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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 13 — Jun. 22, 2009
  • pp: 11230–11235
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Polyaniline/polystyrene single-nanowire devices for highly selective optical detection of gas mixtures

Fuxing Gu, Xuefeng Yin, Huakang Yu, Pan Wang, and Limin Tong  »View Author Affiliations


Optics Express, Vol. 17, Issue 13, pp. 11230-11235 (2009)
http://dx.doi.org/10.1364/OE.17.011230


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Abstract

By using spectral analysis in the visible/near-infrared region, we demonstrate a single waveguiding polyaniline/polystyrene nanowire for highly selective detection of gas mixtures with a NH3 detection limit on parts-per-million level and relative humidity sensing ranging from 37% to 84%. The compact and flexible sensing scheme shown here may be attractive for highly selective optical detection in complex chemical or biological environments with a single nanowire.

© 2009 OSA

1. Introduction

Gas detection is particularly important in both environmental protection and human health. In recent decades, polyaniline (PANI) has been widely used for electrical or optical detection of a variety of gases such as HCl, NH3, H2S and NO2, due to its reversible optical and electrical response to certain gas species, as well as easy processing and environmental stability [1

1. J. X. Huang, S. Virji, B. H. Weiller, and R. B. Kaner, “Polyaniline nanofibers: facile synthesis and chemical sensors,” J. Am. Chem. Soc. 125(2), 314–315 (2003). [CrossRef] [PubMed]

9

9. X. B. Yan, Z. J. Han, Y. Yang, and B. K. Tay, “NO2 gas sensing with polyaniline nanofibers synthesized by a facile aqueous/organic interfacial polymerization,” Sens. Actuators B Chem. 123(1), 107–113 (2007). [CrossRef]

]. Recently, there has been a move towards making nanoscale sensors using single PANI-based nanowires due to the high surface-to-volume ratios that facilitate the diffusion of gas molecules into the structures [4

4. H. Q. Liu, J. Kameoka, D. A. Czaplewski, and H. G. Craighead, “Polymeric nanowire chemical sensor,” Nano Lett. 4(4), 671–675 (2004). [CrossRef]

,6

6. N. T. Kemp, D. McGrouther, J. W. Cochrane, and R. Newbury, “Bridging the gap: polymer nanowire devices,” Adv. Mater. 19(18), 2634–2638 (2007). [CrossRef]

]. To date, most of these single-nanowire devices rely on the electrical conductance change when exposed to the gas species. However, in electrical response, it is difficult to determine individual responses in gas mixtures with cross-sensitivity. So far selective multicomponent detection on a single-nanowire scale has not been realized, although integrated nanowire arrays have been reported for selective multicomponent detection based on multiple-nanowire electrical responses [10

10. L. Senesac and T. G. Thundat, “Nanosensors for trace explosive detection,” Mater. Today 11(3), 28–36 (2008). [CrossRef]

13

13. M. C. McAlpine, H. Ahmad, D. W. Wang, and J. R. Heath, “Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors,” Nat. Mater. 6(5), 379–384 (2007). [CrossRef] [PubMed]

]. In contrast to electrical schemes, optical sensing offers more options for signal retrieval from optical intensity, spectrum, phase, polarization, and fluorescence lifetime, and may offer possibility for selective detection of gas mixtures using a single sensing element [14

14. D. A. Skoog, D. M. West, F. J. Holler, and S. R. Crouch, Fundamental of Analytical Chemistry (Brooks Cole, 2004).

16

16. D. J. Sirbuly, S. E. Letant, and T. V. Ratto, “Hydrogen sensing with subwavelength pptical waveguides via porous silsesquioxane-palladium nanocomposites,” Adv. Mater. 20(24), 4724–4727 (2008). [CrossRef]

].

Most recently, using the evanescent coupling method, the waveguiding polymer single nanowires drawn from solvated polymers have been demonstrated for gas sensing with extraordinary fast response and high sensitivity [17

17. F. X. Gu, L. Zhang, X. F. Yin, and L. M. Tong, “Polymer single-nanowire optical sensors,” Nano Lett. 8(9), 2757–2761 (2008). [CrossRef] [PubMed]

]. Owing to its high efficiency and compactness, the evanescent coupling between a nanowire and a nanoscale fiber taper enables broadband light launching and collection from the nanowire with wavelengths selected for spectral analysis in the visible/near-infrared (VIS/NIR) region [17

17. F. X. Gu, L. Zhang, X. F. Yin, and L. M. Tong, “Polymer single-nanowire optical sensors,” Nano Lett. 8(9), 2757–2761 (2008). [CrossRef] [PubMed]

20

20. K. J. Huang, S. Y. Yang, and L. M. Tong, “Modeling of evanescent coupling between two parallel optical nanowires,” Appl. Opt. 46(9), 1429–1434 (2007). [CrossRef] [PubMed]

]. The spectral selectivity could provide identity information of an analyte at multiple wavelengths; thus the possibility to determine a multicomponent mixture using a waveguiding single nanowire could be realized [14

14. D. A. Skoog, D. M. West, F. J. Holler, and S. R. Crouch, Fundamental of Analytical Chemistry (Brooks Cole, 2004).

]. In this work, we demonstrate a facile approach to highly selective optical detection of gas mixtures of NH3 and humidity using a single waveguiding polyaniline/polystyrene (PANI/PS) nanowire in the VIS/NIR region, in which optical absorption bands change of PANI is used for NH3 sensing, and the coupling efficiency change between the PANI/PS nanowire and the nanoscale fiber tapers is used for relative humidity (RH) sensing. Our results show that a polymer single nanowire is very promising for developing highly sensitive optical sensors to detect individual responses in complex chemical and biological mixtures.

2. Sensor configuration

Due to the poor mechanical property of PANI [21

21. A. Pud, N. Ogurtsova, A. Korzhenkob, and G. Shapovala, “Some aspects of preparation methods and properties of polyaniline blends and composites with organic polymers,” Prog. Polym. Sci. 28(12), 1701–1753 (2003). [CrossRef]

], it is essential to blend it with soluble matrix polymers to fabricate waveguiding nanowires with good mechanical property and low optical loss. Here, polystyrene (PS) is used to blend with PANI due to its compatibility with PANI and excellent optical properties, such as good transparency in VIS/NIR region and high refractive index (about 1.59). PANI/PS nanowires are fabricated by direct drawing of a polymer-blend solution of 2 wt % PANI (M w = 50 000; Fluka) doped with 10-camphorsulfonic acid (Alfa Aesar) and 5 wt % PS (M w = 100 000; Alfa Aesar) in chloroform [4

4. H. Q. Liu, J. Kameoka, D. A. Czaplewski, and H. G. Craighead, “Polymeric nanowire chemical sensor,” Nano Lett. 4(4), 671–675 (2004). [CrossRef]

,17

17. F. X. Gu, L. Zhang, X. F. Yin, and L. M. Tong, “Polymer single-nanowire optical sensors,” Nano Lett. 8(9), 2757–2761 (2008). [CrossRef] [PubMed]

]. As-fabricated PANI/PS nanowire is placed across a 250-μm-width MgF2 microchannel and two ends of the nanowire are coupled to fiber tapers with an overlap of a few micrometers as shown in Fig. 1(a)
Fig. 1 (a) Schematic diagram of a nanowire sensing device. (b) Optical micrographs of a 370-nm-diameter nanowire guiding a 633-nm light. Scale bar, 50 μm. The white arrow indicates the direction of light propagation. (c) Optical micrograph of a nanowire device. Scale bar, 1 cm.
, where the close contact between the nanowire and the fiber taper can be maintained by Van der Waals or electrostatic attraction [18

18. L. M. Tong, R. R. Gattass, J. B. Ashcom, S. L. He, J. Y. Lou, M. Y. Shen, I. Maxwell, and E. Mazur, “Subwavelength-diameter silica wires for low-loss optical wave guiding,” Nature 426(6968), 816–819 (2003). [CrossRef] [PubMed]

,19

19. L. M. Tong, J. Y. Lou, R. R. Gattass, S. L. He, X. W. Chen, L. Liu, and E. Mazur, “Assembly of silica nanowires on silica aerogels for microphotonic devices,” Nano Lett. 5(2), 259–262 (2005). [CrossRef] [PubMed]

]. For robust gas sensing, the tapering region on MgF2 substrate are firmly bound at both sides using low-index UV-cured fluoropolymer (EFIRON PC-373; Luvantix Co. Ltd.). For reference, Fig. 1(b) shows an optical microscope image of a 370-nm-diameter PANI/PS nanowire guiding a 633-nm light while being supported and coupled with two fiber tapers. The total coupling loss between the nanowire and the nanotapers is typically around 10 dB.

The sensor elements are sealed in a poly(methyl methacrylate) chamber (Fig. 1(c)) with a vapor inlet/outlet and a hygrometer monitoring the humidity. The analyte gas diluted with air is introduced into the chamber at a flow rate of about 100 mL/min and the output of the nanowire is measured simultaneously. The broadband light is from a fiber-coupled supercontinuum source (SC450, Fianium Ltd.), and the 633-nm and 808-nm light sources are from continuous wave lasers.

3. Experimental results and discussions

It is well known that camphorsulfonic acid doped PANI shows the emeraldine salt (ES) form and can be transferred to the emeraldine base (EB) form when exposed to NH3 [1

1. J. X. Huang, S. Virji, B. H. Weiller, and R. B. Kaner, “Polyaniline nanofibers: facile synthesis and chemical sensors,” J. Am. Chem. Soc. 125(2), 314–315 (2003). [CrossRef] [PubMed]

3

3. S. Christie, E. Scorsone, K. Persaud, and F. Kvasnik, “Remote detection of gaseous ammonia using the near infrared transmission properties of polyaniline,” Sens. Actuators B Chem. 90(1-3), 163–169 (2003). [CrossRef]

]. The ES and EB forms absorb light at different spectral regions, which can be used for optical sensing. The output spectral intensity of a 370-nm-diameter PANI/PS nanowire in dry air is shown in Fig. 2(a)
Fig. 2 (a) Output intensity of a 370-nm-diameter PANI/PS nanowire versus wavelength in dry air without NH3 (gray line) and with 20 ppm NH3 (black line). (b) Absorption spectra of the 370-nm-diameter PANI/PS nanowire exposed to dry air with NH3 concentrations from 0.5 to 32 ppm. Inset shows the NH3-concentration dependence of ΔA 600-835.
(gray line). Upon exposure to 20 ppm NH3 diluted with dry air, a decrease in intensity of around 600-nm wavelength and an increase of around 830-nm wavelength are observed (black line), suggesting that ammonia gas molecules diffuse into the nanowire and deprotonate PANI from ES form to EB form. It should be noticed that a pure PS nanowire is non-dissipative within the spectral range and shows no detectable optical response to NH3 in dry air.

The absorbance of light guided along the nanowire (defined as A r = log [I 0/I], where I 0 and I are the output intensity in the absence and presence of the analyte gas, respectively) at a single wavelength λ can be expressed as [14

14. D. A. Skoog, D. M. West, F. J. Holler, and S. R. Crouch, Fundamental of Analytical Chemistry (Brooks Cole, 2004).

,15

15. D. J. Sirbuly, A. Tao, M. Law, R. Fan, and P. D. Yang, “Multifunctional nanowire evanescent wave optical sensors advanced materials,” Adv. Mater. 19(1), 61–66 (2007). [CrossRef]

]

Ar(λ)=κλεληλbc+An,
(1)

where κλ, ελ, and ηλ is the coupling efficiency between the nanowire and the nanotapers, the nanowire absorptivity, and the fractional energy confined in the nanowire at the wavelength λ, respectively; and An is the attenuation induced by optical scattering and/or background absorbance. The output intensity spectrum in dry air is used as a reference; thus the absorption spectra of the 370-nm-diameter PANI/PS nanowire exposed to NH3 diluted with dry air with concentrations from 0.5 to 32 ppm can be obtained (see Fig. 2(b)). The absorption spectra show a peak around 600 nm (λ max) that increases monotonously with the increasing NH3 concentrations, and a valley (λ min) around 835 nm that decreases monotonously with the increasing NH3 concentrations. Because of the opposite response of the nanowire to NH3 at λ max and λ min, the differential absorbance (defined as ΔA λ1-λ2 = A r(λ 1) - A r(λ 2)) between the λ max and λ min can be used to quantify the NH3 concentrations with enhanced sensitivity [14

14. D. A. Skoog, D. M. West, F. J. Holler, and S. R. Crouch, Fundamental of Analytical Chemistry (Brooks Cole, 2004).

]. The NH3-concentration dependence of the ΔA 600-835 is plotted in the inset of Fig. 2(b). The near linear dependence of the ΔA 600-835 with the NH3 concentration (< 10 ppm) indicates that the PANI/PS nanowire could function as a NH3 optical sensor in dry air. With the increase in NH3 concentration (e.g., > 15 ppm), the A r shows a nonlinear NH3 dependence, which can be contributed to the saturation at high NH3 concentrations due to the limited number of imine-nitrogen sites that can be protonated in the nanowire [4

4. H. Q. Liu, J. Kameoka, D. A. Czaplewski, and H. G. Craighead, “Polymeric nanowire chemical sensor,” Nano Lett. 4(4), 671–675 (2004). [CrossRef]

,5

5. J. Jang, J. Ha, and J. Cho, “Fabrication of water-dispersible polyaniline-poly(4-styrenesulfonate) nanoparticles for inkjet-printed chemical-sensor applications,” Adv. Mater. 19(13), 1772–1775 (2007). [CrossRef]

].

Water molecules are ubiquitous in the environment and humidity is a parameter that must be considered in a PANI-based device for reliable NH3 sensing [3

3. S. Christie, E. Scorsone, K. Persaud, and F. Kvasnik, “Remote detection of gaseous ammonia using the near infrared transmission properties of polyaniline,” Sens. Actuators B Chem. 90(1-3), 163–169 (2003). [CrossRef]

,22

22. M. Matsuguchi, A. Okamoto, and Y. Sakai, “Effect of humidity on NH3 gas sensitivity of polyaniline blend films,” Sens. Actuators B Chem. 94(1), 46–52 (2003). [CrossRef]

,23

23. A. Vijayan, M. Fuke, R. Hawaldar, M. Kulkarni, D. Amalnerkar, and R. C. Aiyer, “Sens. “Optical fibre based humidity sensor using Co-polyaniline clad,” Sens. Actuators B Chem. 129(1), 106–112 (2008). [CrossRef]

]. While it is difficult to determine individual responses in gas mixtures of NH3 and humidity with a single PANI-based nanowire by electrical detection [22

22. M. Matsuguchi, A. Okamoto, and Y. Sakai, “Effect of humidity on NH3 gas sensitivity of polyaniline blend films,” Sens. Actuators B Chem. 94(1), 46–52 (2003). [CrossRef]

], here we employ a single PANI/PS nanowire for RH sensing based on a RH-dependent evanescent coupling efficiency between the PANI/PS nanowire and the nanoscale fiber tapers. Figure 3(a)
Fig. 3 (a) Absorption spectra of a 350-nm-diameter PANI/PS nanowire exposed to air with RH ranging from 37% to 84%. (b) RH-concentration dependence of A r at wavelengths of 617-, 770-, and 860 nm, respectively.
gives the absorption spectra of a 350-nm-diameter PANI/PS nanowire with RH ranging from 37 to 84%. It shows that the valleys in the absorption spectra around the wavelengths of 617-, 770- and 860 nm decrease with increasing RH level. The distinct response spectra for humidity and NH3 (in Fig. 2) are apparent. It can be used to identify the response to humidity and NH3 using multiple-wavelength measurement. The behavior can be explained as follows: as the RH increases, the refractive index of the PANI/PS nanowire decreases as a result of diffusion of water molecules and subsequently changes the coupling efficiency, resulting in RH-dependent intensity measured at the output end [20

20. K. J. Huang, S. Y. Yang, and L. M. Tong, “Modeling of evanescent coupling between two parallel optical nanowires,” Appl. Opt. 46(9), 1429–1434 (2007). [CrossRef] [PubMed]

,23

23. A. Vijayan, M. Fuke, R. Hawaldar, M. Kulkarni, D. Amalnerkar, and R. C. Aiyer, “Sens. “Optical fibre based humidity sensor using Co-polyaniline clad,” Sens. Actuators B Chem. 129(1), 106–112 (2008). [CrossRef]

]. Figure 3(b) shows the RH-dependent Ar of the nanowire with RH ranging from 37 to 84% at the wavelengths of 617-, 770- and 860 nm, respectively. It suggests that the PANI/PS nanowire could operate as a RH sensor within the range of 37% and 84%.

To test the capability of selective detection of NH3 and humidity in gas mixtures, the PANI/PS nanowire is first exposed to 70% RH air, and then to 5 ppm NH3 diluted with 84% RH air (2-minute exposure). Figure 4
Fig. 4 Output intensity spectra of a 350-nm-diameter PANI/PS nanowire in 70% RH (gray line) and 5 ppm NH3 diluted with 84% RH air (black line). Inset, absorption spectrum of the PANI/PS nanowire to 5 ppm NH3 diluted with 84% RH air.
shows the output intensity spectra of the 350-nm-diameter PANI/PS nanowire in 70% RH air (gray line) and 5 ppm NH3/84% RH air (black line). In this case, the spectrum of 70% RH air is used as a reference. As can be seen from Fig. 4, an increase in intensity in the long wavelengths range (> 650 nm) is observed when 5 ppm NH3/84% RH air is introduced. Inset of Fig. 4 shows the absorption spectrum of the PANI/PS nanowire to 5 ppm NH3/84% RH air with a λ min around 780 nm. The reason for this result is that for detection of NH3 and RH in a gas mixture, the absorbance of the nanowire at a given wavelength is caused by both NH3 and RH: at long wavelengths the sensitivity of the nanowire to NH3 is enhanced by RH and results in a blue shift of the λ min in absorption spectrum compared with that in Fig. 2; on the contrary, at short wavelengths the sensitivity to NH3 is counteracted by RH.

Using the two independent sensing mechanisms above, gas mixtures of NH3 and humidity can be determined using a single nanowire by dual-wavelength measurements. Here 633-nm and 808-nm-wavelength lights are used to simultaneously monitor the Ar of the 350-nm-diameter PANI/PS nanowire. The nanowire is first exposed to 70% RH air as a reference, and then to the analyte gases. As shown in Fig. 5(a)
Fig. 5 (a) Time-dependent response of the nanowire exposed to (1) 84% RH air, (2) 5 ppm NH3, (3) 5 ppm NH3 with 79% RH air, and (4) 5 ppm NH3 with 84% RH air respectively, which are simultaneously monitored using two lasers with wavelengths of 633 and 808 nm. (b) Bar graph summarizing the optical response of the nanowire to the analyte gases at wavelengths of 633- and 808 nm.
, upon exposure to 84% RH air, decrease in Ar at both 633- and 808-nm are observed; yet upon exposure to 5 ppm NH3/dry air, an increase in Ar at 633 nm and a decrease in Ar at 808 nm are observed. The distinguishable response between humidity and NH3 is clearly seen. Upon addition of 5 ppm NH3/79% RH air, an increase in Ar at 633 nm and a decrease in A r at 808 nm are observed; however, the Ar at the two wavelengths show little decrease. This effect is much more obvious in the response to 5 ppm NH3/84% RH air: only decreases in Ar at 633 nm and 808 nm are observed, which is in accordance with that in Fig. 4. These results make it possible in principle to determine the individual responses in a gas mixture of NH3 and humidity by dual-wavelength measurement.

The bar graph in Fig. 5(b) summarizes the response of the nanowire to the analyte gases at 633-nm and 808-nm wavelengths. The height of each bar represents the maximum Ar of the responses to analyte gases at each wavelength. The distinction between each analyte gas is immediately apparent. The concentrations of individual gas components may be calculated by solving the simultaneous equations associated with the nanowire absorptivity ελ, which can be determined from the individual response to NH3 and humidity respectively, the sensing length b, and the fractional energy η λ confined in the nanowire at wavelength λ which can be calculated by solving the Maxwell’s Equations [24

24. L. M. Tong, J. Y. Lou, and E. Mazur, “Single-mode guiding properties of subwavelength-diameter silica and silicon wire waveguides,” Opt. Express 12(6), 1025–1035 (2004). [CrossRef] [PubMed]

]. Moreover, the measurement precision can be further increased by including more sensing results or by choosing more suitable wavelengths [14

14. D. A. Skoog, D. M. West, F. J. Holler, and S. R. Crouch, Fundamental of Analytical Chemistry (Brooks Cole, 2004).

].

4. Conclusions

In conclusion, by using spectral analysis in the VIS/NIR region, we have demonstrated optical waveguiding PANI/PS single-nanowire devices for highly selective detection of gas mixtures of NH3 and humidity, based on the absorption band change of PANI and the coupling efficiency change between the PANI/PS nanowire and the nanoscale fiber taper. In addition, compared with existing techniques for gas sensing relying on electrical response of nanowires such as metal oxide nanowire gas sensors, the use of functionalized polymer nanowire makes it simpler and easier to operate: the high temperature or UV exposure that is required for refreshing the sensing elements in most of metal oxide nanowire gas sensors [11

11. P. F. Qi, O. Vermesh, M. Grecu, A. Javey, Q. Wang, H. J. Dai, S. Peng, and K. J. Cho, “Toward large arrays of multiplex functionalized carbon nanotube sensors for highly sensitive and selective molecular detection,” Nano Lett. 3(3), 347–351 (2003). [CrossRef]

,25

25. E. Comini, “Metal oxide nano-crystals for gas sensing,” Anal. Chim. Acta 568(1-2), 28–40 (2006). [CrossRef]

28

28. M. Law, H. Kind, B. Messer, F. Kim, and P. D. Yang, “Photochemical sensing of NO2 with SnO2 nanoribbon nanosensors at room temperature,” Angew. Chem. Int. Ed. 41(13), 2405–2408 (2002). [CrossRef]

], is not needed here. Furthermore, the nanoscale fiber taper is directly connected to a standard optical fiber through the tapering region and has a simple optical power readout, which offer several advantages: possibility of remote sensing, continuous monitoring, and feasibility of multiplexing the information from different sensors in one optical fiber, which may open interesting perspectives for highly selective detection in complex chemical and biological environments with a single nanowire.

Acknowledgements

This work was supported by the National Basic Research Programs of China (No. 2007CB307003) and the National Natural Science Foundation of China (No. 60728309 and 20775072).

References and links

1.

J. X. Huang, S. Virji, B. H. Weiller, and R. B. Kaner, “Polyaniline nanofibers: facile synthesis and chemical sensors,” J. Am. Chem. Soc. 125(2), 314–315 (2003). [CrossRef] [PubMed]

2.

M. E. Nicho, M. Trejo, A. Garcia-Valenzuela, J. M. Saniger, J. Palacios, and H. Hub, “Polyaniline composite coatings interrogated by a nulling optical-transmittance bridge for sensing low concentrations of ammonia gas,” Sens. Actuators B Chem. 76(1-3), 18–24 (2001). [CrossRef]

3.

S. Christie, E. Scorsone, K. Persaud, and F. Kvasnik, “Remote detection of gaseous ammonia using the near infrared transmission properties of polyaniline,” Sens. Actuators B Chem. 90(1-3), 163–169 (2003). [CrossRef]

4.

H. Q. Liu, J. Kameoka, D. A. Czaplewski, and H. G. Craighead, “Polymeric nanowire chemical sensor,” Nano Lett. 4(4), 671–675 (2004). [CrossRef]

5.

J. Jang, J. Ha, and J. Cho, “Fabrication of water-dispersible polyaniline-poly(4-styrenesulfonate) nanoparticles for inkjet-printed chemical-sensor applications,” Adv. Mater. 19(13), 1772–1775 (2007). [CrossRef]

6.

N. T. Kemp, D. McGrouther, J. W. Cochrane, and R. Newbury, “Bridging the gap: polymer nanowire devices,” Adv. Mater. 19(18), 2634–2638 (2007). [CrossRef]

7.

S. Virji, J. D. Fowler, C. O. Baker, J. X. Huang, R. B. Kaner, and B. H. Weiller, “Polyaniline nanofiber composites with metal salts: chemical sensors for hydrogen sulfide,” Small 1(6), 624–627 (2005). [CrossRef]

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J. Elizalde-Torres, H. L. Hu, and A. Garcia-Valenzuela, “NO2-induced optical absorbance changes in semiconductor polyaniline thin films,” Sens. Actuators B Chem. 98(2-3), 218–226 (2004). [CrossRef]

9.

X. B. Yan, Z. J. Han, Y. Yang, and B. K. Tay, “NO2 gas sensing with polyaniline nanofibers synthesized by a facile aqueous/organic interfacial polymerization,” Sens. Actuators B Chem. 123(1), 107–113 (2007). [CrossRef]

10.

L. Senesac and T. G. Thundat, “Nanosensors for trace explosive detection,” Mater. Today 11(3), 28–36 (2008). [CrossRef]

11.

P. F. Qi, O. Vermesh, M. Grecu, A. Javey, Q. Wang, H. J. Dai, S. Peng, and K. J. Cho, “Toward large arrays of multiplex functionalized carbon nanotube sensors for highly sensitive and selective molecular detection,” Nano Lett. 3(3), 347–351 (2003). [CrossRef]

12.

G. F. Zheng, F. Patolsky, Y. Cui, W. U. Wang, and C. M. Lieber, “Multiplexed electrical detection of cancer markers with nanowire sensor arrays,” Nat. Biotechnol. 23(10), 1294–1301 (2005). [CrossRef] [PubMed]

13.

M. C. McAlpine, H. Ahmad, D. W. Wang, and J. R. Heath, “Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors,” Nat. Mater. 6(5), 379–384 (2007). [CrossRef] [PubMed]

14.

D. A. Skoog, D. M. West, F. J. Holler, and S. R. Crouch, Fundamental of Analytical Chemistry (Brooks Cole, 2004).

15.

D. J. Sirbuly, A. Tao, M. Law, R. Fan, and P. D. Yang, “Multifunctional nanowire evanescent wave optical sensors advanced materials,” Adv. Mater. 19(1), 61–66 (2007). [CrossRef]

16.

D. J. Sirbuly, S. E. Letant, and T. V. Ratto, “Hydrogen sensing with subwavelength pptical waveguides via porous silsesquioxane-palladium nanocomposites,” Adv. Mater. 20(24), 4724–4727 (2008). [CrossRef]

17.

F. X. Gu, L. Zhang, X. F. Yin, and L. M. Tong, “Polymer single-nanowire optical sensors,” Nano Lett. 8(9), 2757–2761 (2008). [CrossRef] [PubMed]

18.

L. M. Tong, R. R. Gattass, J. B. Ashcom, S. L. He, J. Y. Lou, M. Y. Shen, I. Maxwell, and E. Mazur, “Subwavelength-diameter silica wires for low-loss optical wave guiding,” Nature 426(6968), 816–819 (2003). [CrossRef] [PubMed]

19.

L. M. Tong, J. Y. Lou, R. R. Gattass, S. L. He, X. W. Chen, L. Liu, and E. Mazur, “Assembly of silica nanowires on silica aerogels for microphotonic devices,” Nano Lett. 5(2), 259–262 (2005). [CrossRef] [PubMed]

20.

K. J. Huang, S. Y. Yang, and L. M. Tong, “Modeling of evanescent coupling between two parallel optical nanowires,” Appl. Opt. 46(9), 1429–1434 (2007). [CrossRef] [PubMed]

21.

A. Pud, N. Ogurtsova, A. Korzhenkob, and G. Shapovala, “Some aspects of preparation methods and properties of polyaniline blends and composites with organic polymers,” Prog. Polym. Sci. 28(12), 1701–1753 (2003). [CrossRef]

22.

M. Matsuguchi, A. Okamoto, and Y. Sakai, “Effect of humidity on NH3 gas sensitivity of polyaniline blend films,” Sens. Actuators B Chem. 94(1), 46–52 (2003). [CrossRef]

23.

A. Vijayan, M. Fuke, R. Hawaldar, M. Kulkarni, D. Amalnerkar, and R. C. Aiyer, “Sens. “Optical fibre based humidity sensor using Co-polyaniline clad,” Sens. Actuators B Chem. 129(1), 106–112 (2008). [CrossRef]

24.

L. M. Tong, J. Y. Lou, and E. Mazur, “Single-mode guiding properties of subwavelength-diameter silica and silicon wire waveguides,” Opt. Express 12(6), 1025–1035 (2004). [CrossRef] [PubMed]

25.

E. Comini, “Metal oxide nano-crystals for gas sensing,” Anal. Chim. Acta 568(1-2), 28–40 (2006). [CrossRef]

26.

A. Kolmakov, Y. X. Zhang, G. S. Cheng, and M. Moskovits, “Detection of CO and O2 using tin oxide nanowire sensors,” Adv. Mater. 15(12), 997–1000 (2003). [CrossRef]

27.

H. W. Ra, K. S. Choi, J. H. Kim, Y. B. Hahn, and Y. H. Im, “Fabrication of ZnO nanowires using nanoscale spacer lithography for gas sensors,” Small 4(8), 1105–1109 (2008). [CrossRef] [PubMed]

28.

M. Law, H. Kind, B. Messer, F. Kim, and P. D. Yang, “Photochemical sensing of NO2 with SnO2 nanoribbon nanosensors at room temperature,” Angew. Chem. Int. Ed. 41(13), 2405–2408 (2002). [CrossRef]

OCIS Codes
(130.6010) Integrated optics : Sensors
(230.7370) Optical devices : Waveguides

ToC Category:
Optical Devices

History
Original Manuscript: May 18, 2009
Revised Manuscript: June 15, 2009
Manuscript Accepted: June 15, 2009
Published: June 19, 2009

Citation
Fuxing Gu, Xuefeng Yin, Huakang Yu, Pan Wang, and Limin Tong, "Polyaniline/polystyrene single-nanowire devices for highly selective optical detection of gas mixtures," Opt. Express 17, 11230-11235 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-13-11230


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References

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