Ag-grafted on ZnO nanorod arrays using UV-assisted irradiation for enhanced SERS behavior in CV detection

Nội dung text: Ag-grafted on ZnO nanorod arrays using UV-assisted irradiation for enhanced SERS behavior in CV detection

1. Science & Technology Development Journal, 24(2):1938-1946 Open Access Full Text Article Research Article Ag-grafted on ZnO nanorod arrays using UV-assisted irradiation for enhanced SERS behavior in CV detection Ton Nu Quynh Trang1,2, Le To Cam Huong1,2, Thai Duong3, Vu Thi Hanh Thu1,2,* ABSTRACT Introduction: Semiconductor-based surface-enhanced Raman scattering (SERS) substrates with high stability and reproducibility have become one of the essential analytical tools in the analysis of Use your smartphone to scan this chemical and biological at trace levels. Herein, a growth of the hexagonal-wrapped ZnO nanorod QR code and download this article arrays decorating with Ag nanoparticles (AgNPs) at different concentrations of Ag was proposed. Methods: The crystallinity, morphology, chemical composition, and optical properties of the pre- pared samples were investigated by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Raman system, respec- tively. Results: The results revealed that the SERS performance of ZnO NRs incorporating with AgNPs exhibited higher detection of crystal violet (CV) probe molecules at a low concentration of 10−8 M than that of the pristine ZnO NRs. This effect originates from the localized surface plasmonic resonance of AgNPs that could cause a strong electromagnetic field and synergistic effects ofAg, ZnO, and CV molecules in ZnONRs@Ag/CV SERS system. Conclusion: These outcomes reveal that AgNPs play a crucial role in enhanced SERS performance for chemical and biological detection of ZnO substrate. Key words: AgNPs, ZnO nanorod arrays, surface-enhanced Raman scattering (SERS), electromag- netic mechanism, chemical mechanism 1Faculty of Physics and Physics Engineering, University of Science, Ho Chi Minh City 700000, Vietnam INTRODUCTION magnetic amplifications depend on the shapes, sizes, 2Vietnam National University, Ho Chi composition, number of NPs, and position of Raman Minh City 700000, Vietnam In recent decades, surface-enhanced Raman scat- reporters at the surface 5–7. Despite recent progress in 3Research Laboratories of Sai Gon tering (SERS) is a powerful spectroscopic analytical Hi-Tech Park tool that enables the identification and characteri- SERS applications of noble metals, their practical ap- plication has been hindered by the uniformity, repro- Correspondence zation at trace detection of chemical and biological molecules due to its attractive properties such as ex- ducibility, and instability with easy aggregation and Vu Thi Hanh Thu, Faculty of Physics and oxidation and the high cost 8,9. To overcome these Physics Engineering, University of tremely rapid, ultra-sensitive and fingerprint diagnos- Science, Ho Chi Minh City 700000, tics, non-destructive data acquisition. The basic con- drawbacks, most efforts have gone into developing 10–12 Vietnam cept of SERS is that the amplification of the signals flexible and uniform SERS substrates , a promis- Vietnam National University, Ho Chi of the analyte is created by the interaction between ing alternative approach for designing hybrid ternary Minh City 700000, Vietnam the substrate, target molecules, and lights on the sur- nanocomposite by combining noble metals and semi- Email: vththu@hcmus.edu.vn face. The SERS effect is based on two main mecha- conductor materials has been proposed. SERS per- History nisms: chemical mechanism (CM) 1 and electromag- formance based on semiconductors is an attractive • Received: 2021-02-19 netic mechanism (EM) enhancements 2. The EM en- characteristic such as low cost, resource abundance, • Accepted: 2021-05-09 high chemical stability, biocompatible and piezoelec- • Published: 2021-05-13 hancement is obtained by the electric field induced the localized surface plasmonic resonance (LSPR) re- tric properties. However, these strategies face a signif- DOI : 10.32508/stdj.v24i2.2519 lated to noble metal nanostructures with a typical icant challenge because the SERS sensitivity of these enhancement factor of 104-107 folds, while the CM semiconductor substrates is relatively low, becoming enhancement is directly correlated with the charge a bottleneck in the semiconductor SERS development. transfer process between adsorbed molecules and the Therefore, it is vital to develop SERS semiconductor Copyright substrate materials such as semiconductors with en- substrates with high sensitivity, low cost, uniformity, © VNU-HCM Press. This is an open- − 3,4 and reproducibility. Compared with other metal ox- access article distributed under the hancement factors in the range 10 100 times . terms of the Creative Commons Most of these studies reported that plasmonic metal ide materials, Zinc oxide (ZnO) has been intensively Attribution 4.0 International license. nanoparticles (NPs) were employed for SERS; it sup- carried out for SERS because of its enrichment, eco- plies highly sensitive detections based on the en- nomical fabrication, nontoxicity, and photochemical hancement of the EM. The strong near-field electro- stability 13,14. Plasmonic nanoparticles are deposited Cite this article : Trang T N Q, Huong L T C, Duong T, Thu V T H. Ag-grafted on ZnO nanorod arrays using UV-assisted irradiation for enhanced SERS behavior in CV detection. Sci. Tech. Dev. J.; 24(2):1938- 1946. 1938
2. Science & Technology Development Journal, 24(2):1938-1946 on the semiconductor material’s surface and have Torr at 70 W in an Ar flow for deposition times 70 been an efficient pathway for enhancing the SERS ac- min. Afterward, ZnO NRs were fabricated by the hy- tivity 15,16. When the ZnO is connected with plas- drothermal method. A typical process, was placed the monic metals, it provides the LSPR of metals and ex- growth solution containing 25 mM Zn (NO3)2.6H2O hibits the charge-transfer process in the SERS system and 25 mM C6H12N4 with an equivalent concentra- between semiconductors, noble metal nanomaterials, tion of 25 mM dissolved in 200 mL of DI water was and target molecules. Therefore, both EM and CM stirred for 60 min at room temperature. The achieved enhancements may be observed on these hybrid SERS mixture was transferred into an autoclave with Teflon- substrates, leading to a significant SERS performance. liner. The ZnO growth layer was vertically immersed Recently, ZnO nanorods (NRs) array increasing the into the solution. The autoclave was placed in an oven ◦ surface area to decorate plasmonic structures for en- at 90 C for 7 hours. After the growth duration, the so- hancing Raman scattering have been easily grown via lution was cooled at room temperature. The resulted hydrothermal procedure on any substrates 17. More- sample was carefully rinsed with double-distilled wa- over, the nanostructures with highly ordered arrange- ter to remove contaminations on the surface and dried ment can improve the light absorption capability that under an N2 environment. After that, the decora- could further promote the robust enhancement ef- tion of AgNPs on the ZnO NRs platform was obtained fects of SERS 18. by UV-assisted illumination. The aqueous solution of In view of the above considerations, a 1D ZnO AgNO3 was prepared by adding AgNO3 at different nanorods decorated with Ag NPs were fabricated us- concentrations of Ag (amounts of AgNO3: 0.5 wt.%, ing a facile and low-cost approach for SERS perfor- 1.0 wt.%, and 2.0 wt.%.) into the 5 mL double-distilled mances in this work. The growth of ZnO NR ar- water and stirred in 10 min. Next, the ZnO NFs sub- rays on ZnO seed layer using hydrothermal method strate was immersed in the above aqueous solution and Ag NPs deposition on the surface of ZnO NRs using UV-assisted irradiation. After being decorated by photoreduction method were proposed by UV- with AgNPs, the obtained samples were thoroughly assisted irradiation. The synthesized Ag/ZnO NRS washed with double-distilled water and then dried in substrate shows good SERS activity at a low concen- N2 environment. The ZnONFs@Ag substrate was en- tration of CV molecules compared to the pristine gineered on the ZnO growth layer throughout proce- ZnO. A mechanism of SERS activity of Ag/ZnO NRs dures as presented in Figure 1. active-platform is proposed. Material characterization MATERIALS - METHODS The morphologies of the ZnONFs@Ag substrate were Materials characterized using a field emission scanning elec- tron microscope (FESEM, Hitachi) equipped with en- Zinc nitrate hexahydrate (Zn(NO3)2.6H2O, ergy dispersive spectroscopy (EDS) spectra. In ad- 99%, Merck, United States), crystal violet (CV, dition, the crystalline structure of specimens was in- C25H30ClN3, 99%, Merck, United States), hexam- vestigated by an X-ray diffractometer (XRD, D8, AD- ethylenetetramine (HMTA, C6H12N4, 99%, Merck, VANCE, BURKER). SERS spectra were carried out United States), hydrochloric acid (HCl, 38%, Sigma- using a green laser of 532 nm wavelength with a Aldrich, United States), ethanol solution (C2H5OH, laser power of 1 mW and an integration time of 10 s < 99.5%, Merck, United States), ZnO target (99%, (Horiba XploRA PLUS). For SERS measurement, CV Singapore Advantech, Singapore) silver nitrate was used as the target molecules with various con- − − (AgNO3, 99%, Merck, United States). De-ionised centrations (from 10 3 to 10 8 M), dropped onto the (DI) water was utilized in all experiments. Glass SERS platform, and then dried under room tempera- wafers were employed to fabricate the SERS-active ture before the evaluation. platform. RESULTS Synthesis of ZnO nanorod arrays (NRs)@Ag The crystalline structure of the as-prepared samples A ZnO growth layer was fabricated on the glass slides was characterized by X-ray diffraction (XRD) spec- using RF magnetron sputtering. Before the deposi- troscopy, as illustrated in Figure 2. The diffraction ◦ tion, 1 cm x 1 cm glass slides were washed by ultrason- peak at 2θ = 35 can be assigned to the (002) crys- ication in an aqueous solution of C2H5OH and HCl tal plane of hexagonal wurtzite ZnO (JCPDS card No. and dried with nitrogen flux. Then, the ZnO growth 36-1451). The strong and dominant peak in the XRD − layer was deposited at a working pressure of 3 x 10 3 analysis is preferential growth along the c-axis of the 1939
3. Science & Technology Development Journal, 24(2):1938-1946 Figure 1: Schematic for the fabrication of the ZnONRs@Ag platform.(A) Preparation of the glass substrate. (B) Covering ZnO growth layer through magnetron sputtering. (C) The obtained ZnO NRs sample after synthesized by hydrothermal method. (D) the decoration of Ag NPs onto the surface of ZnO NRs via photoreduction approach. (E) Ag assembled onto the ZnO NRs platform. ZnO nanorod arrays. No other peaks were recorded. in ZnONRs/Ag platform, and the main peak of ZnO The other diffraction peak (labeled with *) at 2q value NRs has maintained. This outcome suggests that the ◦ of 38 maybe indexed as the diffraction peak of the deposition of AgNPs onto the surface of ZnO NRs is face-centered cubic (fcc) Ag peaks (JCPDS card No. not significant change any phase structure and vibra- 04-0783) related to the (111) plane. This implies that tional modes. the AgNPs are well-formed on the surface of ZnO NRs The SERS sensing of the pristine ZnO NRs and the with no contamination. hybrid nanostructures of Ag-decorated ZnO NRS The morphological characteristic of the as- was evaluated using Crystal Violet (CV) as a tar- synthesized ZnO NRs and ZnONRs@Ag was get molecule under the excitation wavelength of 532 investigated via SEM images (Figure 3). As shown nm. The SERS spectra of CV are presented in Fig- in Figure 3a,b, the ZnO nanorod arrays are vertically ure 5a. A significant difference between the inten- ~ grown with an average diameter of 50 nm. The sity of signals assessed on the glass, pristine ZnO growth of ZnO NRs oriented onto the ZnO seed layer NRs, and Ag-decorated ZnO NRs platform. The can supply an enhanced SERS performance based on Ag-decorated ZnO NRs platform exhibits the highest the photon scattering and charge transfer process of SERS signals among these substrates due to the syn- the ZnO NRs. Figure 3c shows the morphology of ergistic effects between Ag, ZnO, and R6G. No Ra- AgNPs anchored on the ZnO NRs surface. As shown man signals of the CV molecules are recorded using in Figure 3c, these Ag nanoparticles are anchored the glass and the ZnO NRs substrate due to the large on the surface of ZnO NRs with a diameter of forbidden of ZnO NRs. All the typical characteris- approximately ~20 nm, leading to an enhanced SERS tic peaks of the CV molecules centered at (526, 561 behavior due to the strong electric field effects related − − − − − cm 1), 729 cm 1, 804 cm 1, 916 cm 1, 1174 cm 1, to the EM. Next, to further determine the Ag NPs’ − − − 1383 cm 1, 1537 cm 1, and 1620 cm 1 could be as- composition onto the ZnO nanorods, EDS-mapping signed to the C-N-C antisymmetric bending, C-N- analysis of the sample was carried out as depicted in C symmetric stretching, Phenyl-H out-of-plane an- Figure. Figure 3d-g shows the presence of O (red), Ti (green), and Ag (blue). Additionally, the EDS tisymmetric bending, Phenyl ring breathing mode, spectrum (Figure 3h) proves proof associated with C-H in-plane antisymmetric stretching, Phenyl-C- the corresponding elemental mapping for Zn, O, and phenyl antisymmetric stretching, Phenyl-N antisym- Ag, suggesting that AgNPs decorated successfully on metric stretching, and C-phenyl in-plane antisym- 20,21 the surface of the ZnO NRs. metric stretching, respectively . The results indi- To evaluate the vibration modes of the as-obtained cate that ZnONRs/Ag is responsible for amplification samples, Raman spectra of the pristine ZnO NRs and of SERS signals based on i) plasmonic hot spots that Ag decorated ZnO NRs as illustrated in Figure 4. It is can efficiently focus electromagnetic fields at/near the noted that the vibration mode attributed to the ZnO metal-semiconductor interface; ii) the charge trans- − nanorods is at 438 cm 1, which corresponds to the E2 fer process between Fermi levels of the ZnO NRs, optical phonon band 19. Moreover, it is seen that the Ag, and CV molecules; and iii) the chemical interac- intensity of the pristine ZnO NRs is very weak, when tions between semiconductor and molecules related the presence of Ag induces a high intensity of ZnO Ra- to matching of the energy structure band in the sys- man signal, implying an enhanced SERS performance tem. 1940
4. Science & Technology Development Journal, 24(2):1938-1946 Figure 2: The crystallinity through XRD patterns of the pristine ZnO and ZnONRs@Ag substrate. To further understand the role of Ag NP concentra- These results also suggested that adjusting Ag concen- tion on the SERS performance, the sensitivity of the tration in ZnONRs/Ag system are favorable for im- ZnONRs/Ag samples with different Ag loadings was proving SERS activity owing to a change in the local − exposed in 10 6 M CV solution. As shown in Fig- electromagnetic field. In this paper, the ZnONRs/Ag ure 5b, all the typically characteristic peaks of CV at 1.0 wt.% is chosen as the optimal SERS substrate to − molecules could be detected at concentrations of 10 7 assess the SERS activity further. M, suggesting a good SERS signal in the ZnONRs/Ag Then, the sensitivity of ZnONRs/Ag at 1.0 wt.% was platform. The Raman intensities of the obtained plat- carried out Raman enhancement ability at different forms were gradually increased with increasing Ag CV molecule concentrations as depicted in Figure 6. content. The SERS signal of the 1.0 wt.% Ag has the The R6G characteristic peaks are distinguished even − highest intensity. The lowest SERS signals are ob- at a low concentration of 10 8 M and gradually de- tained after using of ZnONRs/Ag at 2.0 wt.%, indi- creased with the decreasing R6G concentration, indi- cating that an excess amount of Ag deposition is not cating good SERS sensitivity of the ZnONRs/Ag plat- favorable for SERS activity. At an Ag concentration form. of 0.5%, the density of the hot spots is low, lead- ing to a weak Raman signal of the substrate. When DISCUSSION the Ag concentration is 1.0 wt%, many AgNPs and Herein, to further understand the SERS perfor- high-density nanogaps between adjacent AgNPs dec- mance, energy structure band, and a charge-transfer orated homogenously onto the ZnO surface can cause process in ZnONRs/Ag system are critical to ex- a strong local electric field enhancement. Therefore, plaining SERS enhancement (Figure 7). The po- the SERS signal is significantly boosted. However, the sition of the energy levels of the highest occupied SERS signals decline sharply when the Ag concentra- molecular orbital/lowest unoccupied molecular or- tion is 2.0 wt.%. This would be assigned to the de- bital (HOMO/LUMO) of the Raman probe, the CB crease in the electromagnetic field distribution due to and VB level of ZnO NRs, and the Fermi energy level the formation of larger Ag NPs on the ZnO NRs sur- (FF ) of the Ag NPs plays a significant role in the face caused by the merging of the adjacent AgNPs. charge-transfer process between SERS platform and 1941
5. Science & Technology Development Journal, 24(2):1938-1946 Figure 3: Morphological characteristics and elemental composition of the obtained ZnONRs@Ag substrate. (a,b) SEM images of ZnO NRs, (c) SEM image of ZnONRs@Ag, (d) SEM-elemental mapping of ZnONRs@Ag, (e-g) EDS-mapping of O (red), Zn (green), and Ag (blue), respectively, (h) EDS energy spectrum of the ZnONRs@Ag. molecules. As shown in Figure 7, when CV molecules molecules in the platform and the induced “hot charge are employed as target molecules, the HOMO and carriers” of AgNPs based on LSPR are accountable for LUMO level is at -6.0 and -4.1 eV, respectively 22. The the enhanced SERS performance. position of VB and CB of ZnO is centered at -7.7 CONCLUSION eV and -4.5 eV, respectively. FF of AgNPs is -4.84 eV. Under green laser illumination of 532 nm, hot In summary, a pathway for the preparation of the charge carriers of the Ag are produced and jumped SERS platform as depicted in this work. The as- to the LUMO level of the CV molecules. Therefore, fabricated ZnONRs with growth on the ZnO seed the chare-transfer process from FF to the LUMO level layer and decorated Ag on the surface of ZnO NRs of the CV occurred at 0.74 eV. Furthermore, the hot without contaminations have been easily prepared charge carriers are transported from the FF to the CB by facile and cost-effective approaches, in which the at 0.34 eV and shifted to the LUMO level at 0.4 eV ZnO NRs were prepared through the hydrothermal that could promote the charge-transfer activity and method and then loaded AgNPs by photoreduction further enhance SERS behavior. It can be concluded approach. A high detection of SERS substrate com- that the design of AgNPs, ZnO NRs, and CV probe posing of a hexagonal structure of ZnO NRs deco- 1942
6. Science & Technology Development Journal, 24(2):1938-1946 Figure 4: The vibrational modes through Raman spectra of the pristine ZnONRs and ZnONRs@Ag substrate. Figure 5: SERS signal spectra of CV molecules (a) on the glass, the pristine ZnO NRs, and the ZnONRs@Ag platforms, respectively, (b) on the ZnONRs@Ag at different concentrations of Ag from 0.5 to 2.0 wt.%. − rated with AgNPs was fabricated through two steps: even ultra-low concentration of 10 8M. This perfor- ZnO nanorod array was grown via hydrothermal pro- mance could be attributed to the i) plasmonic hot cedures. Then, AgNPs were grafted onto the sur- spots of AgNPs related to the EM; ii) the charge face of ZnO NRs using the photoreduction method. transfer between ZnO NRs, Ag, and CV molecules Compared to pristine ZnO NRs, the highly sensitive ZnONRs@Ag/CV system; and iii) the chemical inter- ZnONRs@Ag active-platform in CV detection at a actions semiconductor and molecules associated with −6 −8 low concentration from 10 M to 10 M was ex- CM. Therefore, heterostructure material-based sens- hibited. Especially, the optimal ZnONRs@Ag sub- ing platforms may pave a facile route for highly sensi- strate at Ag concentration of 1 wt.% could be well- tive detection at trace levels in practical application. identified characteristic peaks of CV target molecules 1943
7. Science & Technology Development Journal, 24(2):1938-1946 Figure 6: Raman spectra of CV molecules obtained from the ZnONRs@Ag-1.0 platform at different concen- trations from 10−6 to 10−8M. ABBREVIATIONS 2. Moskovits M. Surface roughness and the enhanced inten- sity of Raman scattering by molecules adsorbed on metals. CM: chemical mechanism The Journal of Chemical Physics. 1978;69(9):4159-61;Available EM: electromagnetic mechanism from: 3. Korkmaz A, Kenton M, Aksin G, Kahraman M, Wachsmann- ZnO: Zinc oxide Hogiu S. Inexpensive and flexible SERS substrates on adhesive tape based on biosilica plasmonic nanocomposites. ACS Ap- COMPETING INTERESTS plied Nano Materials. 2018;1(9):5316-26;Available from: https: //doi.org/10.1021/acsanm.8b01336. The authors declare that there is no conflict of interest 4. Pérez-Jiménez AI, Lyu D, Lu Z, Liu G, Ren B. Surface-enhanced regarding the publication of this article. Raman spectroscopy: benefits, trade-offs and future devel- opments. Chemical Science. 2020;11(18):4563-77;Available AUTHORS’ CONTRIBUTIONS from: 5. Langer J, Jimenez de AD, Aizpurua J, Alvarez-Puebla RA, Au- Ton Nu Quynh Trang has conceived of the present guié B, Baumberg JJ, Bazan GC, Bell SE, Boisen A, Brolo AG, idea, carried out and written the manuscript with sup- Choo J. Present and future of surface-enhanced Raman scat- tering. ACS nano. 2019;14(1):28-117;PMID: 31478375. Avail- port from Vu Thi Hanh Thu able from: Le To Cam Huong and Thai Duong have done all ex- 6. Lindquist NC, de Albuquerque CD, Sobral-Filho RG, Paci I, Brolo AG. High-speed imaging of surface-enhanced Raman periments. scattering fluctuations from individual nanoparticles. Nature nanotechnology. 2019;14(10):981-7;PMID: 31527841. Avail- ACKNOWLEDGMENTS able from: 7. Trang TN, Vinh LQ, Doanh TT, Thu VT. Structure-adjustable This research is funded by Vietnam National Uni- colloidal silver nanoparticles on polymers grafted cellulose versity Ho Chi Minh City (VNU-HCM) under grant paper-based highly sensitive and selective SERS sensing plat- number VL2019-18-01. form with analyte enrichment function. Journal of Alloys and Compounds. 2021:159158;Available from: REFERENCES 1016/j.jallcom.2021.159158. 8. Chaudhari K, Ahuja T, Murugesan V, Subramanian V, Ganayee 1. Pérez-Jiménez AI, Lyu D, Lu Z, Liu G, Ren B. Surface-enhanced MA, Thundat T, Pradeep T. Appearance of SERS activity Raman spectroscopy: benefits, trade-offs and future devel- in single silver nanoparticles by laser-induced reshaping. opments. Chemical Science. 2020;11(18):4563-77;Available Nanoscale. 2019;11(1):321-30;PMID: 30534777. Available from: from: 1944
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