A Turn-On Quinazolinone-Based Fluorescence Probe for Selective Detection of Carbon Monoxide

Abstract

Carbon monoxide (CO) is a toxic, hazardous gas that has a colorless and odorless nature. On the other hand, CO possesses some physiological roles as a signaling molecule that regulates neurotransmitters in addition to its hazardous effects. Because of the dual nature of CO, there is a need to develop a sensitive, selective, and rapid method for its detection. Herein, we designed and synthesized a turn-on fluorescence probe, 2-(2'-nitrophenyl)-4(3H)-quinazolinone (NPQ), for the detection of CO. NPQ provided a turn-on fluorescence response to CO and the fluorescence intensity at 500 nm was increased with increasing the concentration of CO. This fluorescence enhancement could be attributed to the conversion of the nitro group of NPQ to an amino group by the reducing ability of CO. The fluorescence assay for CO using NPQ as a reagent was confirmed to have a good linear relationship in the range of 1.0 to 50 µM with an excellent correlation coefficient (r) of 0.997 and good sensitivity down to a limit of detection at 0.73 µM (20 ppb) defined as mean blank+3SD. Finally, we successfully applied NPQ to the preparation of a test paper that can detect CO generated from charcoal combustion.

Keywords: carbon monoxide; fluorescence probe; metal free; quinazolinone; test paper.

Figure 1

Fluorogenic sensing of CO through its reduction action on NPQ forming APQ.

Figure 2

(a) The excitation spectra (λ_ex = 500 nm) and (b) emission spectra (λ_ex = 280 nm) of NPQ (30 µM) upon the addition of different concentrations of CORM-3 (0, 10, 20, 50, 100, 200 µM). The reaction time was 30 min at room temperature. The solvents for NPQ and CORM-3 are as described in the experimental section. The insets are (A) a photograph of NPQ (30 µM) and (B) a photograph of NPQ (30 µM) upon the addition of CORM-3 (100 µM). RFI refers to relative fluorescence intensity.

Figure 3

The fluorescence emission spectra of APQ (30 µM); λ_ex = 280 nm. The solvent for APQ was PBS buffer (pH 7.0, 10 mM, containing 30% DMSO).

Figure 4

HPLC with fluorescence detection chromatograms of (a) NPQ, (b) NPQ after the reaction with CORM-3, and (c) APQ. HPLC conditions: column, Nacalai Cosimosil 5C18-AR-II (4.6 × 150 mm); mobile phase, CH₃CN/H₂O (50/50, v/v%); flow rate, 0.5 mL/min; detection wavelength, λ_ex = 280 nm and λ_em = 500 nm; injection volume, 20 µL.

Figure 5

(a) Absorption spectra and (b) normalized emission spectra (λ_ex = 280 nm) of APQ (30 µM) in different organic solvents.

Figure 6

Fluorescence responses of NPQ (30 μM) at 500 nm after adding CO, reductants, reactive oxygen species, and gaseous transmitters in PBS buffer. The concentrations of CO, Fe²⁺, Fe³⁺, Cys, Hcy, Cu⁺, and Cu²⁺ were 100 µM, while the concentrations of other substances were 1 mM. The reaction time was 30 min at room temperature. The solvent for NPQ is described in the experimental section.

Figure 7

Fluorescence responses of NPQ (30 µM) upon addition of CORM-3 (100 µM) in the presence of reactive oxygen species (1 mM) in PBS buffer. The reaction time was 30 min at room temperature. The solvent for NPQ is described in the experimental section.

Figure 8

The effects of pH on the fluorescence intensity of NPQ (30 µM) upon the addition of CORM-3 (100 µM). The reaction time was 30 min at room temperature. The solvents for NPQ and CORM-3 are as described in the experimental section, except for pH.

Figure 9

The effect of reaction time on the fluorescence intensity of NPQ (30 µM) upon the addition of CORM-3 (100 µM). The solvents for NPQ and CORM-3 are as described in the experimental section. The arrow indicates the optimum reaction time.

Figure 10

The effects of the DMSO contents in the PBS buffer (10 mM, pH 7.0) of NPQ (30 µM) upon the addition of CORM-3 (100 µM). The reaction time was 30 min at room temperature. The solvents for NPQ and CORM-3 are as described in the experimental section, except for DMSO contents.

Figure 11

The calibration curve was constructed by plotting the concentration CORM-3 from 1.0 to 50 µM versus the fluorescence intensity.

Figure 12

Photographs of NPQ in the solid state under (a) natural light and (b) UV irradiation with a handy UV lamp (λ_ex = 365 nm).

Figure 13

Fluorescence of the NPQ (30 µM) test paper dropped with CORM-3 solution (100 µM): (a) before dropping the CORM-3 solution; (b) 5 min and 10 min after dropping the CORM-3 solution.

Figure 14

Fluorescence of the NPQ test paper exposed to smoke generated from charcoal combustion. (a) Photograph of test paper as it is exposed to smoke. (b) Fluorescence in areas exposed to smoke for 30 min.