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As programmed death-ligand 1 (PD-L1) is considered a referenced therapeutic biomarker, a rapid and low-cost method to detect PD-L1 in body fluids is necessary. In this work, a paper-based microfluidic aptasensor for label-free electrochemical detection of PD-L1 in liquids was fabricated. The aptasensor integrates a reaction cell and a three-electrode system, and a differential pulse voltammetry electrochemical method was adopted. PD-L1 aptamer with a low equilibrium dissociation constant was used as a biorecognition molecule. To bind the aptamer and assist in the electrochemical measurement, nanocomposites were synthesized and used to modify the working electrode, which was composed of an amine-functionalized single-walled carbon nanotube, new methylene blue and gold nanoparticles. The basic performance of the aptasensor was tested in phosphate-buffered saline: the linear range was between 10 pg mL -1 and 2.5 ng mL -1 , and the detection limit was 10 pg mL -1 (signal/noise = 3). Moreover, the aptasensor was used for the detection of serum samples and compared with an enzyme linked immunosorbent assay (ELISA). The results showed that the aptasensor provides a new low-cost, portable and highly sensitive detection method for PD-L1, as an alternative to ELISA., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)