Copper is an excellent transducer for the electrochemical detection of creatinine in biofluids; however, the sensitivity and selectivity of Cu-based materials remain challenging. In this work, copper¿aluminum layered double hydroxides (CuAl LDHs) were synthesized by a co-precipitation method while adjusting the Cu-to-Al atomic ratio (1:1, 2:1 and 3:1) for the rational design of layered structures. The CuAl 1:1 LDH contained a mixture of CuO x (52%) and CuAl LDH (48%). Increasing the Cu content to a 2:1 improved the LDH phase proportion (73%), while the highest LDH content was achieved at a 3:1 ratio (75%). Transmission electron microscopy (TEM) revealed different morphologies among the three materials, evolving from nanowires (1:1) to hexagonal nanosheets (3:1). This indicates a growth mechanism consisting of four stages: 1D growth, 1D-to-2D transition, 2D stacking, and 2D lateral and vertical growth. Creatinine detection by cyclic voltammetry showed that CuAl 1:1 and CuAl 3:1 LDHs exhibited similar performance, with a linear range of 10¿600 ¿M (r2 = 0.98). However, in the selectivity tests, only CuAl 3:1 LDH exhibited no interference from uric acid, urea, glucose, or ascorbic acid. Tests in human saliva confirmed functionality at 1:10 and 1:100 dilution ratios for single-use sensors, demonstrating that bidimensional materials such as LDHs are strong candidates for creatinine sensing under real conditions.
