- Email: [email protected]
In situ-synthesized cadmium sulfide nanowire photosensor with a parylene passivation layer for chemiluminescent immunoassays
Biosensors and Bioelectronics 92 (2017) 221–228
Contents lists available at ScienceDirect
Biosensors and Bioelectronics journal homepage: www.elsevier.com/locate/bios
In situ-synthesized cadmium sulfide nanowire photosensor with a parylene passivation layer for chemiluminescent immunoassays
MARK
Ju-Hee Ima,b,1, Hong-Rae Kima,1, Byoung-Gi Ana,c, Young Wook Changa, Min-Jung Kangb, Tae⁎ Geol Leed, Jin Gyeng Sond, Jae-Gwan Parkb, Jae-Chul Pyuna, a
Department of Materials Sciences and Engineering, Yonsei University, 50 Yonsei-Ro, Seo-dae-mun-gu, Seoul 120-749, Republic of Korea Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea c Samsung Electro-Mechanics, Kyonggi, Republic of Korea d Korea Research Institute of Standards and Science (KRISS), Daejeon, Republic of Korea b
A R T I C L E I N F O
A BS T RAC T
Keywords: CdS Nanowire Photosensor Parylene-C Passivation Chemiluminescence
The direct in situ synthesis of cadmium sulfide (CdS) nanowires (NWs) was presented by direct synthesis of CdS NWs on the gold surface of an interdigitated electrode (IDE). In this work, we investigated the effect of a strong oxidant on the surfaces of the CdS NWs using X-ray photoelectron spectroscopy, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry. We also fabricated a parylene-C film as a surface passivation layer for in situ-synthesized CdS NW photosensors and investigated the influence of the parylene-C passivation layer on the photoresponse during the coating of parylene-C under vacuum using a quartz crystal microbalance and a photoanalyzer. Finally, we used the in situ-synthesized CdS NW photosensor with the parylene-C passivation layer to detect the chemiluminescence of horseradish peroxidase and luminol and applied it to medical detection of carcinoembryonic antigen.
1. Introduction Recently, we reported the direct synthesis of cadmium sulfide (CdS) nanowires (NWs) on the gold surface of an interdigitated electrode (IDE) (An et al., 2015). Such a direct approach is called in situ synthesis. An in situ-synthesized CdS NW photosensor has the following advantages: (1) the NWs have enhanced surface density, which is related to the sensitivity of the photosensors; (2) ultrasonication, which may induce physical changes in the NWs, is not required to isolate them; and (3) there is improved contact between the NWs and the IDE surface. Usually, NW photosensors made of materials such as ZnO, Ge, and GaN show a reduced photoresponse after adsorbing oxygen or water molecules (Armstrong et al., 2010; Ghosh et al., 2007; Gu and Lauhon, 2006; Han et al., 2016; Hanrath and Korgel, 2004; Jeong et al., 2005; Park et al., 2016; Prades et al., 2008; Wang et al., 2004). Such an effect is explained by the electrostatic interaction between the adsorbed molecules and the photocarriers, which reduces the photocurrents (Ahn et al., 2007; Gao et al., 2005; Ghosh et al., 2007; Gu and Lauhon, 2006; Law and Thong, 2006; Li et al., 2005). Therefore, various types of polymers, such as poly(methyl methacrylate) (PMMA), polyimide, and polyacrylonitrile, have been used for the surface
⁎
1
passivation of NW photosensors (He et al., 2007; Hong et al., 2008; Park et al., 2004). Although ZnO nanowires are strongly affected by O2 molecules in ambient atmosphere, the electrical properties of ZnO nanowires were reported to have exhibited better performance when they were coated with PMMA (200 nm thick) and polyimide (nmethoxy methylated nylon, 2 µm thick) in comparison to unpassivated devices (Hong et al., 2008; Park et al., 2004). ZnO nanobelts also showed an enhanced photoresponse, up to 750 times higher than that of bare ZnO nanobelts, after they were coated with a plasma-polymerized acrylonitrile film with a thickness of less than 20 nm (He et al., 2007). Surface passivation of NW photosensors requires certain properties, including transparency, chemical resistance, and water repellence. In this work, we used a strong oxidant [hydrogen peroxide (H2O2)] to study the influence of surface oxidation on the photoresponsiveness of CdS NWs (Lee et al., 2012) using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). We fabricated a parylene-C film as a surface passivation layer for in situ-synthesized CdS NW photosensors and investigated the influence of the parylene-C passivation layer on the photoresponse during the coating of parylene-
Corresponding author. E-mail address: [email protected] (J.-C. Pyun). These authors contributed equally to this work.
http://dx.doi.org/10.1016/j.bios.2017.02.021 Received 28 November 2016; Received in revised form 25 January 2017; Accepted 13 February 2017 Available online 16 February 2017 0956-5663/ © 2017 Elsevier B.V. All rights reserved.
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
2. Material and methods
Fig. 1(a). Once the temperature reached 650 °C, the KrF excimer laser was focused on the CdS target and the laser energy density was maintained at 1–5 J/cm2. The synthesis temperature was maintained at 650 °C for 30 min under a N2 and H2 atmosphere with a constant inner pressure of ~667 Pa (~5 Torr). IDEs with a width of 5 µm were located 9–13 cm from the sintered CdS target in the furnace tube (An et al., 2016).
2.1. Materials
2.3. Parylene deposition
Cadmium sulfide powder ( > 99.9%, < 1 µm), HRP, and other analytical-grade chemicals were purchased from Sigma-Aldrich Korea (Seoul, Korea). Dichloro-di-p-xylylene powder was purchased from Daisan Kasei Co. Ltd. (Tokyo, Japan). CEA enzyme immunoassay test kits were purchased from the Perfemed Group Inc. (San Francisco, CA, USA). Luminol was purchased from Pierce Co. (Rockford, IL, USA) (Park et al., 2015).
We used a commercial parylene deposition system (Kisco, Japan) to prepare parylene-C-coated CdS NWs. The parylene-C film was deposited in the following three steps: (1) evaporation of the dimers of parylene-C at 160 °C; (2) pyrolysis at 650 °C to transform the parylene dimers into highly reactive free radicals; and (3) deposition and polymerization on the CdS NWs at room temperature under a vacuum of less than 5.3 Pa (40 mTorr). The thickness of the parylene film was controlled by adjusting the initial amount of parylene dimers (Ko et al., 2015).
C under vacuum using a quartz crystal microbalance (QCM) and a photoanalyzer. Finally, we used the in situ-synthesized CdS NW photosensor with the parylene-C passivation layer to detect the chemiluminescence of horseradish peroxidase (HRP) and luminol and applied it to medical detection of carcinoembryonic antigen (CEA).
2.2. In situ synthesis of CdS NW photosensor The CdS NWs were synthesized using a pulsed-laser deposition system with a KrF excimer laser (Compex-205, Lambda Physik, Germany) excited at 248 nm (An et al., 2015). As the source material, CdS powder was sintered at 600 °C for 1 h in a hot-wall furnace (Ajeon, Korea). The sintered CdS target was located at the center of a quartz tube with a diameter of 5 cm in the hot-wall furnace, as shown in
2.4. Surface analysis We used XPS (XPS-PHI from VersaProbe Co., USA) to detect any modification of the CdS NWs resulting from H2O2 treatment. We recorded the Cd 3d, S 2p, and O 1 s spectra of the surfaces of the CdS NWs (Lee et al., 2012; Pushpalatha and Ganesha, 2014). A Maple-II
Fig. 1. In situ synthesis of CdS NW photosensor. (a) Vacuum tube with CdS target and IDEs before and after the in situ-synthesis process. (b) In situ synthesis of CdS NW photosensor mounted on a printed circuit board.
222
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 2. Changes to in situ-synthesized CdS NW photosensor after treatment with H2O2. (a) SEM images before and after treatment with H2O2. (b) Changes to photoresponsiveness (I–V curve). (c) Changes to photoresponsiveness and reproducibility for repeated measurements. (d) Changes to sensitivity after treatment with H2O2.
Japan) using an Ultima IV goniometer. The Cu Kα radiation X-ray beam was operated at a potential of 40 kV (30 mA) with a 2ϴ range of 20–60 °.
photoluminescence spectroscopy system (DongWoo Optron, Korea) with a He–Cd laser (IK3301R-G, Kimmon, Co. Ltd., Japan) was used at 10 K to minimize the thermal effect (Hoang et al., 2006). SIMS was carried out using a TOF mass spectrometer and pulsed primary ion sources (TOF-SIMS V from ION-TOF GmbH, Germany). To detect the chemical species resulting from the H2O2 surface treatment of the CdS NWs, we used Bi3+ ions, which have a pulse of 150 µs and an ion current of 0.5 pA, as the primary ion source. The primary ion beam was focused on an analytical area of 200 µm ×200 µm, and the extracted ion density was 5×1011 ions/cm2. The crystal structure of the H2O2-treated CdS NWs was characterized by X-ray diffraction (D/MAX-2200/PC from Rigaku, Tokyo,
2.5. CEA enzyme-linked immunosorbent assay tests The CEA enzyme-linked immunosorbent assay (ELISA) tests were carried out using a 96-well microplate coated with anti-CEA antibodies (Perfemed Group Inc., San Francisco, USA). Commercially available ELISA test kits were used according to the manufacturer's instructions. The concentration range of CEA was 0–120 ng/mL. The CEA and antiCEA detection antibody with HRP were diluted in each well and reacted 223
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 3. Analysis of effects of surface treatment with H2O2 on CdS NWs. (a) XPS analysis, (b) PL analysis, and (c) TOF-SIMS analysis.
the CdS nanowires and nanobelts (Gao et al., 2005). Water vapor in the air is known to have more of an influence on the photoresponse characteristics of ZnO thin films and nanowires than oxygen molecules. Because water vapor can capture both electrons and holes, it can more effectively shorten the photoresponse in comparison to oxygen molecules, which only capture electrons (Law and Thong, 2006). In the current work, the influence of surface oxidation on the photoresponsive properties of CdS NWs was assessed by treatment with H2O2, which is a strong oxidant (Lee et al., 2012). In the first step, changes in surface morphology were assessed before and after treatment of the in situsynthesized CdS NW photosensor with H2O2. The scanning electron microscope (SEM) images shown in Fig. 2(a) reveal that the diameters and lengths of the in situ-synthesized NWs apparently changed from 127 ± 39 nm and 4.5 ± 1.68 µm, respectively, before H2O2 treatment to 108 ± 39 nm and 4.1 ± 1.41 µm, respectively, after treatment. Moreover, the surface coverage of the NWs on the IDE electrode changed only slightly from 42.7% to 43.5%. Such a change in surface coverage indicates that the attachment between the NWs and the electrode was not influenced by H2O2 treatment. These results show that H2O2 treatment did not significantly change the morphology or the electrode contact of the in situ-synthesized NWs. When the photoresponse of the CdS NW photosensor was assessed before and after H2O2 treatment, a dramatic change was observed. The in situ-synthesized CdS NW photosensor showed a markedly different photoresponse under dark and light conditions [Fig. 2(b)]. The changes in photoresponse were assessed by repeated irradiation with light at the same intensity. As shown in Fig. 2(c), the photocurrent before H2O2 treatment was 531.3 ± 9.3 (1.8%) nA when the photosensor was irradiated five times with a light of 28.07 µW/cm2 intensity. After H2O2 treatment, the photocurrent was 7.8 ± 1.1 (14.2%) nA under identical conditions. Therefore, the photocurrent significantly decreased by 1.5% and the reproducibility of the measurement increased by eight times as compared to the photocurrent before H2O2 treatment. The change in photoresponse sensitivity was then estimated using light
for 1 h at room temperature. After washing three times, the CEA was quantified by reacting with a 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2 solution for 20 min. A 2 M sulfuric acid solution was used to stop the reaction. The optical density was measured at a wavelength of 450 nm using a VersaMax ELISA reader (Molecular Devices, Sunnyvale, CA, USA). To compare the chromogenic reaction to the chemiluminescence reaction, luminol and H2O2 solution were injected into an incubated microplate well and the chemiluminescence of the CEA was measured using a commercial luminometer with an LB960 photomultiplier tube (Berthold Technologies GmbH & Co., KG, Germany) at 420 nm; the chromogenic reaction was assessed using the in situ-synthesized CdS NW photosensor (Lee et al., 2016). 3. Results and discussion 3.1. Influence of H2O2 on CdS NW photosensor It is well-known that the photoresponse characteristics of nanostructures are significantly influenced by a number of factors, such as defect concentration, crystallographic orientation, grain size, and processing conditions, such as annealing treatment in H2/O2 (Law and Thong, 2006). The surface adsorption of oxygen and water molecules is known to reduce the NW photosensor response of many materials, including as ZnO, Ge, and GaN (Armstrong et al., 2010; Ghosh et al., 2007; Gu and Lauhon, 2006; Hanrath and Korgel, 2004; Jeong et al., 2005; Prades et al., 2008; Wang et al., 2004). The effect is thought to be caused by the electrostatic interaction between the adsorbed molecules and the photocarriers, which reduces the photocurrents (Gao et al., 2005; Gu and Lauhon, 2006; Li et al., 2005). Especially, the adsorption of oxygen on CdS nanowire and nanobelt surfaces is known to be notable, and the oxygen molecules adsorb on the CdS nanowire and nanobelt surfaces as negatively charged ions by capturing free electrons from the n-type CdS. Such adsorption is known to produce a depletion layer with low conductivity near the surfaces of 224
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 4. Parylene-C film as a passivation layer for CdS NW photosensor. (a) Parylene-C coating process: evaporation (160 °C), pyrolysis (650–700 °C), and polymerization (at room temperature). (b) SEM images of CdS NWs after parylene-C coating.
results indicate that the reduction in the photoresponse after H2O2 treatment was caused by surface oxidation. Moreover, the H2O2 reacted with the CdS NW surface to produce CdSO4, which has no photoresponsive properties: CdS + O2 + H2O ↔ CdSO4∙H2O (Lee et al., 2016; Group and Laboratod, 1988). Therefore, the surfaces of the CdS NWs need to be passivated to prevent oxidation and to maintain the photoresponsive properties.
at a series of intensities. As shown in Fig. 2(d), the sensitivity before H2O2 treatment was 10.44 nA/(µW/cm2) for irradiation with light in the intensity range 28.07–188.7 µW/cm2. After H2O2 treatment, the photocurrent was 0.55 nA/(µW/cm2) for light in the same intensity range. Therefore, the sensitivity decreased by 5% as compared to the sensitivity before H2O2 treatment. These results show that the photoresponse significantly decreased after H2O2 treatment. Because the morphology and the surface coverage of the in situ-synthesized CdS NW photosensor exhibited minimal change, we think that the decrease in the photoresponse was caused by the oxidation of the CdS NW surface resulting from H2O2 treatment. The XPS analysis was carried out on the CdS NWs before and after H2O2 treatment. As shown in Fig. 3(a), the XPS peaks due to the Cd 3d orbital did not change significantly. However, the XPS peaks due to the S 2 P and O 1 S orbitals revealed the presence of CdSO4 on the CdS NW surface after treatment with H2O2. The photoluminescence (PL) analysis was carried out on the CdS NWs before and after H2O2 treatment. As shown in Fig. 3(b), the near-band edge peak at 484 nm did not change significantly. However, the intensity of the defectrelated peak at 486 nm changed significantly after treatment with H2O2. These results indicate that changes occurred on the surfaces of the in situ-synthesized NWs after H2O2 treatment. The TOF-SIMS analysis was carried out on the CdS NWs before and after treatment with H2O2. As shown in Fig. 3(c), the number of ejected CdS anions decreased and the number of ejected CdSO4 anions increased after H2O2 treatment. These results also suggest that CdSO4 was produced on the surfaces of the CdS NWs during treatment with H2O2. These
3.2. Effect of parylene coating on CdS NW photosensor The passivation layer on the CdS NW photosensor must have certain properties, including transparency, chemical resistance, and water resistance. Parylene films satisfy these requirements; they have high chemical resistance to organic solvents such as alcohols and acetone, high transparency over the visible spectrum (400–700 nm), electrically insulating properties, water resistance, etc. In this work, parylene-C was used for the passivation of CdS NWs. As shown schematically in Fig. 4(a), a parylene-C film was coated onto the surfaces of the CdS NWs by thermal deposition involving evaporation (160 °C), pyrolysis (650 °C), and polymerization at room temperature. Because the parylene-C film was deposited in a gas-phase reaction, the coating enveloped the surface NWs or nanoribbons to provide a uniform thickness, as shown in Fig. 4(b). The parylene-C film was coated to prevent the surface reactions that influence the photoresponsive properties of CdS NWs. To assess the ability of the parylene-C film to prevent the oxidation of the CdS NW surface, H2O2 was used to treat the parylene-C-coated CdS NWs. As 225
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 5. Influence of parylene-C film on photoresponsiveness of CdS NW. (a) Changes in photoresponsiveness (I–V curve) after coating with different thicknesses of paryleneC. (b) Analysis of the change in photoresponsiveness of the CdS NW photosensor during the parylene-C coating process using a QCM. (c) Changes in photoresponsiveness for repeated measurements during parylene-C coating process. (d) Averaged photoresponsiveness and reproducibility for repeated measurements during parylene-C coating process. (e) Changes in photoresponsiveness according to the thickness of the parylene-C film. (f) Influence of vacuum on the sensitivity of the CdS NW photosensor.
226
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
photoresponse of the NWs was monitored on-line during the coating process. On-line monitoring of the photoresponsiveness of the CdS NWs was achieved by installing a CdS NW photosensor and a light source inside the parylene coater. At the same time, the thickness of the parylene-C film was monitored using a QCM, which was also installed inside the parylene coater. As shown in Fig. 5(b), the resonance frequency was gradually reduced from 9.972 to 9.837 MHz during the deposition of the parylene-C film. The change in resonance frequency (135,539 Hz) corresponded to the thickness of the coated parylene-C film (1.4 µm). During parylene-C film deposition, changes in the photoresponsiveness of the in situ-synthesized CdS NW photosensor were monitored on-line 10 times inside the parylene coater, as shown in Fig. 5(c). For each measurement, light of 28.07 µW/cm2 intensity was irradiated five times, and the average value of the photocurrent was taken as the photoresponse. As shown in Fig. 5(d) and Fig. 5(e), the photoresponse measured on-line increased as the thickness of the parylene-C film increased during parylene-C film deposition to a thickness of 1.4 µm. As shown in Fig. 5(f), the photoresponses under vacuum and in air were compared before and after deposition of the parylene-C film. The parylene-C-coated CdS NWs had a higher photoresponse than the uncoated CdS NW photosensor under vacuum as well as in air. Moreover, the parylene-C-coated CdS NWs showed a small (11.3%) difference in photoresponsiveness under vacuum and in air as compared to the uncoated CdS NW photosensor (43.0%). 3.3. Application to chemiluminescence detection Usually, chemiluminescent immunoassays depend on the reaction between an enzyme called HRP and a luminescent chemical probe such as luminol. The chemiluminescence reaction between HRP and luminol generates light at a wavelength of 420 nm, and it has been applied to immunoassays for the sensitive detection of target analytes. Immunoassays based on chemiluminescence detection are reported to have a far higher sensitivity than those based on fluorescence or chromogenic reactions. However, the intensity of the chemiluminescence from HRP and luminol is quite low, and therefore detection requires specialized image sensors with a cooling device or photomultiplier tubes (PMTs) (An et al., 2015). In the current work, we used the in situ-synthesized CdS NW photosensor to detect the chemiluminescence reaction between HRP and luminol to compare the sensitivity of the photosensor to that of a commercial PMT-based luminometer. First, anti-HRP antibodies were coated onto a 96-well microplate and HRP solutions of known concentrations were added as samples. The bound HRP was quantified by the addition of a luminol solution to generate a chemiluminescence signal. As shown in Fig. 6(a), the limit of detection (LOD) of the luminometer was estimated to be 3.1ng/mL and that of the CdS NW photosensor was estimated to be 4.0 ng/mL. The sensitivity of the CdS NW photosensor was thus comparable to that of the PMT-based luminometer over the whole HRP concentration range. These results suggest that the in situ-synthesized CdS NW photosensor had a sensitivity that was comparable to that of a PMT-based luminometer. The in situ-synthesized CdS NW photosensor was applied to the medical detection of different concentrations of CEA using ELISA kits based on a chemiluminescent reaction. The tests were carried out by establishing a cutoff value for determining the presence of the analyte in the sample. If the test result was higher (or lower) than the cutoff value, the sample was determined to be positive (or negative) for the corresponding test. Such a cutoff value was established according to the instructions provided by the manufacturer using the negative and positive control samples included in each ELISA kit. As shown in Fig. 6(b), the ELISA kits for the analysis of CEA used to quantify CEA in the samples. The chemiluminescence from the reaction was measured using a commercial luminometer with a photomultiplier tube (from Berthold) and the CdS NW photosensor coated with parylene-C.
Fig. 6. Application of in situ-synthesized CdS NW photosensor with parylene-C coating to immunoassays. (a) Comparison of quantitative analysis results from the CdS NW photosensor and a commercial PMT-based luminometer. (b) Application to medical detection of CEA in phosphate-buffered saline and comparison of quantitative analysis results from the CdS NW photosensor and the commercial PMTbased luminometer. (c) medical detection of CEA spiked in serum sample and comparison of quantitative analysis results from the CdS NW photosensor and the commercial PMT-based luminometer.
shown in Fig. 5(a), the parylene-C-coated NWs had nearly the same photoresponsive properties as before the coating. When H2O2 was used to treat NWs that had been coated with a 1-μm-thick parylene-C film, the photoresponsive properties changed slightly as compared to before the H2O2 treatment. For the CdS NWs that had been coated with a 2μm-thick parylene-C film, the reduction in the photoresponse was almost insignificant. To investigate the relationship between the thickness of the parylene-C coating and the photoresponsiveness of the CdS NWs, the 227
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Planning (MSIP, Korea) and the Ministry of Trade, Industry and Energy (MOTIE, Korea), and by the Industry Technology Development Program (10063335) funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea).
As shown in Fig. 6(b), the cutoff value was set to be 5 ng/mL. The LOD of the luminometer was 0.8 ng/mL and that of the CdS NW photosensor was 3.2 ng/mL, and thus the sensitivity of the CdS NW photosensor was comparable to that of the PMT-based luminometer over the whole CEA concentration range. Additionally, the same ELISA kits used for the analysis of CEA were used to quantify the CEA spiked in the serum samples. As shown in Fig. 6(c), the cutoff value was again set to be 5 ng/mL. The LOD of the luminometer was 1.9ng/mL and that of the CdS NW photosensor was 1.7 ng/mL, and thus the sensitivity of the CdS NW photosensor was comparable to that of the PMT-based luminometer over the whole CEA concentration range. These results suggest that the in situ-synthesized CdS NW photosensor had a sensitivity that was comparable to that of the PMT-based luminometer and that the photosensor could be used for CEA detection in medical diagnoses.
References Ahn, S.E., Ji, H.J., Kim, K., Kim, G.T., Bae, C.H., Park, S.M., Kim, Y.K., Ha, J.S., 2007. Appl. Phys. Lett. 90 (15), 2005–2008. An, B.G., Chang, Y.W., Kim, H.R., Lee, G., Kang, M.J., Park, J.K., Pyun, J.C., 2015. Sens. Actuators, B 221, 884–890. An, B.G., Kim, H.R., Kang, M.J., Park, J.G., Chang, Y.W., Pyun, J.C., 2016. Anal. Chim. Acta 927, 99–106. Armstrong, A., Li, Q., Lin, Y., Talin, A.A., Wang, G.T., 2010. Appl. Phys. Lett. 96 (16), 16–19. Gao, T., Li, Q.H., Wang, T.H., 2005. Appl. Phys. Lett. 86 (16), 1–3. Ghosh, R., Dutta, M., Basak, D., 2007. Appl. Phys. Lett. 91 (7), 1–4. Group, P., Laboratod, S.C., 1988. Appl. Surf. Sci. 32 (1–2), 218–232. Gu, Y., Lauhon, L.J., 2006. Appl. Phys. Lett. 89 (14), 1–4. Han, C.S., Lee, T.H., Kim, G.M., Lee, D.Y., Cho, Y.S., 2016. J. Korean Ceram. Soc. 53 (2), 167–170. Hanrath, T., Korgel, B.A., 2004. J. Am. Chem. Soc. 126 (47), 15466–15472. He, J.H., Lin, Y.H., McConney, M.E., Tsukruk, V.V., Wang, Z.L., Bao, G., 2007. J. Appl. Phys. 102 (8), 084303. Hoang, T.B., Titova, L.V., Jackson, H.E., Smith, L.M., Yarrison-Rice, J.M., Lensch, J.L., Lauhon, L.J., 2006. Appl. Phys. Lett. 89 (12), 2–5. Hong, W.-K., Kim, B.-J., Kim, T.-W., Jo, G., Song, S., Kwon, S.-S., Yoon, A., Stach, E.A., Lee, T., 2008. Colloids Surf., A 313–314, 378–382. Jeong, M., Oh, B., Lee, W., Myoung, J., 2005. Appl. Phys. Lett. 86 (10), 103105. Park, J.C., Yoon, Y.S., Kang, S.J., 2016. J. Korean Ceram. Soc. 53 (5), 563–567. Ko, H., Choi, Y.H., Chang, S.Y., Lee, G.Y., Song, H.W., Chang, Y.W., Kang, M.J., Pyun, J.C., 2015. Eur. Polym. J. 68, 36–46. Law, J.B.K., Thong, J.T.L., 2006. Appl. Phys. Lett. 88 (13), 133114. Lee, G.-Y., Chang, Y.W., Ko, H., Kang, M.-J., Pyun, J.-C., 2016. Anal. Chim. Acta 928, 39–48. Lee, W., Kim, H., Jung, D.-R., Kim, J., Nahm, C., Lee, J., Kang, S., Lee, B., Park, B., 2012. Nanoscale Res. Lett. 7 (1), 672. Li, Q.H., Gao, T., Wang, T.H., 2005. Appl. Phys. Lett. 86 (19), 1–3. Park, J.M., Jung, H.W., Chang, Y.W., Kim, H.S., Kang, M.J., Pyun, J.C., 2015. Anal. Chim. Acta 853, 360–367. Park, W. Il, Kim, J.S., Yi, G.C., Bae, M.H., Lee, H.J., 2004. Appl. Phys. Lett. 85 (21), 5052–5054. Prades, J.D., Jimenez-Diaz, R., Hernandez-Ramirez, F., Fernandez-Romero, L., Andreu, T., Cirera, A., Romano-Rodriguez, A., Cornet, A., Morante, J.R., Barth, S., Mathur, S., 2008. J. Phys. Chem. C. 112 (37), 14639–14644. Pushpalatha, H.L., Ganesha, R., 2014. Int. J. ChemTech Res. 7 (5), 2171–2175. Wang, D., Chang, Y.L., Wang, Q., Cao, J., Farmer, D.B., Gordon, R.G., Dai, H., 2004. J. Am. Chem. Soc. 126 (37), 11602–11611.
4. Conclusions An in situ-synthesized CdS NW photosensor showed a dramatic change in photoresponse after H2O2 treatment. SEM analysis revealed that the H2O2 treatment made no significant change to the morphology or the electrode contact of the in situ-synthesized CdS NWs. TOF-SIMS analysis revealed that the H2O2 reacted with the CdS NW surface to produce CdSO4, which had no photoresponsive properties: CdS + O2 + H2O ↔ CdSO4∙H2O. Therefore, the surfaces of CdS NWs needed to be passivated to prevent oxidation and to retain photoresponsiveness. When H2O2 peroxide was used to treat NWs coated with a 2-μm-thick layer of parylene-C, the reduction in the photoresponse was almost insignificant. The influence of the parylene-C passivation layer on photoresponsiveness was investigated during the parylene-C coating process under vacuum using a QCM and a photoanalyzer. Finally, an in situ-synthesized CdS NW photosensor with a parylene-C passivation layer was used to detect the chemiluminescent reaction of HRP and luminol and for the medical detection of CEA. Acknowledgements This work was supported by Nano-Convergence Foundation (R201602210) funded by the Ministry of Science, ICT and Future
228
Contents lists available at ScienceDirect
Biosensors and Bioelectronics journal homepage: www.elsevier.com/locate/bios
In situ-synthesized cadmium sulfide nanowire photosensor with a parylene passivation layer for chemiluminescent immunoassays
MARK
Ju-Hee Ima,b,1, Hong-Rae Kima,1, Byoung-Gi Ana,c, Young Wook Changa, Min-Jung Kangb, Tae⁎ Geol Leed, Jin Gyeng Sond, Jae-Gwan Parkb, Jae-Chul Pyuna, a
Department of Materials Sciences and Engineering, Yonsei University, 50 Yonsei-Ro, Seo-dae-mun-gu, Seoul 120-749, Republic of Korea Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea c Samsung Electro-Mechanics, Kyonggi, Republic of Korea d Korea Research Institute of Standards and Science (KRISS), Daejeon, Republic of Korea b
A R T I C L E I N F O
A BS T RAC T
Keywords: CdS Nanowire Photosensor Parylene-C Passivation Chemiluminescence
The direct in situ synthesis of cadmium sulfide (CdS) nanowires (NWs) was presented by direct synthesis of CdS NWs on the gold surface of an interdigitated electrode (IDE). In this work, we investigated the effect of a strong oxidant on the surfaces of the CdS NWs using X-ray photoelectron spectroscopy, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry. We also fabricated a parylene-C film as a surface passivation layer for in situ-synthesized CdS NW photosensors and investigated the influence of the parylene-C passivation layer on the photoresponse during the coating of parylene-C under vacuum using a quartz crystal microbalance and a photoanalyzer. Finally, we used the in situ-synthesized CdS NW photosensor with the parylene-C passivation layer to detect the chemiluminescence of horseradish peroxidase and luminol and applied it to medical detection of carcinoembryonic antigen.
1. Introduction Recently, we reported the direct synthesis of cadmium sulfide (CdS) nanowires (NWs) on the gold surface of an interdigitated electrode (IDE) (An et al., 2015). Such a direct approach is called in situ synthesis. An in situ-synthesized CdS NW photosensor has the following advantages: (1) the NWs have enhanced surface density, which is related to the sensitivity of the photosensors; (2) ultrasonication, which may induce physical changes in the NWs, is not required to isolate them; and (3) there is improved contact between the NWs and the IDE surface. Usually, NW photosensors made of materials such as ZnO, Ge, and GaN show a reduced photoresponse after adsorbing oxygen or water molecules (Armstrong et al., 2010; Ghosh et al., 2007; Gu and Lauhon, 2006; Han et al., 2016; Hanrath and Korgel, 2004; Jeong et al., 2005; Park et al., 2016; Prades et al., 2008; Wang et al., 2004). Such an effect is explained by the electrostatic interaction between the adsorbed molecules and the photocarriers, which reduces the photocurrents (Ahn et al., 2007; Gao et al., 2005; Ghosh et al., 2007; Gu and Lauhon, 2006; Law and Thong, 2006; Li et al., 2005). Therefore, various types of polymers, such as poly(methyl methacrylate) (PMMA), polyimide, and polyacrylonitrile, have been used for the surface
⁎
1
passivation of NW photosensors (He et al., 2007; Hong et al., 2008; Park et al., 2004). Although ZnO nanowires are strongly affected by O2 molecules in ambient atmosphere, the electrical properties of ZnO nanowires were reported to have exhibited better performance when they were coated with PMMA (200 nm thick) and polyimide (nmethoxy methylated nylon, 2 µm thick) in comparison to unpassivated devices (Hong et al., 2008; Park et al., 2004). ZnO nanobelts also showed an enhanced photoresponse, up to 750 times higher than that of bare ZnO nanobelts, after they were coated with a plasma-polymerized acrylonitrile film with a thickness of less than 20 nm (He et al., 2007). Surface passivation of NW photosensors requires certain properties, including transparency, chemical resistance, and water repellence. In this work, we used a strong oxidant [hydrogen peroxide (H2O2)] to study the influence of surface oxidation on the photoresponsiveness of CdS NWs (Lee et al., 2012) using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). We fabricated a parylene-C film as a surface passivation layer for in situ-synthesized CdS NW photosensors and investigated the influence of the parylene-C passivation layer on the photoresponse during the coating of parylene-
Corresponding author. E-mail address: [email protected] (J.-C. Pyun). These authors contributed equally to this work.
http://dx.doi.org/10.1016/j.bios.2017.02.021 Received 28 November 2016; Received in revised form 25 January 2017; Accepted 13 February 2017 Available online 16 February 2017 0956-5663/ © 2017 Elsevier B.V. All rights reserved.
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
2. Material and methods
Fig. 1(a). Once the temperature reached 650 °C, the KrF excimer laser was focused on the CdS target and the laser energy density was maintained at 1–5 J/cm2. The synthesis temperature was maintained at 650 °C for 30 min under a N2 and H2 atmosphere with a constant inner pressure of ~667 Pa (~5 Torr). IDEs with a width of 5 µm were located 9–13 cm from the sintered CdS target in the furnace tube (An et al., 2016).
2.1. Materials
2.3. Parylene deposition
Cadmium sulfide powder ( > 99.9%, < 1 µm), HRP, and other analytical-grade chemicals were purchased from Sigma-Aldrich Korea (Seoul, Korea). Dichloro-di-p-xylylene powder was purchased from Daisan Kasei Co. Ltd. (Tokyo, Japan). CEA enzyme immunoassay test kits were purchased from the Perfemed Group Inc. (San Francisco, CA, USA). Luminol was purchased from Pierce Co. (Rockford, IL, USA) (Park et al., 2015).
We used a commercial parylene deposition system (Kisco, Japan) to prepare parylene-C-coated CdS NWs. The parylene-C film was deposited in the following three steps: (1) evaporation of the dimers of parylene-C at 160 °C; (2) pyrolysis at 650 °C to transform the parylene dimers into highly reactive free radicals; and (3) deposition and polymerization on the CdS NWs at room temperature under a vacuum of less than 5.3 Pa (40 mTorr). The thickness of the parylene film was controlled by adjusting the initial amount of parylene dimers (Ko et al., 2015).
C under vacuum using a quartz crystal microbalance (QCM) and a photoanalyzer. Finally, we used the in situ-synthesized CdS NW photosensor with the parylene-C passivation layer to detect the chemiluminescence of horseradish peroxidase (HRP) and luminol and applied it to medical detection of carcinoembryonic antigen (CEA).
2.2. In situ synthesis of CdS NW photosensor The CdS NWs were synthesized using a pulsed-laser deposition system with a KrF excimer laser (Compex-205, Lambda Physik, Germany) excited at 248 nm (An et al., 2015). As the source material, CdS powder was sintered at 600 °C for 1 h in a hot-wall furnace (Ajeon, Korea). The sintered CdS target was located at the center of a quartz tube with a diameter of 5 cm in the hot-wall furnace, as shown in
2.4. Surface analysis We used XPS (XPS-PHI from VersaProbe Co., USA) to detect any modification of the CdS NWs resulting from H2O2 treatment. We recorded the Cd 3d, S 2p, and O 1 s spectra of the surfaces of the CdS NWs (Lee et al., 2012; Pushpalatha and Ganesha, 2014). A Maple-II
Fig. 1. In situ synthesis of CdS NW photosensor. (a) Vacuum tube with CdS target and IDEs before and after the in situ-synthesis process. (b) In situ synthesis of CdS NW photosensor mounted on a printed circuit board.
222
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 2. Changes to in situ-synthesized CdS NW photosensor after treatment with H2O2. (a) SEM images before and after treatment with H2O2. (b) Changes to photoresponsiveness (I–V curve). (c) Changes to photoresponsiveness and reproducibility for repeated measurements. (d) Changes to sensitivity after treatment with H2O2.
Japan) using an Ultima IV goniometer. The Cu Kα radiation X-ray beam was operated at a potential of 40 kV (30 mA) with a 2ϴ range of 20–60 °.
photoluminescence spectroscopy system (DongWoo Optron, Korea) with a He–Cd laser (IK3301R-G, Kimmon, Co. Ltd., Japan) was used at 10 K to minimize the thermal effect (Hoang et al., 2006). SIMS was carried out using a TOF mass spectrometer and pulsed primary ion sources (TOF-SIMS V from ION-TOF GmbH, Germany). To detect the chemical species resulting from the H2O2 surface treatment of the CdS NWs, we used Bi3+ ions, which have a pulse of 150 µs and an ion current of 0.5 pA, as the primary ion source. The primary ion beam was focused on an analytical area of 200 µm ×200 µm, and the extracted ion density was 5×1011 ions/cm2. The crystal structure of the H2O2-treated CdS NWs was characterized by X-ray diffraction (D/MAX-2200/PC from Rigaku, Tokyo,
2.5. CEA enzyme-linked immunosorbent assay tests The CEA enzyme-linked immunosorbent assay (ELISA) tests were carried out using a 96-well microplate coated with anti-CEA antibodies (Perfemed Group Inc., San Francisco, USA). Commercially available ELISA test kits were used according to the manufacturer's instructions. The concentration range of CEA was 0–120 ng/mL. The CEA and antiCEA detection antibody with HRP were diluted in each well and reacted 223
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 3. Analysis of effects of surface treatment with H2O2 on CdS NWs. (a) XPS analysis, (b) PL analysis, and (c) TOF-SIMS analysis.
the CdS nanowires and nanobelts (Gao et al., 2005). Water vapor in the air is known to have more of an influence on the photoresponse characteristics of ZnO thin films and nanowires than oxygen molecules. Because water vapor can capture both electrons and holes, it can more effectively shorten the photoresponse in comparison to oxygen molecules, which only capture electrons (Law and Thong, 2006). In the current work, the influence of surface oxidation on the photoresponsive properties of CdS NWs was assessed by treatment with H2O2, which is a strong oxidant (Lee et al., 2012). In the first step, changes in surface morphology were assessed before and after treatment of the in situsynthesized CdS NW photosensor with H2O2. The scanning electron microscope (SEM) images shown in Fig. 2(a) reveal that the diameters and lengths of the in situ-synthesized NWs apparently changed from 127 ± 39 nm and 4.5 ± 1.68 µm, respectively, before H2O2 treatment to 108 ± 39 nm and 4.1 ± 1.41 µm, respectively, after treatment. Moreover, the surface coverage of the NWs on the IDE electrode changed only slightly from 42.7% to 43.5%. Such a change in surface coverage indicates that the attachment between the NWs and the electrode was not influenced by H2O2 treatment. These results show that H2O2 treatment did not significantly change the morphology or the electrode contact of the in situ-synthesized NWs. When the photoresponse of the CdS NW photosensor was assessed before and after H2O2 treatment, a dramatic change was observed. The in situ-synthesized CdS NW photosensor showed a markedly different photoresponse under dark and light conditions [Fig. 2(b)]. The changes in photoresponse were assessed by repeated irradiation with light at the same intensity. As shown in Fig. 2(c), the photocurrent before H2O2 treatment was 531.3 ± 9.3 (1.8%) nA when the photosensor was irradiated five times with a light of 28.07 µW/cm2 intensity. After H2O2 treatment, the photocurrent was 7.8 ± 1.1 (14.2%) nA under identical conditions. Therefore, the photocurrent significantly decreased by 1.5% and the reproducibility of the measurement increased by eight times as compared to the photocurrent before H2O2 treatment. The change in photoresponse sensitivity was then estimated using light
for 1 h at room temperature. After washing three times, the CEA was quantified by reacting with a 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2 solution for 20 min. A 2 M sulfuric acid solution was used to stop the reaction. The optical density was measured at a wavelength of 450 nm using a VersaMax ELISA reader (Molecular Devices, Sunnyvale, CA, USA). To compare the chromogenic reaction to the chemiluminescence reaction, luminol and H2O2 solution were injected into an incubated microplate well and the chemiluminescence of the CEA was measured using a commercial luminometer with an LB960 photomultiplier tube (Berthold Technologies GmbH & Co., KG, Germany) at 420 nm; the chromogenic reaction was assessed using the in situ-synthesized CdS NW photosensor (Lee et al., 2016). 3. Results and discussion 3.1. Influence of H2O2 on CdS NW photosensor It is well-known that the photoresponse characteristics of nanostructures are significantly influenced by a number of factors, such as defect concentration, crystallographic orientation, grain size, and processing conditions, such as annealing treatment in H2/O2 (Law and Thong, 2006). The surface adsorption of oxygen and water molecules is known to reduce the NW photosensor response of many materials, including as ZnO, Ge, and GaN (Armstrong et al., 2010; Ghosh et al., 2007; Gu and Lauhon, 2006; Hanrath and Korgel, 2004; Jeong et al., 2005; Prades et al., 2008; Wang et al., 2004). The effect is thought to be caused by the electrostatic interaction between the adsorbed molecules and the photocarriers, which reduces the photocurrents (Gao et al., 2005; Gu and Lauhon, 2006; Li et al., 2005). Especially, the adsorption of oxygen on CdS nanowire and nanobelt surfaces is known to be notable, and the oxygen molecules adsorb on the CdS nanowire and nanobelt surfaces as negatively charged ions by capturing free electrons from the n-type CdS. Such adsorption is known to produce a depletion layer with low conductivity near the surfaces of 224
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 4. Parylene-C film as a passivation layer for CdS NW photosensor. (a) Parylene-C coating process: evaporation (160 °C), pyrolysis (650–700 °C), and polymerization (at room temperature). (b) SEM images of CdS NWs after parylene-C coating.
results indicate that the reduction in the photoresponse after H2O2 treatment was caused by surface oxidation. Moreover, the H2O2 reacted with the CdS NW surface to produce CdSO4, which has no photoresponsive properties: CdS + O2 + H2O ↔ CdSO4∙H2O (Lee et al., 2016; Group and Laboratod, 1988). Therefore, the surfaces of the CdS NWs need to be passivated to prevent oxidation and to maintain the photoresponsive properties.
at a series of intensities. As shown in Fig. 2(d), the sensitivity before H2O2 treatment was 10.44 nA/(µW/cm2) for irradiation with light in the intensity range 28.07–188.7 µW/cm2. After H2O2 treatment, the photocurrent was 0.55 nA/(µW/cm2) for light in the same intensity range. Therefore, the sensitivity decreased by 5% as compared to the sensitivity before H2O2 treatment. These results show that the photoresponse significantly decreased after H2O2 treatment. Because the morphology and the surface coverage of the in situ-synthesized CdS NW photosensor exhibited minimal change, we think that the decrease in the photoresponse was caused by the oxidation of the CdS NW surface resulting from H2O2 treatment. The XPS analysis was carried out on the CdS NWs before and after H2O2 treatment. As shown in Fig. 3(a), the XPS peaks due to the Cd 3d orbital did not change significantly. However, the XPS peaks due to the S 2 P and O 1 S orbitals revealed the presence of CdSO4 on the CdS NW surface after treatment with H2O2. The photoluminescence (PL) analysis was carried out on the CdS NWs before and after H2O2 treatment. As shown in Fig. 3(b), the near-band edge peak at 484 nm did not change significantly. However, the intensity of the defectrelated peak at 486 nm changed significantly after treatment with H2O2. These results indicate that changes occurred on the surfaces of the in situ-synthesized NWs after H2O2 treatment. The TOF-SIMS analysis was carried out on the CdS NWs before and after treatment with H2O2. As shown in Fig. 3(c), the number of ejected CdS anions decreased and the number of ejected CdSO4 anions increased after H2O2 treatment. These results also suggest that CdSO4 was produced on the surfaces of the CdS NWs during treatment with H2O2. These
3.2. Effect of parylene coating on CdS NW photosensor The passivation layer on the CdS NW photosensor must have certain properties, including transparency, chemical resistance, and water resistance. Parylene films satisfy these requirements; they have high chemical resistance to organic solvents such as alcohols and acetone, high transparency over the visible spectrum (400–700 nm), electrically insulating properties, water resistance, etc. In this work, parylene-C was used for the passivation of CdS NWs. As shown schematically in Fig. 4(a), a parylene-C film was coated onto the surfaces of the CdS NWs by thermal deposition involving evaporation (160 °C), pyrolysis (650 °C), and polymerization at room temperature. Because the parylene-C film was deposited in a gas-phase reaction, the coating enveloped the surface NWs or nanoribbons to provide a uniform thickness, as shown in Fig. 4(b). The parylene-C film was coated to prevent the surface reactions that influence the photoresponsive properties of CdS NWs. To assess the ability of the parylene-C film to prevent the oxidation of the CdS NW surface, H2O2 was used to treat the parylene-C-coated CdS NWs. As 225
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Fig. 5. Influence of parylene-C film on photoresponsiveness of CdS NW. (a) Changes in photoresponsiveness (I–V curve) after coating with different thicknesses of paryleneC. (b) Analysis of the change in photoresponsiveness of the CdS NW photosensor during the parylene-C coating process using a QCM. (c) Changes in photoresponsiveness for repeated measurements during parylene-C coating process. (d) Averaged photoresponsiveness and reproducibility for repeated measurements during parylene-C coating process. (e) Changes in photoresponsiveness according to the thickness of the parylene-C film. (f) Influence of vacuum on the sensitivity of the CdS NW photosensor.
226
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
photoresponse of the NWs was monitored on-line during the coating process. On-line monitoring of the photoresponsiveness of the CdS NWs was achieved by installing a CdS NW photosensor and a light source inside the parylene coater. At the same time, the thickness of the parylene-C film was monitored using a QCM, which was also installed inside the parylene coater. As shown in Fig. 5(b), the resonance frequency was gradually reduced from 9.972 to 9.837 MHz during the deposition of the parylene-C film. The change in resonance frequency (135,539 Hz) corresponded to the thickness of the coated parylene-C film (1.4 µm). During parylene-C film deposition, changes in the photoresponsiveness of the in situ-synthesized CdS NW photosensor were monitored on-line 10 times inside the parylene coater, as shown in Fig. 5(c). For each measurement, light of 28.07 µW/cm2 intensity was irradiated five times, and the average value of the photocurrent was taken as the photoresponse. As shown in Fig. 5(d) and Fig. 5(e), the photoresponse measured on-line increased as the thickness of the parylene-C film increased during parylene-C film deposition to a thickness of 1.4 µm. As shown in Fig. 5(f), the photoresponses under vacuum and in air were compared before and after deposition of the parylene-C film. The parylene-C-coated CdS NWs had a higher photoresponse than the uncoated CdS NW photosensor under vacuum as well as in air. Moreover, the parylene-C-coated CdS NWs showed a small (11.3%) difference in photoresponsiveness under vacuum and in air as compared to the uncoated CdS NW photosensor (43.0%). 3.3. Application to chemiluminescence detection Usually, chemiluminescent immunoassays depend on the reaction between an enzyme called HRP and a luminescent chemical probe such as luminol. The chemiluminescence reaction between HRP and luminol generates light at a wavelength of 420 nm, and it has been applied to immunoassays for the sensitive detection of target analytes. Immunoassays based on chemiluminescence detection are reported to have a far higher sensitivity than those based on fluorescence or chromogenic reactions. However, the intensity of the chemiluminescence from HRP and luminol is quite low, and therefore detection requires specialized image sensors with a cooling device or photomultiplier tubes (PMTs) (An et al., 2015). In the current work, we used the in situ-synthesized CdS NW photosensor to detect the chemiluminescence reaction between HRP and luminol to compare the sensitivity of the photosensor to that of a commercial PMT-based luminometer. First, anti-HRP antibodies were coated onto a 96-well microplate and HRP solutions of known concentrations were added as samples. The bound HRP was quantified by the addition of a luminol solution to generate a chemiluminescence signal. As shown in Fig. 6(a), the limit of detection (LOD) of the luminometer was estimated to be 3.1ng/mL and that of the CdS NW photosensor was estimated to be 4.0 ng/mL. The sensitivity of the CdS NW photosensor was thus comparable to that of the PMT-based luminometer over the whole HRP concentration range. These results suggest that the in situ-synthesized CdS NW photosensor had a sensitivity that was comparable to that of a PMT-based luminometer. The in situ-synthesized CdS NW photosensor was applied to the medical detection of different concentrations of CEA using ELISA kits based on a chemiluminescent reaction. The tests were carried out by establishing a cutoff value for determining the presence of the analyte in the sample. If the test result was higher (or lower) than the cutoff value, the sample was determined to be positive (or negative) for the corresponding test. Such a cutoff value was established according to the instructions provided by the manufacturer using the negative and positive control samples included in each ELISA kit. As shown in Fig. 6(b), the ELISA kits for the analysis of CEA used to quantify CEA in the samples. The chemiluminescence from the reaction was measured using a commercial luminometer with a photomultiplier tube (from Berthold) and the CdS NW photosensor coated with parylene-C.
Fig. 6. Application of in situ-synthesized CdS NW photosensor with parylene-C coating to immunoassays. (a) Comparison of quantitative analysis results from the CdS NW photosensor and a commercial PMT-based luminometer. (b) Application to medical detection of CEA in phosphate-buffered saline and comparison of quantitative analysis results from the CdS NW photosensor and the commercial PMTbased luminometer. (c) medical detection of CEA spiked in serum sample and comparison of quantitative analysis results from the CdS NW photosensor and the commercial PMT-based luminometer.
shown in Fig. 5(a), the parylene-C-coated NWs had nearly the same photoresponsive properties as before the coating. When H2O2 was used to treat NWs that had been coated with a 1-μm-thick parylene-C film, the photoresponsive properties changed slightly as compared to before the H2O2 treatment. For the CdS NWs that had been coated with a 2μm-thick parylene-C film, the reduction in the photoresponse was almost insignificant. To investigate the relationship between the thickness of the parylene-C coating and the photoresponsiveness of the CdS NWs, the 227
Biosensors and Bioelectronics 92 (2017) 221–228
J.-H. Im et al.
Planning (MSIP, Korea) and the Ministry of Trade, Industry and Energy (MOTIE, Korea), and by the Industry Technology Development Program (10063335) funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea).
As shown in Fig. 6(b), the cutoff value was set to be 5 ng/mL. The LOD of the luminometer was 0.8 ng/mL and that of the CdS NW photosensor was 3.2 ng/mL, and thus the sensitivity of the CdS NW photosensor was comparable to that of the PMT-based luminometer over the whole CEA concentration range. Additionally, the same ELISA kits used for the analysis of CEA were used to quantify the CEA spiked in the serum samples. As shown in Fig. 6(c), the cutoff value was again set to be 5 ng/mL. The LOD of the luminometer was 1.9ng/mL and that of the CdS NW photosensor was 1.7 ng/mL, and thus the sensitivity of the CdS NW photosensor was comparable to that of the PMT-based luminometer over the whole CEA concentration range. These results suggest that the in situ-synthesized CdS NW photosensor had a sensitivity that was comparable to that of the PMT-based luminometer and that the photosensor could be used for CEA detection in medical diagnoses.
References Ahn, S.E., Ji, H.J., Kim, K., Kim, G.T., Bae, C.H., Park, S.M., Kim, Y.K., Ha, J.S., 2007. Appl. Phys. Lett. 90 (15), 2005–2008. An, B.G., Chang, Y.W., Kim, H.R., Lee, G., Kang, M.J., Park, J.K., Pyun, J.C., 2015. Sens. Actuators, B 221, 884–890. An, B.G., Kim, H.R., Kang, M.J., Park, J.G., Chang, Y.W., Pyun, J.C., 2016. Anal. Chim. Acta 927, 99–106. Armstrong, A., Li, Q., Lin, Y., Talin, A.A., Wang, G.T., 2010. Appl. Phys. Lett. 96 (16), 16–19. Gao, T., Li, Q.H., Wang, T.H., 2005. Appl. Phys. Lett. 86 (16), 1–3. Ghosh, R., Dutta, M., Basak, D., 2007. Appl. Phys. Lett. 91 (7), 1–4. Group, P., Laboratod, S.C., 1988. Appl. Surf. Sci. 32 (1–2), 218–232. Gu, Y., Lauhon, L.J., 2006. Appl. Phys. Lett. 89 (14), 1–4. Han, C.S., Lee, T.H., Kim, G.M., Lee, D.Y., Cho, Y.S., 2016. J. Korean Ceram. Soc. 53 (2), 167–170. Hanrath, T., Korgel, B.A., 2004. J. Am. Chem. Soc. 126 (47), 15466–15472. He, J.H., Lin, Y.H., McConney, M.E., Tsukruk, V.V., Wang, Z.L., Bao, G., 2007. J. Appl. Phys. 102 (8), 084303. Hoang, T.B., Titova, L.V., Jackson, H.E., Smith, L.M., Yarrison-Rice, J.M., Lensch, J.L., Lauhon, L.J., 2006. Appl. Phys. Lett. 89 (12), 2–5. Hong, W.-K., Kim, B.-J., Kim, T.-W., Jo, G., Song, S., Kwon, S.-S., Yoon, A., Stach, E.A., Lee, T., 2008. Colloids Surf., A 313–314, 378–382. Jeong, M., Oh, B., Lee, W., Myoung, J., 2005. Appl. Phys. Lett. 86 (10), 103105. Park, J.C., Yoon, Y.S., Kang, S.J., 2016. J. Korean Ceram. Soc. 53 (5), 563–567. Ko, H., Choi, Y.H., Chang, S.Y., Lee, G.Y., Song, H.W., Chang, Y.W., Kang, M.J., Pyun, J.C., 2015. Eur. Polym. J. 68, 36–46. Law, J.B.K., Thong, J.T.L., 2006. Appl. Phys. Lett. 88 (13), 133114. Lee, G.-Y., Chang, Y.W., Ko, H., Kang, M.-J., Pyun, J.-C., 2016. Anal. Chim. Acta 928, 39–48. Lee, W., Kim, H., Jung, D.-R., Kim, J., Nahm, C., Lee, J., Kang, S., Lee, B., Park, B., 2012. Nanoscale Res. Lett. 7 (1), 672. Li, Q.H., Gao, T., Wang, T.H., 2005. Appl. Phys. Lett. 86 (19), 1–3. Park, J.M., Jung, H.W., Chang, Y.W., Kim, H.S., Kang, M.J., Pyun, J.C., 2015. Anal. Chim. Acta 853, 360–367. Park, W. Il, Kim, J.S., Yi, G.C., Bae, M.H., Lee, H.J., 2004. Appl. Phys. Lett. 85 (21), 5052–5054. Prades, J.D., Jimenez-Diaz, R., Hernandez-Ramirez, F., Fernandez-Romero, L., Andreu, T., Cirera, A., Romano-Rodriguez, A., Cornet, A., Morante, J.R., Barth, S., Mathur, S., 2008. J. Phys. Chem. C. 112 (37), 14639–14644. Pushpalatha, H.L., Ganesha, R., 2014. Int. J. ChemTech Res. 7 (5), 2171–2175. Wang, D., Chang, Y.L., Wang, Q., Cao, J., Farmer, D.B., Gordon, R.G., Dai, H., 2004. J. Am. Chem. Soc. 126 (37), 11602–11611.
4. Conclusions An in situ-synthesized CdS NW photosensor showed a dramatic change in photoresponse after H2O2 treatment. SEM analysis revealed that the H2O2 treatment made no significant change to the morphology or the electrode contact of the in situ-synthesized CdS NWs. TOF-SIMS analysis revealed that the H2O2 reacted with the CdS NW surface to produce CdSO4, which had no photoresponsive properties: CdS + O2 + H2O ↔ CdSO4∙H2O. Therefore, the surfaces of CdS NWs needed to be passivated to prevent oxidation and to retain photoresponsiveness. When H2O2 peroxide was used to treat NWs coated with a 2-μm-thick layer of parylene-C, the reduction in the photoresponse was almost insignificant. The influence of the parylene-C passivation layer on photoresponsiveness was investigated during the parylene-C coating process under vacuum using a QCM and a photoanalyzer. Finally, an in situ-synthesized CdS NW photosensor with a parylene-C passivation layer was used to detect the chemiluminescent reaction of HRP and luminol and for the medical detection of CEA. Acknowledgements This work was supported by Nano-Convergence Foundation (R201602210) funded by the Ministry of Science, ICT and Future
228