A fluorescent sensor for low pH values based on a covalently immobilized rhodamine–napthalimide conjugate

This article presents the fabrication and analytical characteristics of fluorescence-based pH-sensing glass slides. In order to fabricate the sensor, a rhodamine–naphthalimide conjugate with a terminal double bond was prepared and photo-copolymerized with 2-hydroxyethyl methacrylate (HEMA) on the silanized glass surface. The described sensor is based on the pH-dependent fluorescence intensities in different pH ranges. With an increase of hydrogen ions concentration, the resulting optical sensor undergoes fluorescence enhancement and color change from yellow to red. The linear response range covers the acidic pH range from 1.40 to 3.60. In addition, the sensor shows satisfactory selectivity, reproducibility and response time. The sensing membrane was found to have a lifetime of at least one month. The proposed sensor has been successfully applied to determine the pH of wastewater and artificial sample.