Hrishikesh Joshi

Fluorescence Turn-on Chemosensor for the Detection of Dissolved CO2 Based on Ion-Induced Aggregation of Tetraphenylethylene Derivative

Herein, a sensitive fluorimetric assay for dissolved carbon dioxide (dCO2) was developed by using ion-induced self-assembly of a tetraphenylethylene derivative by taking advantage of its aggregation induced emission property. Chitosan, a commercially available polymer having amine functionality was utilized for the ion induced assay. In the presence of dCO2, the amine groups in the chitosan get protonated to convert neutral chitosan to a positively charged species, triggering negatively charged tetraphenylethene derivative (probe 1) to aggregate with it by electrostatic interaction. The aggregation causes intense blue fluorescence output from the system. The extent of the aggregation is reliant on the charge density of polymer, which is equivalent to dCO2 concentration. A linear relationship from 5 to 50 μM of dCO2, with a limit of detection of 5 × 10(-6) M (0.00127 hPa) was obtained. This is the first report for detecting dCO2 utilizing the AIE property.

An aggregation-induced emission based “turn-on” fluorescent chemodosimeter for the selective detection of Pb2+ ions

An aggregation-induced emission (AIE) based “turn-on” fluorescent chemodosimeter for the selective detection of ascorbate ions has been developed, making use of the azide–alkyne “click” reaction between two tetraphenylethene (TPE) derivatives (propergyl–TPE and TPE–azide). The present method offers a rapid, economic and effective way to detect ascorbic acid (Vitamin C) in aqueous media with high selectivity and sensitivity.

Development of a novel one-pot synthetic method for the preparation of (Mn0.2Ni0.4Zn0.4Fe2O4)x–(BaFe12O19)1−x nanocomposites and the study of their microwave absorption and magnetic properties

The development of a simple yet novel aqueous solution based ‘one-pot’ method has been reported for the preparation of nanocomposites composed of soft ferrite (Mn0.2Ni0.4Zn0.4Fe2O4) and hard ferrite (BaFe12O19) phases. A physical mixing method has also been employed to prepare nanocomposites having the same compositions. The effects of synthetic methodologies on the microstructures of the nanocomposites as well as their magnetic and microwave absorption properties have been evaluated. The crystal structures and microstructures of these composites have been investigated using X-ray diffraction, transmission electron microscopy and scanning electron microscopy. In the nanocomposites prepared by both methods, the presence of nanocrystalline Mn0.2Ni0.4Zn0.4Fe2O4 and BaFe12O19 phases were detected. However, nanocomposites prepared by the one-pot method possessed better homogeneous distribution of hard and soft ferrite phases than the nanocomposites prepared by the physical mixing method. Very good spring exchange coupling interaction between the hard and soft ferrite phases was observed for the nanocomposites prepared by the one-pot method and these composites exhibited magnetically single phase behaviour. The spring exchange coupling interaction enhanced the magnetic properties (high saturation magnetization and coercivity) and microwave absorption properties of the nanocomposites prepared by the one-pot method, in comparison with the nanocomposites prepared by the physical mixing method as well as pure Mn0.2Ni0.4Zn0.4Fe2O4 and BaFe12O19 nanoparticles. The minimum reflection loss of the composites was found to be ∼−25 dB (i.e. >99% absorption) at 8.2 GHz with an absorber thickness of 3.5 mm.

π-Conjugated Discrete Oligomers Containing Planar and Nonplanar Aromatic Motifs

A new family of π-conjugated oligomers featuring a nonplanar polycyclic aromatic hydrocarbon, corannulene, and a planar aromatic unit, thiophene, is synthesized through an iterative metal-catalyzed coupling protocol. The two structural motifs are connected through an acetylene linkage. In the shorter oligomers, a thiophene unit is attached to one or two corannulenes. In the higher analogues, two, three, and four thiophene units are placed in an alternating fashion with three, four, and five corannulene units, respectively. Photophysical studies reveal extended π-effects that initially increase and then attenuate as a function of the oligomer length. Notably, longer oligomers are found to be highly active for nonlinear absorption and emission properties. The oligomer with three corannulene and two thiophene units exhibits a two-photon absorption cross section of 600 GM and two-photon-excited intense green luminescence. This work, therefore, introduces the concept of combining planar and nonplanar aromatic motifs in the design of π-conjugated discrete oligomers, establishes synthetic feasibility of such hybrid materials, reports on their photophysical properties that is anticipated to have significant implications for future research targets, and features the discovery that corannulene derivatives can exhibit excellent nonlinear optical activity when extended through π-bridges.

Aggregation-Induced Emission-Based Chemodosimeter Approach for Selective Sensing and Imaging of Hg(II) and Methylmercury Species

Methylmercury (CH3Hg+) is the common form of organic mercury and is more toxic than its inorganic or elemental forms. Mercury is emanated in the course of various natural events and human activities and converts to methylmercury by anaerobic organisms. CH3Hg+ are ingested by fish and subsequently bioaccumulated in their tissue and, eventually, enter the human diet, causing serious health issues. Therefore, selective and sensitive detection of bioaccumulated CH3Hg+ in fish samples is essential. Herein, the development of a simple, highly sensitive and selective aggregation-induced emission (AIE)-based turn-on probe for both inorganic mercury ions and organicmercury species is reported. The probes function is based on mercury ion-promoted transmetalation reaction of aryl boronic acid. The probe, a tetraphenylethylene (TPE)-monoboronic acid (1), was successfully utilized for AIE-based fluorescence imaging study on methylmercury-contaminated live cells and zebrafish for the first time. Both Hg(II) and CH3Hg+ ensued a fast transmetalation of TPE-boronic acid causing drastic reduction in the solubility of the resulting product (TPE-HgCl/TPE-HgMe) in the working solvent system. At the dispersed phase, the aggregated form of TPE-mercury ions recovers planarity because of restricted rotational freedom promoting aggregation-induced emission. Simple design, cost-effective synthesis, high selectivity, inexpensive instrumentation, fast signal transduction, and low limit of detection (0.12 ppm) are some of the key merits of this analytical tool.

Host–guest interaction between corannulene and γ-cyclodextrin: mass spectrometric evidence of a 1 : 1 inclusion complex formation

The toroidal cavity of γ-cyclodextrin is shown to interact with a bowl-shaped polycyclic aromatic hydrocarbon, corannulene, through host–guest interactions.

All-organic luminescent nanodots from corannulene and cyclodextrin nano-assembly: continuous-flow synthesis, non-linear optical properties, and bio-imaging applications

Control of structure and function, at the nanometer scale, remains a formidable challenge in the arena of self-assembled soft materials. Here, we report on the design of a small molecule-based two-component assembly system in which the assembly partners can recognize each other through host–guest interactions. One component is hydrophobic and carries a donor–acceptor type of electronic structure. This is realized by employing a bucky-bowl corannulene derivative. The other component is hydrophilic and hollow. This is achieved by using γ-cyclodextrin, the largest and least studied member of the cyclic oligosaccharide family. In a chemically polar aqueous environment, the two partners come together to form an amphiphilic structure that assembles further into nanosized, quasicrystalline, dot-like, non-toxic, all-organic structures showing two-photon activity and bright green luminescence in water upon excitation at 800 nm. The devised synthesis is achieved by a simple mixing process carried out under continuous-flow conditions. Therefore, in a scalable manner, a constant supply of the assembly components results in continuous fabrication of the nanostructures. Non-linear optical activity and biocompatibility aspects suggest utility of the prepared new class of soft organic nano-dots as contrast agents or labeling tags for visualizing biological specimens. This aspect is examined and demonstrated through two-photon fluorescence imaging of cancer cell lines.

Development of a novel and efficient H2O2 sensor by simple modification of a screen printed Au electrode with Ru nanoparticle loaded functionalized mesoporous SBA15

A novel and efficient electrochemical sensor has been developed to quantitatively measure H2O2 concentration by cyclic voltammetry. The sensor was prepared by modifying screen printed gold electrodes by ruthenium nanoparticle (Ru nanoparticle) loaded thiol functionalized mesoporous SBA15 (Ru@SBA15-SH) which was prepared by three simple steps. During measurement H2O2 electrochemically interacted with Ru nanoparticles and was channelled appropriately through the mesoporous structure of SBA15. The developed sensor showed a wide detection range with high sensitivity, durability and reproducibility. Furthermore, a very low limit of detection was reported by the sensor (0.42 μM (∼0.0142 ppm)), which was much lower than the permissible exposure limit.

Graphene-Based Materials in Biosensing, Bioimaging, and Therapeutics

Biomedical research has become extremely important in these days due to its direct impact on human health. The quest for the development of sophisticated materials for sensitive sensing, selective imaging and effective therapeutics has led to the creation of a unique class of materials known as graphene-based materials (GBMs). GBMs can be broadly classified into three groups: graphene-based nanocomposites, graphene quantum dots, and graphene-wrapped hybrids. These materials possess remarkable electrical, physical, and chemical properties, which can be exploited to develop efficient sensors, probes, and drugs. In this chapter, a detailed account about the synthetic strategies of these materials along with the mechanisms governing their performance in biosensing, bioimaging, and therapeutics is presented. The chapter highlights the suitability of GBMs in non-conventional and emerging techniques such as nonlinear photonics and photoacoustic imaging. The GBMs can also be employed to fabricate synergistic materials that are capable of simultaneous imaging and therapeutic actions. Therefore, the GBMs provide a promising platform for cutting-edge developments in the field of biomedical research.