Combination of fluorescence spectroscopy and electrochemical technique as a novel and sensitive electro-optical detection system for gaseous and dissolved oxygen detection using nitrogen-doped quantum dots through the amperomric reduction of oxygen

Abstract

A novel dissolved and gaseous oxygen electro-optical sensor was fabricated based on the dependency of the fluorescence intensity of a synthesized nitrogen-doped carbon nanodots (N-CDots) during the amperometric reduction of O2 at potential of −0.55V (vs. Ag/AgCl) for about 20s using a three-electrode system including gold rod as worker electrode, platinum rod as counter electrode and Ag/AgCl (3.0molL−1 Cl−) as reference electrode, followed by measuring the fluorescence intensity at excitation wavelength of 350nm. Under optimized condition, i.e. 5.0μgmL−1 of N-CDots, ionic strength of 0.5molL−1 and room temperature, the linear range for the dissolved oxygen was estimated to between 0.11 and 22μgmL−1 with detection limit of 0.07μgmL−1 (n=4). For gaseous oxygen the linear dynamic range was between 3.0 and 48.0% with the limit of detection of 0.95% (n=4). The response time (t90) of the sensor was estimated to be 20s. No interfering effect was observed during analysis of at least 200-fold excess (vs. 2.0μgmL−1 dissolved oxygen) of organic and inorganic species such as, K2SO4, KNO3, MgCl2, MnCl2, NaClO4, NaF, NH4Cl, CaCl2 and Na3PO4, except NO2− and HCO3− which interfered for respectively 12-fold and 75-fold excess. The reliability of the method was also evaluated via analyses of waste and industrial samples.