Selective, sensitive, and rapid analysis with lateral-flow assays based on antibody-gated dye-delivery systems: The example of triacetone triperoxide

Article abstract of DOI:10.1002/chem.201300031

Set them free: Brightly fluorescent indicators that are loaded into mesoporous silica nanoparticle carriers, capped with bulky antibodies, are released into the lateral flow of a test strip upon analyte arrival. Integration of the system into a rapid, simple flow test with fluorescence readout is applied for the selective and sensitive determination of the presence of triacetone triperoxide (TATP) as a prototype small-molecule analyte (see figure). Copyright

Full text of DOI:10.1002/chem.201300031

COMMUNICATION
DOI: 10.1002/chem.201300031
Selective, Sensitive, and Rapid Analysis with Lateral-Flow Assays Based on
Antibody-Gated Dye-Delivery Systems: The Example of
Triacetone Triperoxide
[
a]
[b]
[b]
[b]
Estela Climent, Delia Grçninger, Mandy Hecht, M. Astrid Walter,
[
a]
[b]
[a]
[c]
Ramꢀn Martꢁnez-MꢂÇez,* Michael G. Weller, Fꢃlix Sancenꢀn, Pedro Amorꢀs, and
[
b]
Knut Rurack*
Nanoscopic delivery systems have received tremendous
attention in recent years because they can be designed from
a large number of materials in a great variety of architec-
tures, thus enabling precise tailoring and control of their
the number of analytes necessary to induce release, which
results in amplified signaling. The key is thus to equip such
systems with a selective gating mechanism that controls the
release of the measureable cargo. Few examples have been
reported in recent years that operate with specific gating
chemistries and target selected analytes in conventional sol-
[1]
function in a desired location. However, although their
popularity in drug delivery or related biomedical and phar-
[2]
[4]
maceutical applications is well documented, their break-
ution-based experiments. A more general approach and its
[3]
through in the area of analytical sciences is yet to come.
implementation within an actually applicable sensing format
has not been realized so far. Herein, we report the develop-
ment of such a general approach by designing an antibody-
gated dye-delivery system and incorporating it with a con-
ventional test-strip-based lateral-flow assay, finally allowing
for small-molecule sensing at the ppb level in an easy-to-op-
erate manner and an overall assay time of 2–10 min, which
is fast for a biochemical test.
The potential of such systems for analytical purposes is
nonetheless immediately clear. Provided that the carrier
system is loaded with an indicator and the appropriate de-
tection chemistry is implemented in a way that only the
advent of an analyte molecule can trigger delivery, such sys-
tems can release a much larger number of indicators than
The model analyte chosen was triacetone triperoxide
(
TATP). TATP is the prototype of a small-molecule analyte
[
a] Dr. E. Climent, Prof. R. Martꢀnez-MꢁÇez, Dr. F. Sancenꢂn
Centro de Reconocimienro Molecular y
Desarrollo Tecnolꢂgico (IDM)
Unidad mixta Universitat Politꢃcnica de Valꢃncia
Universitat de Valꢃncia, Departamento de Quꢀmica
Universidad Politꢄcnica de Valencia
Camino de Vera s/n, 46022 Valencia (Spain)
Fax : (+34)96-387-93-49
that is difficult to target with supramolecular recognition
chemistry because it lacks functional groups for classical
noncovalent binding and is neither particularly polar nor
apolar. TATP is also a high-priority analyte because of its
popular use in improvised explosive devices (IEDs) for
criminal and terrorist activities. Recent prevention strat-
egies increasingly focus on the tracing of explosives, for in-
stance, in sewage water to locate IED “bomb factories”,
[5]
and
[6]
CIBER de Bioingenierꢀa
Biomateriales y Nanomedicina (CIBER-BBN)
E-mail: rmaez@qim.upv.es
so potent on-site sensing systems for the condensed phase
are required. However, although various methods for lab-
AHCTUNGTRENNUNG
[
b] D. Grçninger, M. Hecht, Dr. M. A. Walter, Dr. M. G. Weller,
Dr. K. Rurack
Abteilung 1 Analytische Chemie, Referenzmaterialien
BAM Bundesanstalt fꢅr Materialforschung und -prꢅfung
Richard-Willstꢆtter-Strasse 11, 12489 Berlin (Germany)
Fax : (+49)30-8104-1157
[
7]
scarce. In addition, because most chemosensing systems
rely on the decomposition of TATP and the subsequent de-
[8]
tection of one of its precursors, hydrogen peroxide, the
direct detection of TATP without interference by other per-
oxide-based explosives and H O would be desirable for
tracing TATP in environments in which cleaning, bleaching,
and other domestic agents are used and could lead to un-
wanted false-positive alarms.
Our approach for the specific detection of TATP in liquid
samples at trace levels with a portable, handheld, and rapid-
ly responding device with straightforward operation is a
test-strip-based assay with simple fluorescence readout.
Test-strip assays for such purposes—especially if neutral
E-mail: knut.rurack@bam.de
[
c] Prof. P. Amorꢂs
Institut de Ciꢃncia dels Materials (ICMUV)
Universitat de Valꢃncia
2
2
P.O. Box 2085, 46071 Valencia (Spain)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300031. It contains details of
general techniques, reagents employed, synthesis of precursors and
solids, and full characterization of compounds and solids, including
figures of XRD and TEM analysis, porosimetry isotherms, antibody–
antigen binding, lateral-flow assay protocols, detailed performance
testing, measurement uncertainties, and LODs.
Chem. Eur. J. 2013, 00, 0 – 0
ꢇ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

tor. The last can be monitored
conveniently at excitation
wavelengths between 500 and
70 nm and emission wave-
lengths between 550 and
50 nm, which cover prominent
5
6
excitation sources and emission
filter windows. The complete
preparation and characteriza-
tion procedures for the materi-
als are given in the Supporting
Information.
An important feature when
aiming to use the capped
hybrid delivery systems in a
test-strip assay is to obtain a
highly selective and sensitive
response while guaranteeing
fast response times, that is,
high delivery rates. Highly se-
lective and sensitive immuno-
logical responses are best ob-
tained with high-affinity anti-
bodies. However, such tightly
binding receptors are usually
characterized by a rather slow
off-rate or dissociation con-
[13]
stant
k .
d
Assuming
a
common on-rate or association
7
À1 À1
constant k of 1ꢉ10 m
s
for
a
Figure 1. A) Schematic representation of the preparation of antibody-gated material S1-AB. B) Sensing
scheme of analyte-mediated displacement of the stoppers and dye release. C) Chemical structures of TATP
and the hapten derivatives I–III employed in this study.
small-molecule hapten–high-af-
finity-antibody interaction,
[14,15]
our TATP-affine sera with high
[
11]
9
À1
affinities
of K ꢀ1ꢉ10 m
0
À2 À1
small organic molecules unable to influence the optical or
redox properties of indicator molecules to a significant
extent are concerned—require the integration of signal amp-
are characterized by k ꢁ1ꢉ10 s , which can be consid-
d
[13]
ered as moderate to slow off-rates. The affinity of the an-
tibody is approximately fourfold higher for hapten I, used
[11]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
lification features. As mentioned above, chemically gated
for animal immunization, than for neat TATP, so an alter-
native hapten had to be developed. We thus opted for the
delivery systems are particularly attractive in this regard.
Based on our experience in the fields of bio-gated release
[16]
slightly mismatching hapten II (Figure 1) and synthesized
its reactive precursor III to be facilely anchored onto the
surface of the mesoporous material. In the next step, MSNs
were added to a solution containing a high concentration of
sulforhodamine B to achieve efficient loading of the pores
(solid S0) before III was anchored on the external surface to
yield S1. For the preparation of the final gated sensing ma-
terial S1-AB, S1 was suspended in phosphate-buffered saline
(PBS) containing the antibody in PBS (pH 7.4) with 0.05%
bovine serum albumin (BSA) and sulforhodamine B. Opti-
mization of the conditions was performed by checking a
range of different serum dilutions. S1-AB was isolated by
centrifugation and washed with PBS. The solid was finally
dried under vacuum overnight and stored at 48C. The pres-
ence of BSA presumably helps in the capping of the pores
by the antibodies, further reducing unspecific leaching of
the dye from the sensor material. The S1-AB hybrids were
obtained as roughly spherical nanoparticles with a diameter
[9]
systems and gated hybrid materials for sensing applica-
[4]
tions, we designed the ensemble sketched in Figure 1. Or-
[10]
dered mesoporous silica nanoparticles (MSNs)
are used
as the nanoscopic support with a defined void structure,
high inner surface area, and flexible functionalization chem-
istry. These MSNs are then loaded with the brightly fluores-
cent indicator dye sulforhodamine B (to yield solid S0) and
the external surface is subsequently functionalized with a
suitable hapten (S1). Finally, a TATP-selective polyclonal
[11,12]
antibody (S1-AB) recently developed by us
serves as a
bulky stopper moiety, which is attached at the void openings
and efficiently closes them. The tailored relay chemistry that
connects stopper and support is thus based on noncovalent
antibody–antigen interactions and (ideally) only TATP as
stimulus should be able to successfully compete with the
hapten for the antibodyꢈs binding sites, to dislocate the stop-
pers, to open the voids, and to release the entrapped indica-
&
2
&
www.chemeurj.org
ꢇ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Assays Based on Antibody-Gated Dye-Delivery Systems
COMMUNICATION
of approximately 100 nm and hapten III, dye, and antibody
therms between the particle-bound antibody and TATP ac-
cording to a Scatchard plot, often used to describe protein–
ligand binding, revealed an apparent equilibrium constant of
À4
À1
contents of 0.17, 0.749, and 5.18ꢉ10 mmol(gSiO2) , respec-
tively; the complete details are given in the Supporting In-
formation.
5
À1
K=4.5ꢉ10 m , the nonlinearity presumably arising from
the polyclonality of the sera. Regarding the limit of detec-
tion (LOD) of the assay, TATP could be detected at concen-
trations as low as 12.5 ppb (details of the analytical perform-
ance are given in the Supporting Information). The amount
of dye released in the working range of the assay at lower
TATP concentrations is about 70 times that of antibody dis-
placed, clearly resembling signal amplification.
The response of S1-AB in the presence of TATP was stud-
ied by suspending S1-AB (0.4 mg) in PBS (0.8 mL) at
À1
pH 7.4 (0.5 mgsolidmL ). This suspension was divided into
two aliquots. To assess the effectiveness of pore closure, one
fraction was mixed with PBS (2.375 mL) containing TATP
(
5 ppm) and the other fraction was only mixed with the
same amount of neat PBS. Fractions of both suspensions
(
(
0.25 mL) were then centrifuged for certain time intervals
0, 0.25, 0.5, 2, and 5 min) and the amount of released dye
The selectivity of the capped material was studied by
monitoring the uncapping process in the presence of other
species, in particular of common explosives such as trinitro-
toluene (TNT), hexogen (RDX), nitropenta (PETN), octo-
gen (HMX), nitroguanidine (NG), and hexamethylene tri-
peroxide diamine (HMTD); see Figure SI-1 in the Support-
ing Information for chemical structures. Furthermore, the
synthetic precursors of TATP and III, namely, hydrogen per-
oxide, acetone, and 7-oxooctanoic acid (7-oxo), as well as
other synthetic cyclic peroxides, that is, tributanone triperox-
ide (but-TP), tri-3-pentanone triperoxide (3-pent-TP), tri-2-
pentanone triperoxide (2-pent-TP), diacetone diperoxide
was measured fluorometrically. The profiles of the delivery
kinetics are shown in Figure 2A. It is clear that the presence
(
DADP), and the structurally related, common crown ether
compounds 18-crown-6 (18C6) and 12-crown-4 (12C4), were
also tested. The uncapping ability of all these compounds at
a concentration of 3 ppm is shown in Figure 3. Evidently,
Figure 2. A) Sulforhodamine B release measured by monitoring the fluo-
rescence at 582 nm (lexc =564 nm) versus time for S1-AB in PBS
Figure 3. Relative release of sulforhodamine B from S1-AB in the pres-
ence of 3 ppm of other common explosives and educts of TATP synthesis
in PBS (pH 7.4); H O is highlighted in gray. Inset: Relative release of
2 2
sulforhodamine B from S1-AB in the presence of 3 ppm of selected com-
pounds that are structurally related to TATP. The amount of dye released
was determined fluorometrically (lem =582 nm, lexc =564 nm); error bars
at 3s.
(
pH 7.4), in the absence (curve b) and the presence (curve a) of 5 ppm
TATP. B) Sulforhodamine B release from S1-AB as a function of TATP
concentration in PBS (pH 7.4) after 5 min of reaction. The amount of
dye released was determined from the emission intensity at 582 nm (with
l
exc =564 nm); error bars at 3s.
of TATP induced a fast opening of the pores with subse-
quent release of the entrapped dye, whereas virtually no re-
lease was observed in the absence of TATP. The maximum
delivery of sulforhodamine B from S1-AB in the presence of
TATP (5 ppm) amounted to 25% of the initial content of
dye in S1-AB. Following a similar procedure, dye delivery
from S1-AB was studied as a function of TATP concentra-
tion (Figure 2B), and the expected correlation was ob-
served, in agreement with a displacement of the antibody
from the solid surface upon successful competition of TATP
with the binding sites (Figure 1). Analysis of the binding iso-
from the structurally related compounds, only the analogous
(yet in realistic scenarios not relevant) triperoxides but-TP
(contains the same triperoxide ring as III), 2-pent-TP, and 3-
pent-TP were able to partially induce dye release from S1-
AB nanoparticles. Among the classical explosives only
PETN and NG induced moderate dye delivery. Besides the
low detection limit for TATP, an important feature of the
system is its excellent discrimination of TATP against H O ,
2
2
the cross-reactant most other methods suffer from.
Chem. Eur. J. 2013, 00, 0 – 0
ꢇ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
3
&
ÞÞ
These are not the final page numbers!

R. Martꢀnez-MꢁÇez, K. Rurack et al.
Encouraged by these results and after demonstrating the
feasibility of the combination of immunological indication
and mesoporous scaffoldings to design antibody-capped
mesoporous materials, we proceeded to integrate S1-AB
with a lateral-flow assay for the straightforward on-site de-
tection of TATP. Such assays commonly rely on test strips
that carry the (bio)chemical part of the detection system
and which, after dipping the strip into the sample solution
and evolution of the flow, develop a color that can be appre-
ciated by eye. Few such assays are known for the determina-
tion of small-molecule analytes of environmental (e.g., atra-
vent front reaches zone A because of competition between
TATP and grafted III for the binding sites of the antibody,
thus leading to formation of the more stable TATP–anti-
body complex, and the liberated dye is transported at the
solvent front due to the flow conditions (Figure 4b). Be-
cause the scaffold MSNs have been chosen to be large
enough not to be transported by an aqueous flow in the
stripꢈs membrane, still capped and uncapped S1-AB are
both retained at the spot of deposition (Figure 4c, zone A).
Depending on the amount of TATP in the sample, the flow
transports a certain amount of released dye away from
zone A and a fluorescence signal can be detected at the sol-
vent front in zone B.
[17]
[18]
zine),
diagnostic (e.g., morphine),
or terroristic (e.g.,
[19]
saxitoxin) concern at trace (lower ppb) levels; those that
are known commonly utilize antibody–gold nanoparticle
A high-flow nitrocellulose membrane was selected as the
support. Strips 0.5ꢉ2.5 cm in size were prepared and S1-AB
(0.5 mL) was deposited from suspensions of the sensing ma-
(
AuNP) conjugates or hapten–protein–AuNP conjugates,
partly in combination with enhancer solutions. Alternatively,
first reports on trace-level analysis by using quantum dot
À1
terial (2 mgmL ) on zone A with a micropipette. The strips
(
QD) conjugates in strip-based assays and handheld fluores-
were then dipped into buffered solutions containing various
amounts of TATP. After 90 s of development, the test strips
were dried and the fluorescence was measured with a flow
assay reader at 625 nm (lexc =520 nm). The drying step is es-
sential because varying amounts of residual liquid on the
strip influence the fluorescence of the dye. This step is also
the time-limiting step, that is, when using a hair dryer (in
cold air blow mode), the assay can be completed in approxi-
mately 2 min (90 s development plus 30 s drying), and when
letting the strip dry at room temperature under normal at-
mosphere, approximately 8 min are required to obtain a
stable signal. When the PBS sample solution did not contain
TATP, a negligible fluorescence signal was recorded in
zone B (Figure 5A). However, when a similar experiment
was performed, for example, with a solution containing
TATP (0.5 ppm), a clear signal was found in zone B (Fig-
ure 5B). To the best of our knowledge, this is the first
report of a flow assay based on massive indicator release
from a nanoscopic chemical container device.
cence readers instead of AuNP-based assays have been re-
[20]
ported recently. Inherent to both approaches are the facts
that such assays are rapid, sensitive, specific, cheap, and
easy to handle, clear advantages in routine applications by
untrained personnel or in emergency cases. However, both
AuNP- and QD-conjugate assays have a significant draw-
back, that is, they require protein conjugates to travel the
active distance of the strip, which renders them prone to
errors due to unspecific binding. As can be deduced from
the scheme sketched in Figure 1, our approach is different.
The strip also contains an interaction and a detection zone
(
(
Figure 4). However, only the first zone A contains the
bio)chemistry—S1-AB (Figure 4a)—that is necessary to
ACHTUNGTRENNUNG
generate the response and the second zone B is an arbitrary
area at the solvent front in which a signal is collected (Fig-
ure 4c). If the investigated sample does not contain the ana-
lyte (TATP) no dye release would be observed and no
signal would be detected in zone B. However, when TATP is
present in the sample, uncapping takes place when the sol-
Following the same procedure as that described above,
the effect of TATP concentration in the lateral-flow assays
was studied. The amount of dye released for each concentra-
tion was calculated through the ratio between the area of
zone A and the total area of the test strip. An LOD of
1
5 ppb of TATP was determined by using this simple proce-
dure (Figure SI-2 in the Supporting Information). The effect
of the educts of the synthesis of TATP, other explosives, and
other peroxides was also assessed in cross-reactivity studies
and the results in terms of selectivity were similar to those
observed by using S1-AB in solution (Figure SI-3 in the Sup-
porting Information). Moreover, besides the manual deposi-
tion procedure described above, we also prepared strips for
the assay with an automated dispenser able to deliver drop-
lets of ꢁ1 nL in volume from suspensions of S1-AB
Figure 4. Design and principle of operation of the lateral-flow assay:
a) S1-AB is deposited at zone A so that the strip can be conveniently
dipped into the sample; b) the presence of the analyte leads to (partial)
uncapping of the pores and release of the dye, which is transported at the
solvent front; c) after development and drying, zone B contains the
amount of dye that corresponds to the amount of analyte in solution and
zone A the residual, unreleased dye. Note that zone B does not contain
any specific focusing chemistry; the dye molecules are already sufficiently
focused at the solvent front.
À1
(5 mgmL ) onto the strips; the final volume deposited was
50 nL in these cases. The advantage of this procedure is that
an automated and reproducible preparation of the test strips
is possible (Figure SI-4 in the Supporting Information). The
same selective uncapping process in the presence of TATP
was observed for these strips with detection limits of 40 ppb.
&
4
&
www.chemeurj.org
ꢇ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Assays Based on Antibody-Gated Dye-Delivery Systems
COMMUNICATION
samples with ethanol contents of 1–10% v/v revealed that
enhanced release is observed only above 5%, most likely
due to accelerated dissociation of the caps (for a detailed
description and representative graphs, see Section 9 and Fig-
ure SI-6 in the Supporting Information). Evidently, the strip-
based assay is robust enough to accomplish the task of reli-
AHCTUNGTRENNUGNa bly determining the presence of TATP in scenarios to
locate IED “bomb factories”, as described in the introduc-
tion.
In summary, we have designed and prepared antibody-
gated MSNs that are loaded with a rhodamine dye and that
can be used for the determination of the presence of perox-
ide-based explosive TATP with a lateral-flow fluorescence
reader, thereby allowing for detection limits in the lower
ppb range. The mechanism of the detection relies on a dis-
placement of the antibody from the surface of the hybrid
material because of highly affine antibody–TATP interac-
tions, which release a much larger number of entrapped dye
molecules from the pores than antibodies are displaced. The
high selectivity of the antibody is retained in the gated ma-
terial, thus allowing for a remarkable discrimination against
H O . System design and optimization led to straightforward
2
2
integration into a lateral-flow assay without further treat-
ment or conditioning of the test strips while guaranteeing
fast overall assay times of ꢁ10 min. Moreover, besides
showing a remarkable robustness, the inherent architecture
of the assay relies on a single-step immunochemical reac-
tion, that is, it can dispense with secondary (labeled) anti-
bodies and enables ratiometric signal assessment in the pres-
ence of the analyte by simple comparison of the fluores-
cence signals in two zones. Because of the modularity of the
approach, the concept is easily generalizable and applicable
for many small-molecule analytes. For instance, assays can
be imagined that contain various hybrids of S1-AB(n) type,
for which each material capped with a certain antibody is
loaded with a different dye, thus envisioning multiplexed
analysis with such simple assays.
Figure 5. Signal obtained with the fluorescence reader (lexc =520 nm,
l
em =625 nm) in zones A and B after dye release and development of the
flow assay in A) the absence and B) the presence of 0.5 ppm TATP in
PBS buffer (pH 7.4); gray shades on the sketched strips resemble signal
intensity.
These experiments have shown that the S1-AB hybrids are
stable enough to be handled in an automated dispensing
process by using a piezo-driven device. In contrast, due to
sedimentation problems of the hybrid nanoparticles in the
reservoir, even the use of high-end array spotters did not
yield satisfactorily reproducible series of strips (Figure SI-5
in the Supporting Information).
Finally, the strips from both deposition procedures,
manual and dispenser, were tested under realistic conditions
and were able to detect TATP in tap water (pH 7.4) as well
as influent (pH 7.9) and effluent (pH 7.5) water of a sewage
treatment plant at lower ppb concentrations, when for in-
stance PBS 10X solution (0.1 mL) was added to the sample
Acknowledgements
Financial support from the Spanish Government (MAT2009-14564-C04-
01), the Generalitat Valenciana (PROMETEO/2009/016), the Innova-
tionsfonds (BAM/Bundesministerium fꢅr Wirtschaft und Technologie),
and BAMꢈs PhD Program (M.A.W.) is gratefully acknowledged. E.C.
thanks the Ministerio de Educaciꢂn for a fellowship. We are indebted to
J. Schenk, BAM-1.0, for help with the piezo dispenser and S. Fischer and
W. Weigel, Scienion AG, Berlin, for support with the spotter.
Keywords: dyes/pigments
· explosives · fluorescence ·
(
0.9 mL) prior to dipping of the strip. Regarding pH toler-
immunoassays · mesoporous materials
ance, the system was tested in the pH range 1–12 and
TATP-induced delivery was observed at any pH value. How-
ever, below pH 4 and above pH 8.5, the delivery rates were
reduced, presumably because at acidic pH, TATP starts to
[
1] a) M. Motornov, Y. Roiter, I. Tokarev, S. Minko, Prog. Polym. Sci.
010, 35, 174–211; b) I. I. Slowing, J. L. Vivero-Escoto, C. W. Wu,
V. S.-Y. Lin, Adv. Drug Delivery Rev. 2008, 60, 1278–1288.
2
[21]
decompose and at alkaline pH, the structure of the silica
[22]
scaffold might be altered. In addition, testing the assay on
[2] A. S. Hoffman, J. Controlled Release 2008, 132, 153–163.
Chem. Eur. J. 2013, 00, 0 – 0
ꢇ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
&
ÞÞ
These are not the final page numbers!

R. Martꢀnez-MꢁÇez, K. Rurack et al.
[
[
3] R. Martꢀnez-MꢁÇez, F. Sancenꢂn, M. Biyikal, M. Hecht, K. Rurack,
J. Mater. Chem. 2011, 21, 12588–12604.
[10] a) J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T.
Kresge, K. D. Schmitt, C. T. W. Chu, D. H. Olson, E. W. Sheppard, J.
Am. Chem. Soc. 1992, 114, 10834–10843; b) F. Hoffmann, M. Cor-
nelius, J. Morell, M. Frçba, Angew. Chem. 2006, 118, 3290–3328;
Angew. Chem. Int. Ed. 2006, 45, 3216–3251.
4] a) E. Climent, M. D. Marcos, R. Martꢀnez-MꢁÇez, F. Sancenꢂn, J.
Soto, K. Rurack, P. Amorꢂs, Angew. Chem. 2009, 121, 8671–8674;
Angew. Chem. Int. Ed. 2009, 48, 8519–8522; b) E. Climent, R. Mar-
tꢀnez-MꢁÇez, F. Sancenꢂn, M. D. Marcos, J. Soto, A. Maquieira, P.
Amorꢂs, Angew. Chem. 2010, 122, 7439–7441; Angew. Chem. Int.
Ed. 2010, 49, 7281–7283.
5] a) Report of the European Security Research Advisory Board
ESRAB—Meeting the Challenge: the European Security Research
Agenda, Office for Official Publications of the European Communi-
ties, Luxembourg., 2006, http://ec.europa.eu/enterprise/policies/se-
curity/files/esrab_report_en.pdf; b) NCTC 2010 Report on Terrorism,
National Counterterrorism Center, Washington DC, 2011, http://
[11] M. A. Walter, U. Panne, M. G. Weller, Biosensors 2011, 1, 93–106.
[12] a) M. A. Walter, D. Pfeifer, W. Kraus, F. Emmerling, R. J. Schneider,
U. Panne, M. G. Weller, Langmuir 2010, 26, 15418–15423; b) J. J.
Carvalho, M. A. Walter, Y. Baermann-Stapel, M. G. Weller, U.
Panne, J. A. Schenk, R. J. Schneider, In Vivo 2012, 26, 63–69.
[13] M. Stenberg, H. Nygren, J. Immunol. Methods 1988, 113, 3–15.
[14] T. W. Smith, K. M. Skubitz, Biochemistry 1975, 14, 1496–1502.
[
7
À1 À1
[15] The values of k
a
ꢀ1ꢉ10 m
s
pertain to interactions of both part-
ners in the liquid phase. For interactions at the solid/liquid interface
when, for instance, one partner is coupled to a solid support such as
www.nctc.gov/witsbanner/docs/2010_report_on_terrorism.pdf
(see,
for example, Chart 10: Wounded Victims Grouped by Weapon
Type); c) K. Yeager, Police Chief 2011, 78 (September Issue), 52–
a microparticle, k
magnitude smaller, that is, 1ꢉ10 m
a
values are commonly approximately one order of
6
À1 À1
s ; see, for example, ref. [14].
5
5.
[16] The affinity of the antibody for the parent compound tributanone
triperoxide (but-TP) is only 4% compared with neat TATP, see
ref. [11].
[
[
6] http://www.fp7projectcommonsense.eu/.
7] a) R. M. Burks, D. S. Hage, Anal. Bioanal. Chem. 2009, 395, 301–
3
13; b) S. Girotti, E. Ferri, E. Maiolini, L. Bolelli, M. D’Elia, D.
[17] J. Kaur, K. V. Singh, R. Boro, K. R. Thampi, M. Raje, G. C. Var-
shney, C. R. Suri, Environ. Sci. Technol. 2007, 41, 5028–5036.
[18] S. Gandhi, N. Caplash, P. Sharma, C. R. Suri, Biosens. Bioelectron.
2009, 25, 502–505.
Coppe, F. S. Romolo, Anal. Bioanal. Chem. 2011, 400, 313–320;
c) R. Schulte-Ladbeck, P. Kolla, U. Karst, Analyst 2002, 127, 1152–
1
154.
[
8] a) M. E. Germain, M. J. Knapp, Inorg. Chem. 2008, 47, 9748–9750;
b) S. Malashikhin, N. S. Finney, J. Am. Chem. Soc. 2008, 130, 12846–
[19] A. Komano, H. Maruko, H. Sekiguchi, Y. Seto, Forensic Toxicol.
2011, 29, 38–43.
1
5
2847; c) J. C. Sanchez, W. C. Trogler, J. Mater. Chem. 2008, 18,
134–5141.
[20] a) Z. Zou, D. Du, J. Wang, J. N. Smith, C. Timchalk, Y. Li, Y. Lin,
Anal. Chem. 2010, 82, 5125–5133; b) Y. Bai, C. Tian, X. Wei, Y.
Wang, D. Wang, X. Shi, RSC Adv. 2012, 2, 1778–1781.
[21] H. W. Lin, K. S. Suslick, J. Am. Chem. Soc. 2010, 132, 15519–15521.
[22] A. L.-T. Pham, D. L. Sedlak, F. M. Doyle, Appl. Catal. B 2012, 126,
258–264.
[
9] a) C. Coll, L. Mondragꢂn, R. Martꢀnez-MꢁÇez, F. Sancenꢂn, M. D.
Marcos, J. Soto, P. Amorꢂs, E. Pꢄrez-Payꢁ, Angew. Chem. 2011, 123,
2
ment, A. Bernardos, R. Martꢀnez-MꢁÇez, A. Maquieira, M. D.
Marcos, N. Pastor-Navarro, R. Puchades, F. Sancenꢂn, J. Soto, P.
Amorꢂs, J. Am. Chem. Soc. 2009, 131, 14075–14080.
186–2188; Angew. Chem. Int. Ed. 2011, 50, 2138–2140; b) E. Cli-
Received: January 4, 2013
Published online: && &&, 0000
&
6
&
www.chemeurj.org
ꢇ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Assays Based on Antibody-Gated Dye-Delivery Systems
COMMUNICATION
Set them free: Brightly fluorescent
indicators that are loaded into meso-
porous silica nanoparticle carriers,
capped with bulky antibodies, are
released into the lateral flow of a test
strip upon analyte arrival. Integration
of the system into a rapid, simple flow
test with fluorescence readout is
applied for the selective and sensitive
determination of the presence of tri-
ACHTUNGTRENNUNGa cetone triperoxide (TATP) as a proto-
type small-molecule analyte (see
figure).
Immunoassays
E. Climent, D. Grçninger, M. Hecht,
M. A. Walter, R. Martꢀnez-MꢁÇez,*
M. G. Weller, F. Sancenꢂn, P. Amorꢂs,
K. Rurack* .................... &&&& — &&&&
Selective, Sensitive, and Rapid Anal-
ysis with Lateral-Flow Assays Based
on Antibody-Gated Dye-Delivery
Systems: The Example of Triacetone
Triperoxide
Chem. Eur. J. 2013, 00, 0 – 0
ꢇ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!