Tuning of Morphology and Stability of Gold Nanostars Through pH Adjustment.

In this study, the morphology and stability of gold nanostars (AuNSs) were investigated under different pH environments. The surface morphologies and plasmonic properties were observed for nanostars (NSs) deposited on glass substrates, using SEM and ultraviolet and visible (UV-Vis) spectroscopy. It is found that gold nanostars can be readily stabilized just by adjusting the initial pH condition of the growth solution. The particle size distribution of gold nanostars under different pH environments has been investigated using UV-Vis spectroscopy and found to be highly dependent on pH. At the optimal pH of 11, the gold nanostars are highly monodisperse, they have longer branches and the Au Localized Surface Plasmon Resonance band (LSPR) at 720 nm. For other pH conditions, particles are non-uniform and polydisperse, showing a red-shift of the plasmon peak due to aggregation and a large particle size distribution. Time-dependent UV-Vis spectra studies hypothesize the pH dependent stabilization mechanism, where the formation and stabilization of AuNS were affected greatly by the aggregation induced by pH of the growth solution. The information obtained in this study can be used to design stable gold nanostars with longer shelf life for biosensing applications.

Nano-Bio Interactions of Extracellular Vesicles with Gold Nanoislands for Early Cancer Diagnosis.

Extracellular vesicles or exosomes are membrane encapsulated biological nanometric particles secreted virtually by all types of cells throughout the animal kingdom. They carry a cargo of active molecules to proximal and distal cells of the body as mechanism of physiological communication, to maintain natural homeostasis as well as pathological responses. Exosomes carry a tremendous potential for liquid biopsy and therapeutic applications. Thus, there is a global demand for simple and robust exosome isolation methods amenable to point-of-care diagnosis and quality control of therapeutic exosome manufacturing. This can be achieved by molecular profiling of the exosomes for use with specific sets of molecular-markers for diagnosis and quality control. Liquid biopsy is undoubtedly the most promising diagnosis process to advance "personalized medicine." Currently, liquid biopsy is based on circulating cancer cells, cell free-DNA, or exosomes. Exosomes potentially provide promise for early-stage diagnostic possibility; in order to facilitate superior diagnosis and isolation of exosomes, a novel platform is developed to detect and capture them, based on localized surface plasmon resonance (LSPR) of gold nanoislands, through strong affinity between exosomes and peptide called Venceremin or Vn96. Physical modeling, based on the characteristics of the gold nanoislands and the bioentities involved in the sensing, is also developed to determine the detection capability of the platform, which is optimized experimentally at each stage. Preliminary results and modeling present a relationship between the plasmonic shift and the concentration of exosomes and, essentially, indicate possibilities for label-free early diagnosis.

Plasmonic Gold Decorated MWCNT Nanocomposite for Localized Plasmon Resonance Sensing.

The synergism of excellent properties of carbon nanotubes and gold nanoparticles is used in this work for bio-sensing of recombinant bovine growth hormones (rbST) by making Multi Wall Carbon Nanotubes (MWCNT) locally optically responsive by augmenting it optical properties through Localized Surface Plasmon Resonance (LSPR). To this purpose, locally gold nano particles decorated gold-MWCNT composite was synthesized from a suspension of MWCNT bundles and hydrogen chloroauric acid in an aqueous solution, activated ultrasonically and, then, drop-casted on a glass substrate. The slow drying of the drop produces a "coffee ring" pattern that is found to contain gold-MWCNT nanocomposites, accumulated mostly along the perimeter of the ring. The reaction is studied also at low-temperature, in the vacuum chamber of the Scanning Electron Microscope and is accounted for by the local melting processes that facilitate the contact between the bundle of tubes and the gold ions. Biosensing applications of the gold-MWCNT nanocomposite using their LSPR properties are demonstrated for the plasmonic detection of traces of bovine growth hormone. The sensitivity of the hybrid platform which is found to be 1 ng/ml is much better than that measuring with gold nanoparticles alone which is only 25 ng/ml.

The effect of hydrogen nanobubbles on the morphology of gold-gelatin bionanocomposite films and their optical properties.

Gold-gelatin bionanocomposite films are prepared by the reduction of gold ions by sodium borohydride in an aqueous solution. It is shown that both the solution and the films on glass substrates contain entrapped hydrogen micro- and nanobubbles with diameters in the range of 200 nm-3 µm. The optical properties of gold nanoparticles in the presence of gelatin and hydrogen nanobubbles are measured and simulated by using the discrete dipole approximation method. The composite films having micro- and nanobubble inclusions have been found to be very stable. The calculated localized surface plasmon resonance band is found in agreement with the experimental band position only when the presence of hydrogen bubbles around the gold nanoparticles is taken into account. The different morphological features engendered by the presence of the bubbles in the film (gelatin receptacles for the nanoparticles, gelatin hemispheres raised by the bubbles under the surface, cavities on the surface of the film, etc) are described in detail and considered for potential applications. This work is highly relevant to the new and exciting topic of nanobubbles on surfaces and interfaces.

Micro-Raman spectroscopy study of colloidal crystal films of polystyrene-gold composites.

Monolayers and multilayers of polystyrene (PS)-gold composite films prepared by two different deposition methods have been investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and confocal Raman microspectroscopy. The intensity of the 1001 cm(-1) ring breathing mode of PS is used to evaluate the degree of ordering of monolayers and multilayers within a colloidal crystal. The depth profiling capability of confocal Raman microscopy is used to probe the regions inside the fractures in multilayered films. The intensity profile of the 1001 cm(-1) peak revealed the presence of fractures of different shapes with some PS microspheres at the bottom of the fracture. A strong increase in the Raman intensity (by 10(3) times) has been observed when probing the regions where Au nanoparticles are concentrated in aggregates of different shapes. This enhancement is attributed to the surface plasmons generated by the periodic structure of the gold nanoparticles.

The protonation of a retinyl Schiff base: a study by FTIR spectroscopy at low temperature in solution.

The hydrogen bonding-protonation equilibrium for retinyl Schiff base/propionic acid or 3-chloropropionic acid systems was examined by Fourier transform infrared spectroscopy in non polar solutions at temperatures ranging from 25 degrees C to about -150 degrees C. The spectra give evidence for the gradual increase in the degree of protonation as temperature is lowered. The bearing of this on applying low temperature spectroscopic results to physiological conditions in rhodopsin research is discussed.