Micro-optical ring electrode: development of a novel electrode for photoelectrochemistry

Abstract

The design of a novel photoelectrochemical sensor, the micro-optical ring electrode (MORE), is described. Based on a thin-ring microelectrode and using a fibre-optic light guide as the insulating material interior to the ring, the MORE is capable of delivering light directly to the region of electrochemical measurement and can therefore be used to conduct microelectrochemical studies of systems with complex photochemistry. A novel fabrication procedure is described, involving the coating of commercially available fibre optics (radius 1.25 X 10-4 m) with a 600 nm layer of gold, so allowing exploitation of the electroanalytical advantages peculiar to thin-ring microelectrodes. The dark electrochemistry of the thin-ring microelectrode is characterized by use of cyclic voltammetry and chronoamperometry and found to agree with previously published theoretical results. Preliminary exploration of the photoelectrochemical response of the MORE is reported, achieved via the interrogation of the photoelectrochemically active phenothiazine dye methylene blue (MB+). Photocurrent signals obtained during cyclic voltammetric and chronoamperometric studies of MB+, conducted with the MORE under illuminated conditions and in the absence of any deliberately added reducing agent, are attributed to the formation and subsequent detection of 3MB+ within the diffusion layer of the microring electrode. The data demonstrate that the use of the MORE for the direct electrochemical detection of photogenerated species with lifetimes of c 9 x 10-5 s is possible. The electrochemistry of 3MB+ over the applied potential range from -0.4 to +1.0 V versus SCE is elucidated and discussed in the context of the behaviour of photoexcited MB+ in the presence of the deliberately added reducing agent Fe2+.

Coupled Electron‐Proton Transport in Electropolymerized Methylene Blue and the Influences of Its Protonation Level on the Rate of Electron Exchange with β‐Nicotinamide Adenine Dinucleotide

“…One or two amino nitrogen atoms of one MB þ molecule can link to a heterocyclic carbon atom of other such molecules, although we failed to confirm this bridge by ATR-IR spectroscopy. This conclusion is supported by the observation [23] that an anodic wave appearing at about 1 V upon oxidation of MB þ corresponds to the generation of a radical cation at the dimethylamino group. The foregoing consideration suggests that the two pairs of redox waves at cyclic voltammetry result from two different types of linking of phenothiazine units [5].…”

“…This change was similar to that observed for the dye in solution. At pH 5, the latter had twice a rate of 30 mV/pH unit expected for a twoelectron, one-proton reduction of MB þ to leucomethylene blue [23]:…”

The micro-optical ring electrode Part 2: Theory for the transport limited, steady-state photocurrent

“…The length of fibre optic employed is usually no more than 7 cm and is held straight along its entire length. Light may therefore be transmitted through the cladding, an expectation confirmed by our earlier study of the electrochemistry of the phenothiazinium dye, methylene blue (MB + ), wherein the photoexcited triplet state of the dye was detected by direct electrochemical oxidation at the ring of the MORE [1].…”

“…Microring electrodes find use in a wide range of electrochemical applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. This is primarily because their large perimeter-to-area ratio results in an enhanced material flux to the electrode surface, leading to higher current densities and improved temporal resolution in the study of reactions with fast chemical and electrochemical kinetics.…”

Métodos para fabricação de microeletrodos visando a detecção em microambientes

“…Processos subseqüentes podem ser utilizados para reparar pequenos defeitos de homogeneidade do processo de isolamento. Outros métodos, como polimento ou corte de um pedaço do microfibra isolada, 35,37,53,75,[88][89][90][91][92][93] descarga aplicada por um campo elétrico, 92 utilização de um feixe de elétrons 94 ou íons 95 e microscopia de tunelamento, 55 são também reportados na literatura para remover a camada de isolante da ponta da microfibra afinada. Além disso, a simples polarização em potenciais negativos da microfibra em meio ácido, resultando na evolução de hidrogênio, pode auxiliar na exposição de microfibras afinadas e isoladas com polifenol.…”