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

Abstract 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.