Determination of formaldehyde in aqueous solutions by a novel fluorescence energy transfer system

An efficient fluorescence energy transfer (FET) system between CePO4:Tb3+ nanocrystals as donor and 6-mercapto-5-triazole[4,3-b]-S-tetrazine as acceptor was built. CePO4:Tb3+ nanocrystals were synthesized in aqueous solutions, and characterized by transmission electron microscopy, electron diffraction pattern spectroscopy and spectrofluorometry. Under alkaline conditions, 6-mercapto-5-triazole[4,3-b]-S-tetrazine was generated by redox reaction of formaldehyde (HCHO) with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT) at room temperature. The degree of the overlap was effective for FET between the emission spectrum of CePO4:Tb3+ and the absorption spectrum of 6-mercapto-5-triazole[4,3-b]-S-tetrazine. Based on this system, a simple and sensitive fluorescence method for the selective determination of formaldehyde in aqueous solutions was developed. Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of HCHO ranging from 1.03 × 10−9 to 1.03 × 10−5 mg mL−1 with a correlation coefficient of 0.9976. The limit of detection was 1.65 × 10−10 mg mL−1. Compared with several methods, the proposed method had a wider linear range, higher selectivity and sensitivity. Moreover, analytical application of the method was demonstrated by water samples.