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An active nano-supported interface designed from gold nanoparticles embedded on ionic liquid for depositing DNA
Applied Surface Science 256 (2009) 52–55
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
An active nano-supported interface designed from gold nanoparticles embedded on ionic liquid for depositing DNA Liping Lu *, Tianfang Kang, Shuiyuan Cheng, Xiurui Guo College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100022, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 April 2009 Received in revised form 13 July 2009 Accepted 17 July 2009 Available online 25 July 2009
The use of an active nano-interface designed from gold nanoparticles embedded on ionic liquid for DNA damage resulted from formalehyde (HCHO) is reported in this article. The active nano-interface was fabricated by depositing gold nanoparticles on the ionic liquid 1-butyl-3-methylimidazolium tetrafluroborate ([bmim][BF4]). A glassy carbon electrode modified by this composite film was fabricated to immobilize DNA for probing into the damage resulted from HCHO. The modifying process was characterized by X-ray photoelectron spectroscopy, atomic force microscopy and electrochemistry involving electrochemical impedance spectroscopy. It was found that the modified film performs effectively in studying the DNA damage by electrocatalytic activity toward HCHO oxidation. ß 2009 Elsevier B.V. All rights reserved.
Keywords: DNA HCHO Ionic liquid Electrochemical sensor
1. Introduction DNA, a very important biomolecule storing the genetic information, plays an essential role in the determination of hereditary characteristics. From this point of view DNA is considered as the major target interacting with various molecules [1]. To detect DNA damage by electrochemistry, natural DNA is usually immobilized on the surface of electrodes. Researching the DNA in vitro, it is important that DNA keeps the native conformation, because its image approaches the biological environments. The inherent stability of biomolecules need keep in a desired environment. A critical issue in the development of a DNA-based biosensor is the sensor material that influences directly the sensor response [2]. Since nanoparticles (NPs) and biomolecules are typically on the same nanometer scale, many types of NP of different sizes and compositions now available facilitate their electrochemical-related applications in enzyme-based sensors, immunosensors and DNA sensors [3–6]. Recently, room temperature ionic liquids (RTILs) have been extensively used in direct electrochemistry and electroanalysis field due to their properties of facilitating direct electron transfer reaction between proteins and electrode surface [7–11]. Apart from its conductive property, it has many other advantages such as robust nature, easy patterning capability and excellent adhesion property to substrates [12]. Ohno et al. successfully construct a continuous ionic liquid domain along the double-strand of DNA
* Corresponding author. Fax: +86 010 67391983. E-mail address: [email protected] (L. Lu). 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.07.056
[13], Pang’s group verified the electrostatic interaction between DNA and [BMIM]BF4 [14]. RTILs open up new opportunities for the development of biosensors, biomacromolecules, and so on. To detect DNA damage by electrochemistry, the native of DNA immobilized on the surface of electrode should be concerned. Surface characterization and modification of electrodes and electronic materials are important criteria in developing forms of biosensor. Facile in vitro electrochemical detection of DNA damage by toxic metabolites could be envisioned by stable solid electrochemical sensors coated with DNA films [15]. In this paper, gold nanoparticles and RTIL are used as modified electrode materials for detecting the HCHO induced DNA damage. 2. Experimental 2.1. Apparatus and reagents Calf thymus DNA (ct-DNA) was purchased from Sigma. [BMIM]BF4 (>99%) was obtained from J&K Chemical Ltd. They were used as received without further purification. All other chemicals were of analytical grade. Solution of DNA was freshly prepared in 5 mM pH 7.4 Tris–HCl buffer solution (THB). All solutions were prepared using doubly distilled water. All electrochemical measurements and impedance spectroscopy were performed on an electrochemistry workstation (CHI660A, CHI, USA). All electrochemical experiments employed a three-electrode cell with a glassy carbon electrode (GCE) as working electrode, and a platinum wire auxiliary electrode and a saturated calomel electrode (SCE) reference electrode. Experiments were carried out at 20 2 8C.
L. Lu et al. / Applied Surface Science 256 (2009) 52–55
53
Scanning electron microscope (SEM) image was obtained on a JEOL 6500F scanning electron microanalyser (NEC). X-ray photoelectron spectroscopy (XPS) spectra were recorded on a spectrometer using Mg Ka X-ray radiation. Atomic force microscopy (AFM) image were recorded on a SPA 300HV with silicon tip in tapping mode at room temperature. 2.2. DNA deposition A GCE (3 mm in diameter) was polished repeatedly with 1.0, 0.3, and 0.05 mm alumina slurry, followed by successive ultrasonic cleaning in acetone and doubly distilled water for 5 min. The cleaned GCE was treated by cyclic voltammetry scanned in the 0.1 M H2SO4 solution between 0 and +1.0 V at a scan rate of 50 mV s1 for 10 cycles. Then, the electrode was immersed in pure [BMIM]BF4 solution for 10 h at 4 8C. After thoroughly rinsed with water, electrodeposition process was accomplished with cyclic voltammetry scanning between 0.2 and +1.0 V at a scan rate of 50 mV s1 for 15 cycles from a fresh solution containing 3 mM HAuCl4 and 0.1 M KCl. The Au nanoparticles and [BMIM]BF4 modified electrode was obtained and denoted as NG/RTIL/GCE. The ct-dsDNA deposition on NG/RTIL/GCE was conducted in 0.1 mg ml1 ct-dsDNA solution and 5% (v/v) [BMIM]BF4 under controlled dc potential of 0.5 V for 15 min, it is denoted as ct-DNA/ NG/RTIL/GCE. 3. Results and discussion 3.1. Surface morphology of the nano-interface Changes of surface composition can affect surface chemistry. Fig. 1 displays the SEM image observed for NG/RTIL/GCE. It clearly shows the uniform distribution of the gold nanoparticles on the [BMIM]BF4 film. The morphology of these nanoparticles is almost identical with cube and the size of them is about 100 nm. XPS spectra of the NG/RTIL/GCE are presented in Fig. 2. The Au (Fig. 2A), F, N, and C (Fig. 2B) peaks were observed, showing the evidence that the Au and [BMIM]BF4 have been immobilized on the surface. Furthermore, Fig. 2C shows the deconvolution spectra of the C1s spectrum, which indicate the presence of C–C (284.8 eV), C–O (286.2 eV), COOH (288.52 eV) surface functional groups. These oxygen containing groups are attributed to the H2SO4 oxidation processes [16]. Since the construction of the [BMIM]BF4, the ionic liquid film is not formed by self-assembly. But the oxygen
Fig. 2. XPS of NG/RTIL/GCE.
Fig. 1. SEM image of NG/RTIL/GCE.
containing groups on the surface of electrode may enhance combination, such as hydrogen bond. The ionic liquid was immobilized successfully on the surface of the electrode. The gold nanoparticles were of a more uniform appearance, which may be due to the presence of ionic liquids optimize the performance of the electrode surface. The gold nanoparticles generally possess excellent catalytic activity and offer a hospitable environment for biomolecules. Fig. 3 (inset) shows the EIS of every modified procedure, which can be seen the charge transfer resistance (Rct) was gradually reduced. IL-robed DNA kept their double-stranded helix structure [13]. The interaction made DNA immobilized on the surface of the electrode stronger [14]. This interface has good electrical conductivity, chemical stability and biocompatibility. The interface has the characteristics of ionic liquids and nano-gold for the electrochemical DNA research.
54
L. Lu et al. / Applied Surface Science 256 (2009) 52–55
Fig. 3. EIS of (a) ct-DNA/NG/RTIL/GCE, (b) ct-DNA/NG/RTIL/GCE incubated by HCHO, (c) bare GCE, (d) GCE activated by H2SO4, (e) RTIL/GCE, (f) NG/RTIL/GCE in 5.0 mM Fe(CN)63/4 and 0.1 M KCl.
Fig. 4. Cyclic voltammograms of 0.02 M HCHO in 0.1 M NaHCO3–Na2CO3 solution at GCE (a), ct-DNA/NG/RTIL/GCE (b), ct-DNA/NG/RTIL/GCE incubated in HCHO (C). (v ¼ 100 mV=s, scan from 0.5 to 1.0 V) (inset: DPV of ct-DNA/NG/RTIL/GCE incubated in HCHO.)
3.2. Eletrochemical analysis DNA damage of HCHO
peak 1 (or curve b: at 0.38 V) may ascribe to the oxidation of HCHOguanine base, this point is supported by the result of the cyclic voltammatry of guanine [18] originated from the degrading of DNA. The differential pulse voltammograms of the incubated ct-DNA/NG/ RTIL/GCE in the 0.02 M HCHO is shown in Fig. 4 (inset), there is a distinct oxidation peak at 1.25 V, corresponding to the oxidation of adenine [19], however, this peak was not existed when it was not HCHO. These dictate the crosslink which HCHO caused make DNA degrade, and the stretching of the molecule may disrupt the base stacking. Meanwhile, it proved DNA on the NG/RTIL/GCE was kept the native conformation. It is because natural DNA gives minimal voltammetric signals, but damage exposes DNA bases to the electrode can be observed the redox peak [20].
The principle of electrochemical impedance sensing of DNA damaging is based on the change of the charge transfer resistance, Rct. The negatively charged redox indicator Fe(CN)63/4 was electrostatically repelled by the resulting negatively charged interface. The electrochemical impedance spectroscopy (EIS) was shown in Fig. 3. It is clear that the electron transfer resistance of Fe(CN)63/4 redox couple is different. We can see from curve a, the ct-DNA is modified on the NG/RTIL/GCE, Rct = 298 V; after the ct-DNA are damaged by incubated in 0.02 M HCHO at 37 8C for 30 min, the Rct = 502 V. This effect was attributed to the reduce electronic conduction via stacked bases. Cyclic voltammograms of HCHO at bare GCE and the modified electrode are comparatively shown in Fig. 4. As shown in Fig. 4, HCHO has no CV peak response at bare GCE (curve a), while the ctDNA/NG/RTIL/GCE (curve b) leads to three current peak at about 0.38, 0.61, and 0.29 V. The peak at 0.61 and 0.29 V are corresponds to the typical oxidation of the HCHO in basic media [17]. In contrast, when ct-DNA/NG/RTIL/GCE is incubated in 0.02 M HCHO at 37 8C for 30 min, the three peaks current increased greatly (Fig. 4, curve c). Additionally, the peak at 0.29 V shifts positively up to 0.35 V. The
3.3. AFM analysis of DNA damage Electrode surface characteristics represent an important aspect on the construction of sensitive DNA electrochemical biosensors for detection of DNA interaction and HCHO. AFM images were obtained on the glass carbon slices (noted GCS). The samples were prepared as the ct-DNA/NG/RTIL/GCE. Fig. 5B is the AFM image of the ct-DNA/ NG/RTIL/GCS, which were incubated in 0.02 M HCHO at 37 8C for
Fig. 5. AFM of ct-DNA/NG/RTIL/GCE (left) and ct-DNA/NG/RTIL/GCE incubated by HCHO (right).
L. Lu et al. / Applied Surface Science 256 (2009) 52–55
30 min; Fig. 5A is the image of the ct-DNA/NG/RTIL/GCS without incubated. Along our consideration, the ct-DNA molecules in their states of compactness were different. They loosely attached to the gold nanoparticles when they were incubated in HCHO, while the ctDNA molecules without processed were closer. The DNA molecules were not priority fabricated on the surface of glass carbon but the gold nanoparticles [21]. HCHO may destroy the close packing model of the DNA molecules by interacted with the DNA. It was known that formaldehyde can induce nucleic acids crosslink [22]. Functional groups that are reactive are amido groups by reactive bridges between reactive groups. The results of the ultraviolet experiments showed the conjugate degree increase of DNA incubated in HCHO, which indicated may form C5 5N bridges as well. Formaldehyde penetrating destroyed the 3D nature structures of DNA, which could lead to long DNA strands relatively loose contact. However, neither the morphology nor the conductivity of DNA was changed. 4. Conclusion An active nano-supported interface was designed from gold nanoparticles embedded on ionic liquid for depositing DNA. DNA maintained the natural structure based the extraordinary biocompatibility of nano-gold and room temperature ionic liquids. The study of DNA damage resulted from formaldehyde proceeded by AFM and electrochemistry. The results show that formaldehyde caused DNA degraded and formaldehyde penetrating combined with DNA forming C5 5N. It is the next work that the further detection of the damage to DNA hybridization by this active nanosupported interface.
55
Acknowledgements The authors gratefully acknowledge Beijing Municipal Natural Science Foundation (no. 8062010), Key Project of Chinese National Programs for Fundamental Research and Development (973 program) (no. 2005CB724201) and BJUT Science Foundation for Youths (no. 97005013200701) References [1] V.C. Diculescu, J.A.P. Piedade, A.M. Oliveira-Brett, Bioelectrochemistry 70 (2007) 141. [2] A.M. Chiorcea, A.M. Oliverira Brett, Bioelectrochemistry 63 (2004) 229. [3] E. Katz, I. Willner, J. Wang, Electroanalysis 16 (2004) 19. [4] J. Wang, Anal. Chem. Acta 500 (2003) 247. [5] A. Merkoci, M. Aldavert, S. Marin, S. Alegret, Trends Anal. Chem. 24 (2005) 341. [6] C.M. Niemeyer, Angew. Chem. Int. Ed. Engl. 40 (2001) 4128. [7] D.L. Compton, J.A. Laszlo, J. Electroanal. Chem. 520 (2002) 71. [8] Z. Guo, S. Dong, Anal. Chem. 76 (2004) 2683. [9] X. Zhang, K. Jiao, X. Wang, Electroanalysis 20 (2008) 1361. [10] Y. Liu, L. Liu, S. Dong, Electroanalysis 19 (2007) 55. [11] S. Ding, M. Xu, G. Zhao, X. Wei, Electrochem. Commun. 9 (2007) 216. [12] E. Moore, D. O’Connell, P. Galvin, Thin Solid Films 515 (2006) 2612. [13] N. Nishimura, Y. Nomura, N. Nakamura, H. Ohno, Biomaterials 26 (2005) 5558. [14] Y.N. Xie, S.F. Wang, Z.L. Zhang, D.W. Pang, J. Phys. Chem. B 112 (2008) 9864. [15] L.P. Zhou, J.F. Rusling, Anal. Chem. 73 (2001) 4780. [16] X.Q. Lin, X.H. Jiang, L.P. Lu, Biosens. Bioelectron. 20 (2005) 1709. [17] B. B.M., Electrochim. Acta 30 (1985) 1193. [18] R.N. Goyal, G. Dryhurst, J. Electroanal. Chem. 135 (1982) 75. [19] C.M.A. Brett, A.M.O. Brett, S.H.P. Serrano, J. Electroanal. Chem. 366 (1994) 255. [20] J. Mbindyo, L.P. Zhou, Zh. Zhang, J.D. Stuart, J.F. Rusling, Anal. Chem. 72 (2000) 2059. [21] L.P. Lu, Q.L. Xin, Anal. Sci. 20 (2004) 527. [22] H.J. Andrew, Y.G. Wang, Y. Gao, Ch. Liaw, Y.K. Li, Biochemistry 30 (1991) 3812.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
An active nano-supported interface designed from gold nanoparticles embedded on ionic liquid for depositing DNA Liping Lu *, Tianfang Kang, Shuiyuan Cheng, Xiurui Guo College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100022, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 April 2009 Received in revised form 13 July 2009 Accepted 17 July 2009 Available online 25 July 2009
The use of an active nano-interface designed from gold nanoparticles embedded on ionic liquid for DNA damage resulted from formalehyde (HCHO) is reported in this article. The active nano-interface was fabricated by depositing gold nanoparticles on the ionic liquid 1-butyl-3-methylimidazolium tetrafluroborate ([bmim][BF4]). A glassy carbon electrode modified by this composite film was fabricated to immobilize DNA for probing into the damage resulted from HCHO. The modifying process was characterized by X-ray photoelectron spectroscopy, atomic force microscopy and electrochemistry involving electrochemical impedance spectroscopy. It was found that the modified film performs effectively in studying the DNA damage by electrocatalytic activity toward HCHO oxidation. ß 2009 Elsevier B.V. All rights reserved.
Keywords: DNA HCHO Ionic liquid Electrochemical sensor
1. Introduction DNA, a very important biomolecule storing the genetic information, plays an essential role in the determination of hereditary characteristics. From this point of view DNA is considered as the major target interacting with various molecules [1]. To detect DNA damage by electrochemistry, natural DNA is usually immobilized on the surface of electrodes. Researching the DNA in vitro, it is important that DNA keeps the native conformation, because its image approaches the biological environments. The inherent stability of biomolecules need keep in a desired environment. A critical issue in the development of a DNA-based biosensor is the sensor material that influences directly the sensor response [2]. Since nanoparticles (NPs) and biomolecules are typically on the same nanometer scale, many types of NP of different sizes and compositions now available facilitate their electrochemical-related applications in enzyme-based sensors, immunosensors and DNA sensors [3–6]. Recently, room temperature ionic liquids (RTILs) have been extensively used in direct electrochemistry and electroanalysis field due to their properties of facilitating direct electron transfer reaction between proteins and electrode surface [7–11]. Apart from its conductive property, it has many other advantages such as robust nature, easy patterning capability and excellent adhesion property to substrates [12]. Ohno et al. successfully construct a continuous ionic liquid domain along the double-strand of DNA
* Corresponding author. Fax: +86 010 67391983. E-mail address: [email protected] (L. Lu). 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.07.056
[13], Pang’s group verified the electrostatic interaction between DNA and [BMIM]BF4 [14]. RTILs open up new opportunities for the development of biosensors, biomacromolecules, and so on. To detect DNA damage by electrochemistry, the native of DNA immobilized on the surface of electrode should be concerned. Surface characterization and modification of electrodes and electronic materials are important criteria in developing forms of biosensor. Facile in vitro electrochemical detection of DNA damage by toxic metabolites could be envisioned by stable solid electrochemical sensors coated with DNA films [15]. In this paper, gold nanoparticles and RTIL are used as modified electrode materials for detecting the HCHO induced DNA damage. 2. Experimental 2.1. Apparatus and reagents Calf thymus DNA (ct-DNA) was purchased from Sigma. [BMIM]BF4 (>99%) was obtained from J&K Chemical Ltd. They were used as received without further purification. All other chemicals were of analytical grade. Solution of DNA was freshly prepared in 5 mM pH 7.4 Tris–HCl buffer solution (THB). All solutions were prepared using doubly distilled water. All electrochemical measurements and impedance spectroscopy were performed on an electrochemistry workstation (CHI660A, CHI, USA). All electrochemical experiments employed a three-electrode cell with a glassy carbon electrode (GCE) as working electrode, and a platinum wire auxiliary electrode and a saturated calomel electrode (SCE) reference electrode. Experiments were carried out at 20 2 8C.
L. Lu et al. / Applied Surface Science 256 (2009) 52–55
53
Scanning electron microscope (SEM) image was obtained on a JEOL 6500F scanning electron microanalyser (NEC). X-ray photoelectron spectroscopy (XPS) spectra were recorded on a spectrometer using Mg Ka X-ray radiation. Atomic force microscopy (AFM) image were recorded on a SPA 300HV with silicon tip in tapping mode at room temperature. 2.2. DNA deposition A GCE (3 mm in diameter) was polished repeatedly with 1.0, 0.3, and 0.05 mm alumina slurry, followed by successive ultrasonic cleaning in acetone and doubly distilled water for 5 min. The cleaned GCE was treated by cyclic voltammetry scanned in the 0.1 M H2SO4 solution between 0 and +1.0 V at a scan rate of 50 mV s1 for 10 cycles. Then, the electrode was immersed in pure [BMIM]BF4 solution for 10 h at 4 8C. After thoroughly rinsed with water, electrodeposition process was accomplished with cyclic voltammetry scanning between 0.2 and +1.0 V at a scan rate of 50 mV s1 for 15 cycles from a fresh solution containing 3 mM HAuCl4 and 0.1 M KCl. The Au nanoparticles and [BMIM]BF4 modified electrode was obtained and denoted as NG/RTIL/GCE. The ct-dsDNA deposition on NG/RTIL/GCE was conducted in 0.1 mg ml1 ct-dsDNA solution and 5% (v/v) [BMIM]BF4 under controlled dc potential of 0.5 V for 15 min, it is denoted as ct-DNA/ NG/RTIL/GCE. 3. Results and discussion 3.1. Surface morphology of the nano-interface Changes of surface composition can affect surface chemistry. Fig. 1 displays the SEM image observed for NG/RTIL/GCE. It clearly shows the uniform distribution of the gold nanoparticles on the [BMIM]BF4 film. The morphology of these nanoparticles is almost identical with cube and the size of them is about 100 nm. XPS spectra of the NG/RTIL/GCE are presented in Fig. 2. The Au (Fig. 2A), F, N, and C (Fig. 2B) peaks were observed, showing the evidence that the Au and [BMIM]BF4 have been immobilized on the surface. Furthermore, Fig. 2C shows the deconvolution spectra of the C1s spectrum, which indicate the presence of C–C (284.8 eV), C–O (286.2 eV), COOH (288.52 eV) surface functional groups. These oxygen containing groups are attributed to the H2SO4 oxidation processes [16]. Since the construction of the [BMIM]BF4, the ionic liquid film is not formed by self-assembly. But the oxygen
Fig. 2. XPS of NG/RTIL/GCE.
Fig. 1. SEM image of NG/RTIL/GCE.
containing groups on the surface of electrode may enhance combination, such as hydrogen bond. The ionic liquid was immobilized successfully on the surface of the electrode. The gold nanoparticles were of a more uniform appearance, which may be due to the presence of ionic liquids optimize the performance of the electrode surface. The gold nanoparticles generally possess excellent catalytic activity and offer a hospitable environment for biomolecules. Fig. 3 (inset) shows the EIS of every modified procedure, which can be seen the charge transfer resistance (Rct) was gradually reduced. IL-robed DNA kept their double-stranded helix structure [13]. The interaction made DNA immobilized on the surface of the electrode stronger [14]. This interface has good electrical conductivity, chemical stability and biocompatibility. The interface has the characteristics of ionic liquids and nano-gold for the electrochemical DNA research.
54
L. Lu et al. / Applied Surface Science 256 (2009) 52–55
Fig. 3. EIS of (a) ct-DNA/NG/RTIL/GCE, (b) ct-DNA/NG/RTIL/GCE incubated by HCHO, (c) bare GCE, (d) GCE activated by H2SO4, (e) RTIL/GCE, (f) NG/RTIL/GCE in 5.0 mM Fe(CN)63/4 and 0.1 M KCl.
Fig. 4. Cyclic voltammograms of 0.02 M HCHO in 0.1 M NaHCO3–Na2CO3 solution at GCE (a), ct-DNA/NG/RTIL/GCE (b), ct-DNA/NG/RTIL/GCE incubated in HCHO (C). (v ¼ 100 mV=s, scan from 0.5 to 1.0 V) (inset: DPV of ct-DNA/NG/RTIL/GCE incubated in HCHO.)
3.2. Eletrochemical analysis DNA damage of HCHO
peak 1 (or curve b: at 0.38 V) may ascribe to the oxidation of HCHOguanine base, this point is supported by the result of the cyclic voltammatry of guanine [18] originated from the degrading of DNA. The differential pulse voltammograms of the incubated ct-DNA/NG/ RTIL/GCE in the 0.02 M HCHO is shown in Fig. 4 (inset), there is a distinct oxidation peak at 1.25 V, corresponding to the oxidation of adenine [19], however, this peak was not existed when it was not HCHO. These dictate the crosslink which HCHO caused make DNA degrade, and the stretching of the molecule may disrupt the base stacking. Meanwhile, it proved DNA on the NG/RTIL/GCE was kept the native conformation. It is because natural DNA gives minimal voltammetric signals, but damage exposes DNA bases to the electrode can be observed the redox peak [20].
The principle of electrochemical impedance sensing of DNA damaging is based on the change of the charge transfer resistance, Rct. The negatively charged redox indicator Fe(CN)63/4 was electrostatically repelled by the resulting negatively charged interface. The electrochemical impedance spectroscopy (EIS) was shown in Fig. 3. It is clear that the electron transfer resistance of Fe(CN)63/4 redox couple is different. We can see from curve a, the ct-DNA is modified on the NG/RTIL/GCE, Rct = 298 V; after the ct-DNA are damaged by incubated in 0.02 M HCHO at 37 8C for 30 min, the Rct = 502 V. This effect was attributed to the reduce electronic conduction via stacked bases. Cyclic voltammograms of HCHO at bare GCE and the modified electrode are comparatively shown in Fig. 4. As shown in Fig. 4, HCHO has no CV peak response at bare GCE (curve a), while the ctDNA/NG/RTIL/GCE (curve b) leads to three current peak at about 0.38, 0.61, and 0.29 V. The peak at 0.61 and 0.29 V are corresponds to the typical oxidation of the HCHO in basic media [17]. In contrast, when ct-DNA/NG/RTIL/GCE is incubated in 0.02 M HCHO at 37 8C for 30 min, the three peaks current increased greatly (Fig. 4, curve c). Additionally, the peak at 0.29 V shifts positively up to 0.35 V. The
3.3. AFM analysis of DNA damage Electrode surface characteristics represent an important aspect on the construction of sensitive DNA electrochemical biosensors for detection of DNA interaction and HCHO. AFM images were obtained on the glass carbon slices (noted GCS). The samples were prepared as the ct-DNA/NG/RTIL/GCE. Fig. 5B is the AFM image of the ct-DNA/ NG/RTIL/GCS, which were incubated in 0.02 M HCHO at 37 8C for
Fig. 5. AFM of ct-DNA/NG/RTIL/GCE (left) and ct-DNA/NG/RTIL/GCE incubated by HCHO (right).
L. Lu et al. / Applied Surface Science 256 (2009) 52–55
30 min; Fig. 5A is the image of the ct-DNA/NG/RTIL/GCS without incubated. Along our consideration, the ct-DNA molecules in their states of compactness were different. They loosely attached to the gold nanoparticles when they were incubated in HCHO, while the ctDNA molecules without processed were closer. The DNA molecules were not priority fabricated on the surface of glass carbon but the gold nanoparticles [21]. HCHO may destroy the close packing model of the DNA molecules by interacted with the DNA. It was known that formaldehyde can induce nucleic acids crosslink [22]. Functional groups that are reactive are amido groups by reactive bridges between reactive groups. The results of the ultraviolet experiments showed the conjugate degree increase of DNA incubated in HCHO, which indicated may form C5 5N bridges as well. Formaldehyde penetrating destroyed the 3D nature structures of DNA, which could lead to long DNA strands relatively loose contact. However, neither the morphology nor the conductivity of DNA was changed. 4. Conclusion An active nano-supported interface was designed from gold nanoparticles embedded on ionic liquid for depositing DNA. DNA maintained the natural structure based the extraordinary biocompatibility of nano-gold and room temperature ionic liquids. The study of DNA damage resulted from formaldehyde proceeded by AFM and electrochemistry. The results show that formaldehyde caused DNA degraded and formaldehyde penetrating combined with DNA forming C5 5N. It is the next work that the further detection of the damage to DNA hybridization by this active nanosupported interface.
55
Acknowledgements The authors gratefully acknowledge Beijing Municipal Natural Science Foundation (no. 8062010), Key Project of Chinese National Programs for Fundamental Research and Development (973 program) (no. 2005CB724201) and BJUT Science Foundation for Youths (no. 97005013200701) References [1] V.C. Diculescu, J.A.P. Piedade, A.M. Oliveira-Brett, Bioelectrochemistry 70 (2007) 141. [2] A.M. Chiorcea, A.M. Oliverira Brett, Bioelectrochemistry 63 (2004) 229. [3] E. Katz, I. Willner, J. Wang, Electroanalysis 16 (2004) 19. [4] J. Wang, Anal. Chem. Acta 500 (2003) 247. [5] A. Merkoci, M. Aldavert, S. Marin, S. Alegret, Trends Anal. Chem. 24 (2005) 341. [6] C.M. Niemeyer, Angew. Chem. Int. Ed. Engl. 40 (2001) 4128. [7] D.L. Compton, J.A. Laszlo, J. Electroanal. Chem. 520 (2002) 71. [8] Z. Guo, S. Dong, Anal. Chem. 76 (2004) 2683. [9] X. Zhang, K. Jiao, X. Wang, Electroanalysis 20 (2008) 1361. [10] Y. Liu, L. Liu, S. Dong, Electroanalysis 19 (2007) 55. [11] S. Ding, M. Xu, G. Zhao, X. Wei, Electrochem. Commun. 9 (2007) 216. [12] E. Moore, D. O’Connell, P. Galvin, Thin Solid Films 515 (2006) 2612. [13] N. Nishimura, Y. Nomura, N. Nakamura, H. Ohno, Biomaterials 26 (2005) 5558. [14] Y.N. Xie, S.F. Wang, Z.L. Zhang, D.W. Pang, J. Phys. Chem. B 112 (2008) 9864. [15] L.P. Zhou, J.F. Rusling, Anal. Chem. 73 (2001) 4780. [16] X.Q. Lin, X.H. Jiang, L.P. Lu, Biosens. Bioelectron. 20 (2005) 1709. [17] B. B.M., Electrochim. Acta 30 (1985) 1193. [18] R.N. Goyal, G. Dryhurst, J. Electroanal. Chem. 135 (1982) 75. [19] C.M.A. Brett, A.M.O. Brett, S.H.P. Serrano, J. Electroanal. Chem. 366 (1994) 255. [20] J. Mbindyo, L.P. Zhou, Zh. Zhang, J.D. Stuart, J.F. Rusling, Anal. Chem. 72 (2000) 2059. [21] L.P. Lu, Q.L. Xin, Anal. Sci. 20 (2004) 527. [22] H.J. Andrew, Y.G. Wang, Y. Gao, Ch. Liaw, Y.K. Li, Biochemistry 30 (1991) 3812.