Miniaturized and low-cost electrochemical sensor based on polyimide laser-scribed graphene modified with Nafion™ and gold-doped titanium dioxide nanocrystals for estriol detection.

Estriol (E3) is an essential hormone during pregnancy and is used as a biomarker to monitor gestational and fetoplacental health. In this study, we propose a miniaturized electrochemical sensor based on polyimide laser-scribed graphene (LSG) modified with a Nafion™ membrane and novel TiO-5%Au nanocrystals for selective detection of E3. The morphology and structure of the sensor were evaluated, and the modification with the nanocomposite improved the analytical signal of E3 by 97% compared with the bare LSG electrode. The detection of E3 was performed using differential pulse voltammetry (DPV) at pH 2, and the device showed a good analytical performance with a linear response (R = 0.998) in the concentration range 5 to 80 µmol L. The values obtained for the limit of detection (LOD) and limit of quantification (LOQ) were 1.00 µmol L and 3.33 µmol L, respectively. The investigation of mass transport revealed that it occurs via a mixed process (diffusional and adsorptive), and the E3 electrooxidation presents a proton-coupled electron transfer mechanism involving a 1:1 electron:proton ratio. The proposed sensor showed high manufacturing reproducibility (RSD = 4.5%, n = 10) and selectivity, with interference levels below 15% from other species. Tests using fortified synthetic urine demonstrated recoveries exceeding 90%, confirming the method's accuracy. The proposed Nafion™/TiO-5%Au/LSG sensor is a viable alternative for E3 determination due to its simple fabrication, low cost, and portability features. In summary, the proposed method offers an efficient and accessible alternative for the rapid detection of E3, highlighting its potential for advancing diagnostic technologies.