The aqueous deposition of a pH sensitive quinone on carbon paste electrodes using linear sweep voltammetry

Abstract

Herein, we report the electrodeposition of a quinone containing diazonium salt onto the surface of carbon paste electrodes (CPE). An extensive characterisation revealed the optimum deposition characteristics to be obtained using Linear Sweep Voltammetry (LSV) over the potential range +400 mV to −800 mV vs. SCE at 100 mV/s, for five sweeps in 0.1 M H 2 SO 4. The corresponding FBRR-modified CPE was cycled in phosphate buffered saline over the potential range +800 mV to −700 mV vs. SCE at 100 mV/s. The anodic peak potential demonstrated excellent stability over 400 cycles and a Nernstian response was recorded (−59 ± 3 mV/pH, n = 39, r 2 = 0.99). The continuous monitoring of pH changes within the same solution exhibited Nernstian behaviour also, confirming the efficacy of the FBRR-modified CPEs for in situ pH monitoring. An extensive shelf-life investigation identified retention of FBRR-modified CPEs sensitivity over 28 days when stored under air conditions at 4°C. The work described within confirms the effectiveness of FBRR-modified CPEs to perform continuous pH monitoring over a small pH range of physiological relevance. (59 mV) per pH unit. Carbon based materials and sensors have been widely used in the field of electrochemistry, because of their good electrical conductivity, ease of modification, low expense [4] and relatively wide operating

Physiological monitoring of tissue pH: In vitro characterisation and in vivo validation of a quinone-modified carbon paste electrode

“…CPEs were manufactured from Teflon ® -insulated silver (Ag) wire (200 mm bare diameter 8T, Advent Research Materials; Oxford, UK) as described previously [26]. A 5 cm length of Teflon insulated Ag wire was cut.…”

“…The surface was then levelled by gently rubbing it on a clean, flat surface. The electrochemical deposition of the quinone containing aryl diazonium salt, FBRR, onto CPEs was achieved by a one-step electrochemical reduction process in 0.1 M H 2 SO 4 using Linear Sweep Voltammetry (LSV) [26]. The first step of the proposed mechanism involves the electrochemical reduction of the aryl diazonium cation (Ar-N 2 þ ) to form the corresponding aryl radical (Ar$), with the loss of N 2 , as described in Equation (4).…”

“…According to Scheme 1, the redox activity of the deposited diazonium salt involves a 2e À oxidation, converting the methoxy to the equivalent quinone, followed by a 2e À /2H þ exchange to form the hydroxy-quinone. The potential at which the redox reactions take place are pH dependent resulting from the protonation/deprotonation of the quinone [26].…”

“…Herein, we describe the in vitro characterisation of a recently reported pH sensitive carbon paste electrode (CPE) [26]. The electrodeposition of the diazonium salt, 4-Benzoylamino-2, 5dimethoxybenzenediazonium chloride -hemi zinc chloride (FBRR), onto CPEs was optimised, to produce a pH sensor that has demonstrated excellent stability and Nernstian behaviour over the physiological range 7.2e7.6.…”

“…Furthermore, increasing the number of calibration points from three to ca. 40 had no significant impact on the sensor's sensitivity and shelf-life investigations identified retention of the FBBR-modified CPE sensitivity over 28 days when stored under air conditions at 4 C [26]. CPEs have demonstrated excellent long term stability for in vivo monitoring of brain tissue [24,27], an environment they are particularly suited to since the interaction between the pasting liquid and brain lipids reduces the electrode fouling caused by the proteins [24].…”