Local-environment-sensitive two-photon dye
Nikolay S. Makarov, Erich Beuerman, Mikhail Drobizhev, Aleksander Rebane
Department of PhysicsMontana State University, Bozeman, MT
Jean StarkeyDepartment of Microbiology
Montana State University, Bozeman, MT
Outline
• Advantages of two-photon microscopy
• Properties of molecular probes for two-photon microscopy
• Two-photon absorption of Styryl-9M
• Linear photophysical properties of Styryl-9M
• pH sensitivity of Styryl-9M
• One-photon sensitivity to local polarity
• Two-photon sensitivity to local polarity
• Two-photon sensitivity to local environment in biological
phantoms
Advantages of two-photon microscopy• Inherent 3D resolution• Larger penetration depth• Lower scattering• Lower photodamage• Lower absorption by intrinsic molecules• Lower autofluorescence background
Probes for two-photon microscopyEndogenous fluorophores
(NADH, NADPH, retinol, lipofucsin, etc.)
+ natural source of 2PA-excited fluorescence
+ fills the whole visible spectrum
- low 2PA cross sections
Fluorescent proteins
+ can be genetically encoded
+ high flexibility studying small animals
- small loading concentration
- substantial size
- faster photobleaching
- higher cost
Exogenous fluorophores
+ high 2PA cross sections
+ possible targeting
+ high stability
+ small size
+ possible near-infrared fluorescence
- delivery problems
- non-specific dying
Two-photon absorption, chloroform
300 350 400 450 500 550 600 650 700 750 800 850 900
0
100
200
300
400
500
600
700
800
900
100030 25 20 15
0
1x104
2x104
3x104
4x104
5x104
6x104
7x104
8x104
9x104
1x105
2, G
M
Transition wavelength, nm
1PA absorption Fluorescence 2PA absorption
Transition frequency, 103 cm-1
, M
-1cm
-1
Polarity dependence of 2PA
300 350 400 450 500 550 600 650 700 750 8000
200
400
600
800
1000
1200
140032 30 28 26 24 22 20 18 16 14
0
1
2
3
4
5
6
7 2,
GM
Transition wavelength, nm
2-Chlorobutane 50% 2-Chlorobutane,
50% Isopropanol Isopropanol Ethanol Acetonitrile
, 1
04 M-1cm
-1
Transition frequency, 103 cm-1
Perrin plot for Styryl-9M
A5.01.5 a
0.0 2.0x10-8 4.0x10-8 6.0x10-8 8.0x10-8 1.0x10-7 1.2x10-7 1.4x10-7
0
2
4
6
8
10
12
0.4
/r-1
/, s/P
0.36 0.40 0.44 0.48 0.52
3000
4000
5000
6000
7000
30%
eth
anol
+ 7
0% w
ater
50%
eth
anol
+ 5
0% w
ater
dich
loro
met
hane
pent
anal
isop
ropa
nol
ethy
lene
gly
col
acet
one
etha
nol
70%
eth
anol
+ 3
0% w
ater
acet
onitr
ile
2-ch
loro
buta
ne
Sto
kes
shift
s, c
m-1
F(n,)
Solvatochromic Stokes shifts for Styryl-9M
22
1,
2
2
i
i
i
i
i n
nnF
D5.25.2401
Fluorescence decay kinetics for Styryl-9M
Methanol=410 ps
Ethanol=570 ps
Ethylene glycol=470 ps
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
0.2
0.4
0.6
0.8
1.0
Flu
ore
sce
nce
, a.u
.
Delay, ns
Methanol Ethanol Ethylene glycol
Two-level model description of the two-photon cross section in chloroform
GM1096.0
01
230120max
2 n
faS
12
32
2
n
nf
GM180600max,2 calc
GM150740max,2 mes
21cos215
22 22
01
2
012
44
2 gnch
f
2
013
013
01
2
012
10ln103
fN
nhcg
A
Dfahc S
3
2
01
pH sensitivity of Styryl-9M: absorption
300 400 500 600 7000.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Ab
sorp
tion
, a.u
.
Wavelength, nm
pH 8.0 pH 8.4 pH 8.8 pH 9.2 pH 9.6 pH 10.0 pH 10.4
pH sensitivity of Styryl-9M: fluorescence
500 600 700 800 9000
25
50
75
100
125F
luo
resc
en
ce, a
.u.
Wavelength, nm
pH 8.0 pH 8.4 pH 8.8 pH 9.2 pH 9.6 pH 10.0 pH 10.4
pH sensitivity of Styryl-9M
8.0 8.5 9.0 9.5 10.0 10.50
1
2
3
4
5
6
7
88.0 8.5 9.0 9.5 10.0 10.5
0
1
2
3
4
5
6
7
8F
luo
resc
en
ce in
ten
sity
(7
95
nm
) /
Flu
ore
sce
nce
inte
nsi
ty (
65
0 n
m)
pH-level
Imaging layoutDirection of the laser beam
One-photon sensitivity to local polarity
0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50
560
570
580
590
600
610
620
630
640
650
660
0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50
560
570
580
590
600
610
620
630
640
650
660
11
10
98
7
6
5
4
3
2
1
Cen
tral
abs
orpt
ion
wav
elen
gth,
nm
Polarity function
1 – 2-chlorobutane; 2 – dichloromethane; 3 – pentanal; 4 – isopropanol; 5 – ethylene glycol; 6 – acetone; 7 – ethanol; 8 – mixture of 70% ethanol + 30% DI water; 9 – mixture of 50% ethanol + 50% DI water; 10 – acetonitrile; 11 – mixture of 30% ethanol + 70% DI water
Two “unknown” samples:(1) mixture of 50% 2-chlorobutane + 50% isopropanol(2) mixture of 40% ethanol + 60% DI waterThe determined polarity function is 0.386 for (1) and 0.497 for (2) which is less than 2% off the “true” values
Two-photon sensitivity to local polarity
0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.500
1
2
3
4
5
6
F(9
00
)/F
(10
00
)
F(n, )
2PA sensitivity to local environment in biological phantoms
1 – 10 l of 5mg/ml Styryl-9M dissolved in DMSO, 5105 Mouse embryo fibroblast cells, 0.6 ml setting solution, 3 ml rat tail collagen, 1 l linoleic/oleic acid mixture, 1 ml serum and phenol red –free medium overlay2 – 25 l of 1mg/ml Styryl-9M dissolved in DMSO, 0.8 ml setting solution, 4 ml rat tail collagen3 – 25 l of 1mg/ml Styryl-9M dissolved in DMSO, 0.8 ml setting solution, 4 ml rat tail collagen, 1 l linoleic/oleic acid mixture4 – 25 l of 1mg/ml Styryl-9M dissolved in DMSO, 0.8 ml setting solution, 4 ml rat tail collagen, 1 l liposin
1 2 3 40.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
F(9
50
)/F
(11
00
)
Sample number
Conclusions
• Styryl-9M shows one of the strongest two-photon cross section
among commercially available chromophores
• The lowest energy absorption peak can be considered as an
effective two-level system
• Both absorption and fluorescence spectra of the dye are highly
sensitive to pH
• Both 1PA and 2PA peaks of the dye are sensitive to the polarity
• These properties can be used for two-photon sensing of local
environment in biological systems
• Might expect to be able to differentiate malignant from normal
cells using polarity images with Styryl-9M -like compounds