Gold nanomakura: nanoarchitectonics and their photothermal response in association with carrageenan hydrogels.

Photothermal conversion of light into heat energy is an intrinsic optical property of metal nanoparticles when irradiated using near-infrared radiation. However, the impact of size and shape on the photothermal behaviour of gold nanomakura particles possessing optical absorption within 600-700 nm as well as on incorporation in hydrogels is not well reported. In this study, nanomakura-shaped anisotropic gold nanoparticles (AuNMs) were synthesized via a surfactant-assisted seed-mediated protocol. Quaternary cationic surfactants having variable carbon tail length (n = 16, 14, 12) were used as capping for tuning the plasmon peak of gold nanomakura within a 600-700 nm wavelength. The aspect ratio as well as anisotropy of synthesized gold nanomakura can influence photothermal response upon near-infrared irradiation. The role of carbon tail length was evident via absorption peaks obtained from longitudinal surface plasmon resonance analysis at 670, 650, and 630 nm in CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM, respectively. Furthermore, the impact of morphology and surrounding milieu of the synthesized nanomakuras on photothermal conversion is investigated owing to their retention of plasmonic stability. Interestingly, we found that photothermal conversion was exclusively assigned to morphological features (i.e., nanoparticles of higher aspect ratio showed higher temperature change and vice versa irrespective of the surfactant used). To enable biofunctionality and stability, we used kappa-carrageenan- (k-CG) based hydrogels for incorporating the nanomakuras and further assessed their photothermal response. Nanomakura particles in association with k-CG were also able to show photothermal conversion, depicting their ability to interact with light without hindrance. The CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM after incorporation into hydrogel beads attained up to ≈17.2, ≈17.2, and ≈15.7 °C, respectively. On the other hand, gold nanorods after incorporation into k-CG did not yield much photothermal response as compared to that of AuNMs. The results showed a promising platform to utilize nanomakura particles along with kappa-carrageenan hydrogels for enabling usage on nanophotonic, photothermal, and bio-imaging applications.

The role of deep eutectic solvents and carrageenan in synthesizing biocompatible anisotropic metal nanoparticles.

Plasmonic metal nanoparticles are widely used for many applications due to their unique optical and chemical properties. Over the past decade, anisotropic metal nanoparticles have been explored for imaging, sensing, and diagnostic applications. The variations and flexibility of tuning the size and shape of the metal nanoparticles at the nanoscale made them promising candidates for biomedical applications such as therapeutics, diagnostics, and drug delivery. However, safety and risk assessment of the nanomaterials for clinical purposes are yet to be made owing to their cytotoxicity. The toxicity concern is primarily due to the conventional synthesis route that involves surfactants as a structure-directing agent and as a capping agent for nanoparticles. Wet chemical methods employ toxic auxiliary chemicals. However, the approach yields monodispersed nanoparticles, an essential criterion for their intended application and a limitation of the green synthesis of nanoparticles using plant extracts. Several biocompatible counterparts such as polymers, lipids, and chitosan-based nanoparticles have been successfully used in the synthesis of safe nanomaterials, but there were issues regarding reproducibility and yield. Enzymatic degradation was one of the factors responsible for limiting the efficacy. Hence, it is necessary to develop a safer and nontoxic route towards synthesizing biocompatible nanomaterials while retaining morphology, high yield, and monodispersity. In this regard, deep eutectic solvents (DESs) and carrageenan as capping agent for nanoparticles can ensure the safety. Carrageenan has the potential to act as antibacterial and antiviral agent, and adds enhanced stability to the nanoparticles. This leads to a multidimensional approach for utilizing safe nanomaterials for advanced biomedical and clinical applications.

A Novel Approach towards Synthesis and Characterization of Non-Cytotoxic Gold Nanoparticles Using Taurine as Capping Agent.

Metal gold nanoparticles are of great interest due to their unique physico-chemical properties and their potential to be used as nano-probes in biosensors, drug delivery, and therapeutic applications. Currently, many capping agents are used for metal gold nanoparticles, such as cetyltrimethylammonium bromide (CTAB) and tri-sodium citrate that have been reported to be toxic and hinders biological applications. To address this issue, we report, for the first time, the use of taurine as a stable non-cytotoxic capping agent for synthesizing gold nanoparticles by using an in situ wet-chemical method. This facile method resulted in monodisperse gold nanospheres with a high yield and stability. Monodisperse gold nanospheres with average diameters of 6.9 nm and 46 nm were synthesized at a high yield with controlled morphology. Temperature played a critical role in determining the size of the taurine-capped gold nanoparticles. The subtle changes in the reaction parameters had a tremendous effect on the final size of nanoparticles and their stability. The synthesized nanoparticles were characterized by using optical spectroscopy, a ZetaSizer, a NanoSight, Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), X-ray Photon Spectroscopy (XPS) and Electron Microscopy to understand their physico-chemical properties. Taurine was explored as a capping and stabilizing agent for gold nanospheres, which were evaluated for their toxicity responses towards human liver carcinoma cells (HepG2) via MTT assay.

Impaired lysosomal activity mediated autophagic flux disruption by graphite carbon nanofibers induce apoptosis in human lung epithelial cells through oxidative stress and energetic impairment.

BACKGROUND: Graphite carbon nanofibers (GCNF) have emerged as a potential alternative of carbon nanotubes (CNT) for various biomedical applications due to their superior physico-chemical properties. Therefore in-depth understanding of the GCNF induced toxic effects and underlying mechanisms in biological systems is of great interest. Currently, autophagy activation by nanomaterials is recognized as an emerging toxicity mechanism. However, the association of GCNF induced toxicity with this form of cell death is largely unknown. In this study, we have assessed the possible mechanism; especially the role of autophagy, underlying the GCNF induced toxicity. METHODS: Human lung adenocarcinoma (A549) cells were exposed to a range of GCNF concentrations and various cellular parameters were analyzed (up to 48 h). Transmission electron microscopy, immunofluorescent staining, western blot and quantitative real time PCR were performed to detect apoptosis, autophagy induction, lysosomal destabilization and cytoskeleton disruption in GCNF exposed cells. DCFDA assay was used to evaluate the reactive oxygen species (ROS) production. Experiments with N-acetyl-L-cysteine (NAC), 3-methyladenine (3-MA) and LC3 siRNA was carried out to confirm the involvement of oxidative stress and autophagy in GCNF induced cell death. Comet assay and micronucleus (MN) assay was performed to assess the genotoxicity potential. RESULTS: In the present study, GCNF was found to induce nanotoxicity in human lung cells through autophagosomes accumulation followed by apoptosis via intracellular ROS generation. Mechanistically, impaired lysosomal function and cytoskeleton disruption mediated autophagic flux blockade was found to be the major cause of accumulation rather than autophagy induction which further activates apoptosis. The whole process was in line with the increased ROS level and their pharmacological inhibition leads to mitigation of GCNF induced cell death. Moreover the inhibition of autophagy attenuates apoptosis indicating the role of autophagy as cell death process. GCNF was also found to induce genomic instability. CONCLUSION: Our present study demonstrates that GCNF perturbs various interrelated signaling pathway and unveils the potential nanotoxicity mechanism of GCNF through targeting ROS-autophagy-apoptosis axis. The current study is significant to evaluate the safety and risk assessment of fibrous carbon nanomaterials prior to their potential use and suggests caution on their utilization for biomedical research.

Iodide impurities in hexadecyltrimethylammonium bromide (CTAB) products: lot-lot variations and influence on gold nanorod synthesis.

Recent reports [Smith and Korgel Langmuir 2008, 24, 644-649 and Smith et al. Langmuir 2009, 25, 9518-9524] have implicated certain hexadecyltrimethylammonium bromide (CTAB) products with iodide impurities, in the failure of a seed-mediated, silver and surfactant-assisted growth protocol, to produce gold nanorods. We used two of the three "suspect" CTAB products and a "good" CTAB product in the protocol, varying silver nitrate solutions in the growth solutions. We obtained excellent gold nanorod samples as witnessed in signature longitudinal plasmon peaks in optical extinction spectra, which we substantiated using electron microscopy. Analysis of these samples using inductively coupled plasma mass spectroscopy (ICP-MS) failed to detect iodide. We subsequently learnt from discussions with Smith et al. that different lot numbers within the same product had been analyzed by our respective laboratories. We can conclude that iodide impurities can vary significantly from lot to lot within a product, to such an extent that there is no guarantee that gold nanorods can be synthesized with one or other CTAB product. Conversely, labeling a CTAB product, identified by a product number or supplier name, as one whose use precludes the formation of nanorods, is also hasty.

Synthesis and bioconjugation of gold nanoparticles as potential molecular probes for light-based imaging techniques.

We have synthesized and characterized gold nanoparticles (spheres and rods) with optical extinction bands within the "optical imaging window." The intense plasmon resonant driven absorption and scattering peaks of these nanoparticles make them suitable as contrast agents for optical imaging techniques. Further, we have conjugated these gold nanoparticles to a mouse monoclonal antibody specific to HER2 overexpressing SKBR3 breast carcinoma cells. The bioconjugation protocol uses noncovalent modes of binding based on a combination of electrostatic and hydrophobic interactions of the antibody and the gold surface. We discuss various aspects of the synthesis and bioconjugation protocols and the characterization results of the functionalized nanoparticles. Some proposed applications of these potential molecular probes in the field of biomedical imaging are also discussed.