Chemistry faculty of M.V. Lomonosov Moscow State University, 119991, Moscow, Russia

Requirements of modern chemical analysis are the high sensitivity and selectivity in combination with the simplicity and low cost. Electrochemical (bio)sensors seem to accomplish these functions most properly, and in addition, allow continuous monitoring of key metabolites. It’s important to note, that modern clinical diagnostics needs improved analytical procedures. In many cases both contact-less tomography and traditional biopsy are not enough informative. Due to inherent instability of some key metabolites of interest chemical analysis has to be carried out directly in the damaged organ (tissue). This can be made exclusively with the use of chemical and biological sensors. Accessing limiting performance characteristics of sensors is possible due to their miniaturization. Micro-electrodes demonstrate significantly improved sensitivity and signal-to-noise ratio, the latter being inversely proportional to the electrode radius. Moreover, microelectrodes are characterized by dramatically faster equilibration of diffusion profiles at the electrodes surface. However, a decrease of electrode dimensions limits sensor response to very low current values. To avoid a necessity to measure units of pico-Amperes and lower it’s possible to use micro-electrode arrays commonly produced by insulating of macro-electrode surface followed by drilling holes in the insulating layer. The latter behave as individual micro-electrodes, generating cumulative response. The novel branch of electroanalytical chemistry is a formation of nano-electrodes arrays. Being synthesized by simple electrochemical methods, such systems provide record performance characteristics of the corresponding chemical sensors. To form nano-electrode arrays we propose nano-structuring of an advanced electrocatalyst on inert electrode support. Indeed, if background electrode reaction is negligible, analyte fluxes are directed to islands of electrocatalyst, which thus behave as nano-electrodes. Hydrogen peroxide sensor made by deposition of Prussian Blue through different templates (nano-structuring has been confirmed by AFM-investigation) in FIA mode displays: (i) diffusion limited sensitivity (0.7 A L mol^-1 cm^-2), (ii) linear calibration range prolonged over 7 orders of magnitude of H₂O₂ concentration with (iii) its lower limit of 10^-9 mol L^-1 (0.03 ppb) H₂O₂; the latter is two orders of magnitude lower compared to the sensor based on conventional (unstructured) Prussian Blue. The 100 times decreased detection limit without loss of sensitivity is the limiting level sensor improvement by forming of micro- or nano-electrode arrays. The analytical characteristics achieved are record in electroanalysis.

References

1. A.A. Karyakin, E.A. Puganova, I.A. Budashov, I.N. Kurochkin, E.E. Karyakina, V.A. Levchenko, V.N. Matveyenko, S.D. Varfolomeyev. Analytical Chemistry 76 (2004) 474-8.

2. A.A. Karyakin, E.A. Puganova, I.A. Bolshakov, E.E. Karyakina. Angewandte Chemie 46 (2007) 7678-80.

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