Dopamine (DA) detection in nanomolar concentration by 2,3-diaminophenazine (DAP) released from (DAP)@BioMOF-1 films

Article abstract of DOI:10.1016/j.poly.2019.05.015

There is a big interest in dopamine (DA) sensors, because dopamine is an important neurotransmitter and its absence results in neurological disorders. Herein we present an application of BioMOF-1, which has been used as a host to introduce 2,3-diaminophenazine (DAP) molecules, obtaining DAP@BioMOF-1 crystals. The crystals were used to prepare films that can serve as reusable sensors for detecting dopamine at nanomolar concentrations by fluorescence in both water and methanol.

Full text of DOI:10.1016/j.poly.2019.05.015

Accepted Manuscript
Dopamine (DA) detection in nanomolar concentration by 2,3-diaminophenazine
(DAP) released from (DAP)@BioMOF-1 films
Javier Neri-Hipólito, Nazario Lopez, Eric W. Reinheimer, Elizabeth Mas-
Hernández, Carlos E. Barrera-Díaz, Víctor Varela-Guerrero, María F.
Ballesteros-Rivas
PII:
S0277-5387(19)30337-7
https://doi.org/10.1016/j.poly.2019.05.015
POLY 13940
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
24 January 2019
7 May 2019
9 May 2019
Please cite this article as: J. Neri-Hipólito, N. Lopez, E.W. Reinheimer, E. Mas-Hernández, C.E. Barrera-Díaz, V.
Varela-Guerrero, M.F. Ballesteros-Rivas, Dopamine (DA) detection in nanomolar concentration by 2,3-
diaminophenazine (DAP) released from (DAP)@BioMOF-1 films, Polyhedron (2019), doi: https://doi.org/10.1016/
j.poly.2019.05.015
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Dopamine (DA) detection in nanomolar concentration by 2,3-diaminophenazine
(DAP) released from (DAP)@BioMOF-1 films
Javier Neri-Hipólitoa, Nazario Lopezc, Eric W. Reinheimerd, Elizabeth Mas-Hernándeza,b, Carlos E.
Barrera-Díaza, b, Víctor Varela-Guerrero*a, b, María F. Ballesteros-Rivas*a, b
a. Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, b. Universidad Autónoma del
Estado de México, Facultad de Química, Paseo Colón S/N, Residencial Colón, 50120 Toluca de Lerdo,
México, c. Centro de Investigaciones Químicas, IICBA, Universidad Autónoma del Estado de Morelos, Av.
Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos 62209, Mexico. d. Rigaku Oxford Diffraction, 9009
New Trails Drive, The Woodlands, TX 77381
Abstract
There is a big interest in dopamine (DA) sensors, because dopamine is an important
neurotransmitter and its absence results in neurological disorders. Herein we present an
application of BioMOF-1, which has been used as a host to introduce 2, 3-
diaminophenazine (DAP) molecules, obtaining DAP@BioMOF-1 crystals. The crystals
were used to prepare films that can serve as reusable sensors for detecting dopamine at
nanomolar concentrations by fluorescence in both water and methanol.
Keywords
Metal-organic frameworks, BioMOF-1, 2, 3-diaminophenazine, dopamine sensing,
nanomolar detection.
1. Introduction
Dopamine (DA) is a neurotransmitter associated with vital brain processes as a chemical
messenger [1] and is crucial for the regulation of functions related to movement, memory,
emotional response, and others. Its absence can result in neurological disorders such as
Parkinson’s disease, schizophrenia, hypertension, and pheochromocytoma [2-4]. As a
consequence, the analysis of dopamine concentration in the body and in biological fluids
such as the encephalon, urine and blood has become a valuable tool for medical diagnosis
[5]. To improve the detection of dopamine, analyses involving electrostatic interactions,
charge transfer, photo induced electron transfer (PET) and molecular beacons have been
developed. However, the majority of those methods are still expensive and incapable of
replacing the conventional detection techniques such as high-performance liquid
chromatography, electrophoresis, among others. Additionally, dopamine sensors must
detect low concentrations of dopamine in biological tissues and avoid the use of toxic
chemicals that could promote cell death or inhibit cellular function [6, 7].
Recently, redox active oligomers and polymers such as poly(o-phenylenediamine)
(PoPDA) have received considerable attention due to their applications in a variety of
devices including sensors, organic batteries, diodes and electrocatalysts [8]. Of special
interest to us are the chromogenic compounds based on o-Phenylenediamine (o-PD) that
can interact with biomolecules exhibiting fluorescence as a response, which have been used
for the quantification of linked enzymes in immunosorbent assays (ELISAs). Quenchers are
1

widely used in analytical methods for the detection of molecules thanks to their
reproducibility based on the PET process [9]. However, fluorescent probes often suffer
from self-quenching produced by high concentration of the sensor molecule in the test,
once solving this issue their potential application in fluorescent sensing is high [6, 10-13].
The potential application of systems based on o-Phenylenediamine (o-PD) molecules such
as 2,3-diaminophenazine (DAP) to detect dopamine by fluorescence assays is a promising
alternative technique, contrasting with other procedures (e.g., spectroscopy,
chromatography and electrochemistry, among others) previously described [5, 14-16]. All
the current methods are impractical as they require higher concentrations of dopamine than
the typical levels encountered in biological tissues close to 25 nM [2]. The metal organic
framework (MOF) Fe-MIL-88 was recently used as a sensor for dopamine. In the presence
of H2O2, Fe-MIL-88 oxidizes the nonfluorescent o-PD into fluorescent DAP molecule with
a detection limit of 46 nM. Bio-MOFs are a subclass of MOFs, constituted of Zn-adenine
vertices and carboxylates as bridging ligands, they have robust frameworks with high
porosity and large surface area with the potential to store small molecules efficiently [17-
19].
Herein, we report DAP inclusion as a guest molecule into BioMOF-1 crystals and its use as
a sensor for nM dopamine concentrations (Scheme 1).
Scheme 1. Representation of DAP inclusion in the pores of BioMOF-1 crystals.
During the DA detection DAP is released from BioMOF-1 in small quantities, preventing
self-quenching of DAP, DA is quantified by the decrease in DAP fluorescence due to
DA‧‧‧DAP interaction [1, 20].
2. Experimental
2.1 Materials and methods
Reagents as adenine (C5H5N5); zinc acetate dihydrate (C4H10O6Zn); Biphenyl - 4,4'-
dicarboxylic acid (HO2CC6H4C6H4CO2H), O–phenylenediamine (C6H8N2), ferric chloride
(FeCl3) dimethylformamide (DMF) and nitric acid (HNO3) were purchased from Sigma-
Aldrich Chemical Co. and used without further purification.
2.2 Synthesis of BioMOF–1 (Zn8(Ad)4(BPDC)6O · 2(NH2(CH3)2)+· 8DMF·11H2O)
2

BioMOF-1 was prepared according to An, Jihyun, and Nathaniel L. Rosi method with a
slight modification [21]. Adenine (0.125 mmol), 4, 4’ – biphenyl dicarboxylic acid (BPDC)
(0.25 mmol), zinc acetate dihydrate (0.375 mmol), 2.5 mL of nitric acid (2.5 mmol) and
DMF (13 mL) were added to a 50.0 mL beaker and mixed at room temperature, later, the
mixed reaction was poured into a stainless autoclave for solvothermal synthesis at 130°C
for 24 h. The solids produced were rod-shaped colorless crystals. The crystals were
collected on a frit funnel and dried under ambient conditions.
2.3 Synthesis of 2, 3-diaminophenazine (DAP)
The DAP molecule was synthesized from o-Phenylenediamine using ferric chloride (FeCl3)
as a catalyst and was characterized according to previous reports (SI) [22].
2.4 DAP inclusion in a BioMOF-1
BioMOF-1 crystals were added into a 0.1 M DAP methanolic solution (soaking) without
agitation for 20 min under ambient conditions; the introduction of the molecule into the
pores of the crystals are noticed by color change from colorless to red crystals.
After 20 min soaking, DAP@BioMOF-1 was removed with a Pasteur pipette and dried
under air on a filter paper, once dried, the crystals were washed with water and dried again.
2.5 Immobilization of DAP@BioMOF-1 crystals on a plastic tape
DAP@BioMOF-1 crystals were immobilized on an adherent film, the crystals (158 mg)
were placed on a flat surface and pressed against an adherent PVC film to immobilize the
crystals, so that they can be used several times (Fig. 1).
Figure 1. Films elaborated with different components, a film control (PVC film without crystals), a film
with BioMOF-1 crystals and a film with DAP incorporated to the crystals of BioMOF-1.
2.6 Exposure of DAP@BioMOF-1 system to dopamine (DA)
DA solutions were prepared according to Pradhan method, emulating the real
concentrations of biological dopamine in situ [2]. The solutions were made with the
following concentrations of DA in water, 0.52 nM, 0.79 nM, 1.05 nM, 1.31 nM, 1.58 nM,
3

1.84 nM, 2.10 nM, 2.37 nM and 2.63 nM. Individual DAP@BioMOF-1 films were exposed
to the different DA solutions for 5 minutes. In the same manner, experiments were carried
out in methanol with DA concentrations of 20 nM, 40 nM, 80 nM, 120 nM, 160 nM, 200
nM, 240 nM, 320 nM, 400 nM, 480 nM, 520 nM and 600 nM.
2.7 Dopamine detection
Dopamine detection method consisted of exposing the DAP@BioMOF-1 film to a
DA solution of known concentration in distilled water or methanol for five minutes,
as mentioned in Section 2.6. DAP is released in low quantities and its interaction
with DA results in decrease of DAP fluorescence. A controlled process is
fundamental to avoid self-quenching due to a high concentration of the sensor in the
solution, therefore obtaining a trustworthy fluorescent measurement for the detection
of nanomolar concentrations of DA [13, 23].
3. Results and discussion
3.1 Crystal structure description and powder XRD diffraction
For BioMOF-1, the unit cell belongs to a tetragonal space group (α= 90°; β= 90° and γ=
90°) with a cell volume of 16339 Å3 and cell parameters of a= 38.237 Å, b= 38.237 Å and
c=11.1753 Å [19]. Single crystal X-ray diffraction indicates that the unit cell for BioMOF-
1 remains without modification after incorporation of DAP guest molecules into the
framework by soaking single crystals in methanolic DAP solutions
(DAP@BioMOF-1) for more than 24 h [19].
(0.1 M)
In addition, Powder X-ray diffraction (PXRD) was used to confirm the crystallinity and
verify that no phase change occurred in the bulk of the sample. We propose that DAP
molecule is inside the pores (see section 3.6) anchored to the MOF by non covalent
interactions, thus, the BioMOF structure does not change, therefore, PXRD spectra are the
same in both materials (BioMOF-1 and DAP@BioMOF-1) [24-27].(Fig. 2 and SI).
Figure 2. PXRD patterns in the 2θ range 6 – 25°, BioMOF-1 synthesized (blue), and synthesized with 2, 3-
diaminophenazine incorporated (red).
4

3.3 Thermogravimetric analysis
Inclusion of guest molecules in BioMOF-1 is evidenced by TGA analysis, there is a plateau
from 25°C to 120°C followed by a gradual loss of solvent (DMA, DMF and water; ~10% in
weight) stored in the pores up to 220°C, from 220°C to 380°C there is an additional plateau
indicating the limit of framework stability, followed by decomposition. On the other hand,
DAP@BioMOF-1 exhibits a characteristic behavior due to possible supramolecular
interactions between DAP molecule and the BioMOF-1 pore; aromatic rings of the sensor
molecule may interact by π-π to ligand 4, 4-biphenyl dicarboxylic acid, H bonds could be
present inside the pore by NH groups of DAP, in summary non covalent interactions can
induce changes in TGA behavior [25, 28]. Describing TGA profile of DAP@BioMOF-1,
the gradual weight loss from 25°C to 400°C, might be due to the loss of stored DAP and
solvent. After 400°C the weight loss is faster due to the decomposition of the BioMOF-1
Figure 3. Thermogravimetric analysis of DAP (red); BioMOF-1 (black) and DAP@BioMOF-1
(green).
(Fig. 3).
3.4 Elemental analysis
The samples (BioMOF-1 and DAP@BioMOF-1) were dried in an oven for 24 hrs.
Elemental Analysis for BioMOF-1: C112H128N24O36Zn8= Zn8(Ad)4(BPDC)6O·10H2O.
Calcd. C, 46.49664; H, 4.424565; N, 11.62029. Found C, 46.45; H, 3.9; N, 11.5. The
5

elemental analysis after the inclusion of the guest molecule (DAP@BioMOF-1) is
C116H1116N24O74Zn8= Zn8(Ad)4(BPDC)6O, · 1(2, 3-diaminophenazine)· 18 H2O. Calcd. C,
45.10156; H, 3.755334; N, 10.88296. Found C, 45; H, 3.73; N, 10.66.
According to data from elemental analysis, the percentage gain in weight of DAP from
DAP@BioMOF-1 versus BioMOF-1 was 5.85%
The results shown above confirm the inclusion of DAP inside the BioMOF-1.
3.5 Infrared spectroscopy
The IR transmittance spectrum of the compounds was recorded on a Shimadzu® FT-IR
spectrometer with the ATR accessory coupled in the 4000-400 cm-1 region with 2 cm-1
resolution and 45 scans and the Lab Solutions IR software package.
To corroborate the correct synthesis of the DAP molecule and its incorporation, IR
measurements were realized (Fig. 4) determining the characteristic peaks of the molecule
spectra; the 3434 cm-1, 3307 cm-1 and 3180 cm-1 bands are assigned to the N-H stretching
vibrations, the bands at 1643 cm-1 and 1562 cm-1 are both attributed to the deformation
vibration of primary amine and C=N stretching vibration, the stretching vibration (C=C) is
registered at 1492 cm-1, the out of plane bands at 586 cm-1 and 487 cm-1 correspond to the
aromatic plane and bending vibration, finally, the overtones between 1744 cm-1 and 2000
cm-1 confirm the presence of the aromatic rings of the compounds [12, 29, 30].
Furthermore, BioMOF-1 characteristic bands are reported by Jihyun An [31] at 3341.39
cm-1, 3188.47 cm-1, 1663.76 cm-1, 1544.77 cm-1, 1280.50 cm-1, 1176.5 cm-1. The IR spectra
of DAP@BioMOF-1 system was analyzed with the purpose of verifying the presence of the
DAP principal functional groups in the BioMOF crystals.
Figure 4. BioMOF-1 spectrum (black), DAP spectrum (blue); and DAP@BioMOF-1 spectrum (red),
violet dashed lines are characteristic BioMOF-1 bands whereas green dash lines represent DAP bands.
6

3.6 Gas sorption Measurements
To evaluate the high porosity and Langmuir surface area of BioMOF-1 and
DAP@BioMOF-1 crystal, nitrogen adsorption studies were carried out. Firstly, the sample
was degassed with vacuum at 120°C for 24 h.
The Langmuir surface area registered at 273 K was of 1071.826 m²/g for BioMOF-1
crystals, exhibiting a type 1 isotherm, which has the property to be completely reversible,
whereas Langmuir surface area of DAP@BioMOF-1 (273 K) was of 760.124 m²/g. The
decrease of the pore volume and surface area were expected due the post-synthetic pore
modification (DAP inclusion) as we confirm, by elemental analysis, the incorporation of
one DAP molecule per Zn8(Ad)4(BPDC)6O fragment in BioMOF-1 (Fig 5)[26].
Figure 5. N2 Isotherms of BioMOF-1 (left) and DAP@BioMOF-1 (right).
3.7 Ultraviolet-Visible Spectrophotometry analysis
UV analysis was performed on a Shimadzu® UV visible spectrophotometer, type UV-2600
to characterize the synthesized DAP; the produced molecule was dissolved in methanol, the
UV spectra showed two characteristic absorption peaks; 260 nm and 432 nm (see Fig. 6);
the peak at 260 nm, according to the literature, is attributed to the phenyl π → π electronic
transition, while the peak at 432 nm is attributed to the n →π * electronic transition in the
aromatic rings [8, 29, 30].
7

Figure 6. UV-vis spectra comparison, reported DAP spectra (left) versus UV-vis analysis performed on
synthesized DAP (right).
UV-absorption spectrum of BioMOF-1 film showed two bands in the range of 200-300 nm,
as well observed in the inclusion compound DAP@BioMOF-1; however, in
DAP@BioMOF-1 a third band appeared at 456 nm which is characteristic of DAP
molecule (Fig. 7) [14, 32].
Figure 7. UV spectra for BioMOF-1 (black) and DAP@BioMOF-1 (red) films. Inset: Fluorescence
microscopy images of BioMOF-1 (A) and DAP@BioMOF-1 crystals (B).
3.8 Fluorescence analysis
The fluorescence emission band at initial DAP concentration (37.25 nM for water
and 287 nM for methanol) from DAP@BioMOF-1 was observed at 541 nm, the
presence of dopamine was detected by a decrease in the intensity of this band due to
quenching of DAP, such decrease is proportional to the DA concentration (Fig. 8).
8

B
A
Figure 8. Fluorescence spectra in water (A) and methanol (B) of DAP released by DAP@BioMOF-1
system, the quenching intensity of the spectra depends on DA concentrations. (excitement: 456 nm,
emission: 541 nm)
The difference between A and B spectra in Fig. 8 can be explained by the effect the
solvent plays in the process. For the system in water (A), the DAP rate liberation is
slower compared to the system in methanol (B), due to a lower solubility of DAP in
water. Therefore, the sensor sensibility in water is higher, because the high
concentration and accelerated accumulation of DAP in methanol promote self-
quenching. Quenching phenomenon (an increment in the concentration of dopamine
decreases the DAP fluorescence intensity) is due to the electron transfer, resulting in
DAP reduction and DA oxidation. This phenomenon is known as a PET process [33,
34].
The reproducibility of DAP release was corroborated by analysis of variance
(1.09968) from the data obtained of the absorbance of two films, there is no
significant difference between DAP release from different films, resulting in good
reproducibility in water (Fig. 9). The films can be reloaded with DAP at least five
times and reused without no change in the crystallinity of the compound. (SI)
Figure 9. Absorbance of DAP released from two different DAP@BioMOF-1 films every five minutes.
9

The lowest sensitivity achieved was 0.52 nM and 20 nM of DA in water and
methanol respectively. Our method has higher sensitivity and is more practical than
assays based on MOF Fe-MIL-88, with a detection limit of 46 nM DA, even though
such assay requires H2O2. Much higher detection limits of 1760 nM were reported
by Shuyan Niu using quenching phenomena [2, 5, 6, 14, 35]. Other studies are
laborious, with additional steps to prepare the sensors. The methodology reported by
Li et al. [29], requires the application of a special drying strategy for the material
(MOG’s), specific preparation of the medium, and the use of luminol as a reporter
molecule. Finally, another laborious strategy for dopamine sensing is the one
reported by Jiang et al. [30], that uses a highly specialized sensing technique such as
the surface-enhanced Raman scattering (SERS) and an elaborated methodology to
synthesize a hybrid material as a sensor (AgNPs/MIL-101).
4. Conclusions
In summary we successfully prepared a sensor for nanomolar concentration of
dopamine by the inclusion of DAP molecules into BioMOF-1 pores. The
DAP@BioMOF-1 was characterized by X-ray diffraction, infrared spectroscopy, TG
analysis, Langmuir method via physisorption, UV-vis spectrophotometry and
fluorescence spectroscopy techniques. Controlled release of DAP was achieved from
DAP@BioMOF-1 deposited on a plastic film, the material is reusable and easy to
manipulate. By this method DAP is released at low concentrations and thus self-
quenching is avoided. We were able to detect dopamine in concentrations similar to
those found in biological tissues, making this technique ideal for its use as a sensor
for biological samples.
Acknowledgments
JNH thanks CONACyT for scholarship and UAEMex. Dr. Alejandro Dorazco-Gonzalez, M.C.
Alejandra Nuñez Pineda and Dr. Diego Martinez-Otero. NL is grateful for financial support from
Secretaría de Educación Pública (Grant UAEMOR-PTC-388). VVG, MFBR and EMH are grateful
for financial support from Secretaría de Educación Pública (Grant UAEM-CA-269).
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There is a big interest in dopamine (DA) sensors, because dopamine is an important
neurotransmitter and its absence results in neurological disorders. Herein we present
an application of BioMOF-1, which has been used as a host to introduce 2, 3-
diaminophenazine (DAP) molecules, obtaining DAP@BioMOF-1 crystals. The
crystals were used to prepare films that can serve as reusable sensors for detecting
dopamine at nanomolar concentrations by fluorescence in both water and methanol.
13