A Novel Electroactive Polymer for pH‐independent Oxygen Sensing

Abstract

O 2 is criticalf or mammalian cell survival asi tf unctions as the finale lectron acceptor in the electron transport chain, which creates aH + gradient that is needed to drive the oxidative phosphorylation of adenosine triphosphate (ATP) in the mitochondria during aerobic cellularr espiration [1].M ammalian cells are sensitive to the levels of dissolved O 2 .W hen the cell is lacking in O 2 ,i ts witches over to anaerobic cellular respiration. However,p rolonged O 2 deprivation can cause cell death. Hence,t he measuremento fd issolved O 2 concentration is clinically important for detectinga nd monitoring ischemia [2],p articularly for patients with traumatic braini njuries [3],a nd for the study of hypoxia in cancer development [4].One major challenget ot he detection of O 2 concentration in biological samples is the change in pH. Fore xample,a ni ncrease in energy metabolism by the cell enhances glycolysis, causing the production of lactate and CO 2 to increase under anaerobic and aerobic conditionsr espectively,l eading to extracellular acidification [5].A lthough buffers such as phosphate buffered saline (PBS) and sodium bicarbonate are commonly used for biological samples,t he useful buffer range is only pK a AE 1p Hu nit. + reactiona tt he electrode [6b,8a-c].H ence,u ndetected changes in the pH of the biological sample will introduce inaccuracies in the concentrationo fd issolved O 2 measured usings uch sensors and materials.T hus,t here is an eed to developamediator for pH-independent O 2 sensing in the range of pH 4t o8w hich is relevant to physiology [9] and it needs to be capable of detecting dissolved O 2 typically below 245 mM [ 10].We chose to use electropolymerisation to prepare the mediator as it is af acile method for modifying the Au electrode,w hich is the electrode material of choice in physiology [11] and is also commonly used in chip-based devices for biological investigations [12].Phenothiazines are attractive materials for electrode modification as they can be electropolymerised. Methylene blue (MB + ) ( Fig. 1a) is ap henothiazine derivative with substituentsa tt he 3a nd 7p ositions [ 13].I tc an undergo as erieso fe lectron transfers and proton transfers depending on the pH to give leuco methylene blue (LMB), which is colourless [14].M B + is electroactive and water-soluble [15] and its electrochemical reduction is shown in Fig. 1b.I th as been used in molecularly imprinted polymerm odified electrodes [16] and as ar edox mediator in enzymatic electrochemical biosensors [17].Abstract:M ethylene blue (MB + )a nd pyrrole were copolymerised to electrodeposit an ovel electroactivep olymer on aA ue lectrode which was assessed for O 2 sensing. The electroactivep olymere xhibits diffusion-limitedb ehaviour and an electrochemical, followedb yc atalytic (EC')mechanism in the presenceo fd issolvedO 2 .N otably,i ti sp Hinsensitive in both N 2 -purged and air-equilibrated phosphate buffered saline( PBS) from pH 4t o8 .I ti s stable over 18 days,p ossesses ag ood sensitivity of 256.335 mAmM À1 cm À2,...

Conducting Polymers in Amperometric Sensors: A State of the Art over the Last 15 Years with a Focus on Polypyrrole-, Polythiophene-, and Poly(3,4-ethylenedioxythiophene)-Based Materials

“…Because of the pH dependence of methylene blue and its polymer form, pyrrole was used as a co-monomer. The sensor was proposed to be used in biological investigations, thanks to its stability (18 days) and sensitivity (256.335 µA mM −1 cm −2 ) performances, wide linear range (15-285 µA), and low detection limit (1.47 µM) [59].…”