The fluctuation of physiological pH from homeostatic levels has the potential to cause life threatening complications unless counteracted in a timely manner. Therefore, the development of reliable and accurate sensors for the continuous monitoring of pH is of vital importance for clinical monitoring. Herein, we describe the extensive in vitro characterisation of a quinone-modified carbon paste electrode (CPE) and its subsequent in vivo validation in the peripheral tissue of anaesthetised rats. Sensocompatibility investigations identified stable and accurate measurements in lipid (phosphatidylethanolamine; PEA) and protein (bovine serum albumin; BSA) solutions when the pH sensor was continuously cycled for nine hours in the physiological contaminants. The influence of endogenous electroactive molecules e.g., ascorbic acid and uric acid and pharmacological interferents e.g., acetaminophen and acetylsalicylic acid was deemed negligible on the pH sensitive peak. Furthermore, there was no impact of ionic strength and the quinone oxidation peak remained selective for H þ over other endogenous cations. The effect of temperature and a pseudo reference electrode (PRE) on the sensor performance have also been elucidated. The efficacy of the modified-CPE to respond to in vivo tissue pH dynamics was demonstrated using a model of peripheral ischaemia and sodium bicarbonate injections. Collectively, this body of evidence clearly support the ability of the quinone-modified CPE to continuously measure pH fluctuations under physiological conditions.

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

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