOWERS

QUANTUM CLUSTERS

SINGLE-MOLECULE DETECTION

Single-particle

ULTRATRACES

VISUAL DETECTION

Hybrid materials

Nanoparticles

Sensors

Explosives detection

Gold

silicon dioxide

Silver

TRINITROTOLUENE

article

chemistry

Fluorescence

Fluorescence microscopy

Microscopy, Fluorescence

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Angewandte Chemie - International Edition

A new synthetic protocol is introduced which preserves the secondary structure of protecting proteins encapsulating a luminescent atomically-precise silver cluster. This was achieved by using a preformed triphenylphosphine (TPP)-protected silver cluster as the precursor forming bovine serum albumin (BSA)- and human serum albumin (HSA)-protected Ag18 clusters. This is the first example of the formation of luminescent protein-protected clusters in a neutral medium, without using any reducing agent, which results in minimal alteration of the protein structure during cluster growth. The cluster formed showed exceptional stability, unlike other silver clusters of this class. The formation of these red luminescent clusters was visualized by UV-vis and photoluminescence spectroscopy. The identification of Ag18 core was made through matrix-assisted laser desorption ionization mass spectrometry (MALDI MS), and a plausible mechanism of the formation was identified by monitoring the systematic growth of the cluster core by time-dependent MALDI MS experiments and electrospray ionization mass spectrometry (ESI MS) of the reaction mixture. The cluster was successfully employed as a luminescent probe for cancer cell imaging. Retention of protein conformation in the clusters was confirmed through circular dichroism (CD) spectroscopy, and the same was reflected in the retention of 89% of the esterase activity of BSA in the Ag18@BSA clusters synthesized by this method, compared to only 28.7% for AgQC@BSA clusters synthesized using previous protocols, conducted in basic medium. © 2019 American Chemical Society.

Journal of Physical Chemistry C

Internalization of a Preformed Atomically Precise Silver Cluster in Proteins by Multistep Events and Emergence of Luminescent Counterparts Retaining Bioactivity

We introduce a cluster coprotected by thiol and diphosphine ligands, [Ag22(dppe)4(2,5-DMBT)12Cl4]2+ (dppe = 1,2-bis(diphenylphosphino)ethane; 2,5-DMBT= 2,5-dimethylbenzenethiol), which has an Ag10 core encapsulated by an Ag12(dppe)4(2,5-DMBT)12Cl4 shell. The Ag10 core comprises two Ag5 distorted trigonal bipyramidal units and is uncommon in Au and Ag nanoclusters. The electrospray ionization mass spectrum reveals that the cluster is divalent and contains four free electrons. An uncommon crystallization-induced enhancement of emission is observed in the cluster. The emission is weak in the solution and amorphous states. However, it is enhanced 12 times in the crystalline state compared to the amorphous state. A detailed investigation of the crystal structure suggests that well-arranged C-H⋯πand π⋯πinteractions between the ligands are the major factors for this enhanced emission. Further, in-depth structural elucidation and density functional theory calculations suggest that the cluster is a superatom with four magic electrons. © 2019 American Chemical Society.

ACS Nano

Confining an Ag10 Core in an Ag12 Shell: A Four-Electron Superatom with Enhanced Photoluminescence upon Crystallization

Fulltext

Sustainable Nanoscale Engineering: From Materials Design to Chemical Processing

Challenges and directions for green chemical engineering-role of nanoscale materials

We probed the interaction between Au38@BSA and various heavy metal ions using luminescence spectroscopy. Interestingly, Au38@BSA showed luminescence enhancement upon interaction with Cd2+ and Pb2+ at concentrations higher than 1 ppm, due to the formation of cluster aggregates. Such aggregates were detected by dynamic light scattering (DLS) and high resolution electron microscopy (HRTEM) studies. Luminescence enhancement of Au38@BSA in the presence of Cd2+ was due to the interaction of Cd2+ with the cluster core, while Pb2+-induced luminescence enhancement was due to BSA-Pb2+ interaction. Observations were further supported by X-ray photoelectron spectroscopy (XPS) studies. This kind of phenomenon has been observed in protein protected clusters for the first time. We believe that such metal-ion-induced luminescence enhancement can be used to synthesize cluster systems with enhanced optical properties and different ion-cluster interactions can be used to develop metal ion sensors using Au38@BSA. © 2019 American Chemical Society.

Metal-Ion-Induced Luminescence Enhancement in Protein Protected Gold Clusters

We report the synthesis and unique reactivity of a new green dithiol protected cluster (DTPC), Ag51(BDT)19(TPP)3 (BDT and TPP are 1,3-benzenedithiol and triphenylphosphine, respectively). The cluster composition was confirmed by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric studies as well as by other supporting data. Surprisingly, the chemical reactivity between this DTPC and Au25(SR)18 involves only metal ion exchange in Au25(SR)18 without any ligand exchange, while reactions between monothiol protected clusters (MTPCs) show both metal and ligand exchange, an example being the reaction between Ag25DMBT18 and Au25PET18 (where DMBT and PET are 2,4-dimethylbenzenethiol and phenylethanethiol, respectively). The conclusions have been confirmed by the reaction of another DTPC, Ag29(BDT)12(TPP)4 with Au25BT18 (where BT corresponds to butanethiol) in which only metal exchange happens in Au25BT18. We also show the conversion of Ag51(BDT)19(TPP)3 to Ag29(BDT)12(TPP)4 in the presence of a second monothiol, DMBT which does not get integrated into the product cluster. This is completely different from the previous understanding wherein the reaction between MTPCs and a second thiol leads to either mixed thiol protected clusters with the same core composition or a completely new cluster core protected with the second thiol. The present study exposes a new avenue of research for monolayer protected clusters, which in turn will give additional impetus to explore the chemistry of DTPCs. © 2017 The Royal Society of Chemistry.

Nanoscale

Unusual reactivity of dithiol protected clusters in comparison to monothiol protected clusters: Studies using Ag51(BDT)19(TPP)3 and Ag29(BDT)12(TPP)4

An alloy cluster containing a 13-atom core, with a composition Ag 7Au 6(H 2MSA) 10 (H 2MSA= mercaptosuccinic acid) was synthesized from silver clusters by a galvanic exchange reaction. The clusters were characterized by several spectroscopic and microscopic methods. The alloy cluster shows luminescence with a quantum yield of 3.5 × 10 -2 at room temperature. Theoretical calculations for Ag 7Au 6(SCH 3) 10 suggest a distorted icosahedral core. Copyright © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Ag 7Au 6: A 13-atom alloy quantum cluster

Luminescent Ag15 clusters confined in bovine serum albumin (BSA) have been prepared by a simple wet chemical route. The luminescence, exhibiting a maximum at 685 nm, is observable to the naked eye. The chemical composition of these clusters was analyzed using matrix assisted laser desorption ionization mass spectrometry (MALDI MS), X-ray photoelectron spectroscopy (XPS), and energy dispersive analysis of X-rays (EDAX). Intact Ag15@BSA is observed by MALDI MS. Multiple charge states of the cluster are observed confirming the mass assignment. The clusters showed a quantum yield of 10.71% in water and the luminescence was stable in a pH range of 1-12. Stability of the clusters was enhanced by the addition of polyvinylpyrrolidone (PVP). The clusters showed luminescence in the solid state as well. Evolution of clusters with variation in the amount of reducing agent added shows that the cluster formation goes through an intermediate state of bound silver, formed instantaneously after the addition of Ag+, which transforms to the cluster. High yield synthesis and exciting photophysical properties make our new material interesting for various applications such as biolabeling and imaging. © 2011 The Royal Society of Chemistry.

Journal of Materials Chemistry

A fifteen atom silver cluster confined in bovine serum albumin

A strategy for the preparation of bimetallic mesoflowers (MFs) has been demonstrated by a simple overgrowth reaction. We make hybrid MFs containing Au core and shells of different metals, such as Ag and Pt, by tuning the experimental conditions so as to study region-specific overgrowth. This selective growth is attributed to the specific binding affinity of cetyltrimethylammonium bromide (CTAB) at different crystal planes of Au MF surfaces. We also studied the region-specific, composition dependent surface-enhanced Raman scattering (SERS) activity of single bimetallic MFs to understand, their chemical environment. Substrate effects on the SERS activity at single particle level were evaluated by a comparative study of the Raman images of Au, Au/Ag, and Au/Pt MFs. Region-specific SERS activity exhibited by single Au/Ag MF provides an insight into the SERS activity of bimetallic MFs over their monometallic analogues. © 2010 American Chemical Society.

Langmuir

Bimetallic mesoflowers: Region-specific overgrowth and substrate dependent surface-enhanced raman scattering at single particle level

A method for the synthesis of a new class of anisotropic mesostructured gold material, which we call "mesoflowers", is demonstrated. The mesoflowers, unsymmetrical at the single particle level, resemble several natural objects and are made up of a large number of stems with unusual pentagonal symmetry. The mesostructured material has a high degree of structural purity with star-shaped, nano-structured stems. The mesoflowers were obtained in high yield, without any contaminating structures and their size could be tuned from nano- to meso-dimensions. The dependence of various properties of the mesoflowers on their conditions of formation was studied. The near-infrared-infrared (NIR-IR) absorption exhibited by the mesoflowers has been used for the development of infrared filters. Using a prototypical device, we demonstrated the utility of the gold mesoflowers in reducing the temperature rise in an enclosure exposed to daylight in peak summer. These structures showed a high degree of surface-enhanced Raman scattering (SERS) activity compared to spherical analogues. SERS-based imaging of a single mesoflower is demonstrated. The high SERS activity and NIR-IR absorption property open up a number of exciting applications in diverse areas. © 2009 Tsinghua University Press and Springer-Verlag GmbH.

Nano Research

Mesoflowers: A new class of highly efficient surface-enhanced Raman active and infrared-absorbing materials

Journal of the American Chemical Society

Attogram Sensing of Trinitrotoluene with a Self-Assembled Molecular Gelator

Selective visual detection of TNT at the sub-zeptomole level

Journal	Angewandte Chemie - International Edition
ISSN	14337851
Open Access	No