Efficient fabrication of paper-based microfluidic biosensors incorporating laser-induced graphene for label-free electrochemical immunoassays.

To improve the performance in electrochemical immunoassays, paper-based devices typically necessitate the introduction of transducing materials through additional preparation steps, and the assay procedures often require labeling steps. Here we show that laser fabrication can generate both transducing and microfluidic components of paper-based devices to support label-free immunoassays. Laser parameters were adjusted to improve the electrochemical properties of paper-based graphenic transducing structures. Surface treatment for label-free biosensing was performed, and the device configuration and operation for electrochemical impedance spectroscopy sensing were explored. Interleukin-6 protein was used as a representative target to evaluate the analytical performance of the developed immunosensors. In phosphate buffered saline, the immunosensors exhibited a sensitivity of 67.95 Ω/decade and a limit of detection of 4.66 pg/mL. In artificial serum, the immunosensors exhibited a sensitivity of 57.08 Ω/decade and a limit of detection of 5.35 pg/mL. The clinical application potential was further demonstrated with human serum samples. The presented approach for developing paper-based microfluidic immunosensors can enhance their performance while maintaining ease of fabrication and usage to meet different requirements in clinical practice.