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Application of MOFs and Their Derived Materials in Sensors

Yong Wang1,2*, Chang Yin1 and Qianfen Zhuang1

1College of Chemistry, Nanchang University, Nanchang, China

2Jiangxi Province Key Laboratory of Modern Analytical Science, Nanchang University, Nanchang, China

Abstract
In the past years, the application of metal organic framework (MOFs) and their derived materials in sensors has attracted wide attention due to their outstanding physical and chemical properties such as large specific surface area, tunable pore size, easy design/functionalization, high stability, good catalytic ability, and so on. In this chapter, we present some recent progress in the sensing field of MOFs and their derived materials. Depending on the signal transduction mechanism, different types of sensors are outlined. Moreover, the present problems and future development of MOFs and their derived materials are also presented.

Keywords: Metal organic framework, derived materials, sensor

1.1 Introduction

Sensor is a material or device that measures a physical or chemical quantity and converts it into an observable signal for detection of specific chemicals at trace levels [1-3]. Generally, sensing-based detection methods are superior to those traditional detection methods such as titration, chromatography, mass spectrometry and so on, because of its rapidity, simplicity, low cost, and suitability for large-scale sample screening [1-3]. On the basis of these advantages, the sensing-based approaches have been widely used in fields of environmental and industrial monitoring, drug quality monitoring, forensic analysis, food safety, medical diagnostics, and national security [1-3]. However, at present, sensors suffer from some disadvantages like poor sensitivity, limited selectivity, slow response time, low lifetime, and stability.

To over these limitations, many advanced materials have been developed to construct various robust sensors [4-10]. Among them, metal- organic frameworks (MOFs) are especially attractive as a novel sensing material [11-18]. This material is a kind of crystalline material possessing nanopore network structure, which are formed by self-assembly of coordination between transition-metal cations and oxygen or nitrogen-containing polydentate organic linkers (see Figure 1.1) [19].

Generally, the large specific surface area of MOFs improves sensor sensitivity [11-18]. The metal ions or polydentate ligands of MOFs can be rationally designed to modulate the pore size of MOF, the number and orientation of catalytically active sites of MOFs, and the different interaction force between the analyte and MOF receptor, which enhance the sensor selectivity and sensitivity [11-18]. In addition, the interaction force and the structural matching between the analyte and MOF receptors can be modulated to increase the reversibility and response time of the sensor toward analyte, leading to the regeneration and real-time monitoring of the sensor [11-18]. On the other hand, MOF-derived materials are usually obtained using MOFs and/or other materials as precursors by various strategies such as high-temperature calcinations, hydrothermal synthesis, solvothermal synthesis, and so on [20-25]. These derived materials can not only retain the original structure of MOFs, but also improve some performances of these materials like electric conductivity, stability, water-solubility, catalytic activity, and mass-transfer ability [20-25]. These merits from the MOF-derived materials lead to the enhancement of the sensor's performances.

Figure 1.1 (a)-(c) Inorganic secondary building units (SBUs) of MOFs. (d)-(f) Organic ligands of MOFs.

Reproduced with permission from Ref. [19]. Copyright 2004 Elsevier.

In the chapter, four different types of sensor, namely, optical sensor, electrochemical sensor, field-effect transistor-based sensor, and mass-sensitive sensor, is respectively described on the basis of the signal transduction mechanism. Particularly, we focus on the use of MOFs and their derived materials in the construction of sensors for detection of analyte, and summarize some representative investigations on the use of MOFs and their derived materials in the above-mentioned four types of sensor.

1.2 Application of MOFs and Their Derived Materials in Sensors

1.2.1 Optical Sensor

Optical sensor has recently attracted wide attention owing to its operation simplicity, time efficiency, and good reproducibility. MOFs and their derived materials can be easily designed to introduce optical probes, facilitating the construction of optical sensor. In addition, MOFs and their derived materials are demonstrated to possess nanozyme activity, which can catalyze various substrates into optical substances. As a result, the nanomaterials with artificial enzymes can be conveniently combined with different optical substances to construct various optical sensors. On the basis of optical transduction mechanism, optical sensors are usually classified into three types: colorimetric sensors, fluorescent sensors, chemiluminescent sensors. Therefore, the three different types of optical sensors will be introduced in the following section.

1.2.1.1 Colorimetric Sensor

In 2013, Li's group synthesized a Fe-MIL-88NH2 MOF using 2-aminoterephthalic acid and FeCl3 as precursors in a medium of acetic acid, and found for the first time that the MOF acted as a peroxidase, and could catalyze the oxidation of 3,3´,5,5´-tetramethylbenzidine (TMB) by H2O2 to produce a blue product [26]. Subsequently, they combined the MOF materials with glucose oxidase to construct a sensitive colorimetric sensor for glucose detection (see Figure 1.2) [26]. Following the work, many researchers exploited the peroxidase-like activity of the MOFs and their derived materials to construct various colorimetric sensor. Tan et al. [27] prepared a nanocomposite (CuNPs@C) composed of copper nanoparticles dispersed in a carbon matrix by one-pot thermal decomposition of a copper-based MOF precursor. The CuNPs@C can also possess peroxidase-like activity, which catalyze the reaction between H2O2 and 3,3,5,5-tetramethyl-benzidine (TMB). Because this CuNPs surface does not contain a stabilizer, a higher affinity of CuNPs@C toward H2O2 can be obtained. Depending on the inhibition of TMB oxidation by ascorbic acid (AA), the material can be used to construct a colorimetric quenching sensor for detecting AA. Hou et al. used magnetic zeolitic imidazolate framework 8 to pack glucose oxidase, and then constructed the nanocomposite-based colorimetric sensor for glucose [28]. Dong et al. [29] encapsulated cobalt nanoparticles into Fe MOF-derived magnetic carbon to produce a nanocomposite, and found that the nanocomposite had much stronger peroxidase-like activity than pure CoNPs and magnetic carbon. Therefore, they combined glucose oxidase with the CoNPs/MC to construct a robust glucose sensor.

Metal ions are present in the ecosystem, and have important influence on the ecosystem. Hence, the construction of sensor for detection of metal ions is necessary for industrial processes, medical diagnosis, and environmental monitoring. In 2015, Gao et al. [30] synthesized a thermostable magnesium metal-organic framework (Mg-MOF), and found that many nanoholes containing non-coordinating nitrogen atoms were present in the material, which is suitable for hosting Eu3+ ions. On the basis of the energy level matching and energy transfer between the Eu3+ and the Mg-MOF, they constructed a sensitive sensor for detection of Eu3+ ions. Khalil et al. [31] used UiO-66 metal-organic frameworks to accommodate diethyldithiocarbamate (DDTC) chromophore, and the obtained DDTC/UiO-66 was used for the construction of digital image-based colorimetric sensor for Cu2+ detection. Zeng et al. [32] synthesized bimetallic (Eu-Tb) lanthanide (Ln) metal-organic frameworks (MOFs) using Tb3+/Eu3+ and 1,4-benzenedicarboxylate (BDC) as precursors for on-site sensitive and selective detection of Pb2+ in environmental waters. Li et al. [33] synthesized a composite containing Pt nanoparticle and UiO-66-NH2 with permanent porosity, strong thermal and high chemical stability, and found that the material displayed high peroxidase-like activity. However, the peroxidase-like behavior of the material was suppressed in the presence of Hg2+, due to the Hg2+/Pt nanoparticle specific interaction. Therefore, they followed the principle to realize the construction of Hg2+ sensor (see Figure 1.3).

Figure 1.2 Schematic illustration of the peroxidase-like activity of Fe-MIL-88NH2 MOFs using TMB and H2O2 as reactants and their applications for glucose sensing.

Reproduced from Ref. [26] with permission. Copyright 2013 Royal Society of Chemistry.

Recently, Wang et al. [34] has exploited the partial oxidation of cerium(III) to prepare the mixed-valence state cerium-based metal-organic framework (MVC-MOF) with the oxidase activity, and demonstrated that the oxidase activity of the MVC-MOF could be suppressed by single-stranded DNA (ssDNA). However, the oxidase activity of the material can be prevented in the presence of double-stranded DNA (dsDNA)....