A metal-organic framework (MOF)-based nanocomposite was designed by incorporating the fluorescent rhodamine B dye (RhB) into a stable copper-based MOF (Cu-MOF). The Cu-MOF was characterized using a variety of techniques, such as Powder X-ray diffraction (PXRD), Infrared (IR) spectroscopy, Scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX) analysis, Transmission electron microscopy (TEM), UV-Visible spectroscopy, Brunauer–Emmett–Teller surface area measurement, Thermogravimetric analysis (TGA), XPS and Photoluminescence spectroscopy. The PXRD analysis confirmed the crystalline nature of the Cu-MOF material. The presence of copper in + 2 oxidation state in the synthesis of metal-organic framework was confirmed by XPS analysis. The BET analysis indicated surface area of 418.854 m2/g and the pore volume is 0.148 cc/g. FT-IR spectrum of Cu-MOF displayed a shift in the carbonyl group stretching peak to a lower wavenumber, confirming the coordination of carboxylate with the metal. FE-SEM images revealed irregular morphology and TEM images were quasi-spherical to irregular in shape. In UV-vis absorption spectra of Cu-MOF, the absorption peak observed at 290 nm is attributed to ligand-centered (LC) π–π* transitions. This nanocomposite serves as a fluorescence-based sensing platform for nitrate detection, wherein the introduction of nitrate causes fluorescence quenching through its interaction with Cu-MOF@RhB which is due dexter type energy transfer mechanism. The system exhibits a linear response across the concentration range of 0.0–4.0 µM and has a limit of detection (LOD) of 1.315 µM. Furthermore, under ultraviolet light, adding nitrate to nanocomposite causes the color change from yellow to orange under UV light. The Stern–Volmer quenching constant was established at 1.7 × 103M−1, affirming the robust interaction between nitrate and the nanocomposite. The device excels in assessing nitrate in intricate materials, including human serum, by photoluminescence spectroscopy. The nanocomposite demonstrated superior performance, with relative standard deviations (RSD) for nitrate concentration measurements in human serum between 0.930% and 2.687%, and recovery rates for nitrate detection in human blood from 99.6 to 103.6%. The detected fluorescence quenching and colorimetric response validate the appropriateness of this sensor for nitrate anion detection. This Cu-MOF@RhB nanocomposite enabled direct detection of nitrate in human serum using photoluminescence spectroscopy. Owing to its robust response, portability, it shows great potential for on-site clinical monitoring of nitrate levels.

Fluorescent Cu-MOF@Rhodamine-B Nanocomposite for the Selective Sensing of Nitrate in Human Serum

期刊论文
发表日期：

2025年8月13日

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Tarun Kumar,
Vimal K. Bhardwaj

摘要

A metal-organic framework (MOF)-based nanocomposite was designed by incorporating the fluorescent rhodamine B dye (RhB) into a stable copper-based MOF (Cu-MOF). The Cu-MOF was characterized using a variety of techniques, such as Powder X-ray diffraction (PXRD), Infrared (IR) spectroscopy, Scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX) analysis, Transmission electron microscopy (TEM), UV-Visible spectroscopy, Brunauer–Emmett–Teller surface area measurement, Thermogravimetric analysis (TGA), XPS and Photoluminescence spectroscopy. The PXRD analysis confirmed the crystalline nature of the Cu-MOF material. The presence of copper in + 2 oxidation state in the synthesis of metal-organic framework was confirmed by XPS analysis. The BET analysis indicated surface area of 418.854 m²/g and the pore volume is 0.148 cc/g. FT-IR spectrum of Cu-MOF displayed a shift in the carbonyl group stretching peak to a lower wavenumber, confirming the coordination of carboxylate with the metal. FE-SEM images revealed irregular morphology and TEM images were quasi-spherical to irregular in shape. In UV-vis absorption spectra of Cu-MOF, the absorption peak observed at 290 nm is attributed to ligand-centered (LC) π–π* transitions. This nanocomposite serves as a fluorescence-based sensing platform for nitrate detection, wherein the introduction of nitrate causes fluorescence quenching through its interaction with Cu-MOF@RhB which is due dexter type energy transfer mechanism. The system exhibits a linear response across the concentration range of 0.0–4.0 µM and has a limit of detection (LOD) of 1.315 µM. Furthermore, under ultraviolet light, adding nitrate to nanocomposite causes the color change from yellow to orange under UV light. The Stern–Volmer quenching constant was established at 1.7 × 10³M⁻¹, affirming the robust interaction between nitrate and the nanocomposite. The device excels in assessing nitrate in intricate materials, including human serum, by photoluminescence spectroscopy. The nanocomposite demonstrated superior performance, with relative standard deviations (RSD) for nitrate concentration measurements in human serum between 0.930% and 2.687%, and recovery rates for nitrate detection in human blood from 99.6 to 103.6%. The detected fluorescence quenching and colorimetric response validate the appropriateness of this sensor for nitrate anion detection. This Cu-MOF@RhB nanocomposite enabled direct detection of nitrate in human serum using photoluminescence spectroscopy. Owing to its robust response, portability, it shows great potential for on-site clinical monitoring of nitrate levels.