Method Optimization of Deoxyribonucleic Acid (DNA)

Thin Films for Biotronics

by Thomas J. Proctor and Amethist S. Finch

ARL-TR-5691 September 2011

Approved for public release; distribution unlimited. 
NOTICES

Disclaimers

The findings in this report are not to be construed as an official Department of the Army position 

unless so designated by other authorized documents.

Citation of manufacturer’s or trade names does not constitute an official endorsement or 

approval of the use thereof.

Destroy this report when it is no longer needed. Do not return it to the originator.
Army Research Laboratory

Adelphi, MD 20783-1197

ARL-TR-5691 September 2011

Method Optimization of Deoxyribonucleic Acid (DNA)

Thin Films for Biotronics

Thomas J. Proctor and Amethist S. Finch

Sensors and Electron Devices Directorate, ARL

Approved for public release; distribution unlimited. 
ii

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently 

valid OMB control number.

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY)

September 2011

2. REPORT TYPE

Final

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Method Optimization of Deoxyribonucleic Acid (DNA) Thin Films for 

Biotronics

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Thomas J. Proctor and Amethist S. Finch

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Army Research Laboratory

ATTN: RDRL-SEE-O

2800 Powder Mill Road

Adelphi, MD 20783-1197

8. PERFORMING ORGANIZATION

 REPORT NUMBER

ARL-TR-5691

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)

11. SPONSOR/MONITOR'S REPORT

 NUMBER(S)

12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release; distribution unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

In today’s Army, there is a pressing need to improve the quality of the electronics used in the field. Some requirements 

include the fabrication of electronic devices that are cheaper, smaller, and lighter, all the while maintaining or even expanding 

their technical capabilities. An example of this research is the use of deoxyribonucleic acid (DNA) to create thin-film 

membranes that could be used in electronics. For example, these thin films have been successfully used in light-emitting 

diodes (LEDs) (1). However, this work focuses on the optimization of membrane fabrication parameters, such as when the 

sample volume should be added to the spin-coater, spin-coat speed, and solvent type. This can be accomplished by mixing a 

surfactant, cetyltrimethylammonium chloride (CTAC), with the DNA, causing DNA-cetyltrimethylammonium (DNA-CTMA) 

to precipitate out of solution. Then, the DNA-CTMA is redissolved in an organic solvent and spin-coated onto a silicon wafer 

to create the thin film. We demonstrated that certain conditions yield DNA-CTMA films that were thinner and more uniform. 

We envision that this work could be used in several electronic, photonic, and electro-optic applications.

15. SUBJECT TERMS

DNA, Organic Electronics, Bio-Electronics, Biotronics, Deoxyribonucleic Acid, CTAC, CTMA

16. SECURITY CLASSIFICATION OF:

17. LIMITATION

 OF 

 ABSTRACT

UU

18. NUMBER

OF 

 PAGES

20

19a. NAME OF RESPONSIBLE PERSON

Amethist S. Finch

a. REPORT

Unclassified

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassified

19b. TELEPHONE NUMBER (Include area code)

(301) 394-0326

Standard Form 298 (Rev. 8/98)

Prescribed by ANSI Std. Z39.18
iii

Contents

List of Figures iv

List of Tables iv

Acknowledgments v

1. Introduction 1

2. Experiment 2

2.1 Materials..........................................................................................................................2

2.2 Thin Film Fabrication......................................................................................................2

2.3 Organic Solvent Selection...............................................................................................3

2.4 Sample Volume Selection ...............................................................................................3

2.5 Thickness Measurements ................................................................................................4

2.6 Surface Characterization .................................................................................................4

3. Results and Discussion 4

3.1 Acquiring Thickness Data ...............................................................................................4

3.2 Sample Volume Added to the Spin-coater......................................................................4

3.3 Comparison of Spin-Coating Speed and Sample Volume ..............................................5

3.4 Solvent Comparisons.......................................................................................................6

4. Summary and Conclusions 9

5. References 10

List of Symbols, Abbreviations, and Acronyms 11

Distribution List 12
iv

List of Figures

Figure 1. A comparison of normal LEDs, (top) “Baseline” to the (bottom) DNA improved 

LEDs “BioLED” (1). .................................................................................................................1

Figure 2. Illustration of typical DNA-CTMA precipitate after centrifugation. ..............................3

Figure 3. Diagram of spin-coating method. First, the DNA-CTMA solution was pipetted 

onto the silicon wafer. Next, the solution was spread out over the wafer due the spinning. 

Finally, the silicon wafer was set aside to dry. ..........................................................................3

Figure 4. Thickness of the DNA-CTMA films for the various sample volumes at different 

spin-coating speeds. ...................................................................................................................6

Figure 5. Thickness of the DNA-CTMA films for the various sample volumes at different 

spin-coating speeds. ...................................................................................................................7

Figure 6. Shows a 3-D representation of the surface of the DNA-CTMA film in the ethanol 

solvent........................................................................................................................................8

Figure 7. Shows a 3-D representation of the surface of the DNA-CTMA film in the 

1-butanol solvent........................................................................................................................8

Figure 8. Shows a 3-D representation of the surface of the DNA-CTMA film in the 

isopropanol solvent. ...................................................................................................................8

List of Tables

Table 1. Sample thickness averaged together and the standard deviations in order to provide 

a comparison of when the sample volume should be added to the spin-coater. ........................5
v

Acknowledgments

Thomas J. Proctor wishes to acknowledge the mentorship of Dr. Amy Finch. Also, he would 

like to acknowledge the assistance and helpful advice throughout this research of Dr. Amy 

Manocchi, Dr. Dimitra Stratis-Cullum, and Dr. James Sumner. 
vi

INTENTIONALLY LEFT BLANK.
1

1. Introduction

In today’s technology-driven society, there is a need to improve the qualities of the electronics 

used. Some requirements are making electronic devices that are cheaper, smaller, and lighter, all 

while maintaining or even expanding, their technical capabilities. Today’s Army has been taking 

notice of all of these developments with the aim to applying them to the Soldier’s heavy and 

bulky electronics. One solution is to integrate biological material into the electronics. A material 

being considered for this integration is deoxyribonucleic acid (DNA). DNA is a good possibility 

because it is cheap, flexible, and lightweight.

One example of this research is using DNA to create thin-film membranes that could eventually 

be used in electronics. Professor Andrew Steckl of the University of Cincinnati and his coworkers used salmon sperm DNA to make light-emitting diodes (LEDs) brighter and last longer

(1). They used DNA-cetyltrimethylammonium (DNA-CTMA) films as an electron blocking 

layer in both green- and blue-emitting organic LEDs making them bio-organic LEDs. This 

resulted in 10 times higher efficiency, 30 times brighter output, and 3 times longer lifetime. As 

shown in figure 1, the LEDs in the top row are the “Baseline” without the DNA-CTMA film as 

an electron blocking layer and the LEDs in the bottom row have been altered with the DNACTMA film as an electron blocking layer. 

Figure 1. A comparison of normal LEDs, (top) “Baseline” to the 

(bottom) DNA improved LEDs “BioLED” (1).

Research in the photonics and optoelectronics fields have shown that thin films are necessary for 

organic electronic devices. They also need to be defect free and provide a surface that will allow 

for optimal packing of the semiconductor material. The packing efficiency will be affected by 

the uniformity and is also a function of the surfactant, DNA sequence, length, and molecular 

weight. Also, it has been shown that the quality of the devices improves when the films are 
2

thinner and more uniform (2). However, this research is mainly focused on the controlled 

fabrication of films that are more uniform and thinner than the previously reported 200-nm-thick 

films (2–4). In order to determine the conditions necessary to create similar films, salmon sperm 

DNA was used for these experiments. This work describes the optimization of parameters

including when the sample volume should be added to the spin-coater, sample volume, spin-coat 

speed, and solvent type. The goal of this work was to improve procedures in order to fabricate

uniform and reproducible DNA-CTMA films thinner than previously reported.

2. Experiment

2.1 Materials

All chemicals were purchased from Sigma-Aldrich (St Louis, MO) and were of the highest grade 

available. Cetyltrimethylammoniumchloride (CTAC) (25 wt. % solution), isopropyl alcohol, 

1-butanol (anhydrous, 99.8%), and ethanol (anhydrous, 200 proof, 99.5+%) were used as 

received. Salmon sperm DNA was purchased from Invitrogen (Carlsbad, CA) with a 

concentration of 10 mg/mL. Other materials used for the general procedure include a VortexGenie 2 (Scientific Industries, Bohemia, New York), a spin-coater (Laurell Technologies, North 

Wales, PA), sample mounts and silicon wafers (Ted Pella Inc., Redding, CA), an ellipsometer

(JA Woollam Co., Lincoln, Nebr), and an atomic force microscope (AFM) (VEECO, Nanoman, 

Monterey, CA).

2.2 Thin Film Fabrication

First, 10 μL of salmon sperm DNA, 2 μL of surfactant (CTAC), and 88 μL of deionized water 

were added to 1.5-mL Eppendorf conical polypropylene tubes with snap caps using Eppendorf 

pipettes, polymerase chain reaction (PCR) clean 10-μL tips, and PCR clean, dual-filter 200-μL 

tips. This solution was vortexed to form a DNA-surfactant complex (DNA-CTMA). Then, the 

solution was placed into an Eppendorf centrifuge. Running the centrifuge for 6 min at 

14000 rpm caused the DNA-CTMA to precipitate out of solution, as seen in the schematic 

diagram in figure 2. Afterwards, the supernatant was pipetted off using the same pipettes as 

before with new tips. This was repeated two more times with deionized water to wash the pellet. 

Next, the precipitate was placed in an Eppendorf vacufuge to vacuum dry for 30 min at 25 °C. 

The dried DNA-CTMA was then redissolved in an organic solvent. The silicon wafers were then 

cleaned using the spin-coater by adding 40 μL of isopropanol to the wafer and spin-coating at 

2000 rpm for 60 s. 
3

Figure 2. Illustration of typical DNA-CTMA precipitate after centrifugation. 

Finally, the redissolved DNA-CTMA solution was spin-coated to the cleaned silicon wafers, as 

illustrated in figure 3. The volume of solution and revolutions per minute changed based on the 

test being conducted.

Figure 3. Diagram of spin-coating method. First, the DNA-CTMA solution was pipetted onto the silicon 

wafer. Next, the solution was spread out over the wafer due the spinning. Finally, the silicon wafer 

was set aside to dry. 

2.3 Organic Solvent Selection

The solvents used in this research were isopropanol, 1-butanol, and ethanol. They were chosen 

because they are fairly volatile, they leave little or no residue after evaporation, and our sample 

(DNA-CTMA) is soluble in these solvents.

2.4 Sample Volume Selection

The thickness of a DNA-CTMA film can vary depending on the volume of solution used to coat 

the silicon wafers. For these experiments, certain volumes of sample solutions were spin-coated 

for 60 s on each of the silicon wafers. These volumes were 20, 20-20, 20-20-20, and 40 μL. In 

order to properly cover the wafers, the 20-20 and 20-20-20 μL volumes were completed in 
4

phases. In other words, 20 μL of solution were added, spin-coated then dried prior to adding the 

next layer. The 20-μL volume gave the opportunity to witness what a relatively small volume 

would be able to cover. While the 40-μL volume provided the opposite effect of having a large 

quantity to cover the silicon wafers. 

2.5 Thickness Measurements

The ellipsometer (JA Woollam Co., Lincoln, NE) was used for determining the thickness of 

DNA-CTMA layer on the silicon (Si) wafer. The thickness of the DNA-CTMA layer was 

calculated by using models with a 1-mm Si layer and a silicon dioxide (SiO2) layer of 

approximately 26 Å. Five measurements were taken on the wafer in different locations. The 

first was in the middle and the other four were near the corners of the silicon wafer. After these 

measurements were taken, they were averaged together to conclude a thickness with the standard 

deviation between the data points. 

2.6 Surface Characterization

Also, the surface topography of the wafers was examined using an AFM in tapping mode. First, 

the tips used in the AFM were changed to a Veeco (VEECO, Nanoman, Monterey, CA) tapping 

mode tip (model: OTESPA). Then, the laser was placed on the tip. Next, the video crosshairs 

were moved to locate the tip. After that the sample was placed on the stage, the tip reflection 

and surface images were focused. Then, the meter dot was adjusted to 0 V. Afterward, the tip 

was auto-tuned. The parameters were then set to a scan size of 0.5 to 1 μm, a scan rate of 

0.501 Hz, 256 samples per line, 256 lines, and the data type in height. Next, the tip was engaged. 

Once engaged, the integral gain and proportional gain were adjusted to give good tracking for the 

scan. Three or four scans were captured per sample. One scan was near the middle of the 

sample and the others were taken about halfway between the middle and the edge. 

3. Results and Discussion

3.1 Acquiring Thickness Data

The primary tool used to collect data for these experiments was the ellipsometer. The 

ellipsometer measures the change of light upon reflection of the sample. The change in the light

is determined by the sample’s thickness. A new model for the ellipsometry was created for each 

set of samples. The main difference in the models was that the thickness of the SiO2 layer would 

vary on the blank Si wafers. 

3.2 Sample Volume Added to the Spin-coater

First, we examined whether it was more beneficial to add the samples to the Si wafers before 

spinning or while spinning. This was tested by selecting two different volumes, 40 and 

20-20 μL, of the DNA-CTMA samples to be applied. The 40-μL volume was selected because 
5

the large quantity would have a greater impact in difference of coverage on the wafers. The 

20-20 μL volume was chosen to view the effects of the spinning during the multiple applications. 

The comparison done between the two volumes of sample was measured by having samples 

added to four Si wafers before the spinning would begin and four Si wafers while the wafers 

were spinning. In each case, two wafers were for the 20-20 μL sample and two wafers were for 

the 40-μL sample. All samples were run for 60 s at 2000 rpm. Table 1 shows the thickness,

determined by using ellipsometry, of the DNA-CTMA films prepared using the different spincoating methods. 

Table 1. Sample thickness averaged together and the standard deviations in order to provide a comparison of 

when the sample volume should be added to the spin-coater.

All of the samples that were added to the Si wafer before spinning were thinner than the samples 

prepared by adding DNA-CTMA while spinning. Also, the standard deviation of thickness was 

smaller for the “before spinning” samples, indicating that this method is more reproducible. 

3.3 Comparison of Spin-Coating Speed and Sample Volume

Next, we determined the optimal spin-coating speed and sample volume used to fabricate spincoated DNA-CTMA films. All four sample volume variations were used in this experiment. 

The samples were spin-coated for 60 s at five different speeds: 500, 1000, 2000, 3000, and 

4000 rpm. Figure 4 shows film thicknesses, determined by the ellipsometry measurements, of 

DNA-CTMA films prepared at five different spin-coating speeds. The thickness of the films 

decreased overall as spin-coating speed increased, but the different volumes of DNA-CTMA 

solution behaved differently. 

Before Spinning

Thickness 

(Å) vs.

Thickness 

(Å) While Spinning

B1-20-20 223.03 292.69 W1-20-20

B2-20-20 240.42 286.93 W2-20-20

Average 231.725 289.81 Average

Standard deviation 10.75 13.75 Standard deviation

B1-40 179.67 188.3 W1-40

B2-40 177.1 193.16 W2-40

Average 178.385 190.73 Average

Standard deviation 4.43 8.11 Standard deviation
6

Figure 4. Thickness of the DNA-CTMA films for the various sample volumes at different spin-coating speeds.

The thickness of films prepared from 20-μL volume had a negative trend as spin-coating speed 

increased. The 20-20 μL samples also had a negative trend in thickness between 500 and 

1000 rpm but then leveled off at higher speeds. The 20-20-20 μL samples had a negative trend

in thickness to 2000 rpm, but showed a slight increase in thickness to 4000 rpm. The 40-μL

DNA-CTMA sample showed a rapid decrease in film thickness between 500 and 1000 rpm, but 

then leveled off with a slight decrease across the other speeds. Even though the various volumes 

of sample behaved differently, at 4000 rpm, three out of the four samples gave a standard 

deviation less than 3Å between the five thickness measurements, indicating that this spin-coating 

speed yielded more uniform films.

3.4 Solvent Comparisons

Next, we compared three solvents used to dissolve DNA-CTMA. The solvent comparison was 

used to determine if another solvent was better than isopropanol to redissolve the DNA-CTMA. 

Therefore, an assessment was made to compare ethanol, 1-butanol, and isopropanol. This time 

only the 40-μL volumes were used. The 40-μL volume was chosen, because its film would be 

thinner at higher spin-coating speeds than the other sample volumes. This volume was also spincoated at various speeds: 2500, 3000, and 4000 rpm. 
7

Figure 5 shows the thickness, established by ellipsometry, of the DNA-CTMA films for the 

various solvents tested. Dissolving DNA-CTMA in isopropanol or ethanol gives similar trends. 

Both thicknesses decreased from 60 and 130 Å at 2500 rpm to 51 and 78 Å at 3000 rpm. The 

thicknesses increased slightly from 3000 to 4000 rpm. Although the trend in thickness was 

comparable, the thicknesses themselves were significantly different. 1-Butanol acted the 

complete opposite of the other two solvents. The thickness of the DNA-CTMA films increased 

from 31.17 Å at 2500 rpm to 54.31 Å at 3000 rpm and slightly decreased to 49.41 Å at 

4000 rpm. Dispersions in 1-butanol and isopropanol produce considerably thinner films 

compared to the ethanol solvent. These dispersions cause the DNA-CTMA to spread out, giving 

a thinner film. Also, 1-butanol has the highest boiling point (82.4 °C) of the three alcohol 

solvents; it produced the most uniform films. This means that the choice of solvent does have an 

impact on the thickness and uniformity of the DNA-CTMA films. 1-Butanol produced better 

films, because the films were thinner and more uniform than previously recorded. 

Figure 5. Thickness of the DNA-CTMA films for the various sample volumes at different spin-coating speeds.

Figures 6 through 8 are three-dimensional (3-D) representations of the DNA-CTMA film

surfaces from the samples spin-coated at 4000 rpm. 

2500 3000 4000

Ethanol 130.52 78.09 80.87

1-Butanol 31.17 54.31 49.41

Isopropanol 59.9 51.12 58.93

0

20

40

60

80

100

120

140

Film Thickness (Å)

Speed (rpm)

Optimizing Solvents
8

Figure 6. Shows a 3-D representation of the surface of the DNA-CTMA film in the ethanol solvent.

Figure 7. Shows a 3-D representation of the surface of the DNA-CTMA film in the 1-butanol solvent.

Figure 8. Shows a 3-D representation of the surface of the DNA-CTMA film in the isopropanol solvent.
9

4. Summary and Conclusions

The results of these three studies were used to determine the optimal fabrication conditions for 

DNA-CTMA thin films. Because of the low average thickness and low standard deviation, 

placing the sample on the Si wafers before spinning should work better. The results showed that 

this method produced a reproducible, more uniform film. The 40-μL volume showed that even 

at lower spin-coating speeds it had the ability to produce a thinner film. Also, a spin-coating 

speed of 4000 rpm should be used, because it allows the film to be thinner across the Si wafer. 

1-Butanol should be the solvent used due to better uniformity.

In conclusion, there are a variety of factors that can affect the thickness and uniformity of DNACTMA films. This project focused on controlling and optimizing these aspects, such as when 

the sample volume should be added to the spin-coater, sample volume, spin-coat speed, and 

solvent type. This work showed that some choices are better than others with regard to these 

factors. However, more work can and should be done. Future work should include the 

examination of different types of DNA beyond salmon sperm, DNA sequence, length, and 

molecular weight. This work will be useful in the preparation of thin films for several electronic

and electro-optic applications. 
10

5. References

1. Hagen, Joshua A.; Grote, James G.; Li, Wayne X.; Steckl, Andrew J.; Diggs, Darnell E.;

Zetts, John S.; Nelson, Robert L.; Hopkins, F. K. Organic Light Emitting Diode with a DNA 

Biopolymer Electron Blocking Layer. Proc. SPIE 6333 2006, 63330J, 

doi:10.1117/12.682251.

2. Heckman, E. M.; Hagen, J. A.; Yaney, P.; Grote, J. G.; Hopkins, F. K. Appl. Phys. Lett.

2005, 87, 211115.

3. Singh, B.; Sarcift ci, N. S.; Grote, J. G.; Hopkins, F. K. J. Appl. Phys. 2006, 100, 024514.

4. Singh, B.; Sarcift ci, N. S.; Grote, J. G. Bio-organic Optoelectronic Devices Using DNA. 

Adv. Polym. Sci. 2009, doi:10.1007/12_2009_6.
11

List of Symbols, Abbreviations, and Acronyms

AFM atomic force microscope 

CTAC cetyltrimethylammoniumchloride

DNA deoxyribonucleic acid 

DNA-CTMA DNA-cetyltrimethylammonium 

LEDs light-emitting diodes 

PCR polymerase chain reaction 

Si silicon 

SiO2 silicon dioxide 
12

NO. OF

COPIES ORGANIZATION

1 ADMNSTR

DEFNS TECHL INFO CTR

ATTN DTIC OCP

8725 JOHN J KINGMAN RD STE 0944

FT BELVOIR VA 22060-6218

1 CD OFC OF THE SECY OF DEFNS

ATTN ODDRE (R&AT) 

THE PENTAGON

WASHINGTON DC 20301-3080

1 US ARMY RSRCH DEV AND ENGRG CMND

ARMAMENT RSRCH DEV & ENGRG CTR

ARMAMENT ENGRG & TECHNLGY CTR

ATTN AMSRD AAR AEF T J MATTS

BLDG 305

ABERDEEN PROVING GROUND MD 21005-5001

1 US ARMY INFO SYS ENGRG CMND

ATTN AMSEL IE TD A RIVERA

FT HUACHUCA AZ 85613-5300

1 COMMANDER

US ARMY RDECOM

ATTN AMSRD AMR W C MCCORKLE

5400 FOWLER RD

REDSTONE ARSENAL AL 35898-5000

1 US GOVERNMENT PRINT OFF

DEPOSITORY RECEIVING SECTION

ATTN MAIL STOP IDAD J TATE

732 NORTH CAPITOL ST NW

WASHINGTON DC 20402

6 US ARMY RSRCH LAB

ATTN IMNE ALC HRR MAIL & RECORDS MGMT

ATTN RDRL CIO LL TECHL LIB

ATTN RDRL CIO MT TECHL PUB 

ATTN RDRL SEE O A FINCH

ATTN RDRL SEE O N FELL

ATTN RDRL SEE L BLISS

ADELPHI MD 20783-1197