**2.9 Gadolinium oxide (Gd2O3)**

Gd2O3 is a rare earth metal oxide that has been used in biosensors due to its unique magnetic and optical properties. It has been used in applications such as cell imaging and drug delivery [17]. An efficient electrochemical biosensor for vitamin-D3 detection using gadolinium oxide nanorods (Gd2O3NRs) has been reported by Chauhan et al. [18].
