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. 2022 Nov 1;27(21):7431.
doi: 10.3390/molecules27217431.

Sensitive and Facile HCOOH Fluorescence Sensor Based on Highly Active Ir Complexes' Catalytic Transfer Hydrogen Reaction

Caimei Zhang  1 , Wenjuan Zhang  1 , Yiran Wu  1 , Bo Peng  1 , Chunyuan Tian  1 , Feng Luan  1 , Wen Sun  2 , Xuming Zhuang  1 , Lijun Zhao  1
Affiliations

Sensitive and Facile HCOOH Fluorescence Sensor Based on Highly Active Ir Complexes' Catalytic Transfer Hydrogen Reaction

Caimei Zhang et al. Molecules. .

Abstract

With several major polarity and weak optical properties, the sensitive detection of HCOOH remains a major challenge. Given the special role of HCOOH in assisting in the catalytic hydrogenation process of Ir complexes, HCOOH (as a hydrogen source) could rapidly activate Ir complexes as catalysts and further reduce the substrates. This work developed a facile and sensitive HCOOH fluorescence sensor utilizing an optimal catalytic fluorescence generation system, which consists of the phenyl-pyrazole-type Ir-complex PP-Ir-Cl and the coumarin-type fluorescence probe P-coumarin. The sensor demonstrates excellent sensitivity and specificity for HCOOH and formates; the limits of detection for HCOOH, HCOONa, and HCOOEt3N were tested to be 50.6 ppb, 68.0 ppb, and 146.0 ppb, respectively. Compared to previous methods, the proposed sensor exhibits good detection accuracy and excellent sensitivity. Therefore, the proposed HCOOH sensor could be used as a new detection method for HCOOH and could provide a new design path for other sensors.

Keywords: HCOOH detection; Ir complexes; catalytic hydrogenation; fluorescence probe.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Schematic illustration of the Ir-complex catalytic fluorescence turn-on system for HCOO− detection.
Figure 1
Figure 1
The effects of pH (A), organic solvent (B), reaction temperature (C), catalyst amount (D), and reaction time (E) on the Ir-complex catalytic fluorescence sensor. (F) The fluorescence stability test of the dye 7-hydroxycoumain, which is the hydrogenation product of the probe. Conditions: 0.1 M phosphate buffer solution containing 10 v/v% of MeOH (A,C,D–F), 10 μM of Ir complex (A–C), pH = 4.0 (B–F), reaction time of 60 min (A–D,F), and reaction temperature of 60 °C (A,B,D–F).
Figure 2
Figure 2
(A) Fluorescence spectra of the Ir-complex catalytic fluorescence sensor in a series of concentrations of HCOOH (from a to h: 3.9, 7.8, 15.6, 62.5, 125.0, 500, 1000, and 2000 μM, respectively). (B) Calibration curves of the fluorescence intensity versus the concentration of HCOOH; The inset indicates that the curve is linear in the range from 7.8 to 500 μM, I = 410.6logCHCOOH − 136.53, R2 = 0.9871.
Figure 3
Figure 3
(A) Fluorescence spectra of the Ir-complex catalytic fluorescence sensor in a series of concentrations of HCOONa (from a to h: 0.1, 0.5, 1.0, 10.0, 50.0, 100.0, 500.0, and 1000.0 μM, respectively). (B) Calibration curves of the fluorescence intensity versus the concentration of HCOONa; The inset indicates that the curve is linear in the range from 0.1 to 50 μM, I = 667.1logCHCOONa − 1392.5, R2 = 0.9980. (C) Fluorescence spectra of the Ir-complex catalytic fluorescence sensor in a series of concentrations of HCOOEt3N (from a to j: 0.5, 1.0, 10.0, 25.0, 50.0, 100.0, 250.0, 500.0, 1000.0, and 1250.0 μM, respectively). (D) Calibration curves of the fluorescence intensity versus the concentration of HCOOEt3N; The inset indicates that the curve is linear in the range from 10 to 500 μM, I = 1950.5logCHCOOEt3N − 1449.2, R2 = 0.9902.
Figure 4
Figure 4
(A) The interference of various organic acids and ions on the developed HCOOH fluorescence sensor. The concentrations of the HCOOH and HCOONa are 1.0 mM, and the concentrations of the other interfering substances are 5.0 mM. (B) Reproducibility of sensor response to HCOOH fluorescence. Experimental conditions: 1.0 mM HCOOH, 0.1 M PBS solution containing 10 v/v% of MeOH, pH = 4.0, 5.0 μM of Ir complex, reaction time of 30 min, and reaction temperature of 60 °C.
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