Effective Detection of Mycotoxins by a Highly Luminescent Metal-Organic Framework

Article abstract of DOI:10.1021/jacs.5b10308

We designed and synthesized a new luminescent metal-organic framework (LMOF). LMOF-241 is highly porous and emits strong blue light with high efficiency. We demonstrate for the first time that very fast and extremely sensitive optical detection can be ach

Full text of DOI:10.1021/jacs.5b10308

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN
Article
Effective detection of mycotoxins by a
highly luminescent metal-organic framework
Zhichao Hu, William P. Lustig, Jingming Zhang, Chong Zheng, Hao
Wang, Simon J. Teat, Qihan Gong, Nathan D. Rudd, and Jing Li
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b10308 • Publication Date (Web): 11 Dec 2015
Downloaded from http://pubs.acs.org on December 17, 2015
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 9
Journal of the American Chemical Society
1
2
3
4
5
6
Effective detection of mycotoxins by a highly luminescent metal-or-
ganic framework
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
†
, |
†, |
†
#
†
‡
Zhichao Hu, William P. Lustig, Jingming Zhang, Chong Zheng, Hao Wang, Simon J. Teat, Qihan
†
†
, †
Gong, Nathan D. Rudd and Jing Li *
†
Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Rd, Piscataway, USA
#
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115
‡
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, USA
ABSTRACT: We designed and synthesized a new luminescent metal-organic framework (LMOF). LMOF-241 is highly porous and emits
strong blue light with high efficiency. We demonstrate for the first time that very fast and extremely sensitive optical detection can be achieved
making use of the fluorescence quenching of an LMOF material. The compound is responsive to Aflatoxin B at ppb level which makes it the
1
best performing luminescence-based chemical sensor to date. We studied the electronic properties of LMOF-241 and selected mycotoxins, as
well as the extent of mycotoxin-LMOF interactions employing theoretical methods. Possible electron and energy transfer mechanisms are dis-
cussed.
common drawbacks, such as high cost and complex sample prepara-
INTRODUCTION
tion,which makesthemless available to developing countries;places
most prone to mycotoxin contaminations. Therefore, the develop-
ment ofconvenient, cost-effective mycotoxindetection methodshas
significant impact onglobal food safety.
7
Mycotoxins are secondary metabolites produced by certain fungi
that infect and proliferate on diverse food commodities. Mycotoxins
contaminate 25% of the global food crops each year, leading to the
1
Opticalsensing utilizing the change influorescence readout induced
loss of 1 billion metric tons of food products annually. In the U.S.
9
by sensor-analyte interactions is a powerful detection method. The
alone, the economicdamage caused by mycotoxins approaches $1.5
2
choice ofsensor material is centralto achieving effective detectionof
billionper year. Manyof these naturally occurring toxins are terato-
10
thetargeted analyte. Metal-organicframeworks (MOFs) are aclass
of functional crystalline materials constructed by the self-assembly
of metalnodes (metalcations or metal clusters) and organic ligands.
Their tunable properties and facile characterizationhas made MOFs
attractive materials for use in a variety of applications, including gas
genic, mutagenic, and carcinogenic which pose significant adverse
health effects on human beings and animals.
3
Aflatoxins (AFs), mainly produced by Aspergillus flavus and Asper-
gillus parasiticus, are some of the most dominant mycotoxins world-
4
wide. AFs contaminate a wide variety of important agricultural
11
5
storage, gas separation, and catalysis. Luminescent MOFs
LMOFs) are well explored as chemical sensor materials, as their
easy-to-functionalize surface and tunable porosity promote feasible
commodities, including corn and tree nuts. There are four major
(
AFs: B
1
, B
2
1 2
, G , and G , of which AFB is most toxic, and one of the
1
strongest known natural carcinogens. AF-poisoning leads to the de-
velopment of liver cirrhosis or liver cancer (hepatocellular carci-
12b,c
guest-host interactions. Here we demonstrate for the first time
the use of a highly luminescent LMOF for very fast and sensitive flo-
rescence-based mycotoxin detection. A detection limit of 46 ppb is
reached.
6
noma). Ochratoxin A (OTA) produced by Aspergillus ochraceus
and Penicillium verrucosum, is another common mycotoxin that is
hepatotoxic and nephrotoxic.
4
The chemical stability of most mycotoxins enables their survival
through various food manufacture processes such as baking and
cooking at elevated temperatures, which make the prevention of
their entrance into the food chain extremely difficult. Therefore,
monitoring mycotoxins in human foods and animal feeds is crucial
to ensure food safety. The U.S. Food and Drug Administration
EXPERIMENTAL SECTION
General Information
7
All reagents are used as purchased unless specified otherwise. De-
tailed information on sources of chemicals is in the Supporting In-
formation (SI).
(
FDA) established theAFB tolerant level for corn and peanut feeds
1
8
Synthesis of tppe Ligand
intended for finishing beef cattle at 300ppb. Current mycotoxin de-
tection methods focus on the use of antibodies, aptamers, immuno-
assays, and modern instruments (such as chromatography and mass
spectroscopy),which are proveneffective. However theyshare some
Synthesis of the ligand 1,1,2,2-tetrakis(4-(pyridin-4-yl)phe-
13
nyl)ethane (tppe) began with the reaction of solid 1,1,2,2-tetra-
phenylethene (tpe) with liquid bromine to produce 1,1,2,2-
tetrakis(4-bromophenyl)ethene (Br
4
-tpe), which was purified via
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 9
recrystallization in dichloromethane/ methanol. A Suzuki coupling
reaction between Br -tpe and pyridine-4-boronic acid, catalyzed by
palladium (II) acetate, was used to attach the pyridine moiety to the
tpe moiety. The final product was extracted with chloroform and
purified using column chromatography (stationary phase = silica,
Computational Study of LMOF-241 and Mycotoxins
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4
The electronic properties of LMOF-241 and selected mycotoxins
14
were evaluated using extended Hückel (EH) method. To quanti-
tatively measure the interactions between LMOF-241 and Aflatoxin
B
1
and B , simulation of mycotoxin loaded LMOF-241 structures
2
mobile phase = 30:1 CHCl :MeOH).
3
was performed, and configurations with closest analyte-MOF con-
tacts were chosen for each toxin (see S9). A fragment containing a
complete LMOF-241 primary building unit (PBU), composed of 1
2+
Zn , 2 tppe, and 2 bpdc, was used in the calculations, with dangling
carboxylates terminated with hydrogen to ensure a neutral frame-
work (see S10).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Table 1. Single crystal data of LMOF-241
Compound
Formula
M
LMOF-241
C
111
H
72
N
6
O
12Zn
3
Figure 1. tppe synthetic scheme.
1877.85
Crystal system
Space group
a/ Å
Monoclinic
C 2
Synthesis of Zn
In a 20 mL glass vial, Zn(NO
phenyl-4,4 -dicarboxylic acid (H
2
(bpdc)
2
(tppe) (LMOF-241)
·6H O (0.015 g, 0.05 mmol), bi-
bpdc, 0.012 g, 0.05 mmol), and
3
)
2
2
44.091(2)
2
b/ Å
25.4060(14)
17.1248(9)
90
tppe (0.013g, 0.02 mmol) were added. Then N,N-dimethylacetam-
ide (DMA, 8 mL), dimethyl sulfoxide (2 mL), and isopropanol (2
mL) were added to the mixture. The reaction mixture was kept un-
der ultrasonicationuntil allsolids dissolved. The glass vialwas sealed
c/ Å
o
o
o
9
1.176(4)
o
and kept at 150 C for 24hours. The transparent light yellow needle-
90
shaped crystals were harvested by filtration after the reaction mix-
ture cooled down to room temperature.
V/ Å3
19178.7(17)
Z
4
Structure Analysis of LMOF-241
Single crystal diffraction data for LMOF-241 were collected on a
Bruker APEXII CCD diffractometer using the synchrotron source
Temperature/ K
260(2)

(radiation wavelength)/ Å 0.7749
(
 = 0.7749Å) at the Advanced Light Source 11.3.1Chemical Crys-
3
D (g/ cm )
0.650
tallography beamline. All non-hydrogen atoms were refined aniso-
tropically; hydrogen atoms were placed geometrically, constrained
and refined with a riding model. The unresolvable electron density
from the void space in the structure was removed by SQUEEZE.
The powder X-ray diffraction (PXRD) patterns were collected on a
Reflections collected
83865
0.0598
0.1463
0.983
a
R1
I)]
I)]
b
wR2
Goodness-of-fit
CCDC No.
Rigaku Ultima-IV diffractometer using monochromatic Cu K

radi-
o
1006120
ation ( = 1.5406 Å). Data were collected between a 2 of 3 50
o
o
with step size of 0.02 at scanning speed 3.0 / min (Table 1).
a
│F
o
- F
c
│/ ∑│F │
o
Porosity Characterization of LMOF-241
b
2
2
2
2 2 1/ 2
wR2
o
- F
c
) ] / w(F ) ]
o
Gas sorption isotherms were collected on a volumetric gas sorption
analyzer (Autosorb-1 MP, Quantachrome Instruments). Ultra high
purity N (99.999%) was used for the experiment. Liquid nitrogen
2
was used as coolant to achieve cryogenic temperature (77 K). As-
made LMOF-241 (200 mg) was immersed in 15 mL dichloro-
methane (DCM) in aglass vial for 2 hours, then the supernatant was
decanted and 15 mL fresh DCM was replenished. This process was
repeated for 6 times. About 150 mg DCM exchanged sample was
outgassed at 333K overnight under dynamic vacuum and the subse-
quent degassed sample (LMOF-
was collected in a pressure range from 10 to 1 atm at 77 K. Surface
was used. The N isotherm
2
-7
area was analyzed using Autosorb v1.50 software. The Brunauer
2
Emmett Teller (BET) surface area of LMOF-
/g.
2
ACS Paragon Plus Environment

Page 3 of 9
Journal of the American Chemical Society
Optical Characterization
The optical band gap, fluorescence internal quantum yield (IQY),
Fluorescence Titration
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Following solvent exchange with DCM to remove the solvent re-
maining in the structure following its synthesis, LMOF-241 was
added to DCM and the mixture was kept under ultrasonication to
and solid state excitation and emission spectra were measured for
LMOF-241at roomtemperaturein air. Diffusereflectance datawere
collected using a Shimadzu UV-3600 spectrophotometer, and the
Kubelka-Munk function was used to estimate the optical band gap.
IQY measurements were collected using a Hamamatsu C9220-03
spectrophotometer with integrating sphere. Solid state excitation
and emission spectra were collected using a Varian Cary Eclipse
spectrophotometer.
form a suspension (4 mg/mL), and stock solutions of Aflatoxin B
(AFB ) Aflatoxin B (AFB ), Aflatoxin G (AFG ) and OchratoxinA
(OTA) dissolved in DCM were prepared. DCMwas used as the sol-
vent because of its photo-inactivity and LMOF- ty in it
(Figure S2).The fluorescence titrationwasperformedbyadding an-
1
1
2
2
1
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 2. (a) The PBU of LMOF-241, showcasing atetrahedrally coordinated Zn center bound to two tppe molecules and two bpdc molecules. (b)
A single net of LMOF-241 framework viewed along the c -axis, composed of edge-sharing hexagonal channels. (c) A single net of LMOF-241
framework viewed along the b-axis, showing pores that are closed upon the interpenetration. (d) Overall crystal structure demonstrating the 3-fold
interpenetration and 1D pore running along the c-axis. (e) LMOF-241 drawn as 2-nodal (4,4)-c net (mog type), with tppe and bpdc simplified as a
4-c node and 2-c node, respectively. The different colors (red, blue, and aqua) indicate the three distinct interpenetrated networks that form the
complete structure of LMOF-241. In all structures, H atoms are omitted for clarity.
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 9
alyte aliquots to the LMOF-241 suspension. The initial photolumi- (Figure 2b). The overall structure of LMOF-241 is a three-fold in-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
nescence (PL) spectrumofthe suspensionand spectraafter each an-
alyte aliquot addition were recorded on a Varian Cary Eclipse spec-
trophotometer. The suspension was thoroughly stirred before each
PL measurement. Each measurement was repeated three times and
the average value was used.
terpenetrated framework formed by three of these identical nets,
with distorted hexagonal 1D channels of diameter ~16.6 Å along the
c-axis (Figure 2d). If bpdcis simplified as a 2-c node and tppe as a 4-
c node, the framework would be a 2-nodal (4,4)-c net (mog type)
4
2
2
2
with Point symbol {4·6 ·8} {4 ·6 ·8 } (Figure 2e). There are cur-
2
rently 12 reported MOF structures with 3-fold interpenetrated mog
type topology according to the ToposPro database. If tppe is sim-
RESULTS AND DISCUSSION
Topological Analysis
15
plified as two 3-c nodes, the framework would be a 2-nodal (3,4)-c
net (jeb type, or bbe-3,4-Cmmm, derived from mog) with Point
2
LMOF-241 or [Zn (bpdc)
2
(tppe)]·S (S = guest solvent molecules)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
5
16
symbol {6 }{6 ·8}. To the best of our knowledge, only 1 out of all
crystalizes in the monoclinic crystal system with space group C2.
17
2+
8 reported jeb type MOF structures has a 3-fold interpenetration.
Each Zn tetrahedrally coordinates to two monodentate carbox-
ylates frombpdc ligands and two pyridine groups from tppe ligands,
forming the primary building unit (PBU) (Figure 2a). A hexagonal
cage containing 12 Zn centers, 8 bpdc ligands, and 2 tppe ligands
proliferates alongthec-axisto formaone-dimensional(1D) channel;
theedge-sharing channelsexpandinto a three-dimensional(3D) net
However the topology of LMOF-241 is unusual because of its non-
centrosymmetry: two structuralgroups not related byanysymmetry
operations form 3 (2+1) interpenetrated nets.
Optical Properties of LMOF-241
The UV-Vis reflectance spectra of the ligand tppe and LMOF-241
were collected using a Shimadzu UV-3600spectrophotometer, after
b
a
c
d
Figure 3. (a) The excitation (dotted blue) and emission (solid red, ex = 340 nm) spectra of LMOF-241 suspended in DCM. (b) Emission spectra
of LMOF-241 with the incremental addition of AFB in DCM, with toxin concentrations given in the key to the right of the figure. (c) The Stern-
Volmer curves acquired at ex = 340 nm and ex = 410 nm (insert) for AFB (red dot), AFB (orange triangle), AFG (green diamond), and OTA
blue square). (d) Excitation (dotted lines) and emission (solid lines, ex = 340 nm) spectra of AFG (green) and OTA(blue) in DCMwith inten-
sity normalized to concentration.
1
1
2
1
(
1
4
ACS Paragon Plus Environment

Page 5 of 9
Journal of the American Chemical Society
which conversion to the Kubelka-Munk function allowed their
for AFG
gion, and this trendis reversedafter certainconcentrationthresholds.
This is because both AFG and OTA are fluorescent under 340 nm
excitation while both AFB and AFB are non-fluorescent under the
same conditions. As a result, at low concentration, these two toxins
add to the overall emission intensity, causing a decrease in their SV
curves. However, once a certain concentrationthreshold is reached,
interactions between the toxins and LMOF-241 lead to a net
1
and OTA bend downwards first at low concentration re-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
optical band gaps to be estimated. The estimated optical HOMO-
LUMO gaps are 2.3 and 2.6 eV for tppe and LMOF-241,
respectively (Figure S4). Photoluminescence excitation and
emission spectrawere collected for samples of tppe and LMOF-241
at room temperature. Both samples showed strong blue-green
1
1
2
emission when excited by
ex = 340 nm), with tppe having
an emission maximum at 490 nm, while that of LMOF-241 was
slightly redshifted to 500 nm (Figure S5). In designing LMOF-241,
we desired to preserve the strong emission from the tppe ligand in
the final structure. Specifically, the immobilization of the
chromophore ligand in the MOF framework would not alter the
quenching. Compared to OTA, AFG emits more efficiently and
1
also acts as a stronger quencher, as evident from the shape of both
slopes. The threshold concentration from PL enhancement to
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2+
nature of ligand based emission. The Zn ion was chosen for this
10
purpose because, as ad metalwith low-lying d-orbital energies it is
known to contribute negligibly in the luminescence of the resulting
13,19,20
LMOFs.
A Hamamatsu C9220-03 spectrophotometer with integrating
sphere was used to determine the IQY of both samples at 360 nm
excitation.The values are 76.7% and 92.7% for tppe and LMOF-241,
respectively. To the best of our knowledge, the latter represents the
highest value reported so far for green-emitting MOFs. The
significant increase (16%) in quantum yield is consistent with
previous findings, indicating that immobilizing molecular
chromophores (such as tppe) into rigid frameworks canimprove the
fluorescence efficiency by eliminating non-radiative
relaxation pathways such as some vibrational and rotational
13,18,19
motions.
The high efficiency makes LMOF-241 an excellent
candidate as fluorescence-based sensory material.
Figure 4. Schematic demonstrating electron transfer from
LMOF-241 to mycotoxin LUMO resulting in quenched emis-
sion.
Mycotoxin Detection
Mycotoxin detection was achieved by monitoring the PL signal
change of the LMOF-241 suspension before and after the addition
of the analyte. Upon addition of the mycotoxins, the emission in in-
tensityofLMOF-241was quenched.A representative set ofPL titra-
quenching of AFG
tensity change, AFG
1
is also lower than that of OTA. In addition to in-
causes a blue shift of the emission peak while
1
OTA gives a red shift. Such turn-on and turn-off responses are
unique fingerprints of these two mycotoxins.
tion curves for AFB
degree of quenching increases as a function of AFB
The quenching efficiency was quantified using the Stern-Volmer
1
are shownin Figure 3b, demonstrating that the
1
concentration.
Mycotoxin Detection Mechanism
The quenching of LMOF-
AFB
1
and AFB is likely
2
(
I
I
SV) equation:
due to an electron transfer mechanism that we previously discussed
19
for LMOF-based sensors. Based on the results obtained from our
molecular orbital calculations (see S10, Table S1), thebottomof the
LUMO (or CB) energy states of LMOF-241 lies above the LUMO
o
/ I = Ksv[Q] + 1
o
is the initial emission peak intensity, I is the emission peak inten-
energies of AFB
from the MOF to both toxin molecules (Figure 4). In addition, the
LUMO of AFB is lower in energy compared to that of AFB , which
and AFB , allowing an efficient electron transfer
1
2
sity after the addition of analyte, [Q] is molar concentration of the
analyte (quencher), and Ksv is the quenching efficiency, which was
used to quantitatively evaluate the performance of LMOF-241 as
mycotoxin sensor. As shown in Figure 3c, at low concentrations, the
1
2
accounts for its stronger tendency of such electron transfer and
higher degree of quenching effect.
The extent of analyte-sensor interactions also plays an important
I
o
/ I is linearly proportional to concentration for both AFB
AFB ; the slope is the Ksv. The Ksv plots for AFG , and OTA are also
shown in Figure 3c.
For AFB , Ksv is 54227 M , which is among the highest values re-
ported for the known sensory materials. This value is also nearly
1
and
role in the electron-transfer process. With LMOF-
channel di-
2
1
ameterbeing approximately16.6Å, we expect thattheaflatoxinmol-
ecules (measuring approximately 13.3 Å at their widest) would
be able to enter the pores. To confirm this and quantitatively
assess the analyte-sensor interactions, we first carried out a structure
-1
1
-1
twice of that of AFB
LMOF-241 toward AFB
to be 46 ppb, significantly better than 300 ppb, the tolerant level set
2
(32436 M ), indicating a high selectivity of
optimization process on AFB
1
and AFB loaded LMOF-241, using
2
1
. The detection limit for AFB is estimated
1
the Materials Studio Sorption Package, which utilized the GCMC
method and Burchard Universal Force Field. Analyte sites located
within the LMOF pore with the shortest distances to the MOF were
20
bythe FDA for cornandpeanut feeds for beefcattle. The SV curves
identified for each of AFB
1
and AFB
2
by the GCMC simulation
5
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 9
method (see S9, Figure S9 and Figure S10). We then performed
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
a
b
c
overlap population calculations using EH method to quantitatively
measure such interactions. The absolute fragment molecular orbital
overlap population (SAFMOOP) and absolute reduced overlap
population (AROP) between the analytes and the MOF were ob-
tained (see S10andTable S2). The averageof the summed absolute
25000
20000
600
5
4
3
2
1
0
00
00
00
00
00
orbital overlaps betweenAFB
betweenAFB andLMOF-241is 0.17, indicating thatAFB
significantly stronger with the MOF framework than AFB
1
and LMOF-241is 0.57, whereas that
2
1
interacts
. The re-
1
1
5000
0000
2
duced overlap population follows the same order, with the AFB
value 1.4timesof that forAFB .The strongerorbitaloverlapofAFB
with LMOF-241isdue to thehigher -conjugationofAFB , creating
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
1
1
more -type overlapwith the conjugate -orbitals ofLMOF-241. As
a result, it facilitates a more efficient electron transfer and higher ex-
tent of fluorescence quenching.
5
000
0
Energy transfer often contributes significantly in fluorescence
quenching and should also be considered. As can be seen in Figure
300
400
500
600
700
5a, the spectral overlap between the mycotoxin absorption and
Wavelength (nm)
LMOF-241emissionis very limited,which hinders the energytrans-
20
fer from LMOF-241 to AFB
1
and AFB , indicating that it does not
2
2
1
0
likely play a role in the mycotoxin detection. However, when com-
paring the excitation spectrum of LMOF-241 with the emission
spectra ofAFG
it is apparent that there is significant overlap, especially inthe case of
AFG (Figure 5c). The energy transfer between the excited toxins
AFG and OTA) and LMOF-241is likelyto contribute appreciably
to the apparent increase in the fluorescence intensity of LMOF-241
at low concentrations of AFG and OTA (Figure 3c). AFG causes
1
and OTA (note: AFB
1
and AFB
2
are non-emissive),
1
(
1
1
1
a higher degree of increase in LMOF-241 fluorescence intensity, as
its emission overlaps more strongly with LMOF-
spectrum than that of OTA.
Also noted in Figure 5a is that all four mycotoxins absorb the excita-
tion energy used in the sensing experiment (ex = 340 nm). This
suggests that competitionbetween the MOF and the toxins for exci-
tation energy may also contribute to the quenching of LMOF-
emission. However, it is unlikely that competition for excitation en-
ergy plays a significant role in the observed emission quenching, as
the toxins are present in extremely low amounts relative to LMOF-
0
0.004
0.008
0.012
0.016
Concentration (mM)
600
500
400
300
200
100
0
241throughout thesensingtitration.Additionally, ifcompetitionfor
excitation energy was occurring to a significant degree, non-specific
quenching of any fluorophores under 340 nm excitation in the pres-
ence of the mycotoxins would be observed. Figure 5b demonstrates
that luminescence fromtppe linker, itself astrong fluorophore, is not
affected bytitrationwith AFB . The strong and continuing decrease
1
in LMOF-241 emission intensity is primarily due to the electron
transfer process described above.
Figure 5b also reveals that incorporating the fluorophore into a
metal-organic framework is vital for the selective emission quench-
ingtooccur. Whilethetppe moleculeis astrong fluorophore, it does
not strongly interact with the toxin molecules. By anchoring the
fluorophore into a crystalline, porous framework using the metal ox-
ide PBU, we create a well-characterized material that has both an in-
tense emission signal and a strong interaction with the target myco-
toxins.
3
00
400
500
600
700
Wavelength (nm)
Figure 5. (a) Molar absorptivity of AFB
ange), AFG (dotted green), and OTA (dotted blue), and the emission
spectrumofLMOF-241 inDCM(solidblack, λex =340nm). (b) Ksv plot
for the titration of a 4 mg/mL solution of tppe with AFB . (c) Excitation
spectrum of LMOF-241 in DCM (dotted red) overlaid on the emission
ex = 340 nm) of AFG (green), and OTA (blue) in
1
(dotted red), AFB (dotted or-
2
1
1
1
DCM.
6
ACS Paragon Plus Environment

Page 7 of 9
Journal of the American Chemical Society
CONCLUSIONS
REFERENCES
(1) Al-Taher, F.; Banaszewski, K.; Jackson, L.; Zweigenbaum, J.; Ryu, D.;
Cappozzo, J. Journal of Agricultural and Food Chemistry 2013, 61, 2378.
2) David G. Schmale III; Munkvold, G. P. The Plant Health Instructor, 2009.
http:/ / www.apsnet.org/ edcenter/ intropp/ topics/ Mycotoxins/ Pages/ default.a
spx (accessed Mar 16, 2015).
(3) USFDA Compliance Program Guidance Manual 2007.
(4) Bhat, R.; Rai, R. V.; Karim, A. A. Comprehensive Reviews in Food Science
and Food Safety 2010, 9, 57.
5) Shephard, G. S. Chemical Society Reviews 2008, 37, 2468.
6) Song, S.; Liu, N.; Zhao, Z.; Njumbe Ediage, E.; Wu, S.; Sun, C.; De Saeger,
S.; Wu, A. Analytical Chemistry 2014, 86, 4995.
7) Yue, S.; Jie, X.; Wei, L.; Bin, C.; Dou Dou, W.; Yi, Y.; QingXia, L.; JianLin, L.;
TieSong, Z. Analytical Chemistry 2014, 86, 11797.
8) USFDA CPG Sec. 683.100 Action Levels for Aflatoxins in Animal Feeds
014.
9) You, L.; Zha, D.; Anslyn, E. V. Chemical Reviews 2015, 115, 7840.
10) Basabe-Desmonts, L.; Reinhoudt, D. N.; Crego-Calama, M. Chemical
Society Reviews 2007, 36, 993.
(11) (a) Nugent, P.; Belmabkhout, Y.; Burd, S. D.; Cairns, A. J.; Luebke, R.;
Forrest, K.; Pham, T.; Ma, S.; Space, B.; Wojtas, L.; Eddaoudi, M.; Zaworotko,
M. J. Nature 2013, 495, 80; (b) Choi, K. M.; Na, K.; Somorjai, G. A.; Yaghi, O.
M. J. Am. Chem. Soc. 2015, 137, 7810; (c) Fracaroli, A. M.; Furukawa, H.;
Suzuki, M.; Dodd, M.; Okajima, S.; Gandara, F.; Reimer, J. A.; Yaghi, O. M. J. Am.
Chem. Soc. 2014, 136, 8863; (d) Koroush, S.; Lin, Q.; Mao, C.; Feng, P. Chem.
Comm. 2014, 50, 10390; (e) Zhao, X.; Wong, M.; Mao, C.; Trieu, T. X.; Zhang,
J.; Feng, P.; Bu, X. J. Am. Chem. Soc. 2014, 136, 3252; (f) Ma, S.; Sun, D.;
Ambrogio, M.; Fillinger, J. A.; Parkin, S.; Zhou, H.-C. J. Am. Chem. Soc. 2007,
1
We have designed and synthesized a new luminescent MOF and in-
vestigated its luminescent properties as well as related applications
in chemical sensing. LMOF-241 is a blue-green emitting LMOF
with an exceptionally high internalquantumyield (92.7%). We have
demonstrated for the first time the use of this compound for the ef-
fective and selective optical detection of mycotoxins via a lumines-
cence quenching mechanism. LMOF-241 is capable of quickly and
efficiently detecting and differentiating several major Aflatoxins and
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
(
(
Ochratoxin A and is most sensitive towards Aflatoxin B . With a de-
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
tection limit of 46 ppb, LMOF-241 makes one of the best perform-
ingluminescence-based chemicalsensors to date. We have also stud-
ied the electronic properties of LMOF-241 and the selected myco-
toxins by theoretical methods. A possible detection mechanism via
electron, rather than energy, transfer processes is elucidated. These
results suggest that LMOFs have immense potential as simple, low-
cost, easily-portable and readily-available luminescence-based sen-
sors for the detection of biochemical hazards such as toxins and
other toxicmolecular species,which canbeparticularly usefulfor de-
veloping countries. This study opens a new direction for practical
applications making use of multifunctional MOFs.
(
(
2
(
(
ASSOCIATED CONTENT
Supporting Information
PXRD, TGA, computation details, and etc. Thismaterial is availablefree
of charge via the Internet at http:/ / pubs.acs.org.
1
29, 1858.
(12) (a) Zhang, S. H.; Shi, W.; Cheng, P.; Zaworotko, M. J. J. Am. Chem. Soc.
2015, 137, 12203; (b) Hu, Z.; Deibert, B. J.; Li, J. Chemical Society Reviews
2014, 43, 5815; (c) Banerjee, D.; Hu, Z.; Li, J. Dalton Transactions 2014, 43,
10668.
13) Gong, Q.; Hu, Z.; Deibert, B. J.; Emge, T. J.; Teat, S. J.; Banerjee, D.;
Mussman, B.; Rudd, N. D.; Li, J. Journal of the American Chemical Society 2014,
36, 16724.
14) (a) Hoffman, R. J. Chem. Phys. 1963, 39; (b) Whangbo, M. H.; Hoffmann,
R.; Woodward, R. B. Proc. R. Soc. London 1979, A366.
(15) Blatov, V. A.; Shevchenko, A. P.; Proserpio, D. M. Crystal Growth & Design
2014, 14, 3576.
16) (a) Blatov, V. A.; Proserpio, D. M. Acta Crystallographica Section A:
Foundations of Crystallography 2009, 65
Yaghi, O. M. Chemical Reviews 2014, 114, 1343.
17) Farnum, G. A.; LaDuca, R. L. Crystal Growth & Design 2010, 10, 1897.
18) Wei, Z.; Gu, Z.-Y.; Arvapally, R.; Chen, Y.-P.; McDougald, R.; Yakovenko,
A.; Feng, D.; Omary, M.; Zhou, H.-C. J. Am. Chem. Soc. 2014, 136, 8269.
(19) (a) Pramanik, S.; Zheng, C.; Zhang, X.; Emge, T. J.; Li, J. Journal of the
American Chemical Society 2011, 133, 4153; (b) Hu, Z.; Pramanik, S.; Tan, K.;
Zheng, C.; Liu, W.; Zhang, X.; Chabal, Y. J.; Li, J. Crystal Growth & Design 2013,
AUTHOR INFORMATION
Corresponding Author
(
1
(
*
jingli@rutgers.edu
Author Contributions
|
Z. Hu and W. P. Lustig contributed equally.
Notes
(
The authors declare no competing financial interest.
ACKNOWLEDGMENT
(
(
The Rutgers team is grateful for the financial support from the Materials
Sciences and Engineering Division, Office of Basic Energy Sciences, of
the U.S. Department of Energy through Grant No. DE-FG02-08ER-
4
6491. The Advanced Light Source is supported by the Director, Office
of Science, Office of Basic Energy Sciences, of the U.S. Department of
Energy under Contract No. DE-AC02-05CH11231. ZH would like to
thank Prof. Davide M. Proserpio for his insightful analysis of the struc-
ture topology. WPL would like to thank Ben Deibert for his invaluable
assistance with the structure images, as well as general feedback and dis-
cussion.
1
3, 4204; (c) Pramanik, S.; Hu, Z.; Zhang, X.; Zheng, C.; Kelly, S.; Li, J.
Chemistry A European Journal 2013, 19, 15964; (d) Banerjee, D.; Hu, Z.;
Pramanik, S.; Zhang, X.; Wang, H.; Li, J. CrystEngComm 2013, 15, 9745.
(20) Hu, Z.; Tan, K.; Lustig, W. P.; Wang, H.; Zhao, Y.; Zheng, C.; Banerjee, D.;
Emge, T. J.; Chabal, Y. J.; Li, J. Chemical Science 2014, 5, 4873.
7
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 9
TOC Figure
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
8
ACS Paragon Plus Environment

Page 9 of 9
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
TOC Graph
60x444mm (300 x 300 DPI)
6
ACS Paragon Plus Environment