Redox Cycling Amplified Electrochemical Lateral-Flow Immunoassay: Toward Decentralized Sensitive Insulin Detection

While paper-based lateral-flow immunoassays (LFA) offer considerable promise for centralized diagnostic applications, the analytical capability of conventional LFA remains constrained due to the low sensitivity of its common optical detection strategy. To address these issues, we report a simple electrochemical LFA (eLFA) with nanocatalytic redox cycling for decentralized insulin detection. Simultaneous binding of insulin with detection antibodies and capture antibodies through the capillary flow at the LFA platform and signal amplification through the rapid nanocatalytic reduction of [Fe(CN)₆]^3- (Fe³⁺) with Au nanoparticles (AuNP) and ammonia-borane (AB), coupled to electrochemical redox cycling reactions involving Fe³⁺, AuNP, and AB on the carbon working electrode, offer higher sensitivity than conventional colorimetric LFA and enzymatic redox cycling. The resulting integrated eLFA strip allows the detection of low insulin concentrations (LOD = 12 pM) and offers considerable promise for highly sensitive decentralized assays of different biological fluids (saliva and serum) without additional pretreatment or washing steps.