Ratiometric fluorescent detection of Cu²⁺ based on dual‐emission ZIF‐8@rhodamine‐B nanocomposites

Abstract

Zeolitic imidazolate framework-8 (ZIF-8) loading rhodamine-B (ZIF-8@rhodamine-B) nanocomposites was proposed and used as ratiometric fluorescent sensor to detect copper(II) ion (Cu 2+ ). Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, nitrogen adsorption/desorption isotherms and fluorescence emission spectroscopy were employed to characterize the ZIF-8@rhodamine-B nanocomposites. The results showed the rhodamine-B was successfully assembled on ZIF-8 based on the π-π interaction and the hydrogen bond between the nitrogen atom of ZIF-8 and -COOH of rhodamine-B. The as-obtained ZIF-8@rhodamine-B nanocomposites were octahedron with size about 150-200 nm, had good water dispersion, and exhibited the characteristic fluorescence emission of ZIF-8 at 335 nm and rhodamine-B at 575 nm. The Cu 2+ could quench fluorescence of ZIF-8 rather than rhodamine-B. The ZIF-8 not only acted as the template to assemble rhodamine-B, but also was employed as the signal fluorescence together with the fluorescence of rhodamine-B as the reference to construct a novel ratiometric fluorescent sensor to detect Cu 2+ . The resulted ZIF-8@rhodamine-B nanocomposite fluorescence probe showed good linear range (68.4 nM to 125 μM) with a low detection limit (22.8 nM) for Cu 2+ combined with good sensitivity and selectivity. The work also provides a better way to design ratiometric fluorescent sensors from ZIF-8 and other fluorescent molecules. KEYWORDSCu 2 + , ratiometric fluorescent sensor, rhodamine-B, zeolitic imidazolate framework-8 biotoxicity, poor aqueous solubility and stability, etc. Nanomaterial fluorescent probes, especially the metal-organic frameworks (MOFs) or zeolitic imidazolate framework-8 (ZIF-8) based probes, are attracting more and more interest and are used for different applications due to their predictable pore sizes, considerable specific surface area, good encapsulation and hierarchical structures. [35][36][37][38][39] For example, carbon dots (CDs)@MOFs have been prepared to enhance fluorescence sensing. [40] A ratiometric type fluorescence sensor has two or more emission wavelengths, and the target content is usually quantified based on the relationship between the ratio of fluorescence intensities at two wavelengths and the concentration of the analyte. At the same time, this sensor mode enhances the dynamic response range by adjusting the change of intensity ratio, and establishes an internal standard to make it self-regulating, greatly weakening the effect some experimental conditions such as probe concentration, temperature, polarity, environmental pH, and stability. These experimental conditions are usually difficult to control in the experimental process. Moreover, as the concentration of analyte changes, the color of the ratio probe changes step-by-step, thereby enabling visual detection of the analyte, and semi-quantitative and qualitative analysis of the analyte can be achieved depending on the color of the ratio probe. [41,42] Therefore, the construction of rati...

Multichromic Metal-Organic Framework for Multimode Photonic Sensing

“…Conversely, we discovered that the RhB@ZIF-71 exhibits good luminescence ( Figure S14 and Figure 6) in non-polar solvents, and even show sensing property previously not achievable by pure RhB alone. To date, most of the RhB@MOF studies [17][18][19][20][21][22][23][24] have focused on the field of solvatochromism, and many of these systems possess the similar sensing behaviour.…”

“…In this study, we demonstrate a facile method to synthesize a multi-stimuli responsive Guest@MOF luminescent material, by embedding the well-known luminescent dye rhodamine B (RhB) into zeolitic imidazolate framework-71 (ZIF-71). Although a number of RhB@MOF systems have been reported, [17][18][19][20][21][22][23][24] there are certain limitations, such as the use of complex synthesis steps, no control of RhB aggregates, inadequate explanation of the underlying mechanisms, and monotonous functionality (basically only solvatochromism). In contrast, our RhB@ZIF-71 not only shows solvatochromic response with its sensitivity far surpassing all reported examples, [17][18][19][20][21][22][23][24] but also exhibits exceptional mechanochromic and thermochromic sensing properties that are unknown to date.…”

Multichromic Metal-Organic Framework for Multimode Photonic Sensing

“…Conversely, we discovered that the RhB@ZIF-71 exhibits good luminescence ( Figure S14 and Figure 6) in non-polar solvents, and even show sensing property previously not achievable by pure RhB alone. To date, most of the RhB@MOF studies [17][18][19][20][21][22][23][24] have focused on the field of solvatochromism, and many of these systems possess the similar sensing behaviour.…”

“…In this study, we demonstrate a facile method to synthesize a multi-stimuli responsive Guest@MOF luminescent material, by embedding the well-known luminescent dye rhodamine B (RhB) into zeolitic imidazolate framework-71 (ZIF-71). Although a number of RhB@MOF systems have been reported, [17][18][19][20][21][22][23][24] there are certain limitations, such as the use of complex synthesis steps, no control of RhB aggregates, inadequate explanation of the underlying mechanisms, and monotonous functionality (basically only solvatochromism). In contrast, our RhB@ZIF-71 not only shows solvatochromic response with its sensitivity far surpassing all reported examples, [17][18][19][20][21][22][23][24] but also exhibits exceptional mechanochromic and thermochromic sensing properties that are unknown to date.…”

Enhanced chemical sensing for Cu2+ based on composites of ZIF-8 with small molecules

“…Pyridoxal and Rhodamine B are well-known platforms for the development of uorescent or colorimetric chemosensors for metal ions. [23][24][25] Herein, we propose using these two kinds of small molecules to assemble the ZIF-8 sensor for Cu 2+ with excellent spectral properties, sensing efficiency and biocompatibility.…”