FeMn layered double hydroxides: an efficient bifunctional electrocatalyst for real-time tracking of cysteine in whole blood and dopamine in biological samples

Abstract

A peculiar clock-regulated design of FeMn-LDHs (FMH) with specific physiochemical attributes has been developed and used for highly sensitive detection of cysteine (CySH) and dopamine (DA). The FMH nanoparticles were synthesized via a facile hydrothermal approach clocked at various (6 h, 12 h and 18 h) operating periods. Under optimal conditions, FMH were obtained in three unique morphologies such as hexagonal plate like, cubic, and spherical structures corresponding to the clocked periods of 6 h, 12 h, and 18 h, respectively. Among these, FMH-12 h possess the minimal particle size (54.45 nm), a large surface area (7.60 m² g⁻¹) and the highest pore diameter (d = 4.614 nm). In addition to these superior physiochemical attributes, the FMH nanocubes exhibit excellent electrochemical behaviors with the lowest charge transfer resistance (R_ct; 96 Ω), a high heterogeneous rate constant (7.81 × 10⁻⁶ cm s⁻¹) and a good electroactive surface area (0.3613 cm²), among the three. The electrochemical biosensor based on the FMH nanocubes exhibits a remarkable catalytic activity toward CySH and DA with a low detection limit (9.6 nM and 5.3 nM) and a broad linear range (30 nM–6.67 mM and 20 nM–700 μM). The FMH based biosensor is also feasible for the real-world detection of CySH in whole blood and DA in biological fluids with satisfactory results. The proposed sensor possessed high selectivity, good repeatability, and reproducibility toward CySH and DA sensing.