Designing a Modular Approach for the Formation of Rhenium-functionalised Surfaces for SERS-based Sensing

Lea, Joshua and Fletcher, Nick (2022) Designing a Modular Approach for the Formation of Rhenium-functionalised Surfaces for SERS-based Sensing. PhD thesis, Lancaster University.

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Abstract

A modular approach has been designed for the synthesis of labelled nanoparticle films for targeted analyte detection using surface-enhanced Raman spectroscopy (SERS). Interfacial self-assembly of citrate-stabilised silver nanoparticles and photo-deposition of silver salts were employed as possible methods for the generation of reproducible SERS surfaces. The ability to label the platforms with the rhenium complex [Re(L1)(CO)3Br] where L1 is (2,2'-bipyridin-4-ylmethyl)-(1,2-dithiolan-3-yl)pentanoate were also made and assessed using SERS. The complex shows an ability to effectively label the structures via covalent interactions between the silver surface and the dithiol group of the ligand, evidenced by SERS. The complex can modify and position citrate stabilised nanoparticles at the interface between two immiscible liquids, demonstrating that the Re(I)-modified metal liquid-like films (MeLLFs) and surfaceexposed nanosheets (SENS) provide a simple and reproducible method for the synthesis of labelled SERS active surfaces. The [Re(L1)(CO)3Br] complex, also displayed a selective spectroscopic response to the presence of Hg2+ in solution which is believed to be Hg-facilitated Br removal and coordination of the solvent. This interaction was also observed using SERS after treating [Re(L1)(CO)3Br] functionalised MeLLFs and SENS with organic and aqueous solutions of Hg2+. This is evidenced by observable changes to the Re–CO vibration and the appearance of a peak attributed to some form of Hg–Br interaction. The Re(I) complex, [Re(L2)(CO)3(pyr)](PF6) containing a bis-(benzimidazole)-4,4′ -bipyridine, L2 showed individual photophysical responses to dihydrogen phosphate and acetate in solution. H2PO4- causes a sequential quenching while OAccauses a “switch off” of the emissive response. The [Re(L2)(CO)3(pyr)](PF6) and [Re(L2)(CO)3(L3)](BF4) complexes, where L3 is N-(4-pyridylmethyl)lipoamide also formed labelled MeLLF and SENS surfaces. Anion sensing was possible with the SENS films. SENS treated with H2PO4- showed changes to the complex fingerprint with additional peaks attributed to the anion. The detection of OAcis evidenced by an observed vibration and wavenumber shift of ligand specific vibrations attributed to the hydrogen bonding interaction between the complex and anion. The complex, [Re(L4)(CO)3(L3)](BF4) where L4 is dipyridophenazine was synthesised and used to form the interfacial MeLLF and SENS surfaces. Attempts at SERS detection using [Re(L4)(CO)3(L3)](BF4) and [Re(L2)(CO)3(L3)](BF4) SENS platforms for the detection of DNA were made using the SENS platforms. This was unsuccessful however, there is opportunity for further investigation.