“…The conventional methods such as radioimmunoassay, surface-enhanced Raman spectroscopy (SERS), and other chromatographic techniques have already been employed to determine fentanyl in biological matrices such as blood and urine ( Stiller et al, 1990 ; Saraji and Boroujeni, 2011 ; Haddad et al, 2018 ). Among these, special attention has been paid toward the electrochemical method for the fentanyl determination because of sensitivity, selectivity, low cost, rapidity, and safety ( Foroughi et al, 2015 ; Foroughi and Ranjbar, 2017 ; Jahani, 2018 ; Maaref et al, 2018 ; Farvardin et al, 2020 ; Foroughi et al, 2021a ; Moarefdoust et al, 2021 ; Santana et al, 2021 ; Dalkiran and Brett, 2022 ; Foroughi and Jahani, 2022 ; Jahani et al, 2022 ). It is very important to choose the right platform in the electrochemical method, for example, the pencil graphite electrode (PGE) is known as a suitable substrate in electrochemical applications with unique properties such as broad potential range and low background current ( Antherjanam and Saraswathyamma, 2022 ).…”