Anjan Kr. Dasgupta

In Vitro Structural and Functional Evaluation of Gold Nanoparticles Conjugated Antibiotics

Bactericidal efficacy of gold nanoparticles conjugated with ampicillin, streptomycin and kanamycin were evaluated. Gold nanoparticles (Gnps) were conjugated with the antibiotics during the synthesis of nanoparticles utilizing the combined reducing property of antibiotics and sodium borohydride. The conjugation of nanoparticles was confirmed by dynamic light scattering (DLS) and electron microscopic (EM) studies. Such Gnps conjugated antibiotics showed greater bactericidal activity in standard agar well diffusion assay. The minimal inhibitory concentration (MIC) values of all the three antibiotics along with their Gnps conjugated forms were determined in three bacterial strains,Escherichia coli DH5α,Micrococcus luteus andStaphylococcus aureus. Among them, streptomycin and kanamycin showed significant reduction in MIC values in their Gnps conjugated form whereas; Gnps conjugated ampicillin showed slight decrement in the MIC value compared to its free form. On the other hand, all of them showed more heat stability in their Gnps conjugated forms. Thus, our findings indicated that Gnps conjugated antibiotics are more efficient and might have significant therapeutic implications.

Screening of different algae for green synthesis of gold nanoparticles

The cyanobacteria Phormidium valderianum, P. tenue and Microcoleus chthonoplastes and the green algae Rhizoclonium fontinale, Ulva intestinalis, Chara zeylanica and Pithophora oedogoniana were exposed to hydrogen tetrachloroaurate solution and were screened for their suitability for producing nano‐gold. All three cyanobacteria genera and two of the green algae (Rhizoclonium fontinale and Ulva intestinalis) produced gold nanoparticles intracellularly, confirmed by purple colouration of the thallus within 72 h of treatment at 20°C. Extracted nanoparticle solutions were examined by UV‐vis spectroscopy, transmission electron microscopy (TEM) and X‐ray diffractometry (XRD). XRD confirmed the reduction of Au (III) to Au (0). UV‐vis spectroscopy and TEM studies indicated the production of nanoparticles having different shapes and sizes. Phormidium valderianum synthesized mostly spherical nanoparticles, along with hexagonal and triangular nanoparticles, at basic and neutral pHs (pH 9 and pH 7, respectively). Medicinally important gold nanorods were synthesized (together with gold nanospheres) only by P. valderianum at acidic pH (pH 5); this was initially determined by two surface plasmon bands in UV‐vis spectroscopy and later confirmed by TEM. Spherical to somewhat irregular particles were produced by P. tenue and Ulva intestinalis (TEM studies). The UV‐vis spectroscopy of the supernatant of other algal extracts indicated the formation of mostly spherical particles. Production of gold nanoparticles by algae is more ecofriendly than purely chemical synthesis. However, the choice of algae is important: Chara zeylanica and Pithophora oedogoniana were found to be unable to produce nanoparticles.

Multistability in platelets and their response to gold nanoparticles

UNLABELLED The nanoparticle (NP) response of platelets is shown to be critically dependent on extent of preactivation of platelets by an agonist like ADP. A transition from de-aggregatory to aggregatory state is triggered in the presence of gold NPs (AuNP) only in such critical conditions. Adhered and suspended platelets respond differentially to NPs. Preactivation in the adhered state induced by shear force explains such observation. The NP effect is associated with enhanced release reaction, tyrosine phosphorylation and CD62P expression level. Unlike cancer cells, whose response is maximal when NP size is optimal (within the range 50 - 70 nm), the platelet response monotonically increases with reduction of the AuNP size. The uptake study, using quenching of quinacrine hydrochloride fluorescence by AuNP, indicates that accumulation 18 nm AuNP is several-fold higher than the 68 nm AuNP. It is further shown that AuNP response can provide a simple measure for thrombotic risk associated with nano-drugs. FROM THE CLINICAL EDITOR Platelet aggregation can be triggered in the presence of gold nanoparticles (AuNP). Platelet response monotonically increases with reduction of the AuNP size. AuNP response can provide a simple measure for thrombotic risk associated with nano-drugs.

Drug Delivery Using Platelet Cancer Cell Interaction

PurposeTo develop an efficient biocompatible and targeted drug delivery system in which platelets, an essential blood component having a natural affinity for cancer cells, are used as carrier of anticancer drug as delivery of drug to the targeted site is crucial for cancer treatment.MethodsDoxorubicin hydrochloride, a potent anti cancer drug, was delivered in lung adenocarcinoma cell line (A549) using platelet as a delivery agent. This delivery mode was also tested in Ehrlich ascites carcinoma (EAC) bearing mice in presence and absence of platelets.ResultsThe results show that platelets can uptake the drug and release the same upon activation. The efficiency of drug loaded platelets in inducing cytotoxicity was significantly higher in both in vitro and in vivo model, as compared to the free drug.ConclusionsThe proposed drug delivery strategy may lead to clinical improvement in the management of cancer treatment as lower drug concentration can be used in a targeted mode. Additionally the method can be personalized as patients own platelet can be used for deliver various drugs.

Mahanine, A DNA Minor Groove Binding Agent Exerts Cellular Cytotoxicity with Involvement of C-7-OH and −NH Functional Groups

Mahanine, a carbazole alkaloid is a potent anticancer molecule. To recognize the structure-activity correlation, mahanine was chemically modified. Antiproliferative activity of these derivatives was determined in 19 cancer cell lines from 7 different origins. Mahanine showed enhanced apoptosis compared to dehydroxy-mahanine-treated cells, indicating significant contribution of the C-7-OH group. O-Methylated-mahanine and N-methylated dehydroxy-mahanine-treated cells exhibited apoptosis only at higher concentrations, suggesting additional contribution of 9-NH group. Using biophysical techniques, we demonstrated that mahanine interacts with DNA through strong association with phosphate backbone compared to other derivatives but is unable to induce any conformational change in DNA, hence suggesting the possibility of being a minor groove binder. This was corroborated by molecular modeling and isothermal titration calorimetry studies. Taken together, the results of the current study represent the first evidence of involvement of C-7-OH and 9-NH group of mahanine for its cytotoxicity and its minor groove binding ability with DNA.

Enhanced functionality and stabilization of a cold active laccase using nanotechnology based activation-immobilization

A simple nanotechnology based immobilization technique for imparting psychrostability and enhanced activity to a psychrophilic laccase has been described here. Laccase from a psychrophile was supplemented with Copper oxide nanoparticles (NP) corresponding to copper (NP-laccase), the cationic activator of this enzyme and entrapped in single walled nanotube (SWNT). The activity and stability of laccase was enhanced both at temperatures as low as 4°C and as high as 80°C in presence of NP and SWNT. The enzyme could be released and re-trapped (in SWNT) multiple times while retaining significant activity. Laccase, immobilized in SWNT, retained its activity after repeated freezing and thawing. This unique capability of SWNT to activate and stabilize cold active enzymes at temperatures much lower or higher than their optimal range may be utilized for processes that require bio-conversion at low temperatures while allowing for shifts to higher temperature if so required.

Highly lattice-mismatched semiconductor-metal hybrid nanostructures

Synthesis of hybrid core-shell nanostructures requires moderate lattice mismatch (<5%) between the materials of the core and the shell and usually results in the formation of structures with an atomically larger entity comprising the core. A reverse situation, where an atomically larger entity encapsulates a smaller atomic radius component having substantial lattice mismatch is unachievable by conventional growth techniques. Here, we report successful synthesis of ultra-small, light-emitting Si quantum dots (QDs) encapsulated by Au nanoparticles (NPs) forming a hybrid nanocomposite that exhibits intense room temperature photoluminescence (PL) and intriguing plasmon-exciton coupling. A facile strategy was adopted to utilize the active surface of oxide etched Si QDs as preferential sites for Au NP nucleation and growth which resulted in the formation of core-shell nanostructures consisting of an atomically smaller Si QD core surrounded by a substantially lattice-mismatched Au NP shell. The PL characteristics of the luminescent Si QDs (quantum yield ∼28%) are dramatically altered following Au NP encapsulation. Au coverage of the bare Si QDs effectively stabilizes the emission spectrum and leads to a red-shift of the PL maxima by ∼37 nm. The oxide related PL peaks observed in Si QDs are absent in the Au treated sample suggesting the disappearance of oxide states and the appearance of Au NP associated Stark shifted interface states within the widened band-gap of the Si QDs. Emission kinetics of the hybrid system show accelerated decay due to non-radiative energy transfer between the Si QDs and the Au NPs and associated quenching in PL efficiency. Nevertheless, the quantum yield of the hybrid remains high (∼20%) which renders these hetero-nanostructures exciting candidates for multifarious applications.

Cancer cell response to nanoparticles: criticality and optimality

A stochastic variation in size and electrical parameters is common in nanoparticles. Synthesizing gold nanoparticles with a varying range of size and zeta potential, we show that there is clustering at certain regions of hydrodynamic diameter and zeta potentials that can be classified using k-clustering technique. A cluster boundary was observed around 50 nm, a size known for its optimal response to cells. However, neither size nor zeta potential alone determined the optimal cellular response (e.g., percentage cell survival) induced by such nanoparticles. A complex interplay prevails between size, zeta potential, nature of surface functionalization, and extent of adhesion of the cell to a solid matrix. However, it follows that the ratio of zeta potential to surface area, which scales as the electrical field (by Gaussian law), serves as an appropriate indicator for optimal cellular response. The phase plot spanned by fractional survival and effective electric field (charge density) indicates a positive correlation between mean cell survival and the magnitude of the electric field. The phase plot spanned by fractional survival and effective electric field (charge density) associated with the nanosurface shows a bifurcation behavior. Wide variation of cell survival response is observed at certain critical values of the surface charge density, whereas in other ranges the cellular response is well behaved and more predictable. Existence of phase points near the critical region corresponds to wide fluctuation of nanoparticle-induced response, for small changes in the nanosurface property. Smaller nanoparticles with low zeta potential (e.g., those conjugated with arginine) can have such an attribute (i.e., higher electrical field strength), and eventually they cause more cell death. The study may help in optimal design of nanodrugs.

Improved production of reducing sugars from rice husk and rice straw using bacterial cellulase and xylanase activated with hydroxyapatite nanoparticles.

Purified bacterial cellulase and xylanase were activated in the presence of calcium hydroxyapatite nanoparticles (NP) with concomitant increase in thermostability about 35% increment in production of d-xylose and reducing sugars from rice husk and rice straw was obtained at 80°C by the sequential treatment of xylanase and cellulase enzymes in the presence of NP compared to the untreated enzyme sets. Our findings suggested that if the rice husk and the rice straw samples were pre-treated with xylanase prior to treatment with cellulase, the percentage increase of reducing sugar per 100g of substrate (starting material) was enhanced by about 29% and 41%, respectively. These findings can be utilized for the extraction of reducing sugars from cellulose and xylan containing waste material. The purely enzymatic extraction procedure can be substituted for the harsh and bio-adverse chemical methods.

Surface tunability of nanoparticles in modulating platelet functions

Metallic nanoparticles are attractive candidates as MRI contrast agents and mediators for drug delivery, diagnostics, and therapy. Direct contact and exposure to blood circulation is common in many such applications. The consequent thrombotic response may therefore be important to study. The main objective of the present work was to study how platelet functions were changed in the presence of different nano-surface or surface capping, which may provide a measure for the safety of a nanoparticle, and also assess the use of such nanoparticles in platelet modulation. Aggregometry, ATP release reaction, flow cytometry and immune-blotting studies were performed to study platelet response to different nano-particles (iron oxide, gold and silver). For each nanoparticle surface conjugation (capping) was varied. It was found that citric acid functionalized iron oxide nanoparticles have anti-platelet activity, with a decrease in aggregation, tyrosine phosphorylation level, and granule release. On the other hand in other cases (e.g. gold nanoparticles) pro-aggregatory response was observed in the presence of nanoparticles and, in some cases, the nanoparticles behaved neutrally (e.g. for starch-coated iron oxide nanoparticles). Therefore, nanoparticles can induce antiplatelet or a pro-aggregatory response, or remain neutral depending on surface capping. A related observation is that antiplatelet drugs can be made more potent by nanoparticle conjugation.