Voltammetric microsensor using PEDOT-modified gold electrode for the simultaneous assay of ascorbic and uric acids (original) (raw)
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Electrochemistry Communications, 2011
A voltammetric microsensor has been developed for the simultaneous assay of ascorbic (AA) and uric (UA) acids in aqueous solution. The electrode surface has been modified by means of electropolymerized conductive poly(3,4-ethylenedioxythiophene) (PEDOT) organic films. The anodic peak potential separation between both acids was more than 300 mV. The sensitivity of the microsensor for UA was found to be dependent on the presence of AA in the mixture. By using square wave voltammetry (SWV), it increased from 77.5 mA mM −1 cm −2 without AA to 86.2 mA mM −1 cm −2 with AA 1 mM. An EC' catalytic mechanism was highlighted, inducing the regeneration of reduced UA by AA at the vicinity of the electrode surface.
Analytica Chimica Acta, 2000
Uric acid (UA) and ascorbic acid (AA) present in urine were rapidly determined by the amperometric method in association with flow injection analysis. An array of gold microelectrodes modified by electrochemical deposition of palladium was employed as the working electrode. Uric and ascorbic acids were quantified in urine using amperometric differential measurements at +0.75 and +0.55 V, respectively. This method is based on three steps involving the flow injection of: (1) the sample spiked with a standard solution, (2) the pure sample, and (3) the enzymatically treated sample. The enzymatic treatment was carried out with ascorbate oxidase, uricase, and peroxidase at pH 7. The calibration curves for freshly prepared ascorbic and uric acid standards were very linear in the concentration ranges of 0.44-2.64 mg l −1 (AA) and of 0.34-1.68 mg l −1 (UA) with a relative standard deviation (RSD) <1 %. For uric acid, the real sample analyses where compared with the classical spectrophotometric method, showing deviations between 3.1 and 8.6% (n = 9). : S 0 0 0 3 -2 6 7 0 ( 9 9 ) 0 0 6 7 4 -1
Analytical Biochemistry, 2009
Individual and simultaneous determination of 50 nM uric acid (UA) and ascorbic acid (AA) using enlarged, citrate-stabilized gold nanoparticles (AuNPs) self-assembled to 2,5-dimercapto-1,3,4-thiadiazole (DMT) monolayer modified Au (Au/DMT) electrode by an amperometric method is described for the first time. Self-assembly of AuNPs on the electrode surface was confirmed by atomic force microscopy (AFM), attenuated total reflectance FT-IR and diffuse reflectance spectral measurements. The electron transfer reaction (ETR) of [Fe(CN) 6 ] 3À/4À was blocked at Au/DMT electrode, whereas it was restored with a peak separation of 200 mV after the attachment of AuNPs on the Au/DMT (Au/DMT/AuNPs) electrode, which was confirmed from the ETR of the [Fe(CN) 6 ] 3À/4À redox couple. When the self-assembled AuNPs were enlarged by hydroxylamine seeding, the ETR of [Fe(CN) 6 ] 3À/4À was improved significantly with a peak separation of 100 mV. Tapping mode AFM showed that the average size of the enlarged-AuNPs (E-AuNPs) was 50-70 nm. The E-AuNPs modified electrode catalyzes the oxidation of AA and UA, separates their voltammetric signals by 200 mV, and has excellent sensitivity towards AA and UA with a detection limit of 50 nM. The practical application of the modified electrode was demonstrated by measuring the concentration of UA in blood serum and urine.
Biosensors
Potentiometric redox sensing is a relatively inexpensive and passive approach to evaluate the overall redox state of complex biological and environmental solutions. The ability to make such measurements in ultra-small volumes using high surface area, nanoporous electrodes is of particular importance as such electrodes can improve the rates of electron transfer and reduce the effects of biofouling on the electrochemical signal. This work focuses on the fabrication of miniaturized nanoporous gold (NPG) electrodes with a high surface area and a small footprint for the potentiometric redox sensing of three biologically relevant redox molecules (ascorbic acid, uric acid, and cysteine) in microliter volumes. The NPG electrodes were inexpensively made by attaching a nanoporous gold leaf prepared by dealloying 12K gold in nitric acid to a modified glass capillary (1.5 mm id) and establishing an electrode connection with copper tape. The surface area of the electrodes was ~1.5 cm2, providing...