Title of Project: Tip-enhanced Raman Spectroscopy of BioInorganic Nanomaterials

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SALSA doctoral project proposal, September 2012


1


Title of Project
:

Tip
-
enhanced Raman Spectroscopy of BioInorganic Nanomaterials

Co
-
supervisor

1
:

Prof. Renato Zenobi (ETH Zürich)

Co
-
supervisor

2
:

Prof. Jürgen P. Rabe (Humboldt Universität Berlin)

Collaborator(s):

to be determined

Complex of topics:
A2


Localized surface plasmons for bioanalytical applications

Short version

Tip
-
enhanced Raman spectroscopy (TERS
)
has so far mostly targeted organic or
biomolecules for spectroscopic identification an
d

localization
.

With few exceptions such as
carbon nanotub
es, however, the scattering cross section of interesting biomolecuels
(proteins, oligonucleotides, …) is low, resulting in low
S/N

ratios in TERS spectra.

Increasing
the

measurement time or the

illumination laser power can
partially address this problem
, b
ut
introduces artifacts from decomposition of labile biomolecules
, which generates

spurious
peaks

in TERS spectra

from carbonaceous contaminants.

A largely neglected, but promising application of TERS is the
spectroscopic investigation of
(bio)inorganic
nanomaterial
s, which are much more stable.
It is proposed to investigate

materials that play important roles in biomineralization and of
b
iologically
-
formed minerals
with

special uses
,

such as magnetic sensors in
magnetotactic bacteria

(Fe
3
O
4
), gravity
sensing devices (CaCO
3
, CaSO
4
, BaSO
4
) and iron storage and mobilization (Fe
2
O
3
•H
2
O in the
protein
ferritin
)

with nanometer spatial resolu
tion via TERS.

Overall goal of the project

-

TERS spectra of complex biomolecules are often plagued by low S/N ratios, due to
the low intrinsic Raman scattering cross sections of such materials. Increasing the
measurement time or t
he illumination laser power

is
generally

employed to address

this problem, but introduces artifacts from decomposition of labile biomolecules. In
fact, many TERS spectra in the literature contain bands that have been generously
assigned to various biomolecules, but are in reality sp
urious peaks from
carbonaceous contaminants. I
norga
nic nanomaterials

are much more stable
, and are
not expected to decompose even if very high local electromagnetic fields (e.g., due to
high excitation laser power or very highly enhancing TERS tips) and
long
measurement times are used. Interestingly, inorganic nanomaterials have hardly
been studied by TERS

[1
-

3]
. It is proposed here to close this gap and focus the
attention of this project on inorganic (bio)nanomaterials with special function

(
magneti
c sensors in
magnetotactic bacteria
, gravity sensin
g devices,
and iron
storage and mobilization
),
on
materials that play important roles in biomineralization,
and
on
other inorganic materi
als that may be outside of the realm of biology but
nonetheless interesting for nanoscale spectroscopic investigation (e.g., solar cell
materials
, materials used in molecular electronics

[4]
). In general, t
heir investigation

by TERS

is expected to be much

more straightforward than that of bioorganic matter.

An interesting side project that will also be developed from this basic starting point is
the identification of stable reference materials that could be used to
calibrate

TERS
(and, in particular TERS p
robes) in terms of spatial resolution and enhancement
factor. Suitable reference materials are also still lacking in this area; molecular films
are not ideal, again because they are prone to decomposition, and are generally less
long lived than inorganic
materials.

SALSA doctoral project proposal, September 2012


2


-

The area of this doctoral project proposal is the central theme of complex A2 of the
SALSA proposal, localized surface plasmons for bioanalytical applications. TERS is
described as one of the key methodologies in complex A2.

In addition, there

are
clear connections to the Complexes B2 (Multimodal structural and functional analysis
of materials) and B3 (Analytics of internal interfaces in composite materials).

Specific aims and how they may be reached



Objectives
:

-

extend TERS to (bio)inorganic
materials

-

identify problems in biomineralization, in the usage of mineral phases by biological
systems, in solar cell materials, and in molecular electronics whose spectroscopic
investigation with ≈ 10 nm resolution is necessary for functional analysis

-

develop a suitable inorganic nanomaterial into a calibration standard for TERS.



Experimental Strategies:

A key issue in this project will be
to identify suitable sample preparation methods.


The TERS methodology is, by and large, established. One aspect of TERS tips that is
still insufficiently addressed is their characterization (spatial resolution, enhancement
factor), which requires stable reference materials with nanometer dimensions. T
he
bioinorganic and inorganic materials studied in this project are likely to yield a useful
calibrant for TERS.



References:

[1]

M. Sánchez
-
Román, C.

Vasconcelos, T. Schmid, J. A. McKenzie, M. Dittrich, R.
Zenobi and M. A. Rivadeneyra,
Aerobic microbial do
lomite at the nanometer scale:
implications for the geologic record
, Geology

2008,

36
, 879
-
882
.

[2]

T. Schmid, C. Camus, S. Lehmann, D. Abou
-
Ras, C.
-
H. Fischer, M. C. Lux
-
Steiner,
and R Zenobi,
Spatially Resolved Characterization of Chemical Species and
Crystal
Structures in CuInS
2

and CuGa
x
Se
y

Thin Films using Raman Microscopy
, Phys. Stat.
Sol. A

2009
,

206
, 1013
-
1016
.

[3]

L. Hallmann, A. Mehl, P. Ulmer, E. Reusser, B. Stawarczyk, J. Stadler, R. Zenobi,
M. Özcan, and C. Hämmerle,
The Influence of Grain Si
ze on Low Temperature
Degradation of Dental Zirconia
, J. Biomed. Mat.

2012
,

100B
, 447
-
456
.

[4]

P.
Lange,
M.

Dorn,
V.

Severin,
D.A.

Vanden Bout, and
J.P.
Rabe,
Single
-

and
double
-

layer
graphenes as ultrabarriers for fluorescent polymer films
,

J. Phys. Chem.
C,
2011
,
115
,
23057
-
23061
.




Facilities:

The Zenobi lab at ETH Zurich is fully equipped with 2 TERS setups (1 upright /
reflection geometry for opaque sampl
es, and one with inverted ge
ometry for
transparent samples).

Collaboration



The Zenobi lab at ETH Zurich will be the primary lab of the SALSA Ph.D. student

/
Regular stays with collaboration partner(s) in Berlin will be planned to learn proper
sample handling, and to apply complementary methods for nanoscale chemical
characterization, such as electron microscopy, X
-
ray crystallography, and others. A
second goa
l of the mobility & exchange of the Ph.D. student will be the transfer of
know
-
how
to the lab of the Co
-
supervisor (with the goal to establish TERS in the field
of molecular electronics)
and to interested collaborators in Berlin.



The collaboration between
the groups at ETHZ (Zenobi) and HUB (Rabe) will be in
the area of near
-
field optical / spectroscopic methodologies, in particular TERS, and
SALSA doctoral project proposal, September 2012


3


their applications to composite nanomaterials, in particular (bio)inorganic functional
materials

and composite mater
ials used in molecular electronics
.

Connection with other projects


The proposed research has clear connections to the Complexes B2 (Multimodal structural
and functional analysis of materials) and B3 (Analytics of internal interfaces in composite
materials
).