© 2008 OSA / CLEO/QELS 2008
a2892_1.pdf
CWM3.pdf
Detection of Neural Cell Activity Using Plasmonic
Gold Nanoparticles
Jiayi Zhang, Tolga Atay, Arto Nurmikko
Department of Physics and Division of Engineering, Brown University, Providence, Rhode Island02912, USA
Jiayi_Zhang@brown.edu
Abstract: Metal nanoparticles have been studied intensively for their applications using localized
surface plasmon polariton (SPP) resonance. We have demonstrated for the first time that using
gold nanoparticles, one can detect electrical activities from the neurons.
©2008 Optical Society of America
OCIS Codes: (240.6680) Surface plasmons; (170.0170) Medical optics and biotechnology
1. Introduction
Applications of metal nanoparticles are often based on their SPP resonance, which leads to a strong
enhancement of local electromagnetic field. Such resonance also makes it possible to detect a shift in the
extinction spectra when the nanoparticles are exposed to a change of local electric field. On the other hand,
the essence of the neuroscience is to study the neuron activity from single cell to network level, which
requires detecting the transient electric field change in the vicinity of the cell membranes. During the last
few decades, different recording techniques have been developed, ranging from invasive electrical methods
using thin metal wires to non-invasive optical methods using voltage sensitive fluorescent dyes. Having
been able to detect neuron activity successfully, these techniques have various drawbacks, e.g. the toxicity
and bleaching of the fluorescent dye.
Here we report a new non-invasive technique which utilizes the shift in the resonance mode of a
gold nanoparticle array to detect the neural cell activity. We first show that applying an external electric
field, with similar amplitude to that from an active neuron, across a plasmon/electrolyte interface results in
a corresponding transient change in the scattered light from the nanoparticle plasmonic array itself. The
neurons are then grown onto the nanoparticle template, and corresponding transient signals are detected
when the neurons are stimulated by glutamate, a chemical trigger.
2. Electric field modulated scattering light from the nanoparticle array
The shift in SPP resonance is due to the change in the dielectric constant of the metal which results from
the variation in the free electron concentration at the metal-electrolyte interface under the external electric
field. Slow electric field (of less than 1 Hz) modulated SPP resonance shifts in thin gold films has been
reported recently [1]. Yet the “switching” of neural cells happens in a relatively high frequency range of up
to 1kHz and over a relatively small area of (10μm)2. We have chosen a gold nanoparticle array to improve
both the frequency response and the compatibility of such plasmonic devices in neuroscience applications.
It has been shown recently that the fabrication of metal nanoparticles by electron beam lithography
provides the flexibility in tuning the resonance by size, shape and layout of the nanoparticle arrays [2]. The
parameters of the gold nanoparticles that we fabricated, 160nm of diameter and 400nm of center-to-center
distance, are chosen such that, in the presence of an external electric field, the change in the amplitude of
the scattered light is maximized at the excitation laser wavelength of 853nm (Fig.1(a)). In the first step of
our experiments, a 500Hz external electric field of 5V/mm is applied to the nanoparticle array in a saline
solution. Such electric field is typical for the cable model of neuron electrical activity and well simulates
the amplitude of the electric field when the neuron “fires” [3]. Shown in Fig.1(b) is the transient scattered
light from the array collected by a photodiode and amplified by 200 times. Such measurement confirmed
that the change in the scattered light is able to report the electric field change in the vicinity of the
nanoparticle.
© 2008 OSA / CLEO/QELS 2008
a2892_1.pdf
CWM3.pdf
Figure 1(a) SEM image and transmission spectrum of the gold nanoparticle array; (b) transient scattered light from the gold
nanoparticle array when a 500Hz electric field is applied.
3. Neuron activity detection by plasmons from stimulation by a chemical trigger
The dissociated hippocampal neurons are grown directly onto the nanoparticle plasmonic array for two
weeks before the measurement. Both the neuron body and the neuron processes grow directly on the
nanoparticles, showing the healthiness of the neuron (Fig. 2(a)). Glutamate flux to the neuron causes the
neuron activity to temporarily change from single spikes to bursts, which are several consequent spikes.
The scattering signals from the plasmonic array both before and after the glutamate flux are shown in Fig.
2(b) &(c). The signal before the glutamate stimulation shows evident single spikes while bursts can be seen
in the signal after the glutamate stimulation.
Figure 2(a) SEM image of the neuron grown onto the gold nanoparticle array, with traces of neuron body and neuron processes; (b)
transient scattered light before the glutamate flux shows single spike activity; (c) transient scattered light after the glutamate flux
shows burst activity.
4. Conclusions
It is shown for the first time that neuron activity can be detected by the SPP resonance shift in gold
nanoparticles. Such recording technique not only opens up the possibility of applying nanoparticles into in
vivo systems for optical imaging, but also provides the opportunity of probing local neuron activity on
nanometer scale where local membrane ion channels operate.
Research supported by the National Science Foundation.
[1] V. Lioubimov, A. Kolomenskii, A. Mershin, D.V. Nanopoulos, and H.A. Schuessler, “Effect of varying electric potential on
surface-plasmon resonance sensing”, Appl. Optics 43(17), 3426-32(2004).
[2] T. Atay, J.H. Song, and A.V. Nurmikko, “Strongly interacting Plasmon nanoparticle paris: from dipole-dipole interaction to
conductively coupled regime”, Nano Lett. 4(9), 1627-31(2004).
[3] C. Gold, D.A.Henze, C. Koch, and G. Buzsaki, “On the origin of the extracellular action potential waveform: A modeling study”,
J. Neurophysio. 95(5), 3113-28(2006).