Fig. 3
From: Recent advances in electrochemical sensor technologies for THC detection—a narrative review
a Optical image of a carbon beads-based sensor. b SEM (scanning electron microscope) images of carbon beads-based sensor. c CNT (carbon nanotube)-based sensor. d TEM (transmission electron microscope) image of carbon beads based sensor. Taken from (Zhang et al. 2019) with permission from Elsevier (Copyright 2019)