Responsive Microgel Composite
Colloids for Plasmonic Sensing
Luis M. Liz-Marzán
36310 Vigo, Spain
http://webs.uvigo.es/coloides/nano
Surface plasmon resonances in metal nanoparticles
A
1,2
B
C
D
E
Normalized Absorbance
1,0
DE
C
B
A
0,8
0,6
0,4
0,2
0,0
400
600
800
wavelength / nm
1000
Coord. Chem. Rev. 2005, 249, 1870
Langmuir 2006, 22, 32
Adv. Mater. 2006, 18, 2529
Nature Phys. 2007, 3, 348
Angew.Chem.Int.Ed. 2007, 46, 8983
J. Mater. Chem. 2008, 18, 1724
Chem. Soc. Rev. 2008, 37, 1783
Chem. Soc. Rev. 2008, 37, 1792
Adv. Funct. Mater. 2009, 19, 679
Surface Enhanced Raman Scattering
see: Chem. Soc. Rev. 2008, SERS issue
Small 2010, 6, 604
Hot spots
EF up to 103
300 400
Wavelength/nm
EF up to 1012
Average SERS
400
800
1200
Raman shift/cm-1
1600
500 600 700 800 Wavelength/nm
900 SERS as an Analytical Tool

• Selective
(spectroscopic fingerprint)
• Sensitive
(single molecule detection)
• Fast (ms)
• Portable
(no sample preparation)
• Encoding capability
(spatial resolution)
• General application

• Low reproducibility
• Low substrate
uniformity
• Requires direct
contact of analyte
with metal surface
pNIPAM microgels: thermoresponsive colloids
Karg & Hellweg, Curr. Op. Colloid Interface Sci. 2009, 14, 438-450
∆T
N-Isopropylacrylamide
(NIPAM monomer)
∆pH
∆ (Ionic strength)
N,N′-Methylenebisacrylamide
(BIS, crosslinker)
The response to and external stimuli
can be modified with the addition of
a co-monomer:
Acrylic acid
pH and temperature
responsive microgels
Langmuir 2009, 25, 3163
LCST, 32ºC
2,2′-Azobis(2-methylpropionamidine)
dihydrochloride (cationic initiator)
Growing pNIPAM on Au nanoparticles
CTAB promoted polystyrene coating of the particles
Br-
Br-
Br-
N
N
N
Br-
Br-
Br-
N
N
Br-
Br-
N
N
N
Br-
Br-
Br-
N
N
Styrene
Br-
Br-
N
N
N
Br-
Br-
N
N
Initiator
Divinylbenzene
70ºC
Styrene
N
Br-
N
Br-
Br
N
N
N
-
-
-
Br
Gold Surface
Divinylbenzene
+
CTAB
Au
Br
PS shell
Br
N
Br-
N
Br-
N
Br-
N
Br-
Gold Surface
N
Br-
N
Br-
N
Br-
N
Br-
N
Br-
N
Br-
Gold Surface
-
N(CH3)3
Au
growth
60 nm
O’Haver et al. Langmuir 1994, 10, 2588‐2593
Au@PNIPAM core-shell particles
NIPAM, BIS
Initiator, 70 ºC
Au-St
T <32 ºC
C
Contreras-Cáceres et al., Adv. Mater. 2008, 20, 1666
Au@PNIPAM: thermal sensitivity
0.6
Absorbance
0.5
554 nm
55 ºC
Au
0.4
0.3
0.2
544 nm
10 ºC
0.1
Au
300
400
500
600
700
800
Wavelength / nm
500
556
554
400
DH / nm
SPB / nm
552
550
548
300
546
LCST ~ 32ºC
544
542
200
10
20
30
40
Temperature / ºC
Contreras-Cáceres et al., Adv. Mater. 2008, 20, 1666
50
60
10
20
30
40
temperature / ºC
50
Tuning shell response through crosslinking
N,N′-Methylenebisacrylamide
5%
17.5%
Contreras-Cáceres et al., Adv. Funct. Mater. 2009, 19, 3070
10%
Au@PNIPAM as nanoreactors
High [CTAB]
+ HAuCl4 + AA
0.5
589
687
D
Absorbance
0.4
571
0.3
669
0.2
0.1
+ HAuCl4 + AA
Low [CTAB]
Contreras-Cáceres et al., Adv. Mater. 2008, 20, 1666
0.0
400
500
600
700
Wavelength / nm
800
900
Catalysis by Au@pNIPAM:
Reduction of hexacyanoferrate (III) by borohydride
8 Fe(CN )36  BH 4  3H 2O  8 Fe  CN 6  H 2 BO3  8 H 
4
Fe(CN)6 4-
NaBH4
Au
Au
e-
Au
Fe(CN)6 3-
0.45
0,8
A
B
0.40
4
Absorbance
Absorbance
80 s
0,4
0,2
3
0.35
0.30
2
0.25
1
0.20
0
0.15
0,0
300
400
500
600
700
Wavelength / nm
Carregal-Romero et al., Langmuir 2010, 26, 1271
800
0
10
20
30
time / s
40
50
-ln[(At-A)/(A0-A)]
0,6
Tuning the catalytic activity of Au@pNIPAM
∆T
0,12
400
25‐fold decrease
0,08
350
300
0,04
250
0,00
0
10
20
30
T / C
Carregal-Romero et al., Chem. Mater. 2010, 22, 3051
40
50
60
200
DH / nm
kobs / s
-1
450
Influence of crosslinking density
2,2
7%
-15
3,0x10
dt / d52 (Swelling Ratio)
2,0
-15
-1
-2
kobs/A (s nm )
2,5x10
10%
1,8
7% BIS
-15
2,0x10
1,6
15%
1,4
9‐fold increase
1,2
-15
1,5x10
10% 1,0
BIS
10
-15
1,0x10
20
30
40
50
60
T (C)
-16
5,0x10
15%
7 BIS
%
10 %
15 %
0,0
0
10
20
30
T (C)
Carregal-Romero et al., Chem. Mater. 2010, 22, 3051
40
50
60
70
Au@PNIPAM traps for SERS detection
4 oC
60 oC
Alvarez-Puebla et al., Angew. Chem. Int. Ed. 2009, 48, 138
60 oC
4 oC
4 oC
60 oC
Au@Ag@pNIPAM: Increased sensitivity
Contreras-Cáceres et al., Chem. Eur. J. 2010, 16, 9462
Naphthoic acid detection
Multifunctional Au@Ni@pNIPAM
Au@pNIPAM
K2PtCl4
1
Chem. Mater. 2008, 20, 5399
+ CTAB
Ni2+ + 2N 2 H 4
Ascorbic Acid
Sánchez-Iglesias et al., ACS Nano 2009, 3, 3184
2
[Ni(N 2 H 4 ) 2 ] 2+
Au@Ni@pNIPAM
Conclusions
• Core-shell metal-pNIPAM nanocomposites can
be easily obtained through a two-step protocol
• The microgel shell structure can be modulated
through crosslinking with divinylbencene
• Microgel structure allows modulation of
catalytic activity
• The metal cores can be grown in situ, into
various morphologies (and functionalities)
• Au@pNIPAM can be used as colloidal traps for
SERS analysis and sensing
Acknowledgements
Isabel Pastoriza-Santos
Jorge Pérez-Juste
Susana Carregal-Romero
Pablo Hervés
Ana Sánchez-Iglesias
Marek Grzelczak
Jessica Pacifico
Ramón Álvarez-Puebla
Rafael Contreras-Cáceres
Antonio Fernández-Barbero
Matthias Karg
Thomas Hellweg
Thank you!
