Composite Biosensor for Sulfite Assay: Use of Water-Insoluble Hexacyanoferrate(III) Salts as Electron-Transfer Mediators

Abstract

Water-insoluble salts of hexacyanoferrate(III) and cationic surface active agents were synthetized and used as electron-mediators for sulfite oxidase. The biosensor was prepared from a composite consisting of modified graphite (50 % w/w) and n-eicosane (50 % w/w). Graphite was modified with mediators or with both mediator and sulfite oxidase for surface-and bulk-modified electrode, respectively. The main advantage of biosensors with insoluble mediators is the possibility to operate at a potential of 0 mV (vs. SCE), thus less interferences are expected, in comparison to soluble hexacyanoferrate(III) where a potential of +300 mV must be used. The maximum sensitivity 7.8 × 10 ¹4 mA/mM was obtained for bulkmodified biosensor, prepared from graphite modified with 5 % w/w of hexadecyltrimethylammonium hexacyanoferrate(III) and 1.25 units/mg (of graphite) of sulfite oxidase. The sensitivity of the biosensor decreased to 24 % of the initial sensitivity after one month storage in dry state at ambient temperature. The use of trehalose as an enzyme stabilization agent has led to the improved stability: 40 % of the initial stability was retained after one month.

Third‐generation Sulfite Biosensor Based on Sulfite Oxidase Immobilized on Aminopropyltriethoxysilane Modified Indium Tin Oxide

“…However, the main drawbacks are the fouling of electrodes due to the overlapping of the oxidation of sulfite and peroxide . The use of mediators and conductive polymers has been proposed to avoid the interference . This approach is still lacking selectivity due to the adverse reaction of sample components with the mediating partners or the electrode .…”

The oxidation of cysteine by electrogenerated octacyanomolybdate (v)

“…In contrast, the reaction of ferrocyanide with cysteine is well established, [11][12][13] with the reaction process being utilised as a means of detecting these important molecules and a commercially available sulfide sensor having been produced. 14,15 In this report the electrooxidation of octacyanomolybdate(IV) at solid carbon electrodes over a wide pH range was first examined, after which the electrochemically initiated oxidation of cysteine with electrochemically generated octacyanomolybdate(V) was investigated in alkaline solutions. This reaction was found to be similar to that demonstrated for ferrocyanide and cysteine, 16 whereby ferrocyanide is first oxidised to ferricyanide at the electrode surface.…”

A sulfite biosensor fabricated using electrodeposited polytyramine: application to wine analysis

“…Various analytical methods have been used for the determination of sulfite, including titration, 2 spectrophotometry, [3][4][5][6][7][8][9][10][11][12] HPLC [13][14][15][16] and electrochemistry. [17][18][19][20][21][22][23][24][25][26][27][28][29][30] In many of these methods, enzymatic procedures are employed, owing to their rapid, selective and sensitive nature and hence the great accuracy obtained in the measurements. The Monier-Williams procedure followed by titration is still recommended as an official method for sulfite by the Association of Official Analytical Chemists (AOAC).…”