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Content archived on 2024-06-20

Combining electrochemical scanned probe microscopy and cavity ring-down Spectroscopy: A new direction for the study of interfacial processes

Final Activity Report Summary - SECM-CRDS (Combining electrochemical scanned probe microscopy and cavity ring-down Spectroscopy: A new direction for the study of interfacial processes)

Evanescent wave-cavity ring down spectroscopy (EW-CRDS) has been developed as a powerful probe of dynamic processes at interfaces. Such processes are of widespread fundamental, industrial and environmental interest, governing - for example - the operation of fuel cells, sensors, catalysts, geological processes and many phenomena in the life sciences. The most important scientific achievements have been the characterisation of a new instrument built at Warwick University, in terms of spatial-temporal resolution and chemical sensitivity, and application to four major scientific problems:

1) Surface-assembly and redox dissolution of silver nanoparticles.
Nanoparticles are of immense interest as building blocks in nanoscience, with applications ranging from diagnostic sensors to catalysis. A novel methodology employing EW-CRDS combined with thin layer cell electrochemistry has been used to measure the diffusion coefficient, surface coverage, adsorption and redox dissolution kinetics of Ag nanoparticles on functionalized surfaces. The redox-dissolution kinetics are important for new applications such as protein analysis and fingerprint detection. The measurements carried out demonstrate the ability of EW-CRDS to obtain kinetic information; especially on inert supports such as silica or polymer-modified silica which are traditionally challenging to study with conventional techniques available to scientists. The combination of EW-CRDS with electrochemistry and flow techniques shows that dissolution processes can be monitored even when they involve very low fluxes and low concentrations of reagents, making both approaches excellent tools for potential sensing applications.

2) Analysis and review of the application of Scanning Electrochemical Microscopy (SECM) to latent fingerprint imaging and detection.
SECM can be used to detect silver dissolution, allowing researchers to visualise the ultrastructure of human fingerprints on wet porous and nonporous surfaces by combination with silver-staining or multi-metal-deposition technology. This methodology takes significant advantage of the high sensitivity of SECM towards the small variation of electrochemical reaction rates at the substrate surface. The method has the potential to develop fingerprint detection on a range of difficult surfaces that are known to provide poor results with current techniques, such as paper, plastic, banknotes and wet surfaces.

3) Kinetic studies of porphyrin adsorption and DNA-assisted desorption at surfaces.
Porphyrins are an important class of naturally-occurring molecules. We measured the kinetics of porphyrin adsorption to surfaces using EW-CRDS combined with a novel, purpose-designed, impinging jet cell. Complementary finite element modelling of the flow coupled to the solution of the convection-diffusion/binding process provided considerable insight in to the adsorption process, with very high sensitivity. While a monolayer of porphyrin was readily formed on a quartz surface, this was stripped from the surface when exposed to solutions of DNA. The desorption process could also be followed in real time using EW-CRDS. The results suggest that porphyrin-functionalised surfaces, and related functionalized surfaces, coupled to a surface-sensitive spectroscopic technique such as EW-CRDS may be useful as a DNA sensor.

4) Formation of supported lipid bilayers on silica and the interaction with porphyrins.
An understanding has been developed of the process of lipid bilayer formation on quartz surfaces after exposure to small lipid vesicles, to make supported lipid bilayers (SLBs). SLBs are of immense importance for basic studies of cell function. EW-CRDS has been shown to be particularly powerful for monitoring bilayer formation. We further studied the kinetics of porphyrin binding to lipid bilayers using EW-CRDS and an impinging jet cell. The studies provide the first demonstration that EW-CRDS is a powerful technique for probing kinetics of SLB formation and the interactions of proteins or biomolecules with SLBs.