Highly scalable design of 3D copper-doped graphene printed microfluidic chip for the electrochemical quantification of plasma homocysteine

Elevated levels of plasma homocysteine (Hcy) increase the risk of various diseases, but early diagnosis and monitoring can help prevent and treat such diseases. However, current diagnostic assays that quantify Hcy levels fail to detect more complex and rare proteins related to certain mutations, i.e., N-homocysteinylated proteins (N-Hcy-proteins), which are important for clinical decision-making. Therefore, the discrete diagnosis of Hcy in each mutated protein is in high demand. In this study, we design and fabricate a disposable microfluidic Hcy sensor chip (MHS-chip). Specifically, we utilize a laser direct-writing carbonization approach to mount a microfluidic channel filled with three-dimensional Cu-doped graphene and sensing electrodes onto a polyimide film for the first time. This microfluidic channel promotes the binding of N-Hcy-proteins and isolates the Hcy from a 10 µL plasma sample, while the sensing electrode is used for detection. The MHS-chip has a linear dynamic range of 0.01–124 µM and a detection limit of 2.9 nM, which is suitable for clinical application. Moreover, it exhibits good selectivity, high reproducibility, and real-time applicability in plasma samples. Overall, the MHS-chip is an efficient, low-cost device for the early diagnosis of Hcy and can be applied in point-of-care tests.