SERS Platform Based on Hollow-Core Microstructured Optical Fiber: Technology of UV-Mediated Gold Nanoparticle Growth

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for biosensing. However, SERS analysis has several concerns: the signal is limited by a number of molecules and the area of the plasmonic substrate in the laser hotspot, and quantitative analysis in a low-volume droplet is confusing due to the change of concentration during quick drying. The usage of hollow-core microstructured optical fibers (HC-MOFs) is thought to be an effective way to improve SERS sensitivity and limit of detection through the effective irradiation of a small sample volume filling the fiber capillaries. In this paper, we used layer-by-layer assembly as a simple method for the functionalization of fiber capillaries by gold nanoparticles (seeds) with a mean diameter of 8 nm followed by UV-induced chloroauric acid reduction. We also demonstrated a simple and quick technique used for the analysis of the SERS platform formation at every stage through the detection of spectral shifts in the optical transmission of HC-MOFs. The enhancement of the Raman signal of a model analyte Rhodamine 6G was obtained using such type of SERS platform. Thus, a combination of nanostructured gold coating as a SERS-active surface and a hollow-core fiber as a microfluidic channel and a waveguide is perspective for point-of-care medical diagnosis based on liquid biopsy and exhaled air analysis.

Green Synthesis and Characterization of Gold Nanoparticles from Malus viridisand Capsicum annuum as AnticancerAgent

Gold nanoparticles (AuNPs) were synthesied by eco friendly method (green method) through the reduction of aqueous chloroauric acid (HAuCl4.4H2O) solution using apple and pepper (Malusviridis and capsicum annuum) peels extract as a reducing and stabilizing agent. AuNPs were characterized using various instrumental techniques including energy dispersive spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), Atomic force microscope (AFM), field emission scanning electron microscopy (FESEM) ultraviolet-visible spectroscopy (UV-Vis), and Zeta-Potential. The synthesized AuNPs was used against breast cancer cell line MCF-7 to compare their biological effect as anticancer agent. Results showed that the AuNPs formed with both plants had a physical charastaristics differ from each other, even in their effects on cancerous cells, where the inhibition rate of AuNPs synthesized using apple (Malusviridis) peel extrac has larger values than Capsicum annuum. The AuNPs formed from synthesized using both plants showed an acceptable stability.

A New Covalent Organic Framework of Dicyandiamide-Benzaldehyde Nanocatalytic Amplification SERS/RRS Aptamer Assay for Ultratrace Oxytetracycline with the Nanogold Indicator Reaction of Polyethylene Glycol 600

In this paper, dicyandiamide (Dd) and p-benzaldehyde (Bd) were heated at 180 ∘C for 3 h to prepare a new type of stable covalent organic framework (COF) DdBd nanosol with high catalysis. It was characterized by molecular spectroscopy and electron microscopy. The study found that DdBd had a strong catalytic effect on the new indicator reaction of polyethylene glycol 600 (PEG600)-chloroauric acid to form gold nanoparticles (AuNPs). AuNPs have strong resonance Rayleigh scattering (RRS) activity, and in the presence of Victoria Blue B (VBB) molecular probes, they also have a strong surface-enhanced Raman scattering (SERS) effect. Combined with a highly selective oxytetracycline (OTC) aptamer (Apt) reaction, new dual-mode scattering SERS/RRS methods were developed to quantitatively analyze ultratrace OTC. The linear range of RRS is 3.00 × 10−3 –6.00 × 10−2 nmol/L, the detection limit is 1.1 × 10−3 nmol/L, the linear range of SERS is 3.00 × 10−3–7.00 × 10−2 nmol/L, and the detection limit is 9.0 × 10−4 nmol/L. Using the SERS method to analyze OTC in soil samples, the relative standard deviation is 1.35–4.78%, and the recovery rate is 94.3–104.9%.

Synthesis and Characterization of about 20nm Gold Nanoparticles

The synthesis of spherical gold nanoparticles (AuNPs) by the chemical reduction process and the characterization of the synthesized nanoparticles is the main aim of this article. Reduction of Chloroauric acid by trisodium citrate salt was performed to get AuNPs of average diameter 20nm. Trisodium citrate is not only the reducing reagent but also the stabilizer of the synthesized AuNPs. Some important modern techniques like UV-VIS spectroscopy, diffraction light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Selected area electron diffraction (SAED) and electron diffraction X-ray (EDX) were involved for the characterization of synthesized AuNPs. Chemical reduction and Size-controlled growth of spherical AuNPs were followed for this particular synthesis of AuNPs.

Green synthesis of gold nanoparticles using Tribulus terrestris extract and antibacterial activity against Gram-negative bacteria

Aqueous extract of the plant Tribulus terrestris was used to reduce chloroauric acid for synthesizing gold nanoparticles (AuNPs). In this green synthesis, the reaction proceeded to give a red/purple color that was monitored by UV-vis spectrophotometry, where the formed AuNPs had an absorption band with max of 550 nm. In terms of the highest absorbance at 550 nm, reaction conditions were optimized at a temperature of 75°C, at pH 7 and using a reaction time of 4 h. The integrity of the synthesized AuNPs was confirmed and their physical properties were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM), which also showed evidence that plant metabolites contributed to capping or stabilization of the AuNPs. XRD spectra suggested a particle size of around 40 nm and SEM images revealed spherical and relatively uniform and disperse particles with a size of less than 0.1 m. In a broth microdilution assay, the AuNPs showed inhibitory effects against Gram-negative Escherichia coli, but not against Gram-positive Enterococcus faecalis. The AuNPs showed no hemagglutination activity or cytotoxic activity against human blood cells, which is important for them to be explored as therapeutic antibacterial agents.

Synthesis of Gold Nanoparticles Using Tannin-Rich Extract and Coating onto Cotton Textiles for Catalytic Degradation of Congo Red

Gold nanoparticles (AuNPs) were synthesized under ambient conditions from chloroauric acid in aqueous solution at pH 4. Tannin-rich extract from Xylocarpus granatum bark was used as both reducing and capping agent, rapidly converting Au (I) salt to AuNPs. Transmission electron microscopy showed the as-prepared AuNPs to be predominantly spherical, with an average diameter of 17 nm. The AuNPs were tested for catalytic reduction of Congo red (CR), a carcinogenic azo dye, in aqueous sodium borohydride solution. Cotton samples were coated with the AuNPs, taking on a reddish-purple color. The samples showed significantly reduced tearing strength after coating, though tensile strength was unaffected. UV-visible spectroscopy was used to determine the dye concentration in the water. CR degradation was observed only when AuNPs were present, and the efficiency of degradation was strongly linked to the AuNP loading. The AuNP-coated fabrics left only a 4.7% CR concentration in the solution after 24 h and therefore promise as a heterogeneous catalyst for degradation of CR in aqueous solution.

New gold-198 nanoparticle synthesis to be used in cancer treatment

Gold nanoparticles (NPs) have been intriguing scientists for over 100 years. Recently, they have been studied for new applications such as cancer treatment. Although the synthesis of gold nanoparticles is extensively reported, in the majority of cases the methodology is confused and/or not clear. We describe a new synthesis methodology for radioactive gold‐198 NPs. Gold-198 was activated in IPEN IEA-01 nuclear reactor. After that, chloroauric acid (HAuCl4) was formed by dissolving the radioactive gold with aqua regia and performing repeated heating cycles. 0.1 mM HAuCl4 containing 100 μL of 1 M NaOH was prepared in a flask equipped with a reflux condenser. The solution was brought to boil and stirred with a PTFE‐coated magnetic stir‐bar. Then 5 mL of sodium citrate was rapidly added. The reaction turns from light yellow to clear, black, dark purple until the solution attained a wine‐red color (2–3 min). Dynamic light scattering (DLS) confirmed 8 nm particles. The presence of gold‐198 (197.968 g/mol; half‐life: 2.69517; decay mode: β‐; average energy: 1.3723 MeV) was confirmed by an ORTEC HPGe detector. DLS was performed after complete decay confirming the 8 nm diameter maintenance. We were able to achieve radioactive gold‐198 NPs and are performing further studies such as: coating reactions, in‐vitro and in‐vivo studies.

Investigating the Effects of Surface Adsorbates on Gold and Palladium Deposition on Carbon

Surface functional groups have a strong influence on the deposition and final state of nanoparticles adsorbed on to the surface, a role discussed by Professor Spencer in his work. This tribute to Spencer explores the formation of hydroxyls, thiosulfates, sulfites and sulfur atoms on carbon (HOPG) surfaces and their effect on the deposition of gold and palladium from aqueous solutions. Hydroxyls formed from ammonium hydroxide treatment have identical behaviour to those formed by acid treatment, and gold adsorption from Au3+ solutions gives Au0 initially, with Au3+ formed at higher concentrations on these surfaces. In contrast, palladium adsorption is hindered by the presence of the hydroxyls and there is no indication of any reduction to the metallic state. Ammonium thiosulfate adsorbs dissociatively from aqueous solutions on HOPG if the surface is pre-activated by the presence of surface hydroxyls. At low concentrations of ammonium thiosulfate, adsorbed sulfite and sulfur are formed in equimolar concentrations whereas adsorption of high concentrations of ammonium thiosulfate gives some degree of molecular adsorption, with evidence in XP spectra for an ammonium ion and a sulfur 2p peak at 282.9 eV attributed to the undissociated thiosulfate ion. Both sulfur and the sulfite are stable at the surface in neutral solutions but the sulfite desorbs when treated with acidified solutions (~ pH ≤ 6). These two groups are also stable at 373 K but begin to desorb by 473 K. Exposure to a weak chloroauric acid solution causes the desorption of the sulfite and formation of a gold species with an XP binding energy of 84.6 eV; we cannot determine from the present data whether this peak is due to a Au(I) state or very small nanoparticles of Au(0). Graphic Abstract