Speaker: Prof. Jacek Lipkowski

Title1: SERS studies of a biomimetic membrane supported at a nanocavities patterned Ag

Date/Time: 16:00-17:00 PM, Nov. 14, 2018

Location: Room 202, Lujiaxi Building

Abstract:

Surface-enhanced Raman scattering (SERS) was employed to study lipid bilayers deposited on the nano-structured Ag electrode. Highly ordered 2D nano-cavities with sizes ranging from 300 to 750 nm were prepared as SERS active substrates by electrodepositing Ag onto a gold electrode covered by a spin coated polystyrene microspheres film. The surface of the nano-patterned electrode was then coated by a self-assembled monolayer of 1-Thio-β-D-glucose. The surface modified by the SAM of thioglugose had hydrophilic properties. Different types of supported bilayer lipid membranes (sBLM) of 1,2dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were deposited onto that substrate by: a) fusion of unilamellar vesicles, b) Langmuir-Blodgett deposition. The Langmuir-Blodgett technique was used to deposit bilayers with one leaflet composed of deuterium and the second leaflet by hydrogen substituted lipids. SERS spectra of the lipids provided information about the conformation and orientation of the acyl chains as a function of potential applied to the electrode. The results showed that: (i) at ~22oC all sBLMs were in the liquid crystalline state; (ii) at TG modified surface the bilayer is more ordered that when it is in a direct contact with the metal; (iii) the leaflet in contact with TG is more ordered than the leaflet in contact with electrolyte. This model membrane was then used to study the potential controlled behavior of unit A of the cholera toxin protein (CTA). SERS spectra of the amide I and amide II showed that the protein can penetrate the bilayer at negative potentials and that the protein in contact with the metal becomes denatured.

Title2: Nano-patterned electrodes to study temporal changes in the passive layer at a gold electrode surface in a thiosulfate solution

Date/Time: 16:00-17:00 PM, Nov. 19, 2018

Location:  Room 202, Lujiaxi Building

Abstract:

We employed Raman spectroscopy to study time dependent decomposition of thiosulfate at the gold electrode surface. Thiosulfate is used as a replacement of cyanide in gold leaching by gold mining industry. Although the initial leaching rates are higher in the presence of thiosulfate than observed for cyanide, the passive layer formed at longer leaching time is restricting gold recovery from the mineral to about 80%. We used SERS to identify species present in the passive layer and the pathways of thiosulfate decomposition with time. The dissolution of the nanopatterned gold surface created a challenge for this study. We applied two approaches to overcome that obstacle. First, we employed nanorod arrays with the nanorod length up to 20 μm and diameter ~0.280 μm. In this architecture, only transverse plasmons contributed to the SERS signal and the signal was independent of the variable length of the nanrods. However, changes of the band intensity with time displayed spikes caused by intermittent coalescence of nanorods. Therefore, SHINERS was employed to investigate gold dissolution from a smooth gold surface. A film of SHINs did not slow down gold dissolution and the temporal behaviour observed with SHINs and nanorods was similar. However, the time dependent changes of bands intensity recorded using SHINERS were free from intermittent spikes. The SERS spectra were complex because many decomposition products are present in the passive layer. Since the spectra evolved with time, we were able to apply 2DCOS to deconvolute them into individual bands and to identify species present in the passive layer. This study illustrates potential of SERS and SHINERS to solve problems of industrial relevance.