Real-time monitoring of cellular Ca2+ efflux with renewable graphene field effect transistor biosensor

Abstract

Calcium ion (Ca2+) is not only an intracellular second messenger, but also functions as an important messenger outside cells for intercellular communications. It is significant to develop a tool for dynamically probing the release of Ca2+ in the extracellular microenvironment. Here we present a photocatalysis-induced renewable reduced graphene oxide nanosheet field effect transistor (rGON-FET) biosensor for real-time monitoring of extracellular Ca2+ release. The biosensing channel was assembled layer-by-layer with reduced graphene oxide nanosheet (rGON) and titanium dioxide-reduced graphene oxide composites (TiO2-RGO) as a sandwich conducting nanostructure. Importantly, this biosensor was capable of measuring the dynamic extracellular Ca2+ release in a real time manner after immobilization of Ca2+ specific binding molecule Fluo 4-AM on the channel interface, particularly within the nano-confined space between the sensor surface and cell bottom. It was found that this biosensor could achieve a detection limit down to 100 pM in phosphate-buffered saline (PBS), and 1 nM in fetal bovine serum (FBS), respectively. Such a functional nanosensor also showed high selectivity to Ca2+ in the presence of excessive amounts of other metal ions. By using photo-responsive self-cleaning TiO2-based nanointerface, this renewable biosensor could be recycled to detect the exocytotic Ca2+ repeatedly. These advantages allow the rGON-FET biosensor to be further used in environmentally and clinically related metal ions detection.