1 SCIENTIFIC REPORTS | (2020) 10:2946 | https://doi.org/10.1038/s41598-020-59935-y www.nature.com/scientificreports Palladium supported on polypyrrole/reduced graphene oxide nanoparticles for simultaneous biosensing application of ascorbic acid, dopamine, and uric acid Buse Demirkan 1 , Sait Bozkurt 1 , Kemal Cellat 1 , Kubilay Arıkan 1 , Mustafa Yılmaz 1 , Aysun Şavk 1 , Mehmet Harbi Çalımlı 1,2 , Mehmet Salih Nas 1,2 , Mehmet Nuri Atalar 2 , Mehmet Hakkı Alma 2 & Fatih Sen 1* In this study, we report a facile and efective production process of palladium nanoparticles supported on polypyrrole/reduced graphene oxide (rGO/Pd@PPy NPs). A novel electrochemical sensor was fabricated by incorporation of the prepared NPs onto glassy carbon electrode (GCE) for the simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The electrodes modifed with rGO/Pd@PPy NPs were well decorated on the GCE and exhibited superior catalytic activity and conductivity for the detection of these molecules with higher current and oxidation peak intensities. Simultaneous detection of these molecules was achieved due to the high selectivity and sensitivity of rGO/Pd@PPy NPs. For each biomolecule, well-separated voltammetric peaks were obtained at the modifed electrode in cyclic voltammetry (CV) and diferential pulse voltammetry (DPV) measurements. Additionally, the detection of these molecules was performed in blood serum samples with satisfying results. The detection limits and calibration curves for AA, DA, and UA were found to be 4.9 × 10 -8 , 5.6 × 10 -8 , 4.7 × 10 -8 M (S/N = 3) and ranging from 1 × 10 -3 to 1.5 × 10 -2 M (in 0.1M PBS, pH 3.0), respectively. Hereby, the fabricated rGO/Pd@PPy NPs can be used with high reproducibility, selectivity, and catalytic activity for the development of electrochemical applications for the simultaneous detection of these biomolecules. Human body fuids contain very important biomolecules such as ascorbic acid (AA), dopamine (DA) and uric acid (UA), which are very efective in life functions. AA, also called vitamin C, efects as an antioxidant, present in human nutrition, and can be soluble in water. AA plays an important role in biological activities as a reducing agent for the protection of the human body against to side efects of the oxidation process. AA also involved in the activities of living structures such as blood vessels, cell development, bone-cartilage, collagen synthesis, and healing of burns and wounds. Additionally, AA is efective for the prevention and treatment of various diseases, including cancer, mental illness, AIDS, infertility, and colds 1–5 . DA, as an organic cation, is found in the brain and body fuids of tissues. DA acts as a neurotransmitter in the functions of cardiovascular, hormonal, and nervous systems; it has a vital regulating function in cognitive systems. Various neurological disorders and diseases such as Schizophrenia, Parkinson, and Huntington are taken place due to the lack of DA 6–8 . UA is produced as a result of purine metabolism, detection of UA in the products of biological functions indicates the presence of various diseases. For this reason, determining the levels of UA in body fuids is used in the diagnosis of various diseases and disorders. Tese diseases include gout, kidney disease, Lesch-Nyhan syndrome, and organic acidemia. It is 1 Sen Research Group, Department of Biochemistry, Faculty of Arts and Science, Dumlupinar University, Evliya Çelebi Campus, 43100, Kütahya, Turkey. 2 Department of Environmental Engineering, Faculty of Engineering, University of Igdir, Igdir, Turkey. *email: fatih.sen@dpu.edu.tr OPEN