Swarup Kumar Maji

Immobilizing Gold Nanoparticles in Mesoporous Silica Covered Reduced Graphene Oxide: A Hybrid Material for Cancer Cell Detection through Hydrogen Peroxide Sensing

A new kind of two-dimensional (2-D) hybrid material (RGO-PMS@AuNPs), fabricated by the immobilization of ultrasmall gold nanoparticles (AuNPs, ∼3 nm) onto sandwich-like periodic mesopourous silica (PMS) coated reduced graphene oxide (RGO), was employed for both electrocatalytic application and cancer cell detection. The hybrid-based electrode sensor showed attractive electrochemical performance for sensitive and selective nonenzymatic detection of hydrogen peroxide (H2O2) in 0.1 M phosphate buffered saline, with wide linear detection range (0.5 μM to 50 mM), low detection limit (60 nM), and good sensitivity (39.2 μA mM(-1) cm(-2)), and without any interference by common interfering agents. In addition, the sensor exhibited a high capability for glucose sensing and H2O2 detection in human urine. More interestingly, the hybrid was found to be nontoxic, and the electrode sensor could sensitively detect a trace amount of H2O2 in a nanomolar level released from living tumor cells (HeLa and HepG2). Because the hybrid presents significant properties for the detection of bioactive species and certain cancerous cells by the synergistic effect from RGO, PMS, and AuNPs, it could be able to serve as a versatile platform for biosensing, bioanalysis, and biomedical applications.

Upconversion Nanoparticles as a Contrast Agent for Photoacoustic Imaging in Live Mice

An inclusion complex of NaYF4 :Yb(3+) ,Er(3+) upconversion nanoparticles with α-cyclodextrin in aqueous conditions exhibits luminescence quenching when excited at 980 nm. This non-radiative relaxation leads to an unprecedented photoacoustic signal enhancement. In vivo localization of α-cyclodextrin-covered NaYF4 :Yb(3+) ,Er(3+) is demonstrated using photoacoustic tomography in live mice, showing its high capability for photoacoustic imaging.

A ratiometric fluorescent molecular probe with enhanced two-photon response upon Zn2+ binding for in vitro and in vivo bioimaging

A bipyridine centered donor–acceptor–donor (D–π–A–π–D) type ratiometric fluorescent molecular probe exhibited an unprecedented enhancement in the two-photon absorption (2PA) cross section upon Zn2+ binding. Moreover, owing to the excited state charge-transfer of the fluorophore π-backbone, a significant enhancement in the two-photon (2P) excited fluorescence intensity was observed upon Zn2+ binding, resulting in a 13-fold enhancement in the 2PA cross section and a 9-fold enhancement in fluorescence brightness at 620 nm when compared to the cation-free fluorophore. The large 2PA cross section of 1433 GM and 2P action cross section (860 GM), with an excellent 2P excited fluorescence variation from 517 to 620 nm upon Zn2+ binding, facilitated the ratiometric monitoring of free zinc ions in cells. The low cytotoxicity and good photostability of the fluorophore allowed two-photon Zn2+ imaging of HeLa cells. In addition, in vivo two-photon imaging of Zn2+ ions in hepatocytes of live rats illustrated the viability of the probe in tissue imaging and monitoring of free zinc ions in live cells.

Three-photon-excited luminescence from unsymmetrical cyanostilbene aggregates: morphology tuning and targeted bioimaging.

We report an experimental observation of aggregation-induced enhanced luminescence upon three-photon excitation in aggregates formed from a class of unsymmetrical cyanostilbene derivatives. Changing side chains (-CH3, -C6H13, -C7H15O3, and folic acid) attached to the cyanostilbene core leads to instantaneous formation of aggregates with sizes ranging from micrometer to nanometer scale in aqueous conditions. The crystal structure of a derivative with a methyl side chain reveals the planarization in the unsymmetrical cyanostilbene core, causing luminescence from corresponding aggregates upon three-photon excitation. Furthermore, folic acid attached cyanostilbene forms well-dispersed spherical nanoaggregates that show a high three-photon cross-section of 6.0 × 10(-80) cm(6) s(2) photon(-2) and high luminescence quantum yield in water. In order to demonstrate the targeted bioimaging capability of the nanoaggregates, three cell lines (HEK293 healthy cell line, MCF7 cancerous cell line, and HeLa cancerous cell line) were employed for the investigations on the basis of their different folate receptor expression level. Two kinds of nanoaggregates with and without the folic acid targeting ligand were chosen for three-photon bioimaging studies. The cell viability of three types of cells incubated with high concentration of nanoaggregates still remained above 70% after 24 h. It was observed that the nanoaggregates without the folic acid unit could not undergo the endocytosis by both healthy and cancerous cell lines. No obvious endocytosis of folic acid attached nanoaggregates was observed from the HEK293 and MCF7 cell lines having a low expression of the folate receptor. Interestingly, a significant amount of endocytosis and internalization of folic acid attached nanoaggregates was observed from HeLa cells with a high expression of the folate receptor under three-photon excitation, indicating targeted bioimaging of folic acid attached nanoaggregates to the cancer cell line. This study presents a paradigm of using organic nanoaggregates for targeted three-photon bioimaging.

A novel amperometric biosensor for hydrogen peroxide and glucose based on cuprous sulfide nanoplates

A facile, greener and template free route has been developed to produce cuprous sulfide (Cu2S) nanoplates (NPs) with average diameters of 70-150 nm, via one step solvothermal decomposition of a single-source precursor (SSP) Cu(ACDC)2 [ACDC = 2-aminocyclopentene-1-dithiocarboxylate] in the presence of ethylenediamine (EN) and triethylenetetramine (TETA) as structure orienting agents. The precursor complex and nanomaterials were thoroughly characterized by several common techniques and measurements, which give the composition and characteristics of the materials. Amperometric biosensors for hydrogen peroxide (H2O2) and glucose have been constructed by immobilizing the synthesized Cu2S NPs in glutaraldehyde on a glassy carbon (GC) electrode using a direct drop-coating method. The proposed sensor has displayed faster response, high and reproducible sensitivity (64.27 μA mM-1) with linear range of 10 μM to 3.75 mM, towards the electrochemical biosensing of H2O2 at -0.35 V (vs. Ag/AgCl). The sensor also showed high and reproducible sensitivity (61.67 μA mM-1) towards glucose determination with linear range of 10 μM to 3.1 mM. The anti-inference ability of electroactive molecules and favorable stability are some of the advantages of the proposed sensor. Finally, using the sensor we have determined the glucose concentration in a human blood serum sample. The results strongly demonstrate the usefulness of Cu2S NPs for biosensor design and other biological applications.

Synthesis of Ag2S quantum dots by a single-source precursor: an efficient electrode material for rapid detection of phenol

Phenol and its derivatives are highly important chemicals in a variety of industrial products. However, their presence in ppm concentrations is extremely toxic for the environment in general and aquatic life specifically. Herein, we report the synthesis of highly mono-dispersed Ag2S quantum dots (QDs) with an average diameter of 11 nm from a single-source precursor, aiming to employ them as electrode materials for the detection of phenol. The as-prepared Ag2S QDs are immobilized on a glassy carbon (GC) electrode, and the electrochemical sensing of phenol using the developed Ag2S QD/GC electrode is observed to be within a wide range (1 μM to 16 mM). As compared with conventional sensing approaches, the present technique shows a much lower detection limit (0.015 μM) and higher sensitivity (61.2 μA mM−1 cm−2) towards phenol. In addition, the Ag2S QD/GC electrode-based sensor also exhibits good stability, repeatability, reproducibility and anti-interference ability. Thus, the sensor presents a great advantage for sensitive, rapid and cost-effective detection and quantification of phenol, indicating a promising potential for practical sensing applications.

Experimental study on electron field emission, Raman scattering, and low temperature electrical properties of nanocrystalline lead selenide thin films

We report the electron field emission properties, Raman scattering, and low (77 K) and room temperature electrical properties of nanocrystalline PbSe thin films. Structural characterizations (high resolution x-ray diffraction, atomic force microscopy, and high resolution transmission electron microscopy) revealed the formation of cubic PbSe with an average crystallite diameter of ca. 8 nm. Raman analysis showed a strong peak at 136 cm−1. Due to the nanocrystalline nature, the threshold field (5.5 V/μm) and approximate work function values were high, making the films a very efficient field emitter.

Two-dimensional nanohybrid (RGS@AuNPs) as an effective catalyst for the reduction of 4-nitrophenol and photo-degradation of methylene blue dye

Although increasing attention has been focused on gold nanoparticles (AuNPs) as operational catalysts for chemical conversion and pollutant degradation due to their unique reactivity, it is a challenging task to prepare highly active hybrid materials and stabilize their reactivity by preventing serious aggregation of AuNPs along with effective separation. Herein, a two-dimensional nanostructured hybrid material (RGS@AuNPs, ∼1 μm) is developed, which consists of AuNPs (∼10 nm in diameter) immobilized on the surface of sandwich-like periodic mesoporous silica (PMS) coated reduced graphene oxide (RGO). Transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and N2 adsorption/desorption are employed to characterize the obtained hybrid. The hybrid material (RGS@AuNPs) shows superior catalytic activity in the reduction of 4-nitrophenol (4-NP) and methylene blue (MB) dye in the presence of sodium borohydride (NaBH4). In addition, excellent photocatalytic activity is also achieved by the hybrid, as demonstrated through the decomposition of MB dye under visible light irradiation. The rate constants are calculated by considering the pseudo-first-order reaction equation, which shows that the constants are quite impressive compared with that of previous reports. Thus, the present hybrid material is a promising catalyst for the synthesis of some organic chemicals and wastewater management.

Observation of enhanced photocurrent response in M–CuInS2 (M = Au, Ag) heteronanostructures: phase selective synthesis and application

We report controlled synthesis of CuInS2 in wurtzite and zinc blende phases by solution based thermal decomposition of dual precursors [In(acda)3] (acda = 2-aminocyclopentene-1-dithiocarboxylic acid) and [Cu(PPh3)2(acda)] (PPh3 = triphenylphosphine) in the presence of appropriate surface-active agents. Furthermore, the preparation of M–CuInS2 (M = Au and Ag) heteronanostructures on both the phases has been achieved successfully by hot injection of respective gold and silver precursor solutions into the reaction mixture. The characterization of both pure and hybrid nanostructures was carried out by X-ray diffraction (XRD), UV-vis spectroscopy, energy dispersive X-ray (EDX) study and transmission electron microscopy (TEM). A detailed photovoltaic study has been performed with both pure materials and the twin structures and their photocurrent and photoresponse behavior have been compared. The study reveals that upon loading Au and Ag, the material exhibits high photocurrent efficiency compared to pure CuInS2. An appreciable increase in the light to dark current density ratio confirms that these materials can be used in the fabrication of promising photovoltaic devices.