Ion-selective electrodes (ISEs) represent one of the main technologies for developing sensors to measure ions concentration in human tissues. All-solid-state ISEs are of key importance for sensor miniaturization, especially toward point-of-care applications. In this article, we propose an innovative needle-shaped sensor in sub-mm sizes with nanostructured platinum (Pt) for the aim of ion detection. It can be employed in biomedical applications, with particular regard to surgical procedures. The developed sensor has been tested for potassium (K+) detection, which is very important in cells functions assessment. For the first time in the literature, we investigate the effects on the morphology of electrodeposition voltage and time. In the past, similar nanofabrications have been successfully tried on usual planar geometries. Here, instead, Pt nanostructure (Pt-NS) growth is successfully shown on a thin Pt wire with a diameter of 0.1 mm only. Both granular and petal-like nanostructures are obtained depending on the applied deposition voltage. The minimum time needed to nanostructure the whole electrode surface is found for each deposition voltage, suggesting that higher absolute voltage values need higher deposition time. The electrochemical measurements performed on the Pt nanostructured K+ ISEs show enhanced stability over time with respect to non-nanostructured ISEs and a Nernstian response with the best sensitivity of 59.2 +/- 2.4 mV/decade in the linear range from 10(-4 )to 10(-1 )M. These good results encourage to further extend this study toward sensing of other ions by means of these microfabricated needle-shaped sensors, which can be easily integrated into surgical instruments to be then used for diagnosis during surgical operations.