Direct Detection of Dilute Solid Chemicals with Responsive Lateral

Aug 24, 2017 - The response of our diodes upon exposure to solid chemicals can thus be much more significant than that of OFETs. .... Research and Dev...
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Direct Detection of Dilute Solid Chemicals with Responsive Lateral Organic Diodes Jia Huang,*,† Guoqian Zhang,† Xingang Zhao,‡ Xiaohan Wu,† Dapeng Liu,† Yingli Chu,† and Howard E. Katz‡ †

Interdisciplinary Materials Research Center, Department of Polymeric Materials, School of Materials Science and Engineering, Tongji University, Shanghai 201804, China ‡ Department of Material Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, United States S Supporting Information *

films at the organic/dielectric interface define the conduction channels of OFETs and play key roles in determining the charge transport between electrodes.26,27 For analyte vapors or solutions, analyte molecules can first diffuse through the organic semiconductor films and then induce various effects in the conduction channels, such as doping or quenching effects and dipole-induced trapping and retarding of mobile charges.6,7,28 However, the diffusivity of solid analyte (solid powders) in organic semiconductor films is usually much lower than that of vapor and liquid analytes. The solid analytes can be blocked by the organic semiconductor films and cannot have direct interaction with the conduction channel, so that the OFETs cannot have significant response to the solid powder analytes. Here for the first time, as a proof of concept, we describe the direct detection of solid chemical analytes by organic electronic devices. Instead of the OFET structure, an organic diode structure based on a horizontal side-by-side p−n junction was adopted, as shown in Figure 1. With such a lateral device structure, charge carriers near the surface of the OSC films can have direct interaction with analyte solids. As a relevant prototype example, we used the melamine as a solid state target analyte for demonstrating our diodes. Melamine is a hazardous chemical compound with amine structure, that has been found

ABSTRACT: Organic field-effect transistors (OFETs) have emerged as promising sensors targeting chemical analytes in vapors and liquids. However, the direct detection of solid chemicals by OFETs has not been achieved. Here for the first time, we describe the direct detection of solid chemical analytes by organic electronics. An organic diode structure based on a horizontal side-byside p−n junction was adopted and shown to be superior to OFETs for this purpose. The diodes showed more than 40% current decrease upon exposure to 1 ppm melamine powders. The estimated detection limit to melamine can potentially reach the ppb range. This is the first demonstration of an electronic signal from an interaction between a solid and an organic p−n junction directly, which suggests that our lateral organic diodes are excellent platforms for the development of future sensors when direct detection of solid chemicals is needed. The approach developed here is general and can be extended to chemical sensors targeting various analytes, opening unprecedented opportunities for the development of lowcost and high-performance solid chemical sensors.

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ow-cost and rapid detection of amine chemicals is becoming increasingly important for medical purposes, industry monitoring, homeland security and food safety monitoring.1−5 Commercialized approaches are usually expensive, time-consuming and not portable. Analyte extraction and preconcentration are sometimes needed for those detection approaches. In recent years, organic semiconductors have been extensively studied for applications in various sensors to detect pressure, photons, magnetic fields and chemicals.6−22 Chemical sensors based on organic semiconductors can have advantages such as low cost, portability, room temperature operation and easy miniaturization.6−8,19,20,22,23 To date, the most common chemically sensitive organic electronics have been organic fieldeffect transistors (OFETs) targeting chemical vapors such as volatile organic compounds and vapors of chemical solids.6,7,15,18,24 In addition, a few studies have been recently reported to apply OFETs to the detection of chemicals in liquid environments.14,25 However, to the best of our knowledge, the direct detection of solid chemicals by OFETs, or organic semiconductor (OSC) electronics in general, has not been achieved. The first few molecular layers on the bottom of OSC © 2017 American Chemical Society

Figure 1. Schematic illustration of (a) lateral organic diodes in contact with melamine, (b) organic field-effect transistors in contact with melamine, and (c) organic semiconductor molecules. Received: June 16, 2017 Published: August 24, 2017 12366

DOI: 10.1021/jacs.7b06223 J. Am. Chem. Soc. 2017, 139, 12366−12369

Communication

Journal of the American Chemical Society

Figure 2. I−V curves of diodes without and with melamine powders. (a) 6PTTP6-NTCDI_83 diode, showed 28.1% current decrease at 10 V. (b) DNTT-NTCDI_83 diode, showed 42.5% current decrease at 10 V.

in animal feeds, food, and formula milk powders.29 We demonstrated here that our devices exhibited significant, selective and reversible response when trace amounts of melamine powders were placed directly onto the diode surface. When silica powders were used as background agent for dilution, 1 ppm melamine diluted in silica powders can be detected by our devices. Our diode sensors were shown to be superior to OFETs for detecting solid chemicals. This is the first demonstration of an electronic signal from an interaction between a solid and an organic p−n junction directly. Our finding may be used to develop new types of low-cost and portable chemical sensors based on OSCs, and lead to new design concepts and strategies for the direct detection or rapid screening of solid amine chemicals. Figure 1 shows the device and molecule structures of our devices. The fabrication process can be found in the Supporting Information. A lateral side-by-side p−n junction structure was adopted to allow the direct interaction between the analytes and both OSCs, as shown in Figure 1a. The conventional layeron-layer diode structure as shown in Figure S1 was not used because the electrodes would block analytes from interacting with the most sensitive sites on the OSCs. N,N′-Bis(3-(perfl uorocotyl)propyl)-1,4,5,8-naphthalene tetracarboxylic diimide (NTCDI_83) was used as the n-type semiconductor for the demonstration. Two p-type organic semiconductors were studied: 5,5′-bis(4-n-hexyl-phenyl)-2,2′-bithiophene (6PTTP6) with long side chains in the molecular structure, and dinaphtho[2,3-b:2′,3′-f]-thieno[3,2-b]thiophene (DNTT) without side chains, resulting in two types of diodes: devices 6PTTP6-NTCDI_83 and devices DNTT-NTCDI_83. Figure S2 shows the I−V characteristics of the OFETs, whereas Figure S3 shows the almost negligible current response of these OFETs to solid analyte powders. When pure silica and pure melamine powders were placed on the surface of the devices, the source-drain current changes were less than 8% for all OFETs, indicating that OFETs cannot detect the solid chemicals directly with useful sensitivity. As shown in Figure 1b, the first few molecular layers on the bottom of organic semiconductor film at the organic/dielectric interface define the conduction channels of OFETs. The diffusivity of solid analyte (solid powders) in organic semiconductor films is too low to allow the direct interaction between the analyte and the charges in conduction channel, so that the source-drain current showed little response to the solid analyte. As shown in Figure S4, our diodes exhibited typical diode I− V curves with rectification. Changes in the forward currents

were used as output signals. Unlike OFETs, where most charge carriers are concentrated in a few molecular layers close to the dielectrics, the charge carriers in this side-by-side p−n junction diode can be distributed in the entire semiconductor film, as shown in Figure 1a. With such a device structure, charge carriers in both p- and n-type organic semiconductor films can have direct interaction with analyte solids, and lead to changes in the diode output current. The response of our diodes upon exposure to solid chemicals can thus be much more significant than that of OFETs. When melamine powders were placed on the surfaces of the diodes, significant current changes can be observed, as shown in Figure 2. When a bias voltage of 10 V was applied, the 6PTTP6-NTCDI_83 diode showed 28% current reduction, whereas the DNTT-NTCDI_83 diodeshowed 43% current decrease. As will be shown here, these responses are reversible. We postulate that the 6PTTP6NTCDI_83 diode showed less response than that of the DNTT-NTCDI_83 diode because of the different molecular structure of 6PTTP6 and DNTT. The 6PTTP6 molecule has −C6H13 alkyl side-chains attaching to the core structure, whereas the DNTT molecule has a π-conjugated core structure without any shielding by side chains. Melamine molecules have −NH2 groups acting as electron donors. The interaction between melamine molecules and the hole transporting p-type semiconductor molecules leads to a charge quenching effect. Because of the blocking of the alkyl side-chain, the charge quenching effect on 6PTTP6 molecules is less significant than that of DNTT. Because of similar side-chain blocking effects, the doping effect of the −NH2 groups to the n-type NTCDI_83 is less significant than the quenching effect to the p-type semiconductors, because the NTCDI_83 molecule has long and fluorinated −C3H6C8F17 side-chains protecting the core structure. Therefore, the overall response was a decrease in output current upon exposure to melamine. These results suggest that our diodes based on horizontal side-by-side p−n junction can be better platforms than traditional OFETs for applications in the direct detection of solid chemicals. To investigate further the detection sensitivity of the diodes, melamine powders were mixed and diluted with SiO2 powders, and then tested with both diodes. As shown in Figure 3, both 6PTTP6-NTCDI_83 and DNTT-NTCDI_83 diodes exhibited obvious current reduction. It should be emphasized that the devices could return to pristine status after the analyte powders were blown off, which indicates our lateral organic diodes possess good sensory reversibility. These studies highlighted several points. First, the devices showed more significant 12367

DOI: 10.1021/jacs.7b06223 J. Am. Chem. Soc. 2017, 139, 12366−12369

Communication

Journal of the American Chemical Society

Figure 3. Normalized current responses as functions of applied bias voltage and melamine concentration of (a) 6PTTP6-NTCDI_83 diode, and (b) DNTT-NTCDI_83 diode.

normalized responses at lower applied voltage, similar to chemical sensors based on OFET structures in that sensitivity is greatest near the turn-on regime.6−8,30−33 Though the normalized response is larger at lower applied voltage, the absolute current change is larger at higher applied voltage, as shown in Figure 2. Second, the response is a function of the melamine concentration in the analytes, which makes quantitative detection possible for the diodes. Finally, the DNTT-NTCDI_83 diode is more sensitive to the tested analyte than the 6PTTP6-NTCDI_83 diode, which is also consistent with the results shown in Figure 2. Figure 4 shows the normalized current responses ΔI/Iair,0 as the function of melamine concentration at various applied voltages. Here the current change ΔI = Iair,0 − Ianalyte. The solid lines are linearly fitted curves of the measured data. The dashed line shows the normalized current responses ΔIsilica/Iair when the devices were exposed to pure silica powders without the addition of melamine, where ΔIsilica = Iair,0 − Isilica. Here the detection limit is estimated as the corresponding melamine concentration when the normalized current responses read from the fitted curve is close to the dashed line. From Figure 4, the estimated detection limit of melamine concentration at low voltage bias is on the order of 100 ppb weight ratio for the diode 6PTTP6-NTCDI_83, and 0.01 ppb for the diode DNTT-NTCDI_83. It should be noted that this is a rough estimation without considering any signal-to-noise ratio requirement, but a detection limit in subppm range for the 6PTTP6-NTCDI_83 diode, and in subppb range for the DNTT-NTCDI_83 diode, should be achievable with device optimization. The sensing responses of the DNTT-NTCDI_83 diode upon exposure to different pure solid chemical powders were further investigated and compared, as shown in Figure S5. Chemical analytes tested included tetracyanoquinodimethane (TCNQ), 1,5-naphthalenediamine (Naph(NH3)2), naphthalene, melamine and 2,4-dinitrotoluene (DNT). Standard deviations of responses are also given in Figure S5. The diode exhibited more significant current decrease upon

Figure 4. Normalized Responses of the diodes upon exposure to melamine at various concentrations under different applied voltages. (a, c, e) Response of a 6PTTP6-83_NTCDI diode at voltage bias of 5, 10 and 20 V, respectively. (b, d, f) Response of a 6PTTP6-83_NTCDI diode at voltage bias of 5, 10 and 20 V, respectively.

exposure to naphthalenediamine than to other analytes, and current increase in response to TCNQ. It seems that the lateral diode output current is dominated by hole conduction, partly from the series resistance of the p-type semiconductor, but more from the change in the p−n junction potential caused by the solids, which affects the hole side more. We postulate that the junction is affected more than the bulk semiconductor, because melamine did not affect the organic transistors very much. During tests, the diode was operated under forward bias, which means the positive voltage was on the DNTT side and the negative voltage was on the NTCDI side. The junction would be polarized negative on the p-side. From the results shown in Figure S5, it seems that the naphthalenediamine is taking more holes away from the DNTT side of the junction, making that side more negative where the current is flowing, and leading to more significantly reduced output current than those of other analytes. TCNQ as a hole donor compound would add more holes, decreases the negative polarity of the DNTT side, lowering the barrier, and increases the output current. Naphthalene is not a strong electron donor or acceptor and hence induces only a minor current response. In the case of DNT, the hole doping effect would lead to diode current increase, but the current actually reduced by 20%, perhaps because of the additional dipole effect induced from the strong dipole moment of DNT molecules, which has been observed from DNT vapor sensing by OFET chemical sensors.8 In addition to solids, this device can also be used for chemical vapor sensing. As shown in Figure S6, the device showed obvious response to 100 ppb NH3 vapors. Therefore, these results show that the melamine is acting like a hole quencher, but much more actively at the junction than it would be on a 12368

DOI: 10.1021/jacs.7b06223 J. Am. Chem. Soc. 2017, 139, 12366−12369

Communication

Journal of the American Chemical Society

(4) Moore, D. S.; Scharff, R. J. Anal. Bioanal. Chem. 2009, 393, 1571. (5) Yi, D.; Senesac, L.; Thundat, T. Scanning 2008, 30, 208. (6) Huang, J.; Sun, J.; Katz, H. E. Adv. Mater. 2008, 20, 2567. (7) Huang, J.; Miragliotta, J.; Becknell, A.; Katz, H. E. J. Am. Chem. Soc. 2007, 129, 9366. (8) Huang, J.; Dawidczyk, T. J.; Jung, B. J.; Sun, J.; Mason, A. F.; Katz, H. E. J. Mater. Chem. 2010, 20, 2644. (9) Zhang, Y.; Du, J.; Wu, X.; Zhang, G.; Chu, Y.; Liu, D.; Zhao, Y.; Liang, Z.; Huang, J. ACS Appl. Mater. Interfaces 2015, 7, 21634. (10) Wu, X.; Ma, Y.; Zhang, G.; Chu, Y.; Du, J.; Zhang, Y.; Li, Z.; Duan, Y.; Fan, Z.; Huang, J. Adv. Funct. Mater. 2015, 25, 2138. (11) Chu, Y.; Wu, X.; Lu, J.; Liu, D.; Du, J.; Zhang, G.; Huang, J. Adv. Sci. 2016, 3, 1500435. (12) Mannsfeld, S. C. B.; Tee, B. C. K.; Stoltenberg, R. M.; Chen, C. V. H. H.; Barman, S.; Muir, B. V. O.; Sokolov, A. N.; Reese, C.; Bao, Z. Nat. Mater. 2010, 9, 859. (13) Pu, K.; Shuhendler, A. J.; Jokerst, J. V.; Mei, J.; Gambhir, S. S.; Bao, Z.; Rao, J. Nat. Nanotechnol. 2014, 9, 233. (14) Knopfmacher, O.; Hammock, M. L.; Appleton, A. L.; Schwartz, G.; Mei, J.; Lei, T.; Pei, J.; Bao, Z. Nat. Commun. 2014, 5, 149. (15) Torsi, L.; Farinola, G. M.; Marinelli, F.; Tanese, M. C.; Omar, O. H.; Valli, L.; Babudri, F.; Palmisano, F.; Zambonin, P. G.; Naso, F. Nat. Mater. 2008, 7, 412. (16) Lee, S.; Reuveny, A.; Reeder, J.; Lee, S.; Jin, H.; Liu, Q.; Yokota, T.; Sekitani, T.; Isoyama, T.; Abe, Y.; Suo, Z.; Someya, T. Nat. Nanotechnol. 2016, 11, 472. (17) Huang, W.; Sinha, J.; Yeh, M.-L.; Hardigree, J. F. M.; LeCover, R.; Besar, K.; Rule, A. M.; Breysse, P. N.; Katz, H. E. Adv. Funct. Mater. 2013, 23, 4094. (18) Katz, H. E.; Huang, J. Annu. Rev. Mater. Res. 2009, 39, 71−92. (19) Huang, W.; Besar, K.; LeCover, R.; Rule, A. M.; Breysse, P. N.; Katz, H. E. J. Am. Chem. Soc. 2012, 134, 14650. (20) Liu, X.; Luo, X.; Nan, H.; Guo, H.; Wang, P.; Zhang, L.; Zhou, M.; Yang, Z.; Shi, Y.; Hu, W.; Ni, Z.; Qiu, T.; Yu, Z.; Xu, J.-B.; Wang, X. Adv. Mater. 2016, 28, 5200. (21) Zang, Y.; Zhang, F.; Huang, D.; Di, C.-a.; Zhu, D. Adv. Mater. 2015, 27, 7979. (22) Zang, Y.; Zhang, F.; Huang, D.; Di, C.-a.; Meng, Q.; Gao, X.; Zhu, D. Adv. Mater. 2014, 26, 2862. (23) Feng, L.; Tang, W.; Zhao, J.; Yang, R.; Hu, W.; Li, Q.; Wang, R.; Guo, X. Sci. Rep. 2016, 6, 20671. (24) Zhang, C.; Chen, P.; Hu, W. Chem. Soc. Rev. 2015, 44, 2087. (25) Roberts, M. E.; Mannsfeld, S. C. B.; Queralto, N.; Reese, C.; Locklin, J.; Knoll, W.; Bao, Z. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 12134. (26) Dodabalapur, A.; Torsi, L.; Katz, H. E. Science 1995, 268, 270. (27) Horowitz, G.; Hajlaoui, R.; Bourguiga, R.; Hajlaoui, M. Synth. Met. 1999, 101, 401. (28) Wang, B.; Huynh, T.-P.; Wu, W.; Hayek, N.; Do, T. T.; Cancilla, J. C.; Torrecilla, J. S.; Nahid, M. M.; Colwell, J. M.; Gazit, O. M.; Puniredd, S. R.; McNeill, C. R.; Sonar, P.; Haick, H. Adv. Mater. 2016, 28, 4012. (29) Dalal, R. P.; Goldfarb, D. S. Nat. Rev. Nephrol. 2011, 7, 267. (30) Jung, B. J.; Lee, K.; Sun, J.; Andreou, A. G.; Katz, H. E. Adv. Funct. Mater. 2010, 20, 2930. (31) Mushrush, M.; Facchetti, A.; Lefenfeld, M.; Katz, H. E.; Marks, T. J. J. Am. Chem. Soc. 2003, 125, 9414. (32) Yamamoto, T.; Takimiya, K. J. Am. Chem. Soc. 2007, 129, 2224. (33) Huang, J.; Ng, A. L.; Piao, Y.; Chen, C.-F.; Green, A. A.; Sun, C.F.; Hersam, M. C.; Lee, C. S.; Wang, Y. J. Am. Chem. Soc. 2013, 135, 2306.

plain p-semiconductor. There is selectivity over other solids that are not hole quenchers or stronger hole quenchers than melamine, but not for melamine compared to other hole quenchers. Further selectivity would be expected from an array of multiple and varied diodes with surface chemistries and morphologies difference on the semiconductors to distinguish analytes by their surface affinities or sizes. Receptor strategies adopted from selective OFET chemical sensors can also be directly applied to our diode sensors to improve further the selectivity. In summary, this is the first demonstration of electronic signals from interactions between solid chemicals and lateral side-by-side organic p−n junctions directly. Our diodes showed the capability of detecting melamine solids with concentrations in a wide range from ppb level to 100%. The sensitivity of our diodes was much better than that of traditional OFETs. When OFETs showed negligible response to pure melamine, our diodes showed obvious response to 1 ppm melamine solid analytes. Although not completely developed sensors, as a proof of concept, these demonstrations suggest that our organic diodes based on horizontal side-by-side p−n junction are excellent platforms for the development of future sensors when the direct detection of solid chemicals is needed. The concept and structure design presented here comprise a generalizable method to obtain high-quality chemical sensors, and can be adopted to a wide range of sensors to quantitatively monitor various solid chemicals directly, such as disposable food-safety sensors for family use in daily life.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.7b06223. Experimental section including materials and device fabrication, and device measurements (PDF)

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AUTHOR INFORMATION

Corresponding Author

*[email protected] ORCID

Jia Huang: 0000-0002-2873-7704 Xingang Zhao: 0000-0001-5852-9757 Howard E. Katz: 0000-0002-3190-2475 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (51373123), Science & Technology Foundation of Shanghai (17JC1404600), the National Key Research and Development Program of China (2017YFA0103900 & 2017YFA0103904), the Fundamental Research Funds for the Central Universities, and the 1000 youth talent plan.

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REFERENCES

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DOI: 10.1021/jacs.7b06223 J. Am. Chem. Soc. 2017, 139, 12366−12369