In vivo application of an implantable tri-anchored methylene blue-based electrochemical pH sensor

• Published in: Biosensors & bioelectronics Vol. 197; p. 113728
• Main Authors: González-Fernández, Eva, Staderini, Matteo, Marland, Jamie R.K., Gray, Mark E., Uçar, Ahmet, Dunare, Camelia, Blair, Ewen O., Sullivan, Paul, Tsiamis, Andreas, Greenhalgh, Stephen N., Gregson, Rachael, Clutton, Richard Eddie, Smith, Stewart, Terry, Jonathan G., Argyle, David J., Walton, Anthony J., Mount, Andrew R., Bradley, Mark, Murray, Alan F.
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 01-02-2022
• Subjects: Animals; Biosensing Techniques; Electrochemical Techniques; Hydrogen-Ion Concentration; Implantable; Methylene Blue; Microfabrication; Oxidation-Reduction; Sensor; Sheep; Tumour; pH; Tumour; Implantable; Microfabrication; Sensor; Methylene blue
• ISSN: 0956-5663; 1873-4235
• DOI: 10.1016/j.bios.2021.113728

The development of robust implantable sensors is important in the successful advancement of personalised medicine as they have the potential to provide in situ real-time data regarding the status of health and disease and the effectiveness of treatment. Tissue pH is a key physiological parameter and herein, we report the design, fabrication, functionalisation, encapsulation and protection of a miniaturised, self-contained, electrochemical pH sensor system and characterisation of sensor performance. Notably for the first time in this environment the pH sensor was based on a methylene blue redox reporter which showed remarkable robustness, accuracy and sensitivity. This was achieved by encapsulation of a self-assembled monolayer containing methylene blue entrapped within a Nafion layer. Another powerful feature was the incorporation, within the same implanted device, of a fabricated on-chip Ag/AgCl reference electrode – vital in any electrochemical sensor, but often ignored. When utilised in vivo, the sensor allowed accurate tracking of externally induced pH changes within a naturally occurring ovine lung cancer model, and correlated well with single point laboratory measurements made on extracted arterial blood, whilst enabling in vivo time-dependent measurements. The sensors functioned robustly whilst implanted, and maintained in vitro function once extracted and together, these results demonstrate proof-of-concept of the ability to sense real-time intratumoral tissue pH changes in vivo.
•First in vivo use of a pH sensor based on a tri-branched methylene blue redox reporter which showed remarkable robustness, accuracy and sensitivity.•A self-assembled monolayer containing the methylene blue reporter was entrapped within a Nafion layer.•Incorporation within the same implanted device of a fabricated on-chip Ag/AgCl reference electrode vital in any electrochemical sensor.•Invivo, the sensor allowed accurate tracking of externally induced pH changes within a tumour environment.