A platinum electrode was coated with polyelectrolyte multilayer (PEM) films to prepare an amperometric hydrogen peroxide sensor which can be used in the presence of possible interferences such as ascorbic acid, uric acid, and acetaminophen. The PEM films were prepared on the surface of a Pt disk electrode by an alternate deposition of polycation and polyanion from the aqueous solutions through electrostatic force of attraction. The Pt electrodes coated with a poly(allylamine)/poly(vinyl sulfate) or poly(allylamine)/poly(styrenesulfonate) film were used successfully for detecting H2O2 selectively in the presence of the possible interfering agents. It was suggested that H2O2 can diffuse into the PEM film smoothly while the ascorbic acid, uric acid, and acetaminophen cannot penetrate the film by a size exclusion mechanism. On the other hand, the electrodes coated with PEM films containing poly(ethyleneimine) or poly(diallyldimethylammonium chloride) were not useful for the selective determination of H2O2. The results were rationalized based on the different permeability of the films due to the different molecular density or packing in the PEM films. The PEM film-coated electrode was useful for constructing glucose biosensors by coupling with glucose oxidase.

It has been established that an alternate deposition of oppositely charged polyelectrolytes on a solid surface gives a molecular thin film with a layered structure. The polyelectrolyte multilayer (PEM) films are attracting much attention because the thickness of the films can be controlled precisely at nanometer level by regulating the experimental variables such as the concentration of polymer in the bathing solution, pH and ionic strength of the solution, and the number of depositions. 2 PEM films have recently been applied to separation or sensing materials. Schlenoff et al. have reported fused silica capillaries coated with PEM films composed of poly(styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) for electrophoretic separation. 3 The PSS-PDDA thin films were also used by Claus et al. for fabricating an optical fiber humidity sensor. 4 Bruening et al. have studied the permeability of Fe(CN)6 3-and Ru(NH3)6 3+ ions through PEM films which were deposited on the surface of a metal electrode. 5 We report here that PEM film-coated electrodes can be used successfully for amperometric determination of hydrogen peroxide (H2O2) in the presence of possible interferents including ascorbic acid, uric acid, and acetaminophen.Poly(vinyl sulfate) (PVS) (molecular weight, 243000; Nacalai Tesque Co., Japan), poly(allylamine) (PAA) (molecular weight, 10000; Nittobo Co., Japan), and poly(ethylenimine) (PEI) (molecular weight, 60000 -80000; Nacalai Tesque Co., Japan) were used as received. PAA-PVS and PEI-PVS multilayer films were prepared on the surface of a platinum (Pt) disk electrode (3 mm diameter), which was polished thoroughly using alumina powder and rinsed with distilled water before use, according to the reported procedure. 2 The Pt electrode was immersed in PVS (1 mg ml -1 ) and PAA (2 mg ml -1 ) or PEI (1.5 mg ml -1 ) solutions (in 0.1 M phosphate buffer, pH 7.4) for 30 min alternately to deposit the PEM film. It has been reported that the thickness of the polycation-polyanion unit bilayer in the PEM films is typically several nanometers, depending upon the experimental conditions. 3 An amperometric response of the PEM film-coated electrode was measured with a conventional three-electrode system, using a Pt wire as counter electrode and a Ag/AgCl electrode as reference electrode. Figure 1 shows amperometric responses of the Pt electrode to H2O2, ascorbic acid, uric acid, and acetaminophen before and after modification with the PAA-PVS multilayer film. The bare Pt electrode exhibited oxidation current for all substrates at +0.6 V vs. Ag/AgCl; the response currents to ascorbic acid, uric acid, and acetaminophen were ca. 40 -65% of the response to the same concentration of H2O2. Thus, the bare Pt electrode can not be used for amperometric determination of H2O2 in the presence of the interferents. It is known that ascorbic acid, uric acid, and acetaminophen induce significant interference in amperometric sensors for H2O2 determination. 6 On the other hand, after the electrode was coated with t...

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