A fluorescent nanofiber probe for the determination of Ni2+ was developed via the electrospinning of a covalently functionalized pyridylazo-2-naphthol-poly(acrylic acid) polymer. Fluorescent nanofibers with diameters in the range 230-800 nm were produced with uniformly dispersed fluorophores. The excitation and emission fluorescence were at wavelengths 479 and 557 nm respectively, thereby exhibiting a good Stokes' shift. This Ni2+ probe that employs fluorescence quenching in a solid receptor-fluorophore system exhibited a good correlation between the fluorescence intensity and nickel concentration up to 1.0 mu g mL(-1) based on the Stern-Volmer mechanism. The probe achieved a detection limit (3 delta/S) of 0.07 ng mL(-1) and a precision, calculated as a relative standard deviation (RSD) of <4% (n = 8). The concentration of Ni2+ in a certified reference material (SEP-3) was found to be 0.8986 mu g mL(-1), which is significantly comparable with the certified value of 0.8980 mu g mL(-1). The accuracy of the determinations, expressed as a relative error between the certified and the observed values of certified reference groundwater was <= 0.1%. The versatility of the nanofiber probe was demonstrated by affording simple, rapid and selective detection of Ni2+ in the presence of other competing metal ions by direct analysis, without employing any further sample handling steps.