1

Multifunctional Rare-Earth Vanadate Nanoparticles:

Luminescent Labels, Oxidant Sensors, and MRI

Contrast Agents

Mouna Abdesselem‡1, Markus Schoeffel‡

1, Isabelle Maurin

2, Rivo Ramodiharilafy

1, Gwennhael

Autret3, Olivier Clément

3, Pierre-Louis Tharaux,

3 Jean-Pierre Boilot

2, Thierry Gacoin

2, Cedric

Bouzigues1, and Antigoni Alexandrou

1,*

1Laboratoire d'Optique et Biosciences, Ecole Polytechnique, CNRS UMR 7645 - Inserm U 696,

91128 Palaiseau Cedex, France. 2Laboratoire de Physique de la Matière Condensée, Ecole

Polytechnique, CNRS UMR 7643, 91128 Palaiseau Cedex, France. 3

Paris Centre de Recherche

Cardiovasculaire (PARCC), INSERM U970 56 rue Leblanc, 75015 Paris, France

E-mail : antigoni.alexandrou@polytechique.edu

Supplementary information

Dynamic light scattering and zeta potential. Dynamic light scattering and zeta potential of

rare-earth vanadate nanoparticles were measured with a Malvern Nano SZ Zetasizer and are

reported in Table S1.

Composition d <n> (nm) PdI Zeta Potential (mV)

GdVO4 32 0.21 48

GdVO4cit

9 0.14 -13

Gd0.6Eu0.4VO4 54 0.12 8.6

Gd0.6Eu0.4VO4/SiO2 69 0.13 -31

2

Gd0.6Eu0.4VO4/Dextran 72 0.11 -31

Gd0.6Eu0.4VO4cit

23 0.20 -34

Gd0.6Eu0.4VO4cit

/SiO2 29 0.17 -20

Gd0.6Eu0.4VO4cit

/Dextran 34 0.16 -25

Table S1: Size (number average) and zeta potential of rare-earths vanadate nanoparticles. PdI

is the polydispersity index of the size distribution. Note that dynamic light scattering

overestimates the size of polydisperse nanoparticle solutions, as can be seen from the TEM

analysis discussed below and in the main text. The superscript cit denotes nanoparticles formed

via the citrate route.

Microstructural analysis of normal-route nanoparticles from X-ray powder diffraction. At

first, we fitted the Bragg peaks individually to Pseudo-Voigt functions using the FIT subroutine

of the FullProf suite of programs.1 Only non-overlapping and non-degenerate reflections were

used, considering both Kα1 and Kα2 contributions, to obtain the peak position and their integral

breadth as well as their deconvolution in Lorentzian and Gaussian components βL and βG,

respectively. Depending on the peak shape function used, we obtain the integral breadth due to

finite size effects as iLLsL ,, βββ −= for a pure Lorentzian (index L) peak shape and as

222

,, iGGsGβββ −= for a pure Gaussian (index G) peak shape.

2 The index s designates the pure

sample effect and i stands for the contribution of the instrument resolution obtained from the

analysis of the peak breadths of a bulk GdVO4 reference sample. The pure sample contribution

βL,s is then used to determine the coherence length Lc according to the Scherrer equation:

θβ

λ

coss

c

KL = ,

3 where K is the Scherrer constant. K may vary between about 0.5 and 2 depending

on the crystallite shape.4 In the present approximation, we used a value of K = 1. The Lc values

3

obtained range between 15 nm and 30 nm similar to the major and minor axis values derived

from TEM images.

For Williamson-Hall analysis, we considered only the Lorentzian contribution (after correction

for the instrument resolution), which is generally responsible for the crystallite size broadening.5

The strain parameter ε and the coherence length L associated with the apparent crystallite size

can be estimated respectively from the slope and the intercept of the Williamson-Hall plot

according to:

λ

θε

λ

θβ )sin(2.

1)cos(.+=

L (1)

β.cos(θ)/λ is plotted against 2sin(θ)/λ in Fig. S1B. The strain parameter extracted from the linear

fit is small, 0.4 ± 0.2 %, and the apparent crystallite size is 24±0.5 nm. As the model assumes

spherical crystallites, this value is in good agreement with the average value of the long and short

axis found from the statistical analysis of the TEM images (Fig.1C). The data show a rather large

scatter around the linear fit, at least partly due to a direction dependence of the crystallite

dimensions.

4

Figure S1. (A) Microstructural analysis from the refinement of the X-ray diffraction pattern

assuming an arbitrary shape modeled by spherical harmonics. (B) Williamson-Hall plot

derived from powder X-ray diffraction for the GdVO4 particles. The red line is a linear fit to

the data.

Microstructural analysis was also performed using the Rietveld method by fitting the entire

diffraction profile according to the FullProf implementation of the procedure described in Ref. 6.

This model accounts for direction-dependent crystallite sizes. The instrument resolution function

was determined from bulk GdVO4. We modeled an anisotropic crystallite shape by a sum of

spherical harmonics which does not require any assumption on the actual shape. Only the

coefficients with even parity, 0

0P , 0

2P , 0

4P , and 0

6P , were refined according to the crystal

symmetry (tetragonal space group, I41/amd n°141). The refined diffraction pattern obtained by

this method shows very good agreement between the measured and calculated profile (see Figure

S1A) and yields a crystallite form that may be described as a compressed prolate spheroid with a

thickness of 16 nm and a length of 25 nm, in very good agreement with the statistical analysis of

the TEM observations (Fig. 1). This confirms our conclusion based on the TEM images that a

preferential crystallographic orientation is present across the whole nanoparticles. The TEM

contrast variations would thus be representative of internal porosity, of surface roughness or of a

polygranular structure with primary crystallites aggregated in an ordered way in all three

dimensions.

5

Microstructural analysis of citrate-route nanoparticles from TEM and X-ray powder

diffraction. The citrate route synthesis described below (Methods section) results in smaller

sized nanoparticles. We analyzed transmission electron microscopy (TEM) images of over 100

Gd0.6Eu0.4VO4(cit)

particles and found a spherical shape. The distribution follows a log-normal

law centered at 5±0.2 nm (the error bar is that for the log-normal fit and corresponds to the

standard error on the mean; see Fig. S2A and B). We also performed a microstructural analysis

of these particles as discussed above for the normal-route nanoparticles. The X-ray diffraction

pattern and the corresponding refinement are shown in Fig. S2C. We found an average apparent

crystallite size of 4 nm, with coherence length values ranging between 3 and 6 nm depending on

the Bragg reflections, in good agreement with the size obtained from the TEM image analysis

(Fig. S2B).

Figure S2. (A) TEM image of citrate-route Gd0.6Eu0.4VO4 nanoparticles, scale bar: 20 nm. (B)

Size distribution obtained from 104 Gd0.6Eu0.4VO4cit

particles. The solid line is a log-normal fit

of the size distribution. (C) Microstructural analysis of GdVO4cit

nanoparticles from the

refinement of the X-ray diffraction pattern assuming an arbitrary shape modeled by spherical

harmonics.

6

Surface coatings. Surface modifications with silica or dextran enhance the normal-route particle

stability by increasing their surface charge and hence the electrostatic repulsions in the colloid.

Moreover, a dextran coating confers furtivity to the nanoparticles in the blood circulation. The

efficient coating of particles is noticeable in the size increase (see Tab. S1). We further

characterized the surface modifications with Fourier-Transform Infrared (FT-IR) spectroscopy

(Fig. S3). The intense peak at 800 cm-1

corresponds to the asymmetric vibration of the V-O-V

bond. The asymmetric stretching mode of the Si-O-Si bond appears as an intense peak at 1100

cm-1

for the silica-coated nanoparticles (Fig. S3 A). Dextran-coated nanoparticles display the

characteristic peaks of dextran, namely the C-H stretching vibration around 2930 cm-1

and the

valent vibrations in C-O bonds at 1153 cm-1

and in C-C bonds at 1030 cm-1

.

Figure S3. FT-IR spectra of pristine Gd0.6Eu0.4VO4 nanoparticles, silica-coated (A) and dextran-

coated nanoparticles together with a reference dextran spectrum (B). Arrows indicate

characteristic peaks of the V-O-V (800 cm-1

), Si-O-Si (1100 cm-1

), C-C (1030 cm-1

), C-O (1153

cm-1

) and C-H (2930 cm-1

) vibrational modes.

7

Dependence of the emission spectrum on the excitation wavelength. We measured the

emission spectra of Gd0.6Eu0.4VO4 nanoparticles with excitation wavelengths of 396 nm and 466

nm. We found emission spectra similar to those obtained with 280 nm UV excitation (Fig. 2B

and S5B) with a peaks at 617 and 701 nm.

Figure S4. Emission spectra of normal-route Gd0.6Eu0.4VO4 nanoparticles with excitation

wavelengths of 396 nm and 466 nm. The peak positions are indicated. The colloid concentration

in vanadate ions was ~100 mM.

Luminescence properties of citrate-route particles. We measured the excitation and emission

spectra of a suspension of citrate-route Gd0.6Eu0.4VO4 particles (Fig. S5). These showed the same

narrow absorption and emission peaks as their normal-route counterparts with a slight peak

broadening (Fig. 2 A) as expected due to their smaller size.

8

Figure S5. Luminescence properties of citrate-route Gd0.6Eu0.4VO4 nanoparticles. (A) Excitation

spectrum (λem = 615 nm). (B) Emission spectrum (λex = 280 nm). The peak positions as well as

the corresponding transitions are indicated.

Hydrogen peroxide detection. Single 30-nm sized Gd0.6Eu0.4VO4 nanoparticles show similar

behavior both in terms of photo-reduction and recovery in response to hydrogen peroxide

addition (Fig. S6A). More than ten nanoparticles were photoreduced under strong illumination at

466 nm and their luminescence decreased by 30% with an interparticle variation of 5% (Fig.

S6A). After photoreduction and addition of 100 µM hydrogen peroxide, the luminescence of 14

single nanoparticles was measured under weak illumination yielding an average signal increase

of 20% with a response variation of 3%.

9

Figure S6. (A) Luminescence of 11 single Gd0.6Eu0.4VO4 nanoparticles photoreduced at 466 nm.

Laser intensity: 1.6 kW/cm²; acquisition time: 1s. The luminescence signal is normalized to the

initial value before photoreduction (t=0). The red line represents the average luminescence

signal. (B) Luminescence of 14 single Gd0.6Eu0.4VO4 nanoparticles after photoreduction and

addition of 100 µM H2O2. The luminescence signal is normalized to the initial value before

addition of H2O2 (t=0). Laser intensity: 0.3 kW/cm², 466 nm; acquisition time: 3s. The red line

represents the averaged signal.

Reversibility of the photoreduction and reoxidation. We performed a cycling photoreduction and

recovery experiment on single 30-nm Gd0.6Eu0.4VO4 nanoparticles. For practical reasons, we

kept the same illumination parameters for both reduction and oxidation steps (excitation

intensity, 1.6 kW/cm²; acquisition time, 1s). Figure S7 shows that the photoreduction and

oxidation processes are reversible. During the oxidation step, there is an interplay between

photoreduction due to laser excitation and reoxidation due to hydrogen peroxide7. Therefore,

higher illumination intensities are more suitable for the detection of higher hydrogen peroxide

concentrations (10 mM was used for this experiment). The slight luminescence decrease

observed after recovery is also a signature of the competition between oxidation and reduction

reactions.

10

Figure S7: Photoreduction and recovery cycles for a single normal-route Gd0.6Eu0.4VO4 particle.

Illumination intensity at 466 nm, 1.6 kW/cm²; acquisition time, 1s. Red arrows show additions of

10 mM hydrogen peroxide, green arrows show rinsing steps.

Hydrogen peroxide detection in physiological medium. We measured the response of normal-

route Gd0.6Eu0.4VO4 particles to 100 µM hydrogen peroxide in a physiological medium

composed of HBSS (Hank's buffered salt solution) with 10 mM HEPES and 10% fetal bovine

serum (FBS). The luminescence evolution is similar to that observed in phosphate buffer saline

(PBS) for the same nanoparticles (see Fig. S9) as well as to those in pure water (see Fig. 2E).

This demonstrates that the presence of proteins does not modify the oxidant detection response.

11

Figure S8: Luminescence recovery after photoreduction and subsequent addition of 100 µM

H2O2 in HBSS/HEPES (10 mM)/10% fetal bovine serum medium and in phosphate buffer saline

(PBS). Signal averaged for N=4 single nanoparticles for each condition. Photoreduction at 466

nm, 1.6 kW/cm-1

; recovery observation at 466 nm, 0.3 kW/cm-1

. Aquisition time : 3s.

Hydrogen peroxide detection with citrate-route nanoparticles. Citrate-route Gd0.6Eu0.4VO4

nanoparticles show similar photoreduction under strong illumination and subsequent recovery in

an oxidative medium. Figure S9 shows an average luminescence decrease of 25% under 1.6

kW/cm² excitation at 466 nm. The luminescence of 21 single particles is plotted in Fig. S9C and

the average decay signal can be fitted by a biexponential (T1=1.6±0.1 s and T2=15±0.3 s). The

photoreduction is less efficient and faster in this type of particles than in normal-route ones (Fig.

2). After photoreduction, the addition of hydrogen peroxide causes a luminescence recovery

(Fig. S9B and S9D). With respect to normal-route nanoparticles, the reduction is slightly lower

in citrate-route particles (25% versus 30%) and the luminescence recovery is slower: the

12

characteristic recovery time in 50 µM H2O2 is 80 s in citrate-route particles and 25 s in normal-

route particle (Fig. S7B and Fig. 2D). Moreover, the photoreduction and recovery signals in

citrate-route particles have a typical dispersion of 8% which is higher than in normal-route

particles (5%). Normal-route particles are thus more efficient for local oxidant sensing than the

citrate-route ones. The observed differences are probably due to the shorter distances between

particle center and surface in the case of the smaller particles or to differences in surface

properties or in crystallinity.

Figure S9. Hydrogen peroxide detection properties of citrate-route Gd0.6Eu0.4VO4 nanoparticles

(A) Luminescence intensity evolution of under strong illumination (1.6 kW/cm², 466 nm) during

t=200 s (average for ~20 nanoparticles). Acquisition time: 1 s. (B) Luminescence recovery (0.3

kW/cm², 466 nm, acquisition time: 3 s, average for ~20 particles for each concentration) in 5 µM

and 50 µM hydrogen peroxide after prior photoreduction. The luminescence decrease and

13

recoveries are fitted with a biexponential and a monoexponential, respectively (solid lines). (C)

Luminescence evolution upon photoreduction of 21 individually detected particles (same

conditions as in A). The red curve is the average signal shown in (A). (D) Luminescence

recovery signals of 19 individually detected particles in 50 µM hydrogen peroxide (same

conditions as in B). The red curve is the average signal shown in (B).

Magnetic properties of GdVO4 and Gd0.6Eu0.4VO4 nanoparticles. Bulk GdVO4 is known to

display a paramagnetic-antiferromagnetic transition at TN =2.50 K8. The temperature dependence

of the molar susceptibility recorded for GdVO4 and Gd0.6Eu0.4VO4 nanoparticles obtained by the

two coprecipitation methods confirms a paramagnetic behavior down to 5 K (See Fig. S10A for

citrate-route Gd0.6Eu0.4VO4 particles). Note that at low temperatures, the magnetic properties of

the particles are only dependent on Gd3+

and not on Eu3+

ions, which exhibit a zero electronic

spin configuration at their ground state. Fitting the molar susceptibility molχ to a Curie-Weiss

law θ

χ−

=T

Cmol

mol yields a Curie constant 510)02.007.9( −⋅±=molC Km3mol

-1 and a Weiss

temperature 2.1−=θ K, whereas a θ value of -3.2 K is found for bulk GdVO4. Similar results

were found for the normal-route GdVO4 particles where we measured a Weiss temperature of

4.2−=θ K . Both magnetic dilution in the doped samples and finite size effects9,10

should be

responsible for this depressed θ value with respect to bulk GdVO4. Indeed, recent investigations

on DyPO4 and GdPO4 antiferromagnetic compounds with Néel temperatures TN of 3.4 K and

0.77 K, respectively, in the bulk state confirmed a shift to low temperatures of the point of

discontinuity in the magnetic susceptibility for 2.6 nm nanoparticles with respect to the bulk

materials.10

14

The change in magnetization values per Gd3+

ion as a function of the magnetic field is shown

in Figure S10B. The data related to the pure and Eu-doped samples, superimpose fairly well. The

slight deviation, a somewhat steeper increase for the bulk reference, may arise from the 0.2 K

temperature difference between the measurements. This confirms that, in the low temperature

region, doping with Eu3+

ions does not alter the magnetic properties of the host material.

Figure S10. (A) Molar susceptibility of bulk GdVO4 and citrate-route Gd0.6Eu0.4VO4

nanoparticles as a function of temperature (open symbols) fitted to a Curie-Weiss law (solid

lines). (B) Magnetic moment per Gd3+

in citrate-route GdVO4 and Gd0.6Eu0.4VO4nanoparticles as

a function of the magnetic field.

Evaluation of Gd0.6Eu0.4VO4 nanoparticle cytotoxicity.

15

Figure S11. MTT tests on endothelial progenitor cells (N=3 for each condition, error bars are

s.e.m.). Cells were incubated with 200 µL of dextran-coated Gd0.6Eu0.4VO4 colloid (citrate or

normal route, 10 mM in vanadate concentration) added to 2 mL of their ordinary culture

medium. Incubation times were 3 hours and overnight.

Luminescence from urine and tissue homogenates.

16

Figure S12. Luminescence observed under a UV lamp in homogenates of organs of mice injected

with 0.06 mmol/kg 1: Citrate-route dextran-coated Gd0.6Eu0.4VO4 colloid, 2: normal-route

dextran-coated Gd0.6Eu0.4VO4 colloid, 3: distilled water. (A) Solid residues in urine after

centrifugations and washings. (B) Same samples as in (A) and photograph taken with an

interference filter centered at 617 nm in front of the camera objective. (C) Liver homogenates.

Green circles emphasize the characteristic pink emission of Gd0.6Eu0.4VO4 NPs. (D) Kidney

homogenates prepared following the same procedure as for (B) samples.

MRI imaging with 30 nm Gd0.6Eu0.4VO4 particles.

Figure S13. Contrast evolution in bladder, liver, and kidney after antero-orbital injection of 0.06

mmol/kg of normal-route Gd0.6Eu0.4VO4 nanoparticles.

Experimental Methods

17

Nanoparticle synthesis. Sodium orthovanadate Na3VO4 (99.9%, Alfa Aesar) was dissolved in

ultrapure water to a final concentration of 0.1 M. The pH was adjusted to the range 12.5–13.0

and the solution was filtered through a 0.22 µm syringe filter. Gd(NO3)3 · 6H2O (purity 99.9%,

Alfa Aesar), Eu(NO3)3 · 6H2O (99.9%, Alfa Aesar) [and sodium citrate dihydrate C6H5O7Na3 ·

2H2O (> 99%, Sigma Aldrich) for the citrate route] were dissolved in ultrapure water to a final

concentration of 0.1 M and used as prepared.

For the standard coprecipitation route,11

a volume of 0.1 M sodium vanadate solution was

stirred vigorously at ambient temperature. The same volume of 0.1 M rare-earth nitrate solution

was then added with a flow rate of about 1 mL/min. Depending on the intended composition, the

lanthanide solution was a mixture of 60% vol Gd(NO3)3 solution with 40% vol Eu(NO3)3

solution or a pure Gd(NO3)3 solution. During the addition, the pH was verified at regular time

intervals. When the pH approached 9.5, a 1 M NaOH solution was added until the pH reached

10.5. After completion of the addition, the stirring was maintained for 30 min.

For the citrate route,12

1 volume equivalent of 0.1 M lanthanide nitrate solution was stirred

vigorously at 60°C. 0.75 volume equivalents of 0.1 M sodium citrate solution was slowly poured

into the flask forming a white to slightly yellow precipitate. 0.75 equivalents of 0.1 M sodium

vanadate solution was then added resulting, after addition of about 2/3 of the sodium vanadate

solution, in the complete dissolution of the precipitate and the formation of a limpid dispersion.

The reaction medium is stirred for another 30 min at 60°C and then allowed to cool down.

In both protocols, the synthesis was followed by centrifugation at 26,300 g for 20 min for

particles prepared by the normal route or 2 h for those made by the citrate route, or/and dialysis

until the colloid conductivity decreased below 100 µS/cm.

18

Determination of the vanadate concentration. The colloidal solutions were diluted to about

5 mM vanadate concentration in 1 mL. 900 µL of this solution were placed in a glass vial and

100 µl of HCl 37% wt were added. Pristine nanoparticles were readily dissolved by vortexing,

while silica-coated ones need an additional heating step of about 1 min at 100°C for complete

dissolution. The vial was tightly closed during the thermal treatment to avoid water evaporation.

The mixture was then diluted with 6 mL of HCl at 1.15 M. The red-brown color of the

trichloromonoperoxovanadium (V) complex appeared after addition of 105 µL of 3% wt H2O2

and a final vortexing. The absorption was measured using a Carry 50 UV-VIS spectrophotometer

(Agilent Technologies). 1.15 M HCl was used as reference. The vanadate concentration of the

dispersion was obtained by comparing the absorption at 405 nm and 460 nm to those of

calibration samples prepared from sodium orthovanadate Na3VO4 (99.9%, Alfa Aesar) and

containing an equimolar quantity of rare earth chlorides (EuCl3, 99.99%, Sigma Aldrich and/or

GdCl3, pure, Prolabo) in the same ratio as in the nanoparticles.

Determination of rare earth leaching. Titration of the rare-earths in solution was performed

using xylenol orange following an adaptation of a procedure described by Barge et al.13

Xylenol

orange undergoes a change in the relative intensity of its two absorbance peaks in the presence of

free rare-earth ions (Fig. S14). This approach does not allow distinguishing between Eu3+

and

Gd3+

ions but is rather an indicator of the sum of Eu3+

and Gd3+

concentrations.

Immediately after synthesis, the colloids were spun at 13,000 rpm for 10 min. The supernatant

was extracted and the precipitate was dispersed in ultra-pure water. Colorimetric dosage of

100 µL of the extracted supernatant was performed adding 2.8 mL of acetate buffer (50 mM, pH

5.80), and 100 µL xylenol orange solution (36 mg/100 mL, Molecula). The absorption was

measured and the concentration was determined from the A573/A433 ratio, where A573 and

19

A433 are the absorption values at 573 nm and 433 nm, respectively, following a calibration

curve obtained with rare-earth nitrate samples with the same rare-earth Gd:Eu concentration ratio

as in the nanoparticles (Fig. S14). A new calibration was performed for each series of

experiments.

Figure S14. Calibration of free rare-earth titration. (A) Absorption spectra of the xylenol

orange solution in the presence of known rare-earth concentrations in the same Gd:Eu

concentration ratio as for the nanoparticles. (B) Calibration curve obtained from a series of

absorption spectra.

Cell culture and cell mortality assay. Endothelial progenitor cells (EPC) were grown in

endothelial cell growth medium (EGM-2 BulletKit with supplement, Lonza) added with 20%

bovine fetal serum and 1% penicillin-streptomycin. Cell culture medium was changed every two

days and cells were diluted and transferred before 80% confluence. EPC cells originate from a

primary cell line derived from mice endothelial glomerular tissue.

We assessed cell mortality with MTT tests. The reduction of the tetrazolium salt MTT (3-(4,5-

dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) into the blue-colored formazan by the

mitochondrial enzyme succinate dehydrogenase takes place only in living cells. Thus, the

20

produced amount of formazan is proportional to the number of living cells. We grew cells in six-

well plates with three wells for each incubation condition (N=3) with 2 mL of culture medium.

We added 200 µL of dextran- coated Gd0.6Eu0.4VO4 colloid (citrate or normal route, 10 mM in

vanadate concentration) to the culture medium described above. After the incubation time (3

hours or overnight), we measured the sample absorbance A570 nm-A630 nm. The N=3 measurements

were averaged and normalized to the control sample.

Luminescence from urine and tissue homogenates. Homogenates of liver and kidneys were

obtained by mechanical grinding of tissues. We added 1 mL of distilled water and sonicated 3 x

1 minute in order to obtain a homogeneous suspension. The suspensions were then spun at 600 g

during 5 minutes. The precipitates were discarded and the supernatants were spun again at 1500

g during 5 minutes. The obtained precipitates were observed under ultraviolet illumination

(Fisher Bioblock Scientific TCP-20.M, 6x8W 312 nm). Urine samples were sonicated 5 x 1

minute then spun at 5000 g. The supernatants were discarded and the precipitate dispersed in 1

mL of distilled water and sonicated again 5 x 1 minute. The suspensions were then spun at 600 g

and the precipitates were discarded. Finally, the extracted clear supernatants were spun at 5000 g

during 10 minutes and the precipitates were imaged under ultraviolet illumination.

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