New β-diketonate platinum (II) complexes, containing a cyclometalated N-heterocyclic carbene [Pt(Naph^C*iPr)(acac)] (3A) (HNaph^C*-κC* = 3-isopropyl-1-(naphthalen-2-yl)-1H-imidazole-2-ylidene), or a cyclometalated pyrazole, [Pt(Naph^Npz)(acac)] (3B) (HC^Npz = 1-(naphthalen-2-yl)-1H-pyrazole) and [Pt(Naph^Ndmpz)(acac)] (3B') (HC^Ndmpz = 1-(naphthalen-2-yl)-1H-3,5-dimethylpyrazole) have been prepared and characterized. Their absorption and emission properties in films of ethyl cellulose (EC) were determined along with those of the already reported for complex [Pt(Naph^C*Me)(acac)] (3A'). They showed that all four β-diketonate complexes display a bright phosphorescent emission with maxima in the blue region (λmax ∼ 480 nm for 3A and 3A'; 490 nm 3B and 3B'). The higher quantum yield (QY), longer decay times and greater oxygen sensitivity were exhibited by the Naph^C* derivatives, compared to the Naph^N ones. Polyacrylamide membranes with entrapped 3A' as dye, and glucose oxidase (GOx) enzyme were used for monitoring glucose level. The RSD is about 5% and the detection limit is at ∼5·10⁻⁴ M, with a response time usually of 10–15 min working in stop-flow mode. These platinum-based membranes respond reversibly to glucose for, at least, 20 measures. 3A' is the first Pt(II) complex bearing a cyclometalated N-heterocyclic carbene ever used as dye for sensing glucose.