The role of OH- in the formation of highly selective gold nanowires at extreme pH: multi-fold enhancement in the rate of the catalytic reduction reaction by gold nanowires

Optimally biosynthesized, PEGylated gold nanoparticles functionalized with quercetin and camptothecin enhance potential anti-inflammatory, anti-cancer and anti-angiogenic activities

BACKGROUND

The development of nano delivery systems is rapidly emerging area of nanotechnology applications where nanomaterials (NMs) are employed to deliver therapeutic agents to specific site in a controlled manner. To accomplish this, green synthesis of NMs is widely explored as an eco-friendly method for the development of smart drug delivery system. In the recent times, use of green synthesized NMs, especially metallic NMs have fascinated the scientific community as they are excellent carriers for drugs. This work demonstrates optimized green, biogenic synthesis of gold nanoparticles (AuNPs) for functionalization with quercetin (QT) and camptothecin (CPT) to enhance potential anti-inflammatory, anti-cancer and anti-angiogenic activities of these drugs.

RESULTS

Gold nanoparticles were optimally synthesized in 8 min of reaction at 90 °C, pH 6, using 4 mM of HAuCl4 and 4:1 ratio of extract: HAuCl4. Among different capping agents tested, capping of AuNPs with polyethylene glycol 9000 (PG9) was found best suited prior to functionalization. PG9 capped AuNPs were optimally functionalized with QT in 1 h reaction at 70 °C, pH 7, using 1200 ppm of QT and 1:4 ratio of AuNPs-PG9:QT whereas, CPT was best functionalized at RT in 1 h, pH 12, AuNPs-PG9:CPT ratio of 1:1, and 0.5 mM of CPT. QT functionalized AuNPs showed good anti-cancer activity (IC50 687.44 µg/mL) against MCF-7 cell line whereas test of anti-inflammatory activity also showed excellent activity (IC50 287.177 mg/L). The CAM based assessment of anti-angiogenic activity of CPT functionalized AuNPs demonstrated the inhibition of blood vessel branching confirming the anti-angiogenic effect.

CONCLUSIONS

Thus, present study demonstrates that optimally synthesized biogenic AuNPs are best suited for the functionalization with drugs such as QT and CPT. The functionalization of these drugs with biogenic AuNPs enhances the potential anti-inflammatory, anti-cancer and anti-angiogenic activities of these drugs, therefore can be used in biomedical application.

Advances in biogenically synthesized shaped metal- and carbon-based nanoarchitectures and their medicinal applications

Non-spherical metal-based and carbon-based nanostructures have found applications in every facet of scientific endeavors, including engineering and biomedical fields. These nanostructures attract attention because of their biocompatibility and negligible cytotoxicity. Chemical and physical methods have been used for synthesizing earlier generations of metal-based and carbon-based nanostructures with variable architectures, including nanorods, nanowires, nanodots and nanosheets. However, these synthesis strategies utilize organic passivators which are toxic to the environment and the human body. Biogenic synthesis of nanoparticles is becoming increasing popular because of the necessity to develop eco-friendly and non-toxic strategies. Nanoparticles synthesized by natural compounds have immense potential in the biomedical arena. The present review focuses on plant-mediated synthesis of metal-based and carbon-based non-spherical nanoarchitectures and the role of green synthesis in improving their activities for biomedical applications.

Solid-State Green Synthesis of Ag NPs: Higher Temperature Harvests Larger Ag NPs but Smaller Size Has Better Catalytic Reduction Reaction

In this work a novel solid-state green approach without using any solvent environment has been proposed to synthesize Ag NPs. The synthetic condition has been investigated in 4 °C, 20 °C, 40 °C and 60 °C and at ten different time intervals. This synthesis process gives different size and shape of curcumin conjugated Ag NPs, which have been confirmed by various morphological and spectroscopic techniques. It is found that higher temperature and longer time produces larger particles size and different varieties in shapes. For example, Ag NPs prepared at 4 °C are spherical shapes whereas that prepared at 60 °C are of spherical, rods, and many hexagonal shapes. At 60 °C and after 5 and 7 days the size of the prepared Ag NPs exceed the nano scale to reach micro scale level. This size and shape distribution are well reflected in the optical properties as absorbance, fluorescence intensity and SFS intensity of Ag NPs consistently increase with increase in temperature during synthesis. Ag NPs obtained in different temperature and various time intervals have been subsequently tested as catalysts for the reduction reaction, where 4-nitrophenol is reduced to 4-aminophenol in the presence of NaBH₄. It is found that smaller particles have better catalytic properties for the reduction reaction.

Gold and silver nanoparticles in resonance Rayleigh scattering techniques for chemical sensing and biosensing: a review

This review (with 116 refs.) summarizes the state of the art in resonance Rayleigh scattering (RRS)-based analytical methods. Following an introduction into the fundamentals of RRS and on the preparation of metal nanoparticles, a first large section covers RRS detection methods based on the use of gold nanoparticles, with subsections on proteins (albumin, bovine serum albumin and ovalbumin, glycoproteins, folate receptors, iron binding-proteins, G-proteins-coupled receptors, transmembrane proteins, epidermal growth factor receptors), on pesticides, saccharides, vitamins, heavy metal ions (such as mercury, silver, chromium), and on cationic dyes. This is followed by a section on RRS methods based on the use of silver nanoparticles, with subsections on the detection of nucleic acids and insecticides. Several Tables are presented where an RRS method is compared to the performance of other methods. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical Abstract Change in the resonance Rayleigh scattering (RRS) intensity when mixing the nanoparticles with the specific analyte.

Nanosensing of ATP by fluorescence recovery after surface energy transfer between rhodamine B and curcubit[7]uril-capped gold nanoparticles

The authors describe a method for functionalization of gold nanoparticles (AuNPs) with the supramolecular host molecule, curcubit[7]uril (CB[7]) which can bind rhodamine B (RhB). The fluorescence of RhB is quenched by the AuNPs via surface energy transfer. On addition of ATP, a dimeric RhB-ATP complex is formed and RhB is pushed out of CB[7]. Hence, fluorescence increases by a factor of 8. This fluorescence recovery effect has been utilized to develop a new detection scheme for ATP. The assay, measured at fluorescence excitation and emission wavelengths of 500 nm and 574 nm respectively, works in the 0.5-10 μM concentration range and has a 100 nM detection limit. The method is not interfered by UTP, GTP, CTP, TTP, ascorbic acid and glutathione. Graphical abstract Schematic of a method for determination of ATP in the 500 nM to 10 μM concentration range by using fluorescence recovery after surface energy transfer (SET) between rhodamine B (RhB) and gold nanoparticles capped with curcubit[7]uril (CB[7]).

The Langmuir-Hinshelwood approach for kinetic evaluation of cucurbit[7]uril-capped gold nanoparticles in the reduction of the antimicrobial nitrofurantoin

In this work, gold nanoparticles protected by the macrocycle cucurbit[7]uril were used as a catalyst in the reduction of the hazardous antimicrobial nitrofurantoin. 4-Nitrophenol was also employed as the substrate of the reduction for comparative purposes. The kinetic data were modeled to the Langmuir-Hinshelwood equation to know the affinities of the reactants for the surface and the real kinetic constants, a comparison at the molecular level that is made for the first time. From the results, it was observed that the adsorption of nitrofurantoin was stronger than that of 4-nitrophenol whilst the kinetic constant on the surface was higher for 4-nitrophenol than for nitrofurantoin. Additionally, shifts in the nanoparticle surface plasmon band permitted insights to be obtained into the adsorption rate and strength. The reaction induction times were also investigated and were highly dependent on the borohydride concentration and, due to the higher surface affinity of nitrofurantoin compared with 4-nitrophenol, an increase in nitrofurantoin concentration increased the induction time, while a lag phase was not observed for 4-nitrophenol.

Tuning the surface of Au nanoparticles using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol): enzyme free and label free sugar sensing in serum samples using resonance Rayleigh scattering spectroscopy

Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (F-108) functionalized gold nanoparticles (Au NPs) have been successfully synthesized for glucose estimation.

Amplification of resonance Rayleigh scattering of gold nanoparticles by tweaking into nanowires: Bio-sensing of α-tocopherol by enhanced resonance Rayleigh scattering of curcumin capped gold nanowires through non-covalent interaction

Tuning optical properties by controlling size and shape of the metallic nanoparticles has been of great interest to design novel bio-sensing techniques. Here, as a first example we illustrate that resonance Rayleigh scattering (RRS) signal of Au nanoparticles (NPs) can be amplified >10-fold by growing into Au nanowires (NWs). These thin and long NWs of ~20-25nm diameter and >1µm length can be achieved by suitably manipulating the temperature during green synthesis using curcumin. Interestingly, mixture of Au NWs and NPs or shorter NWs gives a moderate increase in RRS signal suggesting formation of longer NWs is crucial for optimal enhancement of RRS signal. Curcumin along with CTAB act as capping and stabilizing agent for Au NWs/NPs in different temperatures, which is confirmed by XRD, TGA, DSC, EDX and FT-IR data. This amplified RRS signal of Au NWs has been employed to design a new optical biosensor for α-tocopherol (α-TOH), which is among the most biologically active form of vitamin E. Association of α-TOH with Au NWs further enhances the RRS signal of Au NWs, ~10 fold through non-covalent interaction. No interference from other antioxidant substances like ascorbic acid and 6-O-Palmitoyl-L-ascorbic acid is observed. The sensing method is simple, fast and offers remarkable linear dynamic ranges, 12.8-1004µmolL^-1, which is larger than reported values. The detection limit for α-TOH estimation has been found to be 50nmolL^-1. The biosensor is found to be stable both in the absence and presence of α-TOH and provides an excellent recovery for synthetic samples.

High-yield synthesis and fine-tuning aspect ratio of (200) faceted gold nanorods by the pH-adjusting method

Tight-controlling of the aspect ratios (ARs) and fine-tailoring of the crystallographic facets of gold nanorods (GNRs) are critical for their further applications in material, biological, and medical fields.