Electroanalysis in 2D‐TiO₂ Nanosheet Hosts: Electrolyte and Selectivity Effects in Ferroceneboronic Acid – Saccharide Binding

Abstract

A 2D-TiO 2 nanosheet material (as a film deposit of approximately 1 mm thickness on glassy carbon) is employed to host ferroceneboronic acid receptor molecules. It is suggested that the negative surface charge on 2D-TiO 2 nanosheets allows weak binding of ferroceneboronic acid, which can then be employed to detect fluoride, glucose, or fructose. The nature of the aqueous electrolyte is shown to strongly affect the ferroceneboronic acidhost interaction. In the presence of di-sodium sulfate stable reversible voltammetric responses are observed. In the presence of fluoride loss of the ferroceneboronic acid occurs probably due to weakening of the boron-titanate interaction. For glucose and for fructose "bound" and "unbound" states of the ferroceneboronic acid are observed as long as fast square wave voltammetry is employed to capture the "bound" state before decomplexation can occur. It is shown that this kinetic selectivity is highly biassed towards fructose and essentially insensitive to glucose.

Voltammetric characterisation of diferrocenylborinic acid in organic solution and in aqueous media when immobilised into a titanate nanosheet film

“…In aqueous electrolyte, 1 is essentially insoluble, thus immobilisation onto the electrode surface was necessary. Titanate nanosheet material has been shown recently to provide a good host for ferroceneboronic acid 25 and for a range of other redox active and hydrophobic redox systems. 19 Therefore, the glassy carbon electrode is firstly covered with a thin (ca.…”

“…Following this, diferrocenylborinic acid 1 was immobilised by absorption from a chloroform solution (1 mM) into the titanate nanosheet film by immersion for 24 h. Cyclic voltammetry measurements were first performed in 0.1 M Na 2 SO 4 as a background electrolyte, as this provided stable and reproducible voltammetric responses for both diferrocenylborinic and ferroceneboronic acid. 25 The composite electrode containing 1 immobilised in a titanate nanosheet host was less suitable for work in organic media due to loss of the redox system into the surrounding solution.…”

“…Very similar reaction sequences have been reported for ferroceneboronic acid. 13,25 Measurements were performed in aqueous 0.1 M NaF to investigate the electrochemically driven binding of fluoride as nucleophile to the borinic acid. Fig.…”

“…24 One of the first studies with modified electrodes based on titanate nanosheets with an embedded electrochemical probe (ferroceneboronic acid) was reported recently. 25 It was shown that the ferroceneboronic redox signal in a titanate nanosheet film immersed in aqueous Na 2 SO 4 was responsive for example to the anions in the electrolyte and to fructose binding. We therefore decided to explore the reactivity of diferrocenylborinic acid 1 under similar conditions in aqueous environments and exposed to nucleophiles such as fluoride.…”

Processes associated with ionic current rectification at a 2D-titanate nanosheet deposit on a microhole poly(ethylene terephthalate) substrate

“…at approximately pH 4 [19]. The colloidal solutions contain single unit cell thick titanate layers, which are typically 200 nm in diameter [20]. The deposits of this colloid when dried up (without heating) give a lamellar gel with typically 1.7 to 1.8 nm unit cell spacing (based on the X-ray diffraction pattern, [21]).…”