I hereby declare that the submitted thesis entitled "Fluorescence-based detection of environmental and biological threats by functionalized aquastable metal-organic frameworks" is the result of research work carried out by me in the Department of Chemistry, Indian Institute of Technology Guwahati, under the supervision of Dr. This is to confirm that the work presented in the thesis entitled "Fluorescence Based Detection of Environmental and Biological Threats by Functionalized Aqua-Stable Metal-Organic Frameworks" by Mr.
PUBLICATIONS AND CONFERENCES ATTENDED 219
Thesis Title: Fluorescence-Based Detection of Environmental and Biological Threats by Functionalized Aqua-Stable Metal-Organic Frameworks.
Thesis Overview
- Chapter 1: Introduction to metal-organic frameworks and their applications in chemical sensing
- Chapter 2: Rapid and highly sensitive detection of extracellular and intracellular H 2 S by an azide-functionalized Al(III)-based metal-organic
- A dinitro-functionalized metal-organic framework featuring visual and fluorogenic sensing of H 2 S in living cells, human blood plasma and environmental
- A metal-organic framework showing selective and sensitive detection of exogenous and endogenous formaldehyde
- Chapter 5: A recyclable post-synthetically modified Al(III) based metal-organic framework for fast and selective fluorogenic recognition of bilirubin in human
The detection limit of the material (2.65 μM) for H2S is lower than for existing MOF-type fluorescent probes for H2S. Furthermore, the ability of the probe to detect FA in the vapor phase was also demonstrated (Figure 7).
Introduction to metal-organic frameworks and their applications in chemical sensing
Introduction
The tunable chemical functionalization, reversible adsorption, high catalytic activity, and diverse structures of MOFs make them ideal candidates as chemical sensors.38 Chemical, physical, or structural changes in a MOF upon adsorption or interaction with guest molecules have been used recent years for the detection of various target components including toxic species, solvents, pesticides, antibiotics, explosives, volatile organic compounds and biological markers.39-42 Moreover, not only target components but also pH,43 humidity44 and temperature45 can also be sensed by MOFs. The numbers were determined based on a May 2020 Scifinder search spanning 2010 to 2019 using keywords: metal-organic framework and water-resistant metal-organic framework for fluorescence sensor.
Background and development of MOFs
- Zr 4+ –Carboxylate based MOFs
- Al 3+ –Carboxylate based MOFs
The large pore (LP) and (c) narrow pore (NP) shapes of the framework viewed along the crystallographic c-axis. Specific arrangement of the inorganic building blocks and ligand molecules results in the formation of square one-dimensional channels in CAU-10-MOF (Figure 1.4).
Basic design strategies of MOFs
The choice of an organic linker depends on the number of Lewis basic sites present in the ligands and the relative angularity of the binding sites. Cationic ligands are generally not used because of their low affinity towards metal ions.94 During the formation of the spacer-node-spacer unit, the spacer linearity breaks.
Synthesis protocols of MOFs
- Diffusion method
- Hydro/solvothermal synthesis
- Microwave method
- Electrochemical method
- Mechanochemical method
- Sonochemistry method
- Post-synthetic modification
At the interface, crystal growth occurs due to the gradual diffusion of the precipitating solvent into the separate layer. The introduction of a certain functional group into MOFs for a special application is sometimes difficult due to the high sensitivity and reactivity of the additional functionality during the formation of MOFs.
Characteristic features of aqua stable MOFs
- High connectivity and bond strength of metal and ligands
- Rigidity of ligand molecule
- Hydrophobicity of ligand
In one method, the ligand present in the MOF can be functionalized with hydrophobic groups using the PSM method.141 For example, Zhang et al. Furthermore, no change in XRPD patterns was observed after PSM (Figure 1.13).142 Second, the surface of the MOF material can be coated with hydrophobic materials to improve moisture stability.143.
Key features of MOFs for fluorescence sensing and bio-imaging
- Predictable structures
- Processability in nanoscale
- Biocompatibility of MOFs
- Collaborative luminescence properties
The nano-MOFs exhibit different or at least improved properties compared to bulk materials due to the high surface area-to-volume ratio and quantum size effects. Moreover, the self-assembly of nano-MOFs can be confined to droplets by microemulsion and have great control over the surface of substrates through templating.
Origin of fluorescence in MOFs
- Ligand based fluorescence
- Metal centered fluorescence
- Charge transfer fluorescence
- Guest induced fluorescence
Additionally, the spatial orientation and arrangement of the linkers and the overall coordination environment within MOFs can have an impact on the fluorescent properties of the organic linkers. Another possibility is direct energy transfer from the S1 singlet excited state to the energy levels of the lanthanide ion, which is known for Eu3+.
Applications of MOFs
- Fluorescence sensing
- Sensing of toxic compounds
- Sensing of biomolecules
Following this mechanism, Ghosh and co-workers also reported a nitro-functionalized Zr-UiO-66 framework for “on” detection of H2S. Qian and co-workers developed a post-synthetically modified MOF (IRMOF-3-N3) for the selective detection of H2S with a detection limit of 28.3 µM.196 The same group reported a framework loaded with Eu3+ and Cu2+ named Eu3+/Cu2+@UiO-66 - (COOH)2.
Conclusions and outlook
Introduction
The higher concentration of H2S in the physiological systems can cause several diseases, including diabetes, Down's syndrome, Alzheimer's disease and liver cirrhosis.3, 4 Despite its toxic effects, H2S has recently been documented as the third member of the family of biological signals. molecules called gasotransmitters, after carbon monoxide (CO) and nitric oxide (NO). A wide variety of techniques have been used until now for the detection and quantification of H2S. Compared to these traditional detection techniques, the fluorescence-based detection method for H2S has recently gained tremendous interests, as it offers a number of advantages, including high selectivity and sensitivity, simple operation, uncomplicated sample preparation, fast response, and non-damaging detection of biological analytes. .11-13 A wide variety of materials have been studied so far for the detection of H2S.
First, the synthesis procedures of MOFs are much easier and simpler than other luminescent probes.33 In addition, the crystalline nature of MOFs helps determine the precise structure by X-ray diffraction, which is useful for describing the possible interaction of MOFs with desired analytes.34 Due to the inherent porosity of sensors based on MOF, the distance between the MOF and the analyte decreases, which can ensure a close interaction between them.35 In addition, post-synthetic modification can be successfully performed on MOFs to incorporate new functional groups that can selectively interact with target species.36 In addition, MOFs are very photostable and can be reused for the detection of various analytes.37, 38 However, so far, very few MOFs have been shown to exhibit fluorescence enhancement characteristics in the presence of H2S.17-22 Four different mechanisms can be identified for H2S sensing by MOFs.
Experimental section
- Materials and physical measurements
- Synthesis of [Al(OH)(IPA-N 3 )]∙3.2H 2 O∙0.4DMF (as-synthesized 1)
- Activation procedure for the compound
- Rietveld refinement
- Preparation of the medium for fluorescence investigations in HEPES buffer 10 mM HEPES buffer solution was prepared by dissolution of the required amount
- Fluorescence sensing experiments in HEPES buffer
- Culture of macrophage cells
- Cellular imaging investigations
Stirring of the as-synthesized 1 (100 mg) was carried out in methanol (20 mL) at ambient conditions for 12 h. The benzene ring of the ligand molecule and the azido group were refined as rigid bodies, while all other atoms were refined freely. The cultivation and maintenance of the macrophage cells was performed according to a previously published procedure.40.
To remove the probe present in the media, the cells were gently washed and subsequently treated with Na2S (10 µM) for 15 minutes to generate H2S gas inside the cells.
Results and discussion
- FT-IR spectroscopy
- Structure description
- Thermal stability
- H 2 S sensing behavior of probe 1′ in HEPES buffer
- Mechanism for the detection of H 2 S
- Suitability of probe 1′ for sensing H 2 S in living cells
Saturation (with a 26-fold increase in fluorescence intensity) of the fluorescence emission intensity of the material occurred after 7 minutes of adding the Na2S solution. Interestingly, there was a 32-fold increase in the luminescence emission intensity of the MOF probe after 7 min. In these experiments, we measured the fluorescence emission spectra of a suspension of CAU-10-N3 in HEPES buffer (10 mM, pH = 7.4) after stepwise addition of Na2S (0 to 10 equivalents based on the azide group). .
It can be observed from Figure 2.13 that the gradual addition of Na2S solution resulted in a progressive increase in the fluorescence emission intensity of the probe.
Conclusions
Brightfield images of untreated cells (a), cells treated with 5 µM probe (c), and cells treated with 5 µM probe and 10 µM Na2S (e). b, d, f) are the fluorescence microscopy images of (a, c, e), respectively.
Introduction
Since H2S is both lethal and beneficial to living organisms, it is a very important and challenging research task to find new methods for the rapid and selective observation as well as the control of the levels of H2S in biological medium. The exact detection of H2S is a very difficult task as it is a highly volatile and reactive gas. Nowadays, reaction-based fluorescent turn-on probes with pendant nitro/azide functionalities have attracted great attention for the sensitive and selective sensing of H2S.28, 30, 31.
The MOF compound has shown great efficiency for the naked eye as well as fluorogenic sensitivity of H2S (Scheme 3.1) under simulated biological conditions (HEPES buffer, pH = 7.4).
Experimental section
- Materials and characterization methods
- Activation of as-synthesized 2
- Preparation of 10 mM HEPES buffer
- H 2 S detection experiments in HEPES buffer
- H 2 S sensing experiments in human blood plasma
- Culture of macrophage cells
- Cell viability assay
- Live-cell imaging experiments
- Sulfide sensing experiments in real water samples
To determine the selectivity of 2′ for Na2S over other analytes, the potentially penetrating analytes (10 equiv.) After choosing ten random fields, imaging of the cells was performed both in the bright field and in the green channel . To evaluate the detection ability of H2S with 2′ in real water samples, three different types of water samples were collected, such as mineral water, tap water and lake water.
In nine separate microcentrifuge tubes, each of the water samples was sprayed with a known amount of Na2S (final concentrations = 50, 75 and 100 µM).
Results and discussion
- Preparation and characterization
- Thermal stability
- Chemical stability
- Sensing of H 2 S in HEPES buffer
- Analytical method validation for the sensing of H 2 S in HEPES buffer
- Sensing of H 2 S in human blood plasma
- Sensing of H 2 S in living cells
- Sensing of sulfide in real water samples
- Mechanistic study for the sensing of H 2 S
For quantification of the fluorescence enhancement characteristics of UiO-66-(NO2)2 in the presence of H2S, fluorescence titration studies were performed. The fluorescence intensity (Figure 3.13) of the probe increased progressively with the gradual addition of Na2S solution. In the concentration range of 100-600 µM, the plot of the fluorescence intensity versus the concentration of Na2S for the suspension of 2' (in HEPES buffer) showed a remarkable linear curve with R Figure 3.15.
In the case of 2' treated with Na2S, the additional signal at 7.18 ppm is clearly for two equivalent aromatic protons of the H2BDC-(NH2)2 ligand, as the peak position closely matches that of the aromatic protons of the H2BDC-(NH2)2 ligand , which occurs at 7.24 ppm (Figure 3.22).
Conclusions
A metal-organic framework showing selective and sensitive detection of exogenous and endogenous
Introduction
After considering the above facts, the detection of FA has been investigated in the last few years. A variety of techniques have been used such as spectrophotometry,27 colorimetry,28 gas chromatography (GC),29 high performance liquid chromatography,30 ion chromatography 31 and polarography32 for the quantification and detection of FA. Moreover, the compound has the potential to detect the change in concentration of FA in cancer cells.
The ability of any of the MOF materials to detect FA in living cells has not been studied, while 3' has the ability to detect FA in cancer cells.
Experimental section
- Materials and characterization methods
- Preparation of H 2 BDC-N 2 H 3 ligand
- Activation of the material
- Fluorescence sensing experiments in aqueous medium
- Fluorescence sensing experiments in vapor phase
- Cell culture and imaging experiments
Prior to the sorption measurement, degassing of the material was carried out at 130 °C for 12 hours under dynamic vacuum. Later, stirring of the filtered compound was carried out in acetone (50 ml) overnight at room temperature. In the third step, heating of the filtered material at 130 °C overnight was carried out using a high vacuum pump.
The solid-state emission spectra of the spin-coated sample were measured initially.
Results and discussion
- FT-IR Spectroscopy
- Structure description
- Thermal stability
- Surface area analysis
- Particle size measurement
- Sensing of FA in HEPES buffer medium
- Sensing of FA in vapor phase
- Sensing of FA in live cancer cells
- Mechanism of FA sensing
- Experimental support for PET mechanism
From Figures 4.11 and 4.12, it becomes clear that the fluorescence intensity (monitored at 436 nm) of the Al-MIL-53-N2H3 probe has hardly changed in the presence of other aldehyde compounds. 81 From Figure 4.23a, it is clear that FA was unable to enhance the emission intensity of the 3' suspension when pretreated with NaHSO3. The poor recyclability of the MOF material for FA detection could be attributed to the fact that the hydrazine functional group was.
Time-resolved fluorescence lifetime decay profiles of the 3' aqueous suspension were collected before and after the addition of FA (20 mM, 500 μl) at different emission wavelengths.
Conclusions
A recyclable post-synthetically modified Al(III) based metal-organic framework for fast and
Introduction
Due to malfunction of liver or biliary obstruction, the concentration of bilirubin in human blood increases from regular level of <25 μmol (<1.2 mg/dL) to >50 μmol/L (>2.5 mg) indicating the condition of jaundice .12 Excessive concentration of bilirubin in blood is terrible for human health because the accumulation of bilirubin in organs can cause organ failure, brain damage or even death.13, 14 Therefore, the detection of bilirubin in blood is important for the diagnosis of jaundice. Therefore, rapid and selective detection and precise quantification of bilirubin in human biofluids is essential for the proper diagnosis of jaundice. The enrichment of hydroxyl groups in 4-NH2@THB provides recognition sites for bilirubin.30, 47 Furthermore, the aromatic ring of bilirubin can interact with π-electron abundant 4-NH2@THB via π-π interactions.48 To date, only one Zr-based MOF materials have been reported in the literature for sensing bilirubin.32 But detailed study of the material for sensing bilirubin in human biofluids (i.e. urine) and reusability of the probe has not been investigated.
Furthermore, economical portable paper test strips were prepared by the dip coating method and used for the rapid detection of bilirubin.
Synthesis scheme of 4-NH 2 @THB
- Experimental section
- Materials and characterization methods
- Preparation of MIL-53-NH 2 (4-NH 2 )
- Fluorescence detection experiments in HEPES buffer
The synthesis of 4-NH2 was carried out by following the previously reported method.49 In a nutshell, a mixture of AlCl3·6H2O (493.6 mg), H2BDC-NH2 ligand (375.6 mg) and 5 mL of deionized water was taken into a hydrothermal autoclave. reactor and heated for 5 hours at 150 °C in a conventional oven. After cooling to room temperature, the light yellow colored solid compound was filtered and washed with deionized water. For the removal of the unreacted H2BDC-NH2 ligand, the as-synthesized compound was heated in DMF solvent at 150 °C for 12 h.
The resulting orange solid was filtered and dried in an oven at 70°C for 24 hours (yield: 56 mg).
- Fluorescence detection experiments in portable paper strips
- Fluorescence detection experiments in human blood serum
- Fluorescence detection experiments in human urine samples
- Results and discussion
- Characterization of material
- Sensing of bilirubin in HEPES buffer medium
- Sensing of bilirubin in portable paper strips
To ensure the specificity of the probe to bilirubin in the coexistence of its generators, bilirubin was introduced into the 4-NH2@THB suspension. This figure shows that significant fluorescence quenching of 4-NH2@THB occurs at lower bilirubin concentration and at higher bilirubin concentration, a significant increase in quenching efficiency occurs. For the estimation of the limit of detection (LOD) of 4-NH2@THB to bilirubin, the fluorescence spectra of the probe were measured after the introduction of much less concentrated bilirubin solution.
A linear curve was obtained by plotting the fluorescence emission intensity of the material against the concentration of bilirubin solution (Figure 5.19).
