A Highly Selective Economical Sensor for 4-Nitrophenol

Abstract

Herein, an inexpensive commercially available sensor is presented for the detection of 4-nitrophenol (4NP) pollutant. Sodium fluorescein (NaFl) is used as a sensor to detect trace amounts of 4NP in acetonitrile (MeCN). The photophysical properties of NaFl were studied in two different solvents, MeCN (aprotic) and water (protic), with varying concentrations of different nitroaromatics using UV-visible absorption and fluorescence spectrophotometry. In an aqueous medium, photophysical properties of NaFl did not change in the presence of nitroaromatics. However, examination of the photodynamics in MeCN demonstrated that NaFl is extremely sensitive to 4NP (limit of detection: 0.29 µg/mL). This extreme specificity of NaFl towards 4NP when dissolved in MeCN, as compared to other nitroaromatics, is attributed to hydrogen bonding of 4NP with NaFl in the absence of water, resulting in both static and dynamic quenching processes. Thus, NaFl is demonstrated as a simple, inexpensive, sensitive, and robust optical turn off sensor for 4NP.

FRET-based carbazole-fluorescein ionic nanoparticle for use as an effective bioimaging agent

“…At pH 2, fluorescein is present as a neutral specie thus there is no pairing with any CI + donor and thus no peak was observed for fluorescein due to absence of energy transfer. Moreover, neutral fluorescein does not exhibit any fluorescent properties at lower pH [ 31 ]. The donor fluorescence emission intensity in the INP was compared to CII fluorescence emission to calculate the FRET efficiency at differing pH and is reported in Table 2 .…”

“…The INP of [CI] 2 [Fl] was prepared through a reprecipitation method [ 31 ]. [CI] 2 [Fl] was dissolved in ethanol at a high concentration.…”

“…The photophysical properties of fluorescein are highly pH-dependent thus indicating the potential for a pH-dependent fluorescent probe. Fluorescein can exist as a dianion, monoanionic, and neutral molecule with pKas of 6.3, 4.3, and 2.2, respectively [ 31 ]. These different forms of fluorescein have unique absorbance and fluorescence emission spectra.…”

“…The fluorescence emission intensity is strong in the dianion form and significantly reduced in the monoanionic form. The neutral form of the molecule has no fluorescent properties [ 31 ]. This unique property of fluoresceine opens the possibility for its use as a biocompatible, pH-dependent fluorescent probe [ 32 ].…”