In this work, a novel catalytic synthesis and functionalization method using apoferritin is used to fabricate RuO2 nanoparticles (NPs) loaded WO3 nanofibers (NFs) for potential diagnosis of diabetes. Catalytic ruthenium (Ru) NPs with very small average diameters of 1.8 +/- 0.9 nm were synthesized using apoferritin which is a hollow protein cage, and were easily functionalized on WO3 NFs by introducing electrospinning solution with W precursor and polyvinylpyrrolidone (PVP). As-spun Ru NPs-loaded W precursor/PVP composite NFs were calcined at 600 degrees C for 1 h in air atmosphere to achieve RuO2-functionalized WO3 NFs. The small size and uniform distribution of catalytic RuO2 NPs were well maintained due to hollow nature of apoferritin cages after calcination. The chemo-resistive sensors using RuO2-functionalized WO3 NFs showed significantly enhanced acetone (CH3COCH3) sensing response (R-air/R-gas = 78.61-5 ppm), which was 7.4 times higher than the response (R-air/R-gas =10.61-5 ppm) of pristine WO3 NFs at highly humid atmosphere (95% RH). In addition, the RuO2-functionalized WO3 NFs showed outstanding selectivity toward acetone gas in comparison with other gases such as hydrogen sulfide (H2S), toluene (C6H5CH3), ethanol (C2H5OH), pentane (C5H12), ammonia (NH3), hydrogen (H-2), and water vapor (H2O) at 5 ppm. These results represent potential feasibility for the detection of acetone in exhaled breath for diagnosis of diabetes. (C) 2016 Elsevier B.V. All rights reserved.