Conducting polymers decorated with noble metals are good electrochemical sensors for biological species. In this work, we developed a polymer of methanethiol-grafted poly(3,4-ethylenedioxythiophene) hollow spheres (Poly(EDOT-MeSH)) using SiO 2 nanospheres as a hard template. The Poly(EDOT-MeSH) spheres were used as both a reductant and stabilizer to decorate gold nanoparticles (Au NPs). FTIR, XRD, EDX, SEM and TEM analyses were used to characterize the Poly(EDOT-MeSH)/Au hollow spheres. The chemical bond between S and Au was confirmed by XPS. The electrochemical performance of the Poly(EDOT-MeSH)/Au hollow spheres was determined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results revealed that the Poly(EDOT-MeSH)/Au hollow sphere-based electrochemical sensor possesses an excellent conductivity and high redox reversibility with detection limits (S/N = 3) of 5.3, 0.04 and 0.12 μM in the linear ranges of 50-320 μM, 0.05 μM − 780 μM and 0.8 μM − 250 μM for the determination of AA, DA and UA, respectively. These results will further the development of this type of electrochemical sensor for biological species. Small biological species usually coexist in physiological fluids, which are very important for maintaining the functions of organisms.1,2 As typical biological species, dopamine (DA), uric acid (UA) and ascorbic acid (AA) are important components of the neural system and play significant roles in physiological functions.3,4 DA is a natural neurotransmitter that plays an important role in controlling the central nervous system and coordinating normal cardiovascular, renal, and hormonal functions. 5,6 The UA concentration in blood and urine is usually related to diseases such as Lesch-Nyhan syndrome, hyperuricemia, gout and kidney stones. 7,8 Therefore, the ability to detect and quantify these biological species is very important. Several analytical techniques, such as liquid chromatography, 9 ultraviolet visible spectroscopy, 10 capillary electrophoresis, 11,12 chemiluminescence 13,14 and spectrometry 15 have been used to detect single or multiple biological species. However, most of these techniques require specialized, expensive instruments and can be utilized only for individual determination. In the last few years, electrochemical techniques have attracted attention for the determination of multiple components due to their simplicity, low cost, minimal analysis time, high sensitivity, good selectivity and simple instrumentation. [16][17][18] However, the electrochemical oxidation of DA and UA is difficult to observe with conventional electrodes, such as glassy carbon, gold and platinum electrodes, because the oxidation products cause electrode surface fouling. 3,19 In addition, AA co-exists with DA and UA in most biological fluids, and the AA concentration is higher than that of DA and UA (100-1000 times higher than that of DA). 20 The AA oxidation peak often overlaps with the DA and UA peaks because their oxidation potentials on conventional electrodes are nearly equal. 21,22 To...