Ca2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranes

•We demonstrate reference electrode free AlGaN/GaN transistor-based Ca2+ sensors.•Lower detection limit 10−8 M and linear response range 10−7-10−2 M in KCl and NaCl.•Lowest reported detection limit for reference electrode free Ca2+ sensors.•Improved detection limits compared to ISEs in classical setup and previous ISFETs.•These findings are critical for in situ applications of calcium ion sensing.

We demonstrate highly selective and sensitive potentiometric ion sensors for calcium ion detection, operated without the use of a reference electrode. The sensors consist of AlGaN/GaN heterostructure-based transistor devices with chemical functionalisation of the gate area using poly (vinylchloride)-based (PVC) membranes having high selectivity towards calcium ions, Ca2+. The sensors exhibited stable and rapid responses when introduced to various concentrations of Ca2+. In both 0.01 M KCl and 0.01 M NaCl ionic strength buffer solutions, the sensors exhibited near Nernstian responses with detection limits of less than 10−7 M, and a linear response range between 10−7-10−2 M. Also, detection limits of less than 10−6 M were achieved for the sensors in both 0.01 M MgCl2 and 0.01 M LiCl buffer solutions. AlGaN/GaN-based devices for Ca2+ detection demonstrate excellent selectivity and response range for a wide variety of applications. This work represents an important step towards multi-ion sensing using arrays of ion-selective field effect transistor (ISFET) devices.

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