- Email: [email protected]
Effect of APTES Percentage towards Reduced Graphene Oxide Screen Printed Electrode Surface for Biosensor Application
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 19 (2019) 1183–1188
www.materialstoday.com/proceedings
ICCSE 2018
Effect of APTES Percentage towards Reduced Graphene Oxide Screen Printed Electrode Surface for Biosensor Application Suhaili Sabdin1*, Mohd Azraie Mohd Azmi1, Nurul Azurin Badruzaman1, Fatihatul Zuriati Makmon1, Azman Abd Aziz1 and Nur Azura Mohd Said2 1
Universiti of Kuala Lumpur British Malaysia Institute (UniKL BMI), Batu 8, Jalan Sungai Pusu, 53100 Gombak, Selangor Darul Ehsan, Malaysia 2 Biotechnology & Nanotechnology Research Centre, MARDI, Persiaran MARDI-UPM, 43400 Serdang, Selangor
Abstract Graphene and its derivatives are popular material nowadays among researchers due to its interesting mechanical, electronic and structural properties. Although pristine graphene have high electrical conductivity, some biosensor application require modified form of graphene such as graphene oxide or reduced graphene oxide because easier attachment of linker due to their oxide layer availability. Common functionalization method is using APTES as a linker that attach to working electrode of screen printed electrode. Certain percentage of APTES will then bind with targeted biomarker. Here, silanization of 2%, 4%, 6%, 8% and 10% APTES were conducted on the surface of reduced graphene oxide screen printed electrode to study the effect of APTES percentage towards reduced graphene oxide surface for stable biosensor platform. The 2% APTES shows stable current result of 0.111µA and potential of 0.18V at 100mV/s. This result significant for concentration to surface area ratio whereby low concentration produced higher surface area and lower resistance for electron transfer. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Chemical Sciences and Engineering: Advance and New Materials, ICCSE 2018. Keywords: Reduced Graphene Oxide; APTES; functionalization; biosensor.
* Corresponding author. Tel.: +6012-2357416
E-mail address: [email protected]
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Chemical Sciences and Engineering: Advance and New Materials, ICCSE 2018.
1184
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
1. Introduction Previous studies faces various circumstances in detecting biomolecules where it involves long response time, low sensitivity and complexity of device preparation [1]. To overcome the issues, biosensor technology is being introduced. Biosensor consist of detector/sensor, transducer and signal processor with digital output [2]. Three most common transducer include optical, piezoelectric and electrochemical sensing platform [3]. Enzyme linked immunosorbent assay (ELISA) technology exhibit lower detection limit, time consuming and complex features compared to biosensor technology which gives instant result [1]. Besides, studies are more focused on electrochemical biosensor due to simple on site analysis, high selectivity and sensitivity, short time response, minimal sample preparation and relatively low cost [4]. Biomaterial selection is important in designing a biosensing element include DNA/RNA, aptamer, organelles, receptors, antibodies, enzymes and animal cells/tissues [2]. Also, performance of biosensor depends on the biofunctionalization of the sensor platform. Thus, electrochemical biosensor using 3 aminopropyltriethoxysilane (APTES) on reduced graphene oxide screen printed electrode has been established. In this case, APTES is a silanization process influenced by biological activity to form bond between organic and inorganic component. Most of this process is widely used in surface modification includes paint making and adhesive [5]. APTES formation starts with hydrolysis of ethoxy group which catalyzed by water to form silanols. The hydrolyzed ethoxy group will react with hydroxide ion from water molecule [6]. Monolayer of APTES will produced from this silanols that condense with surface silanols [7]. These molecules does not produce enough intermolecular van der Waals forces which hinder the molecule to stand straight and pack close to each other to form ordered monolayer [6]. In this work, development of electrochemical biosensor using 3-aminopropyltriethoxysilane (APTES) on dual screen printed reduced graphene oxide (rGO) electrode is described. The approach was based on direct binding of APTES towards reduced graphene oxide substrate. Percentage of APTES will play an important role to obtain optimum attachment to the substrate. Previous work by Zhang and group developed non enzymatic glucose sensor by modifying copper nanoparticle with APTES to render the surface before encapsulated with graphene oxide sheets [8]. The synthesis was quite simple using electrostatic self-assembly route which exhibit excellent catalytic activity for glucose and air stability after 30 days which shows high efficiency material. Unlike Rashid Diyana and group established a spray method for different volume of graphene oxide (GO) on silicon substrate using 2% APTES as a linker to produce reduced graphene oxide (rGO) based biosensor [7]. While Yagati and group using 5% APTES in DI water for development of insulin sensor using reduced graphene oxide substrate [9]. Unlike APTES, Marques and group utilised gold nanoparticles onto dual screen printed carbon electrode to enhance the active site for antibody-antigen attachment to the substrate [10]. The application of nanoparticles can also improve detection sensitivity as well as easy electron transfer process [11-13]. Work by Azrul Syafiq and group utilised aptamer concentration on reduced graphene oxide field effect transistor to develop a biosensor [1]. FET was introduced to increase sensitivity for detection of biomolecules and reduced graphene oxide was chosen for its high conductivity compared to graphene oxide. 2. Methodology 2.1 Equipment and materials Potentiostat µStat 200 from Dropsens, dual screen printed reduced graphene oxide electrode (DRPGPHOX1110) printed on ceramic substrate (3.4x1.0x0.05cm), incorporated two reduced graphene oxide working electrodes (elliptic-shaped, A= 6.3mm2), a silver pseudo-reference electrode and carbon auxiliary electrode, carbon electrode (DRP-110), 3-aminopropyltriethoxysilane (APTES), 20% Ethanol, Phosphate Buffer Saline (PBS), Ferrocene Carboxylic Acid from Sigma Aldrich, reduced graphene oxide powder, distilled water.
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
1185
2.2 Electrode surface pretreatment Reduced graphene oxide screen printed electrode were rinsed with 20% ethanol and washed off with distilled water. Then the SPE is dried at room temperature. 2.3 Preparation of screen printed reduced graphene oxide electrode with APTES Firstly, mixed APTES with distilled water at various percentage (2%, 4%, 6%, 8%, 10%). After surface pretreatment, 2µl of APTES were dropped on the working electrode and incubate for 1 hour at room temperature. Rinse SPE with distilled water and let it dry before CV measurement. Repeat the same steps with other percentage. The sample was prepared under fume hood to avoid vapour inhalation 2.4 Measurement and characterization Reduced graphene oxide screen printed electrode were characterized using cyclic voltammetry before and after APTES. It exhibit decrease in anodic and cathodic peaks for redox couple using APTES compared to bare reduced graphene oxide screen printed electrode. This was due to lower electron mobility pass through the particles which corresponded to the reduced current through the transducer [5]. Smaller peak-to-peak potential separation and higher peak current (ΔEp = 0.01, Ipa = 0.18 V, Ipc= 0.17 V) at 2% APTES were observed. Slight shift of both anodic and cathodic peaks can be observed due to electrocatalytic effect of rGO. According to Hashim and groups, APTES in distilled water displayed relatively stable current compared to acetone. Next, the prepared rGO and carbon SPE were characterized from their Raman spectra, which will include consideration of conjugated and carbon-carbon double bonds. The typical Raman spectrum of rGO is characterized by a G band at 1592 which corresponds to vibration of carbon atom on sp2 in-plane, while D band at 1353 represent disorder or defects in carbon atom [14]. Attachment of APTES can be confirmed through Raman spectra. 3. Result and discussion 3.1 Raman Confocal Microscope RGO SPE were compared with carbon SPE and APTES on rGO SPE using confocal microscope at dimension of 20µm as displayed in Figure 1. The surface of carbon SPE is uneven with dramatic indentation, however for rGO, hilly-shaped roughness was observed on the surface. After functionalization with APTES, the surface become smooth with regards to APTES concentration. Our finding suggest lower percentage of APTES produce high surface area for electron transfer which correspond to good biosensor platform. This concentration will affect the attachment of amino group towards the surface of rGO [15].
(a)
(b)
(c)
Figure 1(a) Carbon SPE; (b) Reduced graphene oxide SPE; (c) APTES on reduced graphene oxide SPE
3.2 Response of APTES concentration towards RGO surface Introduction of APTES on rGO surface is called silanization. Organofunctional molecules such as APTES is an aminosilane with –NH2 terminal group where it allows interaction with hydroxyl group [5] from rGO surface. APTES and other amino terminal group is important in biological application as it act as a linker for biomolecule immobilization, implant and lab on chip applications [16-17]
1186
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
Figure 2 displayed typical cyclic voltammetry (CV) measurement of APTES concentration on surface of rGO SPE at scan rate 100mV/s. As shown in the graph, changes in current was due to availability of active sites for functionalization reaction to occur. Lower current needed for 2% APTES suggest higher surface area compared to 10% APTES in which less resistance needed for 2% APTES. Through peak potential separation data as shown in Figure 2b, 2% APTES exhibit lowest peak potential separation which suggest good electron transfer on rGO electrode surface.
Figure 2(a) CV measurement of APTES concentration towards surface channel; (b) Peak potential separation data
Figure 3 showed CV measurement of rGO SPE before and after functionalized with APTES compared to carbon and graphene SPE at 100mV/s. Graph for rGO SPE after functionalization is slightly shifted due to covalent bonding of APTES towards the surface. Changes in current suggest that APTES has successfully attached to the surface through silanization process of hydroxyl group on rGO surface with alkoxy group on the silane thus forming Si-O-Si covalent bond [5].
Figure 3: CV measurement before and after APTES
3.3 Stability of APTES on rGO surface APTES was functionalized on rGO surface by drop casting 2µl APTES onto rGO working electrode. It acts as linker for immobilization of biomolecules. Figure 4a displays increase in current after rGO surface being washed three times where it shows decrease in APTES covalent bonding towards the surface. It may suggest smaller surface area for reaction, thus higher resistance needed [7]. Smaller surface area was due to washing which transform some reduced graphene oxide surface to graphene, hence higher current produced. To overcome the problem, Yagati and friends recommended electrodeposition method before APTES attachment which produced more oxygen containing functional group for silanization process [9].
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
a)
1187
b)
Figure 4(a) CV measurement after washing; (b) Peak potential separation after washing
3.4 Raman shift Raman spectroscopy is useful in studying the defect and disorder in sp2 and sp3 carbon atom which often employed for characterizing rGO (Figure 5). The shape and intensity of rGO spectrum implies that it is multilayered with defects due to introduction of APTES [18]. The shift in intensity of Raman peak shows the effect of functionalization. Raman spectra shows decrease in intensity due to oxidation and functionalization process [19-21]. The changes also shows in the D and G bands of rGO which was due to APTES attachment. The characteristics of D and G band for 2% APTES are visible between 1330cmˉ1 and 1610cm ˉ1 respectively. D band shape after functionalization is shifted to higher intensity correspond to increase in sp3 defects associate with APTES introduction which increases holes and electron concentration. Moreover, decrease in intensity for G band was due to less defect of sp2 in plane carbon atom.
Figure 5: Raman shifts of rGO
4. Conclusion In summary, we have successfully developed a method to functionalize reduced graphene oxide screen printed electrode with APTES using direct binding with the rGO surface and obtained the effect of different percentage on the substrate. Result from cyclic voltammetry clearly stated that 2% APTES is the optimum amount needed to bind with the oxide layer of the rGO surface which produced high surface area for reaction to occur. It is significant for concentration to surface area ratio whereby lower concentration produce high surface area for electron transfer. Raman spectrometer justifies the result by confirming the attachment of amine group on the substrate. Acknowledgements The author gratefully acknowledge the financial support provided by the Ministry of Higher Education Malaysia under Fundamental Research Grant Scheme (FRGS).
1188
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
References 1. 2. 3. 4. 5 6. 7. 8 9. 10. 11. 12. 13. 14. 15.
16. 17. 18. 19. 20. 21.
Syafiq Zainol Abidin, A., et al., The Effect of Aptamer Concetration towards Reduced Graphene OxideField Effect Transistor Surface Channel for Biosensor Application. Vol. 318. 2018. 012045. Prasad, A., Biomaterials for Biosensing Applications. Vol. 2016. 2016. Altintas, Z. and I. Tothill, Biomarkers and biosensors for the early diagnosis of lung cancer. Sensors and Actuators B: Chemical, 2013. 188: p. 988-998. Liu, S., et al., Electrochemical detection of lung cancer specific microRNAs using 3D DNA origami nanostructures. Biosensors and Bioelectronics, 2015. 71: p. 57-61. Hashim, U., S. Nadzirah, et al. (2015). Silanization using APTES in different solvents on titanium dioxide nanoparticles. 2015 2nd International Conference on Biomedical Engineering (ICoBE). Y. Han, D. Mayer, A. Offenhäusser, S. Ingebrandt, Thin Solid Films, 510 (2006) 175 A. Rashid Diyana, A. Rahim Ruslinda, M. F. Fatin, Saeed S. Ba Hashwan, U. Hashim and M. K. Md Arshad. (2015). The Effect of Solution Volume of Graphene Oxide for the Application on Electrode for Biosensor Detection. ARPN Journal of Engineering and Applied Sciences. 2015. 10. 18. Zhang, Q., Q. Luo, et al. (2018). "Self-Assembly of Graphene-Encapsulated Cu Composites for Nonenzymatic Glucose Sensing." ACS Omega 3(3): 3420-3428. Yagati, A. K., J. Park, et al. "Reduced Graphene Oxide Modified the Interdigitated Chain Electrode for an Insulin Sensor. LID - 10.3390/s16010109 [doi] LID - E109 [pii]." (1424-8220 (Electronic)). Marques, R.C.B., et al., Voltammetric immunosensor for the simultaneous analysis of the breast cancer biomarkers CA 15-3 and HER2-ECD. Sensors and Actuators B: Chemical, 2018. 255: p. 918-925. Xiang, C., et al., A reduced graphene oxide/Co3O4 composite for supercapacitor electrode. Journal of Power Sources, 2013. 226: p. 65-70. Li, S.-J., et al., Electrodeposition of cobalt oxide nanoparticles on reduced graphene oxide: A twodimensional hybrid for enzyme-free glucose sensing. Vol. 18. 2014. Ding, Y., et al., Electrospun Co3O4 nanofibers for sensitive and selective glucose detection. Biosensors and Bioelectronics, 2010. 26(2): p. 542-548. Lee, S.X., et al., Horseradish peroxidase-labeled silver/reduced graphene oxide thin film-modified screenprinted electrode for detection of carcinoembryonic antigen. Biosensors and Bioelectronics, 2017. 89: p. 673-680. Talavera-Pech, W.E., Adriana & Quintana-Owen, Patricia & Vilchis-Nestor, Alfredo & Carrera-Figueras, Cristian & Avila-Ortega, Alejandro, Effects of different amounts of APTES on physicochemical and structural properties of amino-functionalized MCM-41-MSNs. Journal of Sol-Gel Science and Technology, 2016. 80(10.1007/s10971-016-4163-4). M.S. Killian, P. Schmuki, Organic Modification of TiO2 and other Metal Oxides with SAMs and Proteins a Surface Analytical Investigation, Technischen Fakultät FriedrichAlexander-Universität ErlangenNürnberg, 2013, p. 233. G. Arslan, M. Ozmen, B. Gunduz, X. Zhang, M. Ersoz, Turkish Journal of Chemistry, 30 (2006) 203. Dae Sung, K., D. Vivek, et al. (2015). "Study on the Effect of Silanization and Improvement in the Tensile Behavior of Graphene-Chitosan-Composite." Polymers 7(3): 527-551. Nebogatikova, N.A.; Antonova, I.V.; Volodin, V.A.; Prinz, V.Y. Functionalization of graphene and fewlayer graphene with aqueous solution of hydrofluoric acid. Phys. E 2013, 52, 106–111. Okpalugo, T.I.T.; Papakonstantinou, P.; Murphy, H.; Mclaughlin, J.; Brown, N.M.D. Oxidative functionalization of carbon nanotubes in atmospheric pressure filamentary dielectric barrier discharge (APDBD). Carbon 2005, 43, 2951–2959. Saidi, W.A.; Norman, P. Probing single-walled carbon nanotube defect chemistry using resonance Raman spectroscopy. Carbon 2014, 67, 17–26.
ScienceDirect Materials Today: Proceedings 19 (2019) 1183–1188
www.materialstoday.com/proceedings
ICCSE 2018
Effect of APTES Percentage towards Reduced Graphene Oxide Screen Printed Electrode Surface for Biosensor Application Suhaili Sabdin1*, Mohd Azraie Mohd Azmi1, Nurul Azurin Badruzaman1, Fatihatul Zuriati Makmon1, Azman Abd Aziz1 and Nur Azura Mohd Said2 1
Universiti of Kuala Lumpur British Malaysia Institute (UniKL BMI), Batu 8, Jalan Sungai Pusu, 53100 Gombak, Selangor Darul Ehsan, Malaysia 2 Biotechnology & Nanotechnology Research Centre, MARDI, Persiaran MARDI-UPM, 43400 Serdang, Selangor
Abstract Graphene and its derivatives are popular material nowadays among researchers due to its interesting mechanical, electronic and structural properties. Although pristine graphene have high electrical conductivity, some biosensor application require modified form of graphene such as graphene oxide or reduced graphene oxide because easier attachment of linker due to their oxide layer availability. Common functionalization method is using APTES as a linker that attach to working electrode of screen printed electrode. Certain percentage of APTES will then bind with targeted biomarker. Here, silanization of 2%, 4%, 6%, 8% and 10% APTES were conducted on the surface of reduced graphene oxide screen printed electrode to study the effect of APTES percentage towards reduced graphene oxide surface for stable biosensor platform. The 2% APTES shows stable current result of 0.111µA and potential of 0.18V at 100mV/s. This result significant for concentration to surface area ratio whereby low concentration produced higher surface area and lower resistance for electron transfer. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Chemical Sciences and Engineering: Advance and New Materials, ICCSE 2018. Keywords: Reduced Graphene Oxide; APTES; functionalization; biosensor.
* Corresponding author. Tel.: +6012-2357416
E-mail address: [email protected]
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Chemical Sciences and Engineering: Advance and New Materials, ICCSE 2018.
1184
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
1. Introduction Previous studies faces various circumstances in detecting biomolecules where it involves long response time, low sensitivity and complexity of device preparation [1]. To overcome the issues, biosensor technology is being introduced. Biosensor consist of detector/sensor, transducer and signal processor with digital output [2]. Three most common transducer include optical, piezoelectric and electrochemical sensing platform [3]. Enzyme linked immunosorbent assay (ELISA) technology exhibit lower detection limit, time consuming and complex features compared to biosensor technology which gives instant result [1]. Besides, studies are more focused on electrochemical biosensor due to simple on site analysis, high selectivity and sensitivity, short time response, minimal sample preparation and relatively low cost [4]. Biomaterial selection is important in designing a biosensing element include DNA/RNA, aptamer, organelles, receptors, antibodies, enzymes and animal cells/tissues [2]. Also, performance of biosensor depends on the biofunctionalization of the sensor platform. Thus, electrochemical biosensor using 3 aminopropyltriethoxysilane (APTES) on reduced graphene oxide screen printed electrode has been established. In this case, APTES is a silanization process influenced by biological activity to form bond between organic and inorganic component. Most of this process is widely used in surface modification includes paint making and adhesive [5]. APTES formation starts with hydrolysis of ethoxy group which catalyzed by water to form silanols. The hydrolyzed ethoxy group will react with hydroxide ion from water molecule [6]. Monolayer of APTES will produced from this silanols that condense with surface silanols [7]. These molecules does not produce enough intermolecular van der Waals forces which hinder the molecule to stand straight and pack close to each other to form ordered monolayer [6]. In this work, development of electrochemical biosensor using 3-aminopropyltriethoxysilane (APTES) on dual screen printed reduced graphene oxide (rGO) electrode is described. The approach was based on direct binding of APTES towards reduced graphene oxide substrate. Percentage of APTES will play an important role to obtain optimum attachment to the substrate. Previous work by Zhang and group developed non enzymatic glucose sensor by modifying copper nanoparticle with APTES to render the surface before encapsulated with graphene oxide sheets [8]. The synthesis was quite simple using electrostatic self-assembly route which exhibit excellent catalytic activity for glucose and air stability after 30 days which shows high efficiency material. Unlike Rashid Diyana and group established a spray method for different volume of graphene oxide (GO) on silicon substrate using 2% APTES as a linker to produce reduced graphene oxide (rGO) based biosensor [7]. While Yagati and group using 5% APTES in DI water for development of insulin sensor using reduced graphene oxide substrate [9]. Unlike APTES, Marques and group utilised gold nanoparticles onto dual screen printed carbon electrode to enhance the active site for antibody-antigen attachment to the substrate [10]. The application of nanoparticles can also improve detection sensitivity as well as easy electron transfer process [11-13]. Work by Azrul Syafiq and group utilised aptamer concentration on reduced graphene oxide field effect transistor to develop a biosensor [1]. FET was introduced to increase sensitivity for detection of biomolecules and reduced graphene oxide was chosen for its high conductivity compared to graphene oxide. 2. Methodology 2.1 Equipment and materials Potentiostat µStat 200 from Dropsens, dual screen printed reduced graphene oxide electrode (DRPGPHOX1110) printed on ceramic substrate (3.4x1.0x0.05cm), incorporated two reduced graphene oxide working electrodes (elliptic-shaped, A= 6.3mm2), a silver pseudo-reference electrode and carbon auxiliary electrode, carbon electrode (DRP-110), 3-aminopropyltriethoxysilane (APTES), 20% Ethanol, Phosphate Buffer Saline (PBS), Ferrocene Carboxylic Acid from Sigma Aldrich, reduced graphene oxide powder, distilled water.
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
1185
2.2 Electrode surface pretreatment Reduced graphene oxide screen printed electrode were rinsed with 20% ethanol and washed off with distilled water. Then the SPE is dried at room temperature. 2.3 Preparation of screen printed reduced graphene oxide electrode with APTES Firstly, mixed APTES with distilled water at various percentage (2%, 4%, 6%, 8%, 10%). After surface pretreatment, 2µl of APTES were dropped on the working electrode and incubate for 1 hour at room temperature. Rinse SPE with distilled water and let it dry before CV measurement. Repeat the same steps with other percentage. The sample was prepared under fume hood to avoid vapour inhalation 2.4 Measurement and characterization Reduced graphene oxide screen printed electrode were characterized using cyclic voltammetry before and after APTES. It exhibit decrease in anodic and cathodic peaks for redox couple using APTES compared to bare reduced graphene oxide screen printed electrode. This was due to lower electron mobility pass through the particles which corresponded to the reduced current through the transducer [5]. Smaller peak-to-peak potential separation and higher peak current (ΔEp = 0.01, Ipa = 0.18 V, Ipc= 0.17 V) at 2% APTES were observed. Slight shift of both anodic and cathodic peaks can be observed due to electrocatalytic effect of rGO. According to Hashim and groups, APTES in distilled water displayed relatively stable current compared to acetone. Next, the prepared rGO and carbon SPE were characterized from their Raman spectra, which will include consideration of conjugated and carbon-carbon double bonds. The typical Raman spectrum of rGO is characterized by a G band at 1592 which corresponds to vibration of carbon atom on sp2 in-plane, while D band at 1353 represent disorder or defects in carbon atom [14]. Attachment of APTES can be confirmed through Raman spectra. 3. Result and discussion 3.1 Raman Confocal Microscope RGO SPE were compared with carbon SPE and APTES on rGO SPE using confocal microscope at dimension of 20µm as displayed in Figure 1. The surface of carbon SPE is uneven with dramatic indentation, however for rGO, hilly-shaped roughness was observed on the surface. After functionalization with APTES, the surface become smooth with regards to APTES concentration. Our finding suggest lower percentage of APTES produce high surface area for electron transfer which correspond to good biosensor platform. This concentration will affect the attachment of amino group towards the surface of rGO [15].
(a)
(b)
(c)
Figure 1(a) Carbon SPE; (b) Reduced graphene oxide SPE; (c) APTES on reduced graphene oxide SPE
3.2 Response of APTES concentration towards RGO surface Introduction of APTES on rGO surface is called silanization. Organofunctional molecules such as APTES is an aminosilane with –NH2 terminal group where it allows interaction with hydroxyl group [5] from rGO surface. APTES and other amino terminal group is important in biological application as it act as a linker for biomolecule immobilization, implant and lab on chip applications [16-17]
1186
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
Figure 2 displayed typical cyclic voltammetry (CV) measurement of APTES concentration on surface of rGO SPE at scan rate 100mV/s. As shown in the graph, changes in current was due to availability of active sites for functionalization reaction to occur. Lower current needed for 2% APTES suggest higher surface area compared to 10% APTES in which less resistance needed for 2% APTES. Through peak potential separation data as shown in Figure 2b, 2% APTES exhibit lowest peak potential separation which suggest good electron transfer on rGO electrode surface.
Figure 2(a) CV measurement of APTES concentration towards surface channel; (b) Peak potential separation data
Figure 3 showed CV measurement of rGO SPE before and after functionalized with APTES compared to carbon and graphene SPE at 100mV/s. Graph for rGO SPE after functionalization is slightly shifted due to covalent bonding of APTES towards the surface. Changes in current suggest that APTES has successfully attached to the surface through silanization process of hydroxyl group on rGO surface with alkoxy group on the silane thus forming Si-O-Si covalent bond [5].
Figure 3: CV measurement before and after APTES
3.3 Stability of APTES on rGO surface APTES was functionalized on rGO surface by drop casting 2µl APTES onto rGO working electrode. It acts as linker for immobilization of biomolecules. Figure 4a displays increase in current after rGO surface being washed three times where it shows decrease in APTES covalent bonding towards the surface. It may suggest smaller surface area for reaction, thus higher resistance needed [7]. Smaller surface area was due to washing which transform some reduced graphene oxide surface to graphene, hence higher current produced. To overcome the problem, Yagati and friends recommended electrodeposition method before APTES attachment which produced more oxygen containing functional group for silanization process [9].
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
a)
1187
b)
Figure 4(a) CV measurement after washing; (b) Peak potential separation after washing
3.4 Raman shift Raman spectroscopy is useful in studying the defect and disorder in sp2 and sp3 carbon atom which often employed for characterizing rGO (Figure 5). The shape and intensity of rGO spectrum implies that it is multilayered with defects due to introduction of APTES [18]. The shift in intensity of Raman peak shows the effect of functionalization. Raman spectra shows decrease in intensity due to oxidation and functionalization process [19-21]. The changes also shows in the D and G bands of rGO which was due to APTES attachment. The characteristics of D and G band for 2% APTES are visible between 1330cmˉ1 and 1610cm ˉ1 respectively. D band shape after functionalization is shifted to higher intensity correspond to increase in sp3 defects associate with APTES introduction which increases holes and electron concentration. Moreover, decrease in intensity for G band was due to less defect of sp2 in plane carbon atom.
Figure 5: Raman shifts of rGO
4. Conclusion In summary, we have successfully developed a method to functionalize reduced graphene oxide screen printed electrode with APTES using direct binding with the rGO surface and obtained the effect of different percentage on the substrate. Result from cyclic voltammetry clearly stated that 2% APTES is the optimum amount needed to bind with the oxide layer of the rGO surface which produced high surface area for reaction to occur. It is significant for concentration to surface area ratio whereby lower concentration produce high surface area for electron transfer. Raman spectrometer justifies the result by confirming the attachment of amine group on the substrate. Acknowledgements The author gratefully acknowledge the financial support provided by the Ministry of Higher Education Malaysia under Fundamental Research Grant Scheme (FRGS).
1188
S. Sabdin et al. / Materials Today: Proceedings 19 (2019) 1183–1188
References 1. 2. 3. 4. 5 6. 7. 8 9. 10. 11. 12. 13. 14. 15.
16. 17. 18. 19. 20. 21.
Syafiq Zainol Abidin, A., et al., The Effect of Aptamer Concetration towards Reduced Graphene OxideField Effect Transistor Surface Channel for Biosensor Application. Vol. 318. 2018. 012045. Prasad, A., Biomaterials for Biosensing Applications. Vol. 2016. 2016. Altintas, Z. and I. Tothill, Biomarkers and biosensors for the early diagnosis of lung cancer. Sensors and Actuators B: Chemical, 2013. 188: p. 988-998. Liu, S., et al., Electrochemical detection of lung cancer specific microRNAs using 3D DNA origami nanostructures. Biosensors and Bioelectronics, 2015. 71: p. 57-61. Hashim, U., S. Nadzirah, et al. (2015). Silanization using APTES in different solvents on titanium dioxide nanoparticles. 2015 2nd International Conference on Biomedical Engineering (ICoBE). Y. Han, D. Mayer, A. Offenhäusser, S. Ingebrandt, Thin Solid Films, 510 (2006) 175 A. Rashid Diyana, A. Rahim Ruslinda, M. F. Fatin, Saeed S. Ba Hashwan, U. Hashim and M. K. Md Arshad. (2015). The Effect of Solution Volume of Graphene Oxide for the Application on Electrode for Biosensor Detection. ARPN Journal of Engineering and Applied Sciences. 2015. 10. 18. Zhang, Q., Q. Luo, et al. (2018). "Self-Assembly of Graphene-Encapsulated Cu Composites for Nonenzymatic Glucose Sensing." ACS Omega 3(3): 3420-3428. Yagati, A. K., J. Park, et al. "Reduced Graphene Oxide Modified the Interdigitated Chain Electrode for an Insulin Sensor. LID - 10.3390/s16010109 [doi] LID - E109 [pii]." (1424-8220 (Electronic)). Marques, R.C.B., et al., Voltammetric immunosensor for the simultaneous analysis of the breast cancer biomarkers CA 15-3 and HER2-ECD. Sensors and Actuators B: Chemical, 2018. 255: p. 918-925. Xiang, C., et al., A reduced graphene oxide/Co3O4 composite for supercapacitor electrode. Journal of Power Sources, 2013. 226: p. 65-70. Li, S.-J., et al., Electrodeposition of cobalt oxide nanoparticles on reduced graphene oxide: A twodimensional hybrid for enzyme-free glucose sensing. Vol. 18. 2014. Ding, Y., et al., Electrospun Co3O4 nanofibers for sensitive and selective glucose detection. Biosensors and Bioelectronics, 2010. 26(2): p. 542-548. Lee, S.X., et al., Horseradish peroxidase-labeled silver/reduced graphene oxide thin film-modified screenprinted electrode for detection of carcinoembryonic antigen. Biosensors and Bioelectronics, 2017. 89: p. 673-680. Talavera-Pech, W.E., Adriana & Quintana-Owen, Patricia & Vilchis-Nestor, Alfredo & Carrera-Figueras, Cristian & Avila-Ortega, Alejandro, Effects of different amounts of APTES on physicochemical and structural properties of amino-functionalized MCM-41-MSNs. Journal of Sol-Gel Science and Technology, 2016. 80(10.1007/s10971-016-4163-4). M.S. Killian, P. Schmuki, Organic Modification of TiO2 and other Metal Oxides with SAMs and Proteins a Surface Analytical Investigation, Technischen Fakultät FriedrichAlexander-Universität ErlangenNürnberg, 2013, p. 233. G. Arslan, M. Ozmen, B. Gunduz, X. Zhang, M. Ersoz, Turkish Journal of Chemistry, 30 (2006) 203. Dae Sung, K., D. Vivek, et al. (2015). "Study on the Effect of Silanization and Improvement in the Tensile Behavior of Graphene-Chitosan-Composite." Polymers 7(3): 527-551. Nebogatikova, N.A.; Antonova, I.V.; Volodin, V.A.; Prinz, V.Y. Functionalization of graphene and fewlayer graphene with aqueous solution of hydrofluoric acid. Phys. E 2013, 52, 106–111. Okpalugo, T.I.T.; Papakonstantinou, P.; Murphy, H.; Mclaughlin, J.; Brown, N.M.D. Oxidative functionalization of carbon nanotubes in atmospheric pressure filamentary dielectric barrier discharge (APDBD). Carbon 2005, 43, 2951–2959. Saidi, W.A.; Norman, P. Probing single-walled carbon nanotube defect chemistry using resonance Raman spectroscopy. Carbon 2014, 67, 17–26.