A fluorescein sodium wide-area pH optical sensor based on amplification characteristics

Abstract We studied the characteristics of fluorescein sodium (FS) to cause changes in the amplified spontaneous emission (ASE) spectrums under different acid and alkaline environments. According to the characteristics of light amplification, the spectrum width became narrower and the highest peak wavelength of the ASE spectrum became stabilized, establishing a connection between the light wavelength and the solution pH. Compared with the amplifier’s performances, the host and guest materials of different ratios were tested with FS as the host material, and the best ratios were determined to be 1.5 and 0.1 mg/mL for FS and 4-methylumbelliferone, respectively. The gains for signals with wavelengths of 535-555 nm were all greater than 7 dB, and the amplified signal-to-noise ratios (SNRs) were greater than 7 dB. Moreover, the gains of the wavebands (543–550 nm) in the pH test were all greater than 10 dB. The best operating wavelength of the amplifier was 542 nm, and the best gain and SNR were 14.3 and 12.3 dB, respectively. Following this, we measured the output signal wavelengths of the pH standard solutions corresponding pH values of 3-10, and measured the pH values of tap water and three dyeing pigments that could not be measured with pH test paper owing to dyeing. We compared the measured values of the pen-shaped pH meter with the measured pH values of the wavelengths to test the effectiveness of this detection method, which the deviation was all less than 1 pH.