Inkjet-printed flexible non-enzymatic lactate sensor with high sensitivity and low interference using a stacked NiO_x/NiO_x-Nafion nanocomposite electrode with clinical blood test verification

In this paper, we present a flexible, inkjet-printed, non-enzymatic lactate sensor with high sensitivity and specificity, using a stacked nickel oxide-Nafion nanocomposite/nickel oxide working electrode. Instead of deploying a pure Nafion film on the top of the nickel oxide particles, the nickel oxide-Nafion nanocomposite layer in the new electrode scheme functions not only as an anti-interfering layer but also a reactive layer and the bottom pure nickel oxide layer free from interfering substances mainly participates in the redox reaction to enhance the sensing current. Experimental results show that the sensor with a working electrode printed using a 30 μL NiO_x ink and a mixture of 30 μL NiO and 4 μL Nafion ink can exhibit an anti-interference ability of >95%, a sensitivity of 20.56 nA/mM/mm², and limit of detection (LoD) of 0.27 mM satisfying the criteria for human lactate detection. In clinical trial, blood plasma test results show that lactate levels detected using this sensor have a strong linear correlation coefficient square of 0.959 with those measured using the colorimetry method used in hospitals, indicating its potential for application in the management of patients with abnormal lactate values requiring intensive care.