DNA-Functionalized Gold Nanoparticles as Chemiresistive Vapor Sensing Elements

Kan Fu1, Wyatt Pedrick2, Han Wang1, Andrew LaMarche2, Xiaoqiang Jiang2, Brian G. Willis2

1Department of Materials Science and Engineering, 2Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269

Shihui Li, Yong Wang Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802

Introduction and Motivation Vapor Sensing – Array Response II

Vapor Sensing – Length Dependence

Background: Chemiresistors made of films of metal nanoparticles protected with organic ligands are extensively studied for sensing behavior for gas phase analytes. The structural element of this type of films is a metal nanoparticle core surrounded by a self-assembled monolayer shell. As gas phase analytes adsorb into the capping ligand layers, swelling of the films usually results in greater separation of the film, leading to an increase in electrical resistance. In addition, the adsorption vapor changes the dielectric constant of the AuNP film. Hence the chemiresistors can sense a wide variety of vapor and gas analytes. Selectivity of chemiresistors arises from variation in sorption behavior of analytes to different types of ligands. Due to the minute size of nanoparticles, gold-nanoparticle chemiresistors are compatible with microfabricated and nanofabricated structures.

Motivation: 1. Using DNA, a largen number of different sensors can be fabricated – theoretically, the

number of sensors scales with 4N. 2. Specific adsorption yet to be seen in any chemiresistive sensors. Small-molecule

functionalized AuNPs do not confer specificity. 3. DNA has been very recently used for modification of carbon nanotubes and graphene

for chemitransistors and fluorescence-based vapor sensors.

Equation for electron tunneling through a particulate film:

e-

V

- + As only a few percent of the active organic sensing materials are used, NP Chemiresistors have a few advantages over traditional chemiresistors • Reduced volume of organic sensing phase • Fast response • High sensitivity • Miniaturiaztion of devices

Conclusions

References

Financial support for this work was provided by the Office of Naval Research.

Acknowledgement

Name Sequence 10A /HS-C6H12/AAA AAA AAA A 50A /HS-C6H12/AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AA 25A /HS-C6H12/AAA AAA AAA AAA AAA AAA AAA AAA A 25T /HS-C6H12/TTT TTT TTT TTT TTT TTT TTT TTT T 25C /HS-C6H12/CCC CCC CCC CCC CCC CCC CCC CCC C S2 /HS-C6H12/TTT TTA CTC CTT TTC CTC CTC TTT T

DNA-Functionalized Gold Nanoparticles

+

- e-

-

-

-

Preparation method:

ss-DNA sequences

Humidity Effects

Effect of relative humidity (RH) on baseline resistance of DNA-AuNP chemiresistive films (left), as compare to alkanethiol-AuNP chemiresistive films (middle). R/R0 is the ratio of baseline resistance at a specific RH to the resistance at RH = 0%. For all DNA-AuNP sensors, R/R0 increases in the range RH = 0% to 40%, and then decreases rapidly, reaching 0.01 above RH = 50%. In comparison, typical alkanethiol-AuNP sensors made by monolayer-protected clusters show monotonic trend with water. The distinctive behavior of DNA-AuNP films indicates strong influence of water vapor on the sensors. Nyquist plots (right) show single semicircle at low RH levels, indicating an electron-transfer-limited process. At high RH above 50%, a linear response appears in the low frequency region, characteristic of diffusion-limited charge transfer process. The source of this diffusion limited charge transfer is ion diffusion/ transport in the polyelectrolyte (DNA). At very high RH (84% to 100%), the linear portion of the curve becomes increasingly vertical, representing increasing capacitive behavior – a result of ionic conduction being the dominant conduction mechanism.

Fluorescence-based complementary base-paring tests confirm the number of ss-DNA strands per nanoparticle to be approximately 40.

Vapor Sensitivity (ΔR/R)/(p/p0)

10A 50A

Toluene 0.41 1.65

Ethanol 0.35 2.06

Hexane 0.24 0.71

DMMP 0.18 0.47

Real-time sensing plot of toluene and water vapor at p/p0 = 0.5

Sensitivity

Response patterns of 10A and 25A sensors towards 4 common organic vapors across the full concentration range.

DNA-AuNP chemiresistive sensors are • similar to alkanethiol-AuNP sensors in terms of response speed and

stability.

• Response to organic vapors scales with oligonucleotide chain length.

• As the effect of water is unique at high RH levels, which invovles ionic conduction dominance, response to water vapor does not scale with chain length.

• For all other organic vapors, the ΔR/R values are all positive, indicating a swelling-dominated sensor-analyte interaction. Response mostly increases with vapor concentration.

• Toluene may induce conduction pathways in addition to simple swelling.

• Saturation behavior is observed on all sensors at p/p0 greater than 0.3.

• DNA-AuNP sensors are more reliable at lower vapor pressures (p/p0 < 0.3).

• Sensitivity of DNA-AuNP sensors on the same order of magnitude as those of alkanethiol-AuNP sensors.

• Stronger interaction with polar vapors and weaker interaction with non-polar vapors.

Vapor Sensing – Array Response I

As DNA-AuNP sensors are sensitive to water vapor, their sensing behavior towards low organic vapor concentrations as a function of relative humidity (RH) were studied. Under the two different conduction regions, response patterns are very different.

Real-time response of four types of DNA-functionalized gold nanoparticle sensors on hexane vapor at RH = 0% with p/p0 = 0.012, 0.024, and 0.036

Real-time response of a S2 sensor against ethanol vapor equivalent to p/p0 = 0.036 at seven RH levels ranging from 0% to 99%

25A

25T

25C

S2 • Positive ΔR/R at RH from 0% to 30%.

• Negative ΔR/R at RH from 40% and above

• The increase in response over dry state sensors

could partially be attributed to the increase in chain flexibility due to hydration.

• At even higher RH, the sensors again become less sensitive to organic vapors.

3D bar charts of sensor response to five vapors across all RH levels (0%−99%) for (a) ethanol, (b) methanol, (c) hexane, (d) DMMP, and (e) toluene. Concentrations are p/p0 = 0.036 for all five vapors

1. H. Wohltjen, and A. W. Snow, “Colloidal Metal−Insulator−Metal Ensemble Chemiresistor Sensor,” Analytical Chemistry, vol. 70, no. 14, pp. 2856-2859, 1998/07/01, 1998.

2. C. Staii, A. T. Johnson, M. Chen, and A. Gelperin, “DNA-Decorated Carbon Nanotubes for Chemical Sensing,” Nano Letters, vol. 5, no. 9, pp. 1774-1778, 2005/09/01, 2005.

3. J. White, K. Truesdell, L. B. Williams, M. S. AtKisson, and J. S. Kauer, “Solid-State, Dye-Labeled DNA Detects Volatile Compounds in the Vapor Phase,” PLoS Biol, vol. 6, no. 1, pp. e9, 2008.

4. G. Peng, U. Tisch, O. Adams, M. Hakim, N. Shehada, Y. Y. Broza, S. Billan, R. Abdah-Bortnyak, A. Kuten, and H. Haick, “Diagnosing lung cancer in exhaled breath using gold nanoparticles,” Nat Nano, vol. 4, no. 10, pp. 669-673, 2009

5. J. Liu, and Y. Lu, “Preparation of aptamer-linked gold nanoparticle purple aggregates for colorimetric sensing of analytes,” Nat. Protocols, vol. 1, no. 1, pp. 246-252, 2006.

6. K. Fu, S. Li, X. Jiang, Y. Wang, and B. G. Willis, “DNA Gold Nanoparticle Nanocomposite Films for Chemiresistive Vapor Sensing,” Langmuir, 2013. (Accepted)

Temperature dependence of response

Vapor

LOD (ppm)

DNA (RH = 0%) DNA (RH = 50%) octanethiol hexanethiol

Ethanol 475 266 4.9 to 49 242

Methanol 171 145 150 326

Toluene 211 32 0.082 to 2.3 48

Sensitivity

Limits of detection with reference to alkanethiol-AuNP sensors

• Response patterns of sensors with 4 different types of DNA are distinctive, therefore offering vapor identification capabilities.

• High sensitivity appears at intermediate RH levels

• At very high RH levels, the sensors could be highly hydrated, and sensor response is dominated by water vapor

• Higher temperature disfavor vapor adsorption, therefore at 40°C the sensors become unresponsive to methanol, hexane and DMMP.

• Sensors remain sensitive to toluene at 40°C, suggesting stronger affinity of DNA towards toluene vapor.

• Higher sensitivity in humid (RH = 50%)atmosphere as compared to dry atmosphere (RH = 0%).

• Comparable LODs as compared to alkanethiol-AuNP chemiresistive sensors

• High sensitivity to toluene which could arise from favorable interactions with DNA

Heat map shows the average sensor responses towards organic vapors at three different temperatures and their trends with respect to RH.

RH (%)

RH (%) Vapor Sensitivity a

25A 25T 25C S2

0

Ethanol 0.35 0.11 0.92 0.31

Methanol 0.14 0.44 0.2 0.75

Hexane 0.69 0.23 1.22 1.37

DMMP 0 0.23 0.12 0.38

Toluene 0.82 0.19 0.35 0.23

50

Ethanol -2.17 -0.72 -1.06 -1.91

Methanol -9.45 -3.09 -7.85 -7.64

Hexane -1.59 -2.13 -4.5 -3.5

DMMP -2.83 -0.64 -0.66 -0.9

Toluene -9.03 -2.36 -5.64 -5.58

aDefined using Slope from linear approximation of ΔR/R−p/p0 plots

• DNA-AuNP chemiresistive sensors can be made through drop-casting of DNA-functionalized gold nanoparticles.

• Simple readout of electric responses through source measurement units. • DNA-AuNP sensors have similar swelling behavior at low RH, but is dominated by water

vapor at higher RH. • Comparable response compared to alkanethiol-AuNP sensors in terms of response patterns,

but enhanced array dimensions. • Due to high sensitivity to water vapor, RH-related control or correction mechanisms needed

for real-world application.

Ongoing and Future Work

• Principal component analysis of DNA-AuNP sensor arrays to demonstrate application in “electronic nose”

• Engineering specificity for target analytes • Exploring solution-based chemiresistive sensing with DNA-AuNP sensors