A solid-state glucose sensor based on Cu and Fe–doped carbon nitride

Functional nanomaterials find numerous applications in electrochemical biosensors and lab-on-a-chip devices, such as the glucose sensors used by diabetic patients. In this work, polymeric carbon nitride (g-C3N4) −which mimicks peroxidases behavior− was used, in combination with 3,3′,5,5′-tetramethylbenzidine (TMB) −a redox indicator−, to detect glucose in a quantitative way. The utilization of two non-noble metal co-catalysts, Fe(III) and Cu(II), embedded in the polymer structure by adsorption (Cu(II)–Fe(III)-g-C3N4), considerably increased the sensitivity towards glucose as compared to that of pristine g-C3N4. TMB and glucose oxidase (GOx) were also adsorbed on the catalyst, resulting in a solid-state composite that changed its color from yellow to green when exposed to a solution containing glucose. The UV–Vis monitoring of the intensity of the band at 675 nm, associated with oxidized TMB, showed that the response of the Cu(II)–Fe(III)-g-C3N4 system was faster than that of the one based on pristine g-C3N4. This behavior was further confirmed by electron spin resonance (ESR) spectroscopy. Moreover, ESR experiments conducted with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) evidenced that the Cu(II)–Fe(III)-g-C3N4 catalyst was able to produce about twice as many radicals as pristine g-C3N4. The proposed composite material may hold promise as a solid substrate for glucose sensing, given that concentration levels in the low ppb range can be detected by UV–Vis diffuse reflectance spectroscopy and concentrations above 100 ppm (μM) can be easily detected by the naked eye.