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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