“…There are excellent nanomaterials such as graphene oxide (GO) (Jumpathong et al, 2016 ), Au@Bi 2 MoO 6 NTs (Wang et al, 2020 ), Pt–Au alloy nanotube array (Tao et al, 2011 ), Au–Pt nanostructures (Jia et al, 2015 ), Au@Pd/Ag NPs and amination GP (Li N. et al, 2014 ), AuNPs and poly(amidoamine)-MWCNTs-chitosan nanocomposite (Dong et al, 2013 ), AuPd@Au nanocrystals (Wang et al, 2018b ), Au@Pt nanocrystals (Wang et al, 2018c ), AuNPs/Zn/Ni–ZIF-8-800@GP composites (Hu et al, 2019 ), PdCu tripod functionalized porous GP (Tan et al, 2020 ), Cu 3 Pt nanoframes (Wang et al, 2018a ), Pd NPs@3D MoS x (Gao Z. et al, 2019 ), 3D PtCu nanoframes (Chen et al, 2019 ), Ag/MoS 2 /rGO nanocomposites (Wang et al, 2018 ), AuPdCu NPs/N-doped GP quantum dots functionalized polymer nanospheres (Yan et al, 2018 ), Pd NPs functionalized MoS 2 /NiCo heterostructures (Ding et al, 2020 ), Au NPs/MoS 2 -GP aerogels composite (Xu et al, 2020 ), AuNPs–PtNPs–MOFs (Zhao et al, 2019 ), and PtPd NCs@MoS 2 nanoenzymes (Tan et al, 2019 ), which have been employed in the construction of label-free electrochemical immunosensors. Their label-free immunosensors are demonstrated with additional chemicals or redox probes such as H 2 O 2 (Tao et al, 2011 ; Wang et al, 2018 , Leng et al, 2011 ; Yan et al, 2018 ; Chen et al, 2019 ; Gao Z. et al, 2019 ; Pei et al, 2019a , b ; Tan et al, 2019 ; Zhao et al, 2019 ; Ding et al, 2020 ), O 2 (Wang et al, 2018a , c ; Chen et al, 2019 ), methyl orange (Sun et al, 2019 ), and [Fe(CN) 6 ] 4−/3− (Dong et al, 2013 ; Li R. et al, 2014 ; Liu et al, 2015 ; Han et al, 2017 ; Hu et al, 2019 ; Xu et al, 2020 ) to obtain signal amplification via electrocatalytic reductions and charge transfer reactions.…”