Disposable optochemical sensor chip for nitrogen dioxide detection based on oxidation of N,N′-diphenyl-1,4-phenylenediamine

We report on a novel optochemical sensor chip for nitrogen dioxide (NO2) based on the indicator reagent N,N′-diphenyl-1,4-phenylenediamine (DPPD). The sensor chip was manufactured by immobilising DPPD in a highly permeable polymeric layer made from polydimethylsiloxane-polycarbonate block copolymer (PDMS-PC). The presence of NO2 causes oxidation of DPPD, which thereby changes its visible spectrum. The best wavelength for determining NO2 was 480 nm. To realise short measuring times (e.g. 23 s to determine 5 ppm NO2), a measuring procedure was chosen that enables a linear correlation between the rate of change of the transmission of DPPD and the concentration of NO2. A linear calibration function was obtained in the range from 0.1 to 25 ppm NO2. The limit of quantitation (LOQ) was 0.12 ppm and the accuracy exceeds 6%. The stability of the sensor chips, the effect of internal parameters (indicator reagent concentration and thickness of the polymeric layer) and the effect of external parameters (relative humidity (RH), temperature and gas flow) on the sensor chip response were investigated.No cross-sensitivities were observed at concentrations lower than 0.1 ppm ozone (O3), 0.2 ppm chlorine (Cl2) and 250 ppm nitrogen monoxide (NO).The application area of the developed sensor chips is environmental and working place analysis of NO2. For this purpose, the sensor chips will be integrated into a lightweight portable photometer made of semiconductor components.