A biocompatible hydrogel pH sensor to measure tumor acidosis

Extracellular pH in the tumor is particularly promising because they play a key role in cancer metastasis, chemotherapy resistance, however, measuring in situ chemical pH is currently very challenging. We developed a chemically responsive polyacrylic acid-based injectable hydrogel sensor to noninvasively measure local pH in a tumor location biopsied and used for diagnosis using plain radiography. The sensor is based on a polyacrylic acid-based hydrogel which swells according to pH: contracts at low pH, expands at high pH. The hydrogel contains a radiodense tantalum bead within it, so that the pH-dependent hydrogel length can be measured via X-ray imaging. The hydrogel is placed in a porous casing to be able to inject the sensor into a tumor and prevent direct contact. The entire sensor fits inside a biopsy marker needle which will be used to inject the sensor into the tumor tissue. The hydrogel sensor showed a linear response with a precision of 0.07 pH unit and repeatable response to pH cycling in bovine serum in the pH range 6.5 to 7.5, most relevant to tumor acidosis. In vivo studies of the developed hydrogel-based biosensor will be carried out in future on a rat tumor model.