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Gold nanoparticles have found their application as optical probes, antibacterial agents, catalyst and sensors. Here, we report the synthesis of gold nanoparticles (GNPs) using leaf extract (LE) of three different plants viz., Populus alba (PA), Lantana camara (LC) and Hibiscus arboreus (HA). The effect of reaction temperature and concentration of leaf extracts (LEs) were studied in detail on the synthesis and size of GNPs. The prepared GNPs were chemically characterized by UV–Vis and FTIR whereas the morphological analysis was done using DLS, TEM and SEM. When 5% PA LE was used at 65 °C, almost uniform shaped GNPs were obtained of size ~ 16.3 ± 0.7 nm. The as prepared GNPs showed antibacterial activity against both Staphylococcus aureus and Escherichia coli with MIC value of ~ 100 µg/ml. Further, these GNPs were also used for the degradation of toxic dyes viz., methylene blue (MB) and congo red (CR). Overall, present studies suggested the use of green synthesized GNPs in both biomedical and analytical field.

Successful and effective treatment of different types of infections depends upon fast and selective identification of the microorganisms. Pseudomonas aeruginosa is a Gram-negative bacterium which is involved in a number of human infections and may become life-threatening for immunocompromised persons. Pyocyanin is a unique exotoxin which is exclusively secreted as a virulence factor by P. aeruginosa. In this respect, a nano-assembly, composed of a carbon dot conjugated gold nanocomposite (Au@OPCDPEG) having a size of ∼11.5 ± 1.6 nm, was synthesized and used as both a fluorescence resonance energy transfer (FRET) and a colorimetric sensor for pyocyanin detection. When titrated with increasing concentrations of pyocyanin, Au@OPCDPEG NPs showed ∼1.76 ± 0.12 times increase in fluorescence intensity (at ∼505 nm), whereas three distinct isosbestic points were observed in absorption studies. The limit of detection for pyocyanin was found to be ∼3.04 ± 0.27 μM. It was found that Au@OPCDPEG NPs can selectively recognize pyocyanin even in the presence of other toxins under different biological interference. Real-time P. aeruginosa detection studies suggested the minimum detection limit to be ∼1.5 × 106 cfu ml−1 even in the presence of Staphylococcus aureus contamination in the sample. Confocal studies suggested that Au@OPCDPEG NPs can effectively penetrate P. aeruginosa biofilm under laser irradiation. Overall, the present engineered nanoprobe provides an easy, fast and selective method for the detection of P. aeruginosa in biological samples.

Inhibition of hen egg white lysozyme (HEWL) and Aβ42 fibrillation have been established as the main models for the treatment of systemic lysozyme amyloidosis and Alzheimer's disease (AD), respectively. Several antiamyloidogenic nanomaterials have been developed over the period; however, their intracellular mechanism of action is still not well understood. In this context, plant-based, gold-conjugated, injectable, hydrophilic cellulose nanoonions (CNOs), viz., DH-CNO (∼60 ± 5 nm) and LC-CNO (∼55 ± 12 nm), were developed from their respective hydrophobic cellulose nanocrystals (DH-CNC and LC-CNC) using a single-step chemical template-mediated process. This unique nanocellulose architecture was chemically and morphologically characterized by various spectroscopic and microscopic techniques. Further, the different biophysical studies documented marked the inhibition/disintegration potential of gold-conjugated LC-CNO against HEWL and Aβ42 peptide aggregation. It was further observed that inhibition of protein fibrillation could be achieved within ∼10 min when the same materials were used under photoirradiation conditions. In vitro protein aggregation studies using HEK293 cells suggested that gold-conjugated LC-CNO could effectively reduce the cellular toxicity via regulation of oxidative stress and ion homeostasis. The outcome of the present study will help in designing cellulose-based novel functional nanochaperones against various neurodegenerative diseases.

Protein-nanoparticle (NP) interaction, which inevitably form protein corona (PC), has been the subject of much debate about its role in modern biomedical research. In this regard, PC associated with two different NPs viz., magneto-fluorescent (MF) and chitosan coated MF (CMF) NPs were thoroughly investigated, to analyze the effect of polymer coating on protein adsorption. Bradford assay, along with the spectroscopic and microscopic studies suggested increase in adsorbed protein quantity, though the results varied significantly on moving from bare to polymeric coating and in vitro to ex vivo conditions. Interestingly, polymer coated NPs showed increased protein adsorption and induce minimal changes in protein structural integrity under the same conditions. We predict that the changes in secondary structure of primary corona determine the overall signature of surface binding proteins in PC. Our findings suggested that rapid diagnosis of immunoglobulins is possible using the concept of protein corona formation ex vivo.

Protein aggregation leads to the transformation of proteins from their soluble form to the insoluble amyloid fibrils and these aggregates get deposited in the specific body tissues, accounting for various diseases. To prevent such an aggregation, organic–inorganic hybrid nanocomposites of iron oxide nanoparticle (NP, ∼6.5–7.0 nm)-conjugated cellulose nanocrystals (CNCs) isolated from Syzygium cumini (SC) and Pinus roxburghii (PR) were chemically synthesized. Transmission electron microscopy (TEM) images of the nanocomposites suggested that the in situ-synthesized iron oxide NPs were bound to the CNC surface in a uniform and regular fashion. The ThT fluorescence assay together with 8-anilino-1-naphthalenesulfonic acid, Congo Red, and CD studies suggested that short fiber-based SC nanocomposites showed better inhibition as well as dissociation of human serum albumin aggregates. The TEM and fluorescence microscopy studies supported similar observations. Native polyacrylamide gel electrophoresis results documented dissociation of higher protein aggregates in the presence of the developed nanocomposite. Interestingly, the dissociated proteins retained their biological function by maintaining a high amount of α-helix content. The in vitro studies with HEK-293 cells suggested that the developed nanocomposite reduces aggregation-induced cytotoxicity by intracellular reactive oxygen species scavenging and maintaining the Ca2+ ion-channel. These results indicated that the hybrid organic–inorganic nanocomposite, with simultaneous sites for hydrophobic and hydrophilic interactions, tends to provide a larger surface area for nanocomposite–protein interactions, which ultimately disfavors the nucleation step for fibrillation for protein aggregates.

The development of biocompatible, widely applicable fluorescent imaging probe, with emission beyond the cellular and tissue autofluorescence interference, is a challenging task. In this regard, a series of 28 different fluorescent carbon dots (CDs) were synthesized using carbohydrates as carbon and cysteine (Cys) and o-phenylenediamine (OPD) as nitrogen source. The screened CDs showed photostability with bright blue (∼505–520 nm) and red (∼588–596 nm) emission and high fluorescence quantum yield (QY = 72.5 ± 4.5%). FTIR and NMR studies suggested presence of carboxylate and ester group for Cys- and OPD-based CDs, respectively. HRTEM results showed particle size of ∼3.3–5.8 nm for all the developed CDs. The antibacterial studies suggested that the developed CDs showed preferential antibacterial activity against Escherichia coli, with IC50 value of ∼200 μg/mL. Cytotoxicity and confocal microscopy studies of HeLa cells reflected that these CDs showed both anticancer activity and imaging ability. Agarose gel e...

Essential oils (EO), which can be extracted from different edible, therapeutic and herbal plants, have been well known as natural antimicrobial additives. However, it is usually hard to attain high antimicrobial efficacy of these EOs, when these are used in different combinations for the control of foodborne microbes, because of their low solubility in water and interactive binding. Here, we report an optimized oil-in-water (o/w) nanoemulsification process for citral and carvone which generated mean droplet size of 11–19 nm. It was found that nature of surfactant viz., Brij-58 vs leaf extract of Lantana camara (LC) plays crucial role in determining the overall stability and size of the droplets. The screened nanoemulsions (NEs), when stored for long duration, showed minimal decrease in oil content with retention of antioxidant activity. The prepared NEs documented enhanced antibacterial activity compared to pure oils whereas higher degree of killing was observed towards Pseudomonas aeruginosa. The NEs also showed killing of both the bacteria on wound dressing cotton gauze bandages (GB). The outcome of the present study may be used for the development of safe and biocompatible antibacterial agents.

Multifunctional hybrid nanocomposite material, consists of chitosan encapsulated iron oxide (as MRI contrasting agent), CdS (as fluorescent probe) nanoparticles and podophyllotoxin (as anticancer drug) was synthesized and characterized. The TEM studies suggested the size of the NPs to be in the range of 80-100 nm. These nanocomposites were treated with different cancer cell lines viz., KB, C6 and A549 cells. Fluorescence imaging and Perl's Prussian blue staining confirmed the presence of these nanocomposites inside both KB and C6 cells but not in A549 cells. Cytotoxicity experiments revealed that these biopolymer coated nanocomposites showed minimal toxicity towards cancerous cells. Further the intraperitoneal administration of one of the nanoformulations to Wistar rats suggested deposition of these nanocomposites in the lungs. The hematological, biochemical and histopathological analysis confirmed that these nanocomposites are safe to use as a novel dual mode imaging material.

Nanocomposites of plant cellulose nanocrystals (CNCs) were developed by binding model proteins BSA and HSA onto CNCs by physical adsorption and chemical conjugation methods The spectroscopy and microscopy studies confirmed the protein binding onto CNCs. Phosphate buffer saline (pH=4.0, 7.4) and simulated gastric and intestinal fluids (SGF/SIF; pH=1.1/6.5) showed maximum protein release of ∼62% over a period of time. The released proteins were found to retain both structural integrity as well as≥90% of bioactivity. Further, these cytocompatible nanocomposites showed ∼58-85% cholesterol release from HUVEC whereas no selectivity was observed for HCAEC. It is speculated that due to the presence of combination of shuttles (albumins) and sinks (CNCs and albumins), these prepared nanocomposites with increased cholesterol effluxing ability may serve as a potential candidate for future biomedical applications in pharmaceuticals.

A colorimetric chemo-sensor based on citric acid-coated gold NPs (C-GNP) showed a linear increase in fluorescence intensity with increasing concentration of pesticide dimethoate (DM). The limit of detection was found to be between ~8.25± 0.3 and 20 ± 9.5 ppm. The increase in fluorescence intensity was suggested to have originated from the soft–soft interaction between C-GNPs and DM via sulfur group which is absent in pesticide dicofol (DF). Similar studies with citric acid-coated silver NPs (C-SNPs) did not result any change in the fluorescence intensity. The microscopic studies suggested aggregation of C-GNPs in the presence of DM but not in case of DF.

Amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene, L has been shown to be sensitive and selective to Hg(2+) in aqueous acetonitrile solution based on fluorescence spectroscopy, and the stoichiometry of the complexed species has been found to be 1:1. The selectivity of L toward Hg(2+) has been shown among 11 M(2+) ions, viz., Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), Ca(2+), and Mg(2+) studied, including those of the mercury group and none of these ions impede the recognition of Hg(2+) by L. Role of the solvent on the recognition of Hg(2+) has been demonstrated. The role of calix[4]arene platform and the benzimidazole moieties in the recognition of Hg(2+) by L has been delineated upon performing such studies with five different molecules of relevance as reference molecular systems. The binding cores formed by the receptor L and the reference compounds have been established based on the single crystal XRD structures, and the preferential metal ion binding cores have been discussed. The binding of Hg(2+) with L has been further established based on (1)H and (13)C NMR, ESI MS, absorption, and fluorescence lifetime measurements. Some of these techniques have been used to establish the stoichiometry of the species formed. The complex species formed between L and Hg(2+) have been isolated and characterized and found to be 1:1 species even in the isolated complex. Whereas transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) provided the nanostructural behavior of L, the TEM and SEM demonstrated that the mercury complex has different characteristics when compared to L. The TEM, SEM, and powder XRD studies revealed that whereas L is crystalline, that of the mercury complex is not, perhaps a reason for not being able to obtain single crystals of the complex. Binding characteristics of Hg(2+) toward L have been established based on the DFT computational calculations.

The detection of pesticide residues in ground water, food, or soil samples is extremely important. The currently available laboratory techniques have several drawbacks and needs to be replaced. Fluorescent chemosensors for pesticide detection were reported in the literature, with few reports published on quantum dot-based pesticide sensors, but none of these were focused toward differentiating organophosphorus and organochlorine pesticides specifically. In this respect, glutathione-coated CdS nanoparticles were synthesized and characterized. The TEM studies of the nanoparticles suggested mostly monodispersed spherical particles, with size in the range of 11.5±1 nm. The prepared fluorescent nanoparticles were found to selectively recognize organochlorine pesticide dicofol among all the other pesticides studied, by increasing the fluorescence intensity of the nanoparticles ~ 2.5 times. Similar studies carried out with organophosphorous pesticide dimethoate did not result any change in the fluorescence intensity of the nanoparticles. Further studies carried out with commercially available pesticide solutions, also confirmed similar results. The TEM, SEM, and DLS studies suggested aggregation of the nanoparticles in the presence of dicofol. Control experiments suggested possible role of both amine and carboxylic acid functional groups of glutathione in the recognition of dicofol. The limit of detection of dicofol was found to be ~ 55±11 ppb. Glutathione-coated CdS nanoparticles selectively recognize organochlorine pesticide dicofol among all the other pesticides studied, by increasing the fluorescence intensity of the nanoparticles. The TEM, SEM, and DLS studies suggested aggregation of the nanoparticles in the presence of dicofol.

A multifunctional hybrid nanocomposite material of iron oxide nanoparticles and CdS quantum dots was synthesized by a direct amide coupling reaction. The prepared nanoparticles were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and zeta potential studies. The TEM studies suggested that the sizes of the particles were in the range of 13.5 ± 1 nm. The energy dispersive x-ray (EDX) analysis confirmed the presence of Fe, Cd and S in the nanocomposites. To check the utility of this nanocomposite as a molecular imaging probe, these nanoparticles were further conjugated with folic acid. The folic acid conjugated nanocomposites were treated with rat glioma cells (C6, folic acid receptor over-expressing cell lines), human lung adenocarcinoma epithelial cells (A549, folic acid receptor negative cell lines) and normal mouse splenocytes for cell uptake and cytotoxicity studies. The nanoparticle internalization to C6 cells was confirmed by green fluorescence emission from these cells. Prussian blue staining studies suggested the intracellular presence of iron oxide. Further it was found that folic acid conjugated nanocomposites were significantly toxic to C6 cells only after 48 h but not to A549 cells or splenocytes. These studies indicated that the prepared nanocomposites have the potential to be used as delivery agent for magnetic and fluorescent materials towards folic acid receptor over-expressing cells and thus can find their application in the field of in vitro imaging diagnosis.

Lower rim 1,3-diamido conjugates of calix[4]arene have been synthesized and characterized, and the structures of some of these have been established by single crystal XRD. The amido-calix conjugates possessing a terminal -COOH moiety have been shown to exhibit recognition toward guest molecules possessing -COOH moiety, viz., Asp, Glu, and reduced and oxidized glutathione (GSH, GSSG), by switch-on fluorescence in aqueous acetonitrile and methanol solutions when compared to the control molecules via forming a 1:1 complex. The complex formed has been shown by mass spectrometry, and the structural features of the complexes were derived on the basis of DFT computations. The association constants observed for the recognition of Asp/Glu by Phe-calix conjugate, viz., 532/676 M(-1), are higher than that reported for the recognition of Val, Leu, Phe, His, and Trp (16-63 M(-1)) by a water-soluble calixarene (Arena, G., et al. Tetrahedron Lett. 1999, 40, 1597). For this recognition, there should be a free -COOH moiety from the guest molecule. AFM, SEM, and DLS data exhibited spherical particles with a hundred-fold reduction in the size of the complexes when compared to the particles of the precursors. These spherical particles have been computationally modeled to possess hexameric species reminiscent of the hexameric micellar structures shown for a Ag(+) complex of a calix[6]arene reported in the literature (Houmadi, S., et al. Langmuir 2007, 23, 4849). Both AFM and TEM studies demonstrated the formation of nanospheres in the case of GSH-capped Ag nanoparticles in interaction with the amido-calix conjugate that possesses terminal -COOH moiety. The AFM studies demonstrated in this paper have been very well applied to albumin proteins to differentiate the aggregational behavior and nanostructural features exhibited by the complexes of proteins from those of the uncomplexed ones. To our knowledge, this is the first report wherein a amido-calix[4]arene conjugate and its amino acid/peptide/protein complexes have been differentiated on the basis of spectroscopy and microscopy studies followed by species modeling by computations.

This paper deals with the self-assembly of the 1:1 complex of two different amphiphiles, namely, a glucosyl-salicyl-imino conjugate (L) and phenylalanine (Phe), forming nanofibers over a period of time through pi...pi interactions. Significant enhancement observed in the fluorescence intensity of L at approximately 423 nm band and the significant decrease observed in the absorbance of the approximately 215 nm band are some characteristics of this self-assembly. Matrix-assisted laser desorption ionization/time of flight titration carried out at different time intervals supports the formation of higher aggregates. Atomic force microscopy (AFM), transmission electron microscopy, and scanning electron miscroscopy results showed the formation of nanofibers for the solutions of L with phenylalanine. In dynamic light scattering measurements, the distribution of the particles extends to a higher diameter range over time, indicating a slow kinetic process of assembly. Similar spectral and microscopy studies carried out with the control molecules support the role of the amino acid moiety over the simple -COOH moiety as well as the side chain phenyl moiety in association with the amino acid, in the formation of these fibers. All these observations support the presence of pi...pi interactions between the initially formed 1:1 complexes leading to the fiber formation. The aggregation of 1:1 complexes leading to fibers followed by the formation of bundles has been modeled by molecular mechanics studies. Thus the fiber formation with L is limited to phenylalanine and not to any other naturally occurring amino acid and hence a polymer composed of two different biocompatible amphiphiles. AFM studies carried out between the fiber forming mixture and proteins resulted in the observation that only BSA selectively adheres to the fiber among the three alpha-helical and two beta-sheet proteins studied and hence may be of use in some medical applications.

A structurally characterized lower rim 1,3-di{bis(2-picolyl)}amide derivative of calix[4]arene (L) exhibits high selectivity toward Ag(+) by Forming it 1:1 complex, among nine other biologically important metal ions, viz., Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), and Zn(2+), its studied by fluorescence, absorption, and (1)H NMR spectroscopy. The 1:1 complex formed between L and Ag(+) has been further proven on the basis of ESI mass spectrometry and has been shown to have art association constant, K(a), of 11117 +/- 190 M(-1) based on fluorescence data. L acts as it primary ratiometric sensor toward Ag(+) by switch-on fluorescence and exhibits a lowest detectable concentration of 450 ppb. DFT computational studies carried out in mimicking thie formation of a 1:1 complex between L and Ag(+) resulted in it tetrahedral complex wherein the nitrogens of all four pyridyl moieties present on both arms are being coordinated. Whereas these pyridyls are located farther apart in the crystal structure, appropriate dihedral changes are induced in the arms in the presence of silver ion in order to form a coordination complex. Even the nanostructural features obtained in TEM clearly differentiates L from its Ag(+) complex. The in situ prepared silver complex of L detects Cys ratiometrically among the naturally occurring amino acids to a lowest concentration of 514 ppb by releasing L from the complex followed by formation of the cysteine complex of Ag(+). These were demonstrated on the basis of emission,absorption, (1)H NMR,and ESI mass spectra. The INH logic gate has also been generated by choosing Ag(+) and Cys as input and by monitoring the Output signal at 445 nm that originates from the excimer emission of L in the presence of Ag(+). Thus L is a potential primary sensor toward Ag(+) and is it secondary sensor toward Cys.

A highly selective fluorescence switch on sensor, L for detecting Cu2+ has been synthesized by introducing a bis-(2-picolyl)amine moiety at the lower rim of a calix[4]arene platform via amide linkage. Binding properties of L toward ten different biologically relevant Mn+ ions have been studied by fluorescence and absorption spectroscopy in methanol and aqueous methanol. L was found to detect Cu2+ selectively down to a concentration of 196 and 341 ppb, respectively, in methanol and 1:1 aqueous methanol even in the presence of other metal ions. The composition of the complex has been found to be 1:1 based on the Job plot and is further confirmed by ESI MS. The role of calix[4]arene platform as well as the pre-organized binding core in the selective recognition of Cu2+ has been demonstrated by studying appropriate reference molecules. The possible modes of binding of L with Cu2+ have been modeled by computational calculations. L and its Cu2+ complex could very well be differentiated based on the nano-structural features observed in SEM and AFM., © Elsevier