A novel cerium(iii)-isatin Schiff base complex: spectrofluorometric and DFT studies and application as a kidney biomarker for ultrasensitive detection of human creatinine

Abstract

In this paper, a new isatin-Schiff base L1 was prepared via a simple reaction of isatin with 2-amino-3-hydroxypyridin. Subsequently, cerium(iii)-Schiff base complex C1 was obtained through the reaction of the prepared Schiff base L1 with cerium chloride via a hydrothermal method. The prepared L1, as well as C1, were fully characterized using many spectroscopic techniques, such as mass spectra, elemental analysis, UV-vis, FT-IR, ¹H-NMR, ¹³C-NMR, FE-SEM/EDX, and HR-TEM. A photoluminescence study (PL) was carried out for the prepared complex C1. The promising photoluminescence results revealed that C1 could be used for the detection of creatinine in different human biological samples as a selective optical biosensor. The results showed that C1 after excitation at 370 nm has a strong emission band at 560 nm. The calibration graph was obtained in a wide concentration range between 2.5 and 480 nM creatinine with limits of detection (LOD) and quantitation (LOQ) of 1.07 and 3.25 nM, respectively. In addition, the correlation coefficient (r ²) was found to be 0.9890. The PL spectra indicate that C1 has high selectivity toward creatinine without interference from other different analytes and can be successfully used as an optical sensor for creatinine detection. The mechanism of quenching between the Ce(iii) complex and creatinine was a dynamic type. The geometry of Schiff base L1 and its cerium(iii) complex C1 was proven by using density functional theory (DFT). The energy of the LUMO and HOMO, energy gap, dipole moment and structure-activity relationship were determined and confirmed.

Scheme 1. The proposed scheme of the reaction of Schiff base L1, and Ce(iii)-complex C1.

Fig. 1. SEM and EDX images: [a–c] Schiff base L1, and [d–f] Ce(iii)-complex C1.

Fig. 2. TEM image of: [a] Schiff base L1, and [b] Ce(iii)-complex C1.

Fig. 3. Optimized structures of [a] Schiff base L1, and [b] Ce(iii)-complex C1.

Fig. 4. HOMO and LUMO energy level images of: [a and b] Schiff base L1, and [c and d] Ce(iii)-complex C1.

Fig. 5. [a] The PL emission spectra at different excitation wavelengths for C1. [b] Excitation (red line) and emission (black line) spectra of C1. [c] The PL spectra showing the behavior of C1 towards human creatinine. [d] The linear relationship between the photoluminescence intensity of C1 and different concentrations of human creatinine. [e] The PL enhancement efficiency histogram of C1 against different types of interferents. [f] The Stern–Völmer plots for PL quenching of C1 by creatinine at four different temperatures.