Nanoneedle-electrode array packaged withamplifiers for recording biological-signals
with a high voltage gain
1111,21

1Shuhei Tsuruhara , Yoshihiro Kubota , Hiroshi Kubo , Hirohito Sawahata , Shota Yamagiwa , Shinnosuke Idogawa , and Takeshi Kawano
1Toyohashi University of Technology, JAPAN. 2National Institute of Advanced Industrial Science and Technology, JAPAN.

Background(a)

The intracellular recording enables torecord not only the action potentials but
also the postsynaptic potentials (EPSP,IPSP), which reflect the synapse input.

ZeRequirements for the intracellular recording
include :i) Sharpe needle tip, below 1 µm, andii) a high voltage gain.

Action potential

VoutZi(b)
NeuronZeZa

Zc

AMP

Zi

～ 60 % IPSPVoutZaZc

1EPSP～ 100 %

Herein, we proposed a nanoneedleelectrode array, which is packaged with [Ze:needle-electrode Zi:device interconnection Zc:cable Za:input impedance of recording system]
buffer amplifiers for a high voltage gain.
Schematicof
intracellular
recordingusingnanoelectrode.
(a)Conventional
electrodeattenuates
As the buffer amplifier, source followerthe voltage gain due to the high electrode’s impedance and parasitic impedance characteristics.
2was fabricated within 1×1 mm Si-block. (b) Proposed amplifier package to solve the voltage attenuation of the nanoelectrode.

Fabrication of device modules
Nano-electrode array module(a)Buffer-amplifier modules
1mm(b)(a)
VDD
M1VoutM2
VSS

100 μm(d)8.0(b)Ze Parylene-C
Pt/Ti0Si-8.0
500 µm -8.00

8.0

Vin [V]
Amplifier module. (a) Equivalent circuit ofsource follower. (b, c) Layout andphotograph of the fabricated module. (d)Vout-Vin characteristics of the fabricatedamplifier module.

(c)(d)(e) 1087Parylene-CImpedance [Ω](bVout [V](c)Parylene-C

Pt/Ti(b200 µmVBias

Au

1 mmVinSiO2SiPt

Zi

10Z
10 e
6105Zi4

10 0 1 2 3 4 5 65µm
20µm
10 10 10 10 10 10 10
SiO2Frequency [Hz]Nanoneedle-electrode array module. (a) Fabrication process steps. (b) Cross section of thenanoneedle. (c,d) SEM images of some needles and a needle-tip. Section. (e) Impedancecharacteristics of nanoneelde measured in saline solution.

Nanoneedle-electrode packaged with amplifier module
Nanoneedleelectrode array-2.0 Test Reference Device
electrodesignal-4.0

Gain [dB]

Buffer AMP(Source Follower)

0.0
Needleelectrode AMP

V-6.0
-8.0
-10

With AMP
Without AMP

Needleelectrode

23
410
10
10
FPC（Flexible printed circuit）
5mm
Frequency [Hz]Nanoneedle-electrode packaged with amplifier modules. (a, b) Photograph and schematic of the packaged device. (c) Voltage gain
characteristics of the device measured in saline solution. The graph also includes the data of nanoneedle without amplifier module forcomparison.

100101

Conclusion

We have proposed a nanoneedle-electrode device packaged with the buffer amplifier module for the application to intracellular
recording with a high voltage gain. By packaging the buffer amplifier with the nanoneedle array device. This result indicates thatthe proposed nanoneedle-electrode array device will offer high-quality recording of intracellular signals, not only action potentialsof the neuron but also the postsynaptic potentials.

Acknowledgements
Scientific Research (B) (No. 17H03250), for Young Scientists (A) (No. 26709024), the PRESTO Program from JST, and Strategic
Advancement of Multi-Purpose Ultra-Human Robot and Artificial Intelligence Technologies program from NEDO.

A HIGH-DENSITY ARRAY OF 3D MICRONEEDLE-ELECTRODES FOREVALUATION OF SPATIAL RESOLUTION OF NEURONAL ACTIVITY
Yuta Kotani1, Hirohito Sawahata2, Shota Yamagiwa1, Rika Numano1, Kowa Koida1, and Takeshi Kawano1
1Toyohashi University of Technology, JAPAN and 2National Institute of Advanced Industrial Science and Technology, JAPANBackground
Exploring behavior of a micro-scale neural network of corticalcolumn with a high spatiotemporal resolution is important tounderstand how the brain works. The query here is “how highspatial resolution of electrode array is necessary to detect
different signals from neurons within the tissue”. For this query,
however, needle’s pitch of conventional electrodedevices has been limited by the fabrication process(e.g., 400 µm-pitch)

Fabricated high-density needle-electrode array

The microneedle-electrode array device
is fabricated by vapor-liquid-solid (VLS)
growth. The VLS growth employed anarray of 5-µm-diameter and 200-µm-longSi-microneedles. Each Si-microneedle isthen metalized with 200-nm-thickplatinum (Pt) and insulated with 1-µmthick parylene for multichannel recordingof neuronal activities in the tissue.

The tip section was modified with a
low impedance material of Pt black
for the electrode’s impedance
reduction (tip diameter of Pt black= 9.2 µm). The impedance ofneedle measured in saline at 1 kHzshows 208.8 kΩ (average from 7chs.), which is low enough to detect
spike (~ 3,000 Hz) signals.

Neural recording

The needles penetrated the primary somatosensory
barrel cortex (S1B:1-4 mm lateral, 0-3 mm caudal
from bregma) of an anesthetized mouse. During therecording, mouse’s whiskers were physicallystimulated to record the neuronal responses. The
graph shows electrode’s interval (distance)
dependent correlation coefficients of the spike firing
rates, representing the independency of spikesignals between electrode channels. At theelectrode intervals of over 300 μm, the correlation
coefficient ranges from 0-0.4 (average 0.2).
Compared to these interval ranges, we obtained thecorrelation coefficient of 0.3-0.6 (average 0.4) with150 μm interval electrodes of our device.

Conclusiton
In this work, we evaluated spatial resolution of neuronal activities in mouse’s cortex, using a high-density array of microneedle-electrodes. As
the result, the spatial resolution is smaller than the interval of conventional electrode (e.g., ~400 μm) as well as smaller than the corticalcolumn of the somatosensory barrel region (200 –800 μm in diameter). Moreover, these results suggest that the further study on microscaleneural network in the cortex will be required by using higher needle’s density with the interval below 150 μm. As demonstrated here, our Sigrowth based needle-electrode with the diameter of < 10 μm is applicable to this challenge.

Acknowledgements
This work was supported by Grants-in-Aid for Scientific Research (B) (No. 17H03250), for Young Scientist (A) (No. 26709024), on Innovative Areas (Research in a proposed research area) (15H05917), and Strategic
Advancement of Multi-Purpose Ultra-Human Robot and Artificial Intelligence Technologies program from NEDO. R.N. was supported by Takeda Science Foundation. K.K. was supported by Toyota Physical & Chemical
Research Institute Scholars. The authors would like to thank the students of The Kawano lab. in Toyohashi University of Technology (2014 – 2016) and H. Oi for their work on the device fabrication.