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Operandomeasurements of local pH at the nanoscale can significantly improve the understanding of the complex microenvironments that exist in electrochemical systems. However, attempts to easily fabricate a nano-sized pH electrode that can operate under a wide range of pH conditions and have fast temporal responses have been difficult. Here, we show that an anodic-grown Pt/Pt(II) oxide pH sensor manufactured in alkaline conditions (1 M NaOH) shows a near-Nernstian response (−60 mV/pH) from pH 0 to pH 14, is insensitive to dissolved oxygen, cation, and anion identities, and responds correctly in solution with different ionic strengths. This is in contrast to Pt/Pt(II) oxide films grown in acidic media, which do not demonstrate a Nernstian relationship due to cation interference other than H⁺. We observed a response time of 2.25 s, corresponding to 90% of the final measured pH, for an approximately twelve-fold pH step change when growing the Pt(II) oxide layer on a platinum nanoelectrode. Our findings emphasize the influence of solution pH used for anodization synthesis on the anodic Pt(II) oxide pH sensing properties. The direct oxidation approach for fabricating Pt/Pt(II) oxide microelectrode/nanoelectrode pH sensors can simplify the manufacture of real-time pH sensors for complex aqueous environments.