The SERS effect in coordination chemistry

Unusual dark-field hyperspectral and confocal Raman microscopy features of a nanoporous gold electrode coated with porphyrazine complex

Nanoporous gold electrodes are of great interest in electroanalytical chemistry, because of their unusual activity and large surface area. The electrochemical activity can be further improved by coating with molecular catalysts such as the tetraruthenated cobalt-tetrapyridylporphyrazines investigated in this work. The plasmonic enhancement of the scattered light at the nanoholes and borders modifies the electrode's optical characteristics, improving the transmission through the surface-enhanced Raman scattering (SERS) effect. When monitored by hyperspectral dark-field and confocal Raman microscopy, this effect allows probing of the porphyrazine species at the plasmonic nanholes, improving the understanding of the chemically modified gold electrodes.

Effective adsorption of heavy metal ions in water by sulfhydryl modified nano titanium dioxide

Background: The monitoring and removal of heavy metal ions in wastewater will effectively improve the quality of water and promote the green and sustainable development of ecological environment. Using more efficient adsorption materials and more accurate detection means to treat heavy metal ions in water has always been a research focus and target of researchers. Method: A novel titania nanomaterial was modified with sulfhydryl group (nano TiO₂-SH) for detection and adsorption of heavy metal ions in water, and accurately characterize the adsorption process using Surface-Enhanced Raman Spectroscopy (SERS) and other effective testing methods. Results: The maximum adsorption efficiency of nano TiO₂-SH for the Hg²⁺, Cd²⁺, Pb²⁺ three heavy metal ions reached 98.3%, 98.4% and 98.4% respectively. And more importantly, after five cycles of adsorption and desorption, the adsorption efficiency of nano TiO₂-SH for these three metal ions is still above 96%. Conclusion: These results proved the nano TiO₂-SH adsorbent has great potential in practical water pollution purification.

Analytical determination of gold ions based on ranelate induced nanoparticle formation

A ranelate ion, an old antiosteoporotic drug, readily reacts with gold(III) ions generating stable gold nanoparticles (AuNP@Ran). The reaction proceeds rapidly under green conditions and is specific for gold ions at room temperature. Their characteristic color associated with the plasmonic resonance effects allows its use in colorimetric/spectrophotometric analysis, as well as in spot test assays. In addition to the color changes, the gold nanoparticles exhibit surface enhanced Raman scattering (SERS), providing another interesting route for the analytical detection of gold ions. Because of the great simplicity, the ranelate method can be very convenient for monitoring gold ions, especially in metal extraction and hydrometallurgical processes.

Plasmon-Catalysed Decarboxylation of Dicarboxybipyridine Ligands in Ru(II) Complexes Chemisorbed on Ag Nanoparticles: Conditions, Proposed Mechanism and Role of Ag(0) Adsorption Sites

Plasmon-catalyzed decarboxylation reactions of Ru(II) bis(2,2‘-bipyridine)(4,4‘-dicarboxy-bipyridine) denoted as Ru(bpy)2(dcbpy) and Ru(II) tris(4,4‘-dicarboxy-bipyridine) denoted as Ru(dcbpy)3 complexes in hydrosol systems with Ag nanoparticles (NPs) conditioned by the presence of Ag(0) adsorption...

Toxicity of combined exposure of ZnO nanoparticles (NPs) and myricetin to Caco-2 cells: changes of NP colloidal aspects, NP internalization and the apoptosis-endoplasmic reticulum stress pathway

Phytochemicals as typical food components may significantly influence the toxicity of nanoparticles (NPs) in intestinal cells, indicating a need to evaluate the toxicological effects of NPs in a complex situation. Previous studies suggested that the anti-oxidative properties of phytochemicals were important to elicit cytoprotective effects against NP exposure. However, we recently found that the changes of signaling pathways may be more important for cytoprotective effects of phytochemicals. In this study, we investigated the influence of myricetin (MY) on the cytotoxicity of ZnO NPs in Caco-2 cells and the possible mechanism. MY at 50 μM showed minimal impact on the solubility and colloidal aspects of ZnO NPs, but protected Caco-2 cells from NP exposure as it increased the EC50 value. For comparison, dihydromyricetin (DMY; chemical analog of MY) increased the EC50 value to a much lesser extent. Exposure to ZnO NPs significantly induced intracellular Zn ions, whereas MY or DMY did not significantly influence the internalization of NPs. However, ZnO NPs significantly promoted the ratio of caspase-3/pro-caspase-3, which was inhibited by the presence of MY. Exposure to ZnO NPs did not significantly promote the biomarkers of endoplasmic reticulum (ER) stress, but co-exposure to ZnO NPs and MY significantly lowered the levels of a panel of ER stress biomarkers. In conclusion, these results suggested that MY could protect Caco-2 cells from ZnO NP exposure, which may not be related to the changes of colloidal stability or internalization of NPs but could be alternatively related to the reduction of ER stress leading to lower cleaved caspase-3.

Unravelling the nature of the spongy dark material in aged Turkevich gold nanoparticles colloidal solutions by CytoViva® dark-field imaging and HRTEM analysis

Turkevich gold nanoparticles colloidal solutions undergo further changes after ageing for several weeks or months, and in most cases a spongy dark material can be observed suspended in the red solution. CytoViva® dark-field microscopy images and high resolution transmission electron micrographys (HRTEM) of the strange body played a central role and revealed a fibrous structure, consistent with cellulose, as commonly found in the cell-walls of many fungi. Surprisingly, the interior of the fibers are filled with gold nanoparticles, responsible for the high contrasting images obtained in this work. The fungi were replicated in the laboratory, characterized by Infrared Microscopy (FTIR) and revealed an ability to grow in gold-citrate media, even in dark and anaerobical conditions.

Thiosemicarbazone@Gold nanoparticle hybrid as selective SERS substrate for Hg2+ ions

The Raman spectral profile of p-methylcarbohydrazonethioamide (MCHT) is completely changed due to strong SERS effects upon bonding onto gold nanoparticles surface, but some vibrational modes are further enhanced in the presence of Hg(II) ions. The lack of SERS response for most common metal ions indicates that the coordinating groups are interacting with the gold nanoparticles surface and not available for binding metal ions in solution, except for mercury ions. The selective enhancement of some vibrational modes is consistent with significant conformational changes upon binding of Hg(II) ion onto the AuNP@MCHT hybrid, as confirmed by TEM/EDS measurements, demonstrating its potentiality as a highly selective and sensitive SERS substrate.

Photoinduced Enhanced Raman from Lithium Niobate on Insulator Template

Photoinduced enhanced Raman spectroscopy from a lithium niobate on insulator (LNOI)-silver nanoparticle template is demonstrated both by irradiating the template with 254 nm ultraviolet (UV) light before adding an analyte and before placing the substrate in the Raman system (substrate irradiation) and by irradiating the sample in the Raman system after adding the molecule (sample irradiation). The photoinduced enhancement enables up to an ∼sevenfold increase of the surface-enhanced Raman scattering signal strength of an analyte following substrate irradiation, whereas an ∼threefold enhancement above the surface-enhanced signal is obtained for sample irradiation. The photoinduced enhancement relaxes over the course of ∼10 h for a substrate irradiation duration of 150 min before returning to initial signal levels. The increase in Raman scattering intensity following UV irradiation is attributed to photoinduced charge transfer from the LNOI template to the analyte. New Raman bands are observed following UV irradiation, the appearance of which is suggestive of a photocatalytic reaction and highlight the potential of LNOI as a photoactive surface-enhanced Raman spectroscopy substrate.

Real-time optofluidic surface-enhanced Raman spectroscopy based on a graphene oxide/gold nanorod nanocomposite

We demonstrate a glass microcapillary fiber as an optofluidic platform for surface enhanced Raman spectroscopy (SERS), the inner walls of which are coated with a graphene oxide (GO)/gold nanorod (AuNR) nanocomposite. A simple thermal method is used for the coating, allowing for the continuous deposition of the nanocomposite without surface functionalization. We show that the AuNRs can be directly and nondestructively identified on the GO inside the capillaries via identification of the Au-Br SERS peak, as Br- ions from the AuNR synthesis remain on their surface. The coated microcapillary platform is, then, used as a stable SERS substrate for the detection of Rhodamine 6G (R6G) and Rhodamine 640 (RH640) at concentrations down to 10^-7 and 10^-9 M, respectively. As the required sample volumes are as low as a few hundred nanoliters, down to ~75 femtograms of analyte can be detected. The fiber also allows for the detection of the molecules at acquisition times as low as 0.05 s, indicating the platform's suitability for real-time sensing.

The effects of baicalein or baicalin on the colloidal stability of ZnO nanoparticles (NPs) and toxicity of NPs to Caco-2 cells

Recent study suggested that the presence of phytochemicals in food could interact with nanoparticles (NPs) and consequently reduce the toxicity of NPs, which has been attributed to the antioxidant properties of phytochemicals. In this study, we investigated the interactions between ZnO NPs and two flavonoids baicalein (Ba) or baicalin (Bn) as well as the influence of the interactions on the toxicity of ZnO NPs to Caco-2 cells. The antioxidant properties of Ba and Bn were confirmed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays, with Ba being stronger. However, the presence of Ba or Bn did not significantly affect cytotoxicity, intracellular superoxide or release of inflammatory cytokines of Caco-2 cells after ZnO NP exposure. When Ba was present, the cellular viability of Caco-2 cells after exposure to ZnO NPs was slightly increased, associated with a modest decrease of intracellular Zn ions, but these effects were not statistically different. Ba was more effective than Bn at changing the hydrodynamic sizes, Zeta potential and UV-Vis spectra of ZnO NPs, which indicated that Ba might increase the colloidal stability of NPs. Taken together, the results of the present study indicated that the anti-oxidative phytochemical Ba might only modestly protected Caco-2 cells from the exposure to ZnO NPs associated with an insignificant reduction of the accumulation of intracellular Zn ions. These results also indicated that when assessing the combined effects of NPs and phytochemicals to cells lining gastrointestinal tract, it might be necessary to evaluate the changes of colloidal stability of NPs altered by phytochemicals.