Fabrication of NiCo Bimetallic MOF Films on 3D Foam with Assistance of Atomic Layer Deposition for Non-Invasive Lactic Acid Sensing

Lactic acid (LA) is an important downstream product of glycolysis in living cells and is abundant in our body fluids, which are strongly associated with diseases. The development of enzyme-free LA sensors with high sensitivity and low consumption remains a challenge. 2D metal-organic frameworks (MOFs) are considered to be promising electrochemical sensing materials and have attracted much attention in recent years. Compared to monometallic MOFs, the construction of bimetallic MOFs (BMOFs) can obtain a larger specific surface area, thereby increasing the exposed active site. 3D petal-like Ni_xCo_y MOF films on nickel foams (Ni_xCo_y BMOF@Ni foams) are successfully prepared by combining atomic layer deposition-assisted technology and hydrothermal strategy. The established Ni_xCo_y BMOF@Ni foams demonstrate noticeable LA sensing activity, and the study is carried out on behalf of the Ni₁Co₅ BMOF@Ni foam, which has a sensitivity of up to 9030 μA mM^-1 cm^-2 with a linear range of 0.01-2.2 mM and the detection limit is as low as 0.16 μM. Additionally, the composite has excellent stability and repeatability for the detection of LA under a natural air environment with high accuracy and reliability. Density functional theory calculation is applied to study the reaction process between composites and LA, and the result suggests that the active site in the NiCo BMOF film favors the adsorption of LA relative to the active site of monometallic MOF film, resulting in improved performance. The developed composite has a great potential for the application of noninvasive LA biosensors.