Understanding the propagation of LED light in the brain tissue can facilitate the advanced development of LED based neuroprosthetic devices for optogenetic applications. The attenuation coefficient of blue LED light in thin tissue slices and Parylene-C films were quantified, which is 19.9 cm-1 and 1.70 cm-1, respectively. Optical simulations in TracePro show good agreement with the experiments. As a revolutionary neuromodulation technology, optogenetics offers remote manipulation on neural activities of genetically-targeted neural cells with millisecond temporal precision through light illumination. Compared to electrical stimulation, optogenetics has unique benefits including specificity control of neural cell types as well as minimal artifacts and instrumental interferences with electrophysiological recording. Application of optogenetics in neuroscience studies has created an increasing need for the development of light sources and the instruments for light delivery. Among various light sources, micro-light-emitting diodes (μ-LEDs) are favored for its high power efficiency, low cost, and capability of complex system integration. Successful in-vivo optogenetic stimulation on neural cells with the employment of μ-LEDs has been widely reported.

1. SEMINAR on
“OPTICAL PROPAGATION OF BLUE LED LIGHT IN BRAIN TISSUE AND
PARYLENE-C USED IN OPTOGENETICS”
PRESENTED BY
MANJUNATH PUJAR
USN:4SM15EC409
UNDER THE GUIDENCE OF CO-ORDINATOR
1) Kum. FARZANA PARVEEN B A M.tech Sri. SIDDESH K B M.tech
Asst. Prof. Dept. of E & CE Asso. Prof. Dept. of E&CE
SJMIT, Chitradurga SJMIT, Chitradurga
2) Kum. NANDINI G R M.tech
Asst. Prof. Dept. of E & CE
SJMIT, Chitradurga
DEPT. OF ELECTRONICS AND COMMUNICATION, SJMIT, CHITRADURGA

2. INTRODUCTION
 As a revolutionary neuromodulation technology, optogenetics offers remote manipulation on
neural activities of genetically-targeted neural cells with millisecond temporal precision through
light illumination.
 Compared to electrical stimulation, optogenetics has unique benefits including specificity control
of neural cell types as well as minimal artifacts and instrumental interferences with
electrophysiological recording.
 Application of optogenetics in neuroscience studies has created an increasing need for the
development of light sources and the instruments for light delivery.
 Among various light sources, micro-light-emitting diodes (μ-LEDs) are favored for its high power
efficiency, low cost, and capability of complex system integration. Successful in-vivo optogenetic
stimulation on neural cells with the employment of μ-LEDs has been widely reported.

3. OPTOGENETICS
 It is a combination of genetic and optical methods to exert control over targeted
cells within living tissue.
 In wild, Unicellular algae -Known as chlamydomonas and natronomonas produce
proteins called opsins. There are many different types.
 But the most important ones to researchers are
: Channelrhodopsin (ChR), Channelrhodopsin-2 (ChR2), and Halorhodopsin.
 These proteins have the power to convert sunlight to electrical charges by way of
moving ions across the cell membrane

5. SIX STEPS TO OPTOGENETICS ARE
Create a genetic
construct- Transfection
Insert construct into virus
Inject virus into mammal
Insert optrode: fibre optic
cable+electrode
Laser light opens ion
channels in neurons
Record behavioual
results

6. HOW OPTOGENETICS WORKS
By shining light into the mouses brain with fiber optics, researchers stimulate the targeted nerve cells, for
example to make the mouse run in circles or train it to feel pleasure when entering into a certain room.
The virus infects certain nerve cells with the algae protien making them respond to light.
The protien is inserted into a special virus, and researchers inject the virus into the mouse’s brain.
Biologists extracts a light sensitive protien from a kind of pond algae.

7. Sequence

8. Transfection process
• The word transfection is a blend of trans- and
infection. Transfection is the process of deliberately
introducing nucleic acids into cells. Transfection of
animal cells typically involves opening transient pores
or "holes" in the cell membrane to allow the uptake of
material.
• Transfection methods are focused on the construction
of vectorsandpromoters.

10. ADVANCED METHOD
 By considering these all analysed parameters neuroscientists discovered
the optogenetics by using µ-LED coated with Parylene-C
 All steps are same those are included in existing system but the advanced
technology is that instead of using optical fiber, neuroscientists are came
up with optogenetics by using µ-LED coated with Parylene-C

11. FABRICATION OF µ-LED
NEURAL STIMULATOR ON
PARYLENE SUBSTRATE
(a) Parylene-C and copper deposition
(b) Copper patterning
(c) photoresist coating and patterning
(d) applying low melting point (LMP)
solder
(e) μ-LED assembly;
(f) photoresist removal
(g) Parylene-C deposition
(h) peeling μ-LED stimulators off
silicon substrates.

12. FABRICATED µ-LED
(a) A fabricated μ-LED neural stimulator with light illumination.
(b )Microscopic image of the assembled μ-LED chip at 40x magnification.
(c) Microscopic image of the assembled μ-LED chip at 100x magnification.

13. PARYLENE-C
Parylene-C is known as an optically transparent polymer coating material,
which has many prominent advantages such as
• high chemical and biological stability,
• hydrolysis resistance,
• non-toxic and most importantly,
• biocompatibility.
Parylene-C is selected in this study because it has been widely used in the construction of neural implant devices.
During the experiments, the thickness of the tissues slices was estimated by measuring the difference in microscope
focusing distance between the top and bottom surfaces of the tissue slices.
The thicknesses of the Parylene were measured using a profilometer.
The recorded thicknesses were used for drawing and analyzing the relationship between attenuation ratio and the thickness
of rat brain tissue slices or Parylene-C films.

14. When light travels through a medium with thickness t and attenuation coefficient α,
the exponential decay of light can be calculated using the following equation
Two types of samples were explored:
• Brain tissue slices with a thickness range of 100-300 μm:
The brain tissue slices were collected from a rat that was perfused transcardially with 0.5L of
0.9% saline followed by 1.0L of a 10% formalin solution.
• Parylene-C films with a thickness range of 15-100 μm:
Parylene-C is known as an optically transparent polymer coating material, which has many
prominent advantages such as high chemical and biological stability, hydrolysis resistance, non-toxic and
most importantly, biocompatibility
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15. EXPERIMENTAL SETUP
(a) Experimental setup for measuring the
light attenuation through different
materials
(b) Schematic illustration of the
measurement setup

16. Attenuation coefficient of brain tissue slices with different time durations for exposure
Figure: Attenuation coefficient of LED light through brain tissue slices after exposed in air at room
temperature for different time durations

17. Simulation setup in Tracepro
Figure: TracePro model for device simulation.

18. μ-LED light through rat brain tissue slices
Figure: Attenuation coefficient of μ-LED light through fixed rat brain tissue slices, collected from the experiment
(a) and the simulation (b). Simulation was done using both the LED and laser as the light source.

19. μ-LED light through Parylene-C
Figure: Attenuation coefficient of μ-LED light through Parylene-C, collected from the experiment (a) and
the simulation (b). Simulation was done using both the LED and laser as the light source.

20. ADVANTAGES
 Optogenetics is less invasive than electrical stimulation
 Response time is faster than other treatments
 Activate or stop certain groups of neurons in the circuits with a precise
electrophysiology

21. DISADVANTAGES
 Limitations include the introducing a foreign gene into the humanbrain
 Cost effective
 Reports of depression and causing falls

22. APPLICATIONS OF µ-LED LIGHT
• Optogenetics
• Neuroprosthetics
• Neuromodulation technology

23. APPLICATIONS OF OPTOGENETICS
Optogeneticsareusedinmedicalfieldtocure-
 Anxiety
 Addiction
 Chronicpain
 Sleepdisorders
 Attention
 DeficitDisorder
 Migraine

27. For: And For:

29. REFERENCES
[1] Tian Xie*, Xiaopeng Bi, Rui Luo, Fan Bin, Zhe Wang, Wen Li ” Optical Propagation of Blue LED Light in
Brain Tissue and Parylene-C” , Proceedings of the 12th IEEE International Conference on Nano/Micro
Engineered and Molecular Systems April 9-12, 2017, Los Angeles, USA
[2] F. Zhang, et al., “Circuit-breakers: optical technologies for probing neural signals and systems,” Nature
Reviews Neuroscience, vol. 8, no. 8, pp. 577–581, 2007.
[3] H.S. Mayberg, et al., “Deep brain stimulation for treatment-resistant depression,” Neuron, vol. 45, no. 5,
pp. 651–660, 2005.
[4]K. Y. Kwon, B. Sirowatka, A. Weber, and W. Li, "Opto-μECoG array: A hybrid neural interface with
transparent μECoG electrode array and integrated LEDs for optogenetics," IEEE Trans. Biomed. Circuits
Syst., vol. 7, no. 5, pp. 593-600, 2013.

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