- Open Access
Metal oxide modified ZnO nanomaterials for biosensor applications
© The Author(s) 2018
- Received: 7 September 2018
- Accepted: 20 September 2018
- Published: 3 October 2018
Advancing as a biosensing nanotechnology, nanohybrids present a new class of functional materials with high selectivity and sensitivity, enabling integration of nanoscale chemical/biological interactions with biomedical devices. The unique properties of ZnO combined with metal oxide nanostructures were recently demonstrated to be an efficient approach for sensor device fabrication with accurate, real-time and high-throughput biosensing, creating new avenues for diagnosis, disease management and therapeutics. This review article collates recent advances in the modified ZnO nanostructured metal oxide nanohybrids for efficient enzymatic and non-enzymatic biosensor applications. Furthermore, we also discussed future prospects for nanohybrid materials to yield high-performance biosensor devices.
- Metal oxide
- Enzymatic and non-enzymatic
Nanoengineered biosensors have altered the field of biomedical engineering by introduction of smaller sensing structures for highly selective and sensitive detection of biomolecules . Nanomaterials of varied forms, including single or hybrids/combinatorial nanostructures, can be designed with distinctive features that are significantly different from conventional bulk materials. With smart engineering, nanomaterials functionalities and characteristics can be optimized to allow high selectivity binding properties for analyzing nanoscale elements of biomolecules. Additionally, the distinct molecular recognition interactions at the nano-realm level in combination with nanoscale components can further promote high sensitivity of the biosensors . Nanostructured metal oxides have received great attention for biosensing applications owing to several characteristics such as ease of fabrication and controllable size/shape, biocompatibility, catalytic and optical properties, chemical stability, strong adsorption ability and electron-transfer kinetics . Zinc oxide (ZnO), an n-type semiconductor metal oxide with a wide direct band gap of 3.37 eV, a large exciton binding energy of 60 meV, and enhanced electron mobility, that has gathered attention for a broad range of applications in biomedical and clinical sciences. In addition, owing to its excellent film forming and adhesion capability, large surface area, strong adsorption ability due to high isoelectric point (~ 9.5), improved catalytic efficiency (oxygen storage capacity), better chemical stability, resistant against corrosion and oxidation, and small grain size, makes it highly amenable to biomolecular sensing applications [3–8]. Studies focusing on the morphological aspects of the nanostructured-ZnO have highlighted these nanostructures as advantageous because of high crystallinity with negligible structural defects and low-temperature synthesis. It also possesses good electrical conductivity which further makes it highly suitable for developing rapid, stable and reliable sensor devices [9, 10]. Furthermore, the biocompatible nature of ZnO nanostructures makes it a suitable choice for surface functionalization and interfacing with chemical/biological compounds at various temperature and pH levels .
Nanotextured surfaces coupled with metal oxides leads to the creation of nano-hybrid materials, which are expected to establish new avenues for both diagnosis and therapeutics because of these enhanced optical and electronic properties [12, 13]. Furthermore, computational modeling and experimental studies have also suggested that doping densities can greatly affect the sensitivity of bio-recognition [14, 15]. Hence, nanohybrids can be regarded as a promising new multifunctional material for high performance device fabrication. Modification of ZnO with metal oxide nanomaterials can further improve the features of ZnO for the sensing of biomolecules as metal oxide nanomaterials make great catalysts due to their high surface ratio of atoms with free valences of the total atoms in the cluster, which also may lead to electrochemical reversibility for redox reactions [16–18]. Therefore, the integration of ZnO with metal oxide nanomaterials can provide new avenues for the development of highly sensitive biosensors, where the surface functionalized-metal oxides serve as active sites for improving specificity and sensitivity, and the ZnO offers rapid electron transfer in an electrochemical reaction . With regard to the material aspect of design choice, various metal oxide nanomaterials have been utilized for biosensing applications such as iron oxide, copper oxide, cerium oxide, magnesium oxide, and titanium oxide [20–25]. Owing to their size-dependent catalytic and optoelectronic properties, they can be tuned via size variations in nanoparticles, nanowires, nanotubes, nanorods, nanospheres, nanosheets, and quantum dots engineered through low temperature aqueous route, hydrothermal or solvothermal processes, sol–gel synthesis, or chemical vapor deposition are among available options [20–25].
Very recently, nanohybrids comprised of ZnO nanostructures coupled with metal oxide nanomaterials have attracted tremendous interest because of their potency for improving catalytic activity, surface-to-volume ratios and various other functionalities in a manner superior to pure ZnO nanomaterials. Thus, metal oxide modified ZnO nanostructure based biosensors have been highlighted to provide a new and efficient strategy for development of highly sensitive biosensors In this review article, we first discussed utilization of metal oxide modified ZnO nanomaterials for both enzymatic and non-enzymatic biosensor applications and summarized the advancement in sensing properties. Finally, we described the prospects for metal oxide modified ZnO nanomaterials in the context of further advancement in biosensing device fabrication.
2.1 Electrochemical based non-enzymatic biosensor
Vertically-grown/arrays-type orientations of nanostructures also have received attention due to their larger surface area. Soejima et al. synthesized CuO–ZnO composite nanoarrays using a facile one-step and low-temperature route on brass (Cu–Zn alloy) plates . The synthesized nanoarrays were ZnO nanorods (NRs) and CuO nanoflowers. This nanocomposite based non-enzymatic sensor electrodes were electrocatalytically active during glucose oxidation and resulted in a fast response, low limit of detection and high sensitivity. Furthermore, SoYoon et al., and co-authors synthesized CuO nanoleaf–ZnO NRs hierarchical architectures and attached them to the Cu substrate to fabricate a non-enzymatic glucose sensor . Excellent electrocatalytic activity of the nanohybrid composite (CuO nanoleaf–ZnO NRs) was obtained during glucose oxidation in NaOH buffer solution. As discussed earlier, improved performance was due to synergistic effect of CuO nanoleaf and ZnO NRs, which offered high electroactive surface area. Additionally, low working potential, good selectivity, low detection limit, and stable responses were shown in the results. However, this sensor resulted in a low dynamic detection range. In another interesting report, Karuppiah et al. also used a ZnO–CuO heterostructure to fabricate a non-enzymatic glucose biosensor using glassy carbon electrodes (GCE), which demonstrated an enhanced sensitivity, linear detection range, and a better detection limit . Importantly, long-term stability of up to 38 days was achieved, which is acceptable for an assay for the non-enzymatic detection of glucose.
In another attempt to make a porous composite material with enhanced surface area, Cai et al. used a simple controllable top-down method to synthesize ZnO–CuO porous core–shell spheres . The morphological characterization showed a core (CuO) surrounded by a porous shell (ZnO) with a large surface area, and thus the catalytic property of CuO and the electron transfer property of ZnO resulted in improved sensing performance. In another report, Marie et al. grew ZnO NRs vertically on FTO electrodes and functionalized with Fe2O3 to investigate the improvement as a non-enzymatic glucose sensor . During electrode fabrication, they used a simple solution route to grow ZnO NRs followed by a surface dip-coating method to modify its surface with Fe2O3. Further, Nafion was coated to improve the selectivity of the non-enzymatic sensor in the presence of interfering species. Similarly, Strano and Mirabella grew ZnO NRs on Cu wire using a chemical bath deposition method and further modified with Ni(OH)2 flakes by pulsed electrodeposition . ZnO NRs were vertically grown on Cu wire, which resulted in better stability of the electrode during non-enzymatic detection of glucose. This kind of small size working electrode is important for electrochemical measurements in small amounts of buffer solution.
2.2 Non-enzymatic FET based biosensor
2.3 Enzymatic FET based biosensor
Recently, to detect specific species metal/metal oxide modified ZnO nanomaterials were further functionalized with enzymes/selective membranes. By doing this, an enhanced sensing performance was obtained. Ahn et al. immobilized valinomycin on Fe2O3 NPs-modified ZnO NRs to fabricate a FET based potassium sensor . The analytical characterization of this sensor showed remarkably enhanced sensing response after Fe2O3 NPs modification as compared to the ZnO NRs based FET device. This result can be attributed to the high surface area of Fe2O3 NPs-modified ZnO NRs that favors increased valinomycin immobilization. ZnO NRs surface modification with Fe2O3 NPs also provides stability to the ZnO surface from acidic or basic solutions, which may be very useful for device stability during potassium detection. ZnO nanostructures are mostly grown on seeded substrates, however seed layers offer limited conductivity. The conductivity of electrode/seed layer holding nanostructures can also help to achieve improved sensitivity of the fabricated sensing device. Ahmad et al. designed a FET based calcium sensor device using a highly conductive seed layer . First, they prepared a highly conductive seed layer on the substrate by subsequently depositing a ZnO seed layer, Ag nanowires, and then the ZnO seed layer again, which resulted in a sandwich-like layer. The first deposited seed layer was to provide stability by firmly attaching nanowires on the substrate and the second seed layer was used to grow ZnO NRs. During electrochemical characterizations, the role of every material was evaluated which confirmed that the introduction of Ag nanowires was the main contributing factor for enhancing device sensitivity. This study further offered an important strategy to enhance sensing performance which may be useful to design other biosensors with improved performance.
The rapid emergence of nanotechnology has led to the transition from single materials to nanohybrids including several interesting nanostructures such as nanorods, nanowires, hollow spheres, nanodisks, nanotubes, and nanobelts. These represent an expansion of potential detection candidates for fabrication of a wide range of biosensors, including electrochemical, enzymatic, and non-enzymatic biosensors. Key physiochemical and optical characteristics of nanohybrid materials include large surface area and high isoelectric point resulting in high adsorption efficiency, non-toxicity and biocompatibility, mechanical and chemical stability, catalytic efficiency (oxygen storage capacity), and reduction in potential, and electrical conductivity are advantageous for the development of an efficient and high-performance biosensor device. For example, fabrication of enzymatic biosensor devices with enhanced stability can be performed using directly-grown nanostructures on substrates followed by immobilization of specific biomolecules, while electrochemical biosensors can be developed via exploiting catalytic characteristics of various designed nanomaterials or nanostructures. The biosensors developed using ZnO-based nanostructures have immense potential for biomedical applications owing to their effective surface area combined with its biocompatible nature, ease of synthesis with controlled morphologies and pore sizes, and high electron communication. Further their high isoelectric point also ensures stable biomolecule immobilization while maintaining biological functionalities. Functionalization with metal oxides nanostructures not only improves the biosensor device stability, but also enhances selectivity, sensitivity and lowers detection limits of the desired biosensor. This article reviewed the current advancements in the development of metal-oxide modified ZnO nanostructure-supported biosensors with an emphasis on both enzymatic and non-enzymatic sensing devices for different analytes. Overall the appealing characteristics of metal oxides modified ZnO nanostructure based biosensors provide excellent advantages for designing sensors consisting of multifunctional and structural nanomaterials. Such nanohybrids based biosensors can be envisioned to revolutionize the fields of biomedical diagnostics, environmental remediation/monitoring, food safety testing among other applications.
The selection and design of nanomaterials is critical for rapid and accurate biomolecule detection. Thus, constant advancements in material synthesis approaches, enzyme/protein engineering and immobilization/conjugation strategies will continue to yield novel nano-engineered segments with improved functionality. Furthermore, an envisioned combination of newly emerging advanced manufacturing technologies which includes nanoscale-oriented three- or four-dimensional printing of multicomponent, multifunctional nanostructures are expected to bring new avenues to the present sensor design. Research in the field of advanced biosensing with biofunctionalized multifunctional nanomaterials, and the development of cost-effective biochip designs employing nanoscale sensing materials can further pave the way for nano-biosensing platforms and the realization of an economical lab-on-a-chip replacement for real- or near real-time biomolecules sensing.
NT wrote the manuscript and D-HK guided the manuscript preparation. Both authors read and approved the final manuscript.
This work was supported by National Institutes of Health Grants R21EB020132 and R01HL135143 (to D.-H.K).
The authors declare that they have no competing interests.
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- M.-I. Mohammed, M.P. Desmulliez, Lab-on-a-chip based immunosensor principles and technologies for the detection of cardiac biomarkers: a review. Lab Chip 11, 569–595 (2011)View ArticleGoogle Scholar
- Y.-B. Hahn, R. Ahmad, N. Tripathy, Chemical and biological sensors based on metal oxide nanostructures. Chem. Commun. 48, 10369–10385 (2012)View ArticleGoogle Scholar
- S.S. Barkade, D.V. Pinjari, A.K. Singh, P.R. Gogate, J.B. Naik, S.H. Sonawane, M.A. Kumar, A.B. Pandit, Ultrasound assisted miniemulsion polymerization for preparation of polypyrrole-zinc oxide (PPy/ZnO) functional latex for liquefied petroleum gas sensing. Ind. Eng. Chem. Res. 52, 7704–7712 (2013)View ArticleGoogle Scholar
- C.Y. Chen, Y.R. Liu, S.S. Lin, L.J. Hsu, S.L. Tsai, Role of annealing temperature on the formation of aligned zinc oxide nanorod arrays for efficient photocatalysts and photodetectors. Sci. Adv. Mater. 8, 2197–2203 (2016)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, J.-H. Park, Y.-B. Hahn, A comprehensive biosensor integrated with a ZnO nanorod FET array for selective detection of glucose, cholesterol and urea. Chem. Comm. 51, 11968–11971 (2015)View ArticleGoogle Scholar
- M. Mazaheri, H. Aashuri, A. Simchi, Three-dimensional hybrid graphene/nickel electrodes on zinc oxide nanorod arrays as non-enzymatic glucose biosensors. Sens. Actuators B: Chem. 251, 462–471 (2017)View ArticleGoogle Scholar
- J. Zhang, B. Zhao, Z. Pan, M. Gu, A. Punnoose, Synthesis of ZnO nanoparticles with controlled shapes, sizes, aggregations, and surface complex compounds for tuning or switching the photoluminescence. Cryst. Growth Des. 15, 3144–3149 (2015)View ArticleGoogle Scholar
- W. Raza, K. Ahmad, A highly selective Fe@ZnO modified disposable screen printed electrode based non-enzymatic glucose sensor (SPE/Fe@ZnO). Mater. Lett. 212, 231–234 (2018)View ArticleGoogle Scholar
- K.L. Foo, U. Hashim, K. Muhammad, C.H. Voon, Sol-gel synthesized zinc oxide nanorods and their structural and optical investigation for optoelectronic application. Nanoscale Res. Lett. 9, 1–10 (2014)View ArticleGoogle Scholar
- M. Tak, V. Gupta, M. Tomar, Flower-like ZnO nanostructure based electrochemical DNA biosensor for bacterial meningitis detection. Biosens. Bioelectron. 59, 200–207 (2014)View ArticleGoogle Scholar
- J. Geng, G.H. Song, X.D. Jia, F.F. Cheng, J.J. Zhu, Fast one-step synthesis of biocompatible ZnO/Au nanocomposites with hollow doughnut-like and other controlled morphologies. J. Phys. Chem. C 116, 4517–4525 (2012)View ArticleGoogle Scholar
- K. Li, X. Liu, Q. Wang, S. Zhao, Z. Mi, Ultralow-threshold electrically injected AlGaN nanowire ultraviolet lasers on Si operating at low temperature. Nat. Nanotech. 10, 140–144 (2015)View ArticleGoogle Scholar
- W. Chang, S.M. Albrecht, T.S. Jespersen, F. Kuemmeth, P. Krogstrup, J. Nygård, C.M. Marcus, Hard gap in epitaxial semiconductor-superconductor nanowires. Nat. Nanotech. 10, 232–236 (2015)View ArticleGoogle Scholar
- P.R. Nair, M.A. Alam, Design considerations of silicon nanowire biosensors. IEEE T. Electron Dev. 54, 3400–3408 (2007)View ArticleGoogle Scholar
- J. Li, Y. Zhang, S. To, L. You, Y. Sun, Effect of nanowire number, diameter, and doping density on nano-FET biosensor sensitivity. ACS Nano 5, 6661–6668 (2011)View ArticleGoogle Scholar
- S. Hrapovic, E. Majid, Y. Liu, Y. Male, J.H.T. Luong, Metallic nanoparticle carbon nanotube composites for electrochemical determination of explosive nitroaromatic compounds. Anal. Chem. 78, 5504–5512 (2006)View ArticleGoogle Scholar
- M.M. Rahman, A.J.S. Ahammad, J.H. Jin, S.J. Ahn, J.J. Lee, A comprehensive review of glucose biosensors based on nanostructured metal-oxides. Sensors 10, 4588–4886 (2010)View ArticleGoogle Scholar
- E. Katz, I. Willner, J. Wang, Electroanalytical and bioelectroanalytical systems based on metal and semiconductor nanoparticles. Electroanalysis 16, 19–44 (2004)View ArticleGoogle Scholar
- P.R. Solanki, A. Kaushik, V.V. Agrawal, B.D. Malhotra, Nanostructured metal oxide-based biosensors. NPG Asia Materials 3, 17–24 (2011)View ArticleGoogle Scholar
- N. Tripathy, R. Ahmad, H. Kuk, D.H. Lee, Y.-B. Hahn, G. Khang, Rapid methyl orange degradation using porous ZnO spheres photocatalyst. J. Photochem. Photobiol. 161, 312–317 (2016)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, M.Y. Khan, K.S. Bhat, M.-S. Ahn, G. Khang, Y.-B. Hahn, Hierarchically assembled ZnO nanosheets microspheres for enhanced glucose sensing performances. Ceram. Int. 42, 13464–13469 (2016)View ArticleGoogle Scholar
- N. Tripathy, R. Ahmad, H. Kuk, Y.-B. Hahn, G. Khang, Mesoporous ZnO nanoclusters as an ultra-active photocatalyst. Ceram. Int. 42, 9519–9526 (2016)View ArticleGoogle Scholar
- N. Tripathy, R. Ahmad, H.A. Ko, G. Khang, Y.-B. Hahn, Enhanced anticancer potency using an acid-responsive ZnO-incorporated liposomal drug delivery system. Nanoscale 7, 4088–4096 (2015)View ArticleGoogle Scholar
- N. Tripathy, R. Ahmad, H.-S. Jeong, Y.-B. Hahn, Time-dependent control of hole-opening degree of porous ZnO hollow microspheres. Inorg. Chem. 51, 1104–1110 (2012)View ArticleGoogle Scholar
- N. Tripathy, R. Ahmad, H.A. Ko, G. Khang, Y.-B. Hahn, Multi-synergetic ZnO platform for high performance cancer therapy. Chem. Comm. 51, 2585–2588 (2014)View ArticleGoogle Scholar
- R. Ahmad, T. Mahmoudi, M.-Sa. Ahn, Y.-B. Hahn, Recent advances in nanowires-based field-effect transistors for biological sensor applications. Biosens. Bioelectron. 100, 312–325 (2018)View ArticleGoogle Scholar
- Y.-B. Hahn, R. Ahmad, N. Tripathy, Chemical and biological sensors based on metal oxide nanostructures. Chem. Commun. 48, 10369–10385 (2012)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, Y.-B. Hahn, High-performance cholesterol sensor based on the solution-gated field effect transistor fabricated with ZnO nanorods. Biosens. Bioelectron. 45, 281–286 (2013)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, S.H. Kim, A. Umar, A. Al-Hajry, Y.-B. Hahn, High performance cholesterol sensor based on ZnO nanotubes grown on Si/Ag electrodes. Electrochem. Commun. 38, 4–7 (2014)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, Y.-B. Hahn, Highly stable urea sensor based on ZnO nanorods directly grown on Ag/glass electrodes. Sens. Actuators B: Chem. 194, 290–295 (2014)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, N.K. Jang, G. Khang, Y.-B. Hahn, Fabrication of highly sensitive uric acid biosensor based on directly grown ZnO nanosheets on electrode surface. Sens. Actuators B: Chem. 206, 146–151 (2015)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, J.-H. Park, Y.-B. Hahn, A comprehensive biosensor integrated with a ZnO nanorod FET array for selective detection of glucose, cholesterol and urea. Chem. Commun. 51, 11968–11971 (2015)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, M.-S. Ahn, Y.-B. Hahn, Solution process synthesis of high aspect ratio ZnO nanorods on electrode surface for sensitive electrochemical detection of uric acid. Sci. Rep. 7, 46475 (2017)View ArticleGoogle Scholar
- J. Wu, F. Yin, Easy fabrication of a sensitive non-enzymatic glucose sensor based on electrospinning CuO–ZnO nanocomposites. Integr. Ferroelectr. 147, 47–58 (2013)View ArticleGoogle Scholar
- C. Zhou, L. Xu, J. Song, R. Xing, S. Xu, D. Liu, H. Song, Ultrasensitive non-enzymatic glucose sensor based on three-dimensional network of ZnO–CuO hierarchical nanocomposites by electrospinning. Sci. Rep. 4, 7382–7391 (2014)View ArticleGoogle Scholar
- T. Soejima, K. Takada, S. Ito, Alkaline vapor oxidation synthesis and electrocatalytic activity toward glucose oxidation of CuO/ZnO composite nanoarrays. Appl. Surf. Sci. 277, 192–200 (2013)View ArticleGoogle Scholar
- S. SoYoon, A. Ramadoss, B. Saravanakumar, S.J. Kim, Novel Cu/CuO/ZnO hybrid hierarchical nanostructures for non-enzymatic glucose sensor application. J. Electroanal. Chem. 717–718, 90–95 (2014)View ArticleGoogle Scholar
- C. Karuppiah, M. Velmurugan, S.-M. Chen, S.-H. Tsai, B.-S. Lou, M.A. Ali, F.M.A. Al-Hemaid, A simple hydrothermal synthesis and fabrication of zinc oxide-copper oxide heterostructure for the sensitive determination of nonenzymatic glucose biosensor. Sens. Actuators B: Chem. 221, 1299–1306 (2015)View ArticleGoogle Scholar
- B. Cai, Y. Zhou, M. Zhao, H. Cai, Z. Ye, L. Wang, J. Huang, Synthesis of ZnO–CuO porous core-shell spheres and their application for non-enzymatic glucose sensor. Appl. Phys. A 118, 989–996 (2015)View ArticleGoogle Scholar
- M. Marie, A. Manoharan, A. Kuchuk, S. Ang, M.O. Manasreh, Vertically grown zinc oxide nanorods functionalized with ferric oxide for in vivo and non-enzymatic glucose detection. Nanotechnology 29, 115501–115510 (2018)View ArticleGoogle Scholar
- V. Strano, S. Mirabella, Low-cost and facile synthesis of Ni(OH)2/ZnO nanostructures for high-sensitivity glucose detection. Nanotechnology 29, 015502–015509 (2018)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, M.-S. Ahn, K.S. Bhat, T. Mahmoudi, Y. Wang, J.-Y. Yoo, D.-W. Kwon, H.-Y. Yang, Y.-B. Hahn, Highly efficient non-enzymatic glucose sensor based on CuO modified vertically-grown ZnO nanorods on electrode. Sci. Rep. 7, 5715 (2017)View ArticleGoogle Scholar
- J.M. Marioli, T. Kuwana, Electrochemical characterization of carbohydrate oxidation at copper electrodes. Electrochim. Acta 37, 1187–1197 (1992)View ArticleGoogle Scholar
- R. Ahmad, M.-S. Ahn, Y.-B. Hahn, A highly sensitive nonenzymatic sensor based on Fe2O3 nanoparticle coated ZnO nanorods for electrochemical detection of nitrite. Adv. Mater. Interfaces 4, 1700691–1700700 (2017)View ArticleGoogle Scholar
- D.-U.-J. Jung, R. Ahmad, Y.-B. Hahn, Nonenzymatic flexible field-effect transistor based glucose sensor fabricated using NiO quantum dots modified ZnO nanorods. J. Colloid Interface Sci. 512, 21–28 (2018)View ArticleGoogle Scholar
- R. Ahmad, M.-S. Ahn, Y.-B. Hahn, Fabrication of a non-enzymatic glucose sensor field-effect transistor based on vertically-oriented ZnO nanorods modified with Fe2O3. Electrochem. Commun. 77, 107–111 (2017)View ArticleGoogle Scholar
- M.-S. Ahn, R. Ahmad, K.S. Bhat, J.-Y. Yoo, T. Mahmoudi, Y.-B. Hahn, Fabrication of a solution-gated transistor based on valinomycin modified iron oxide nanoparticles decorated zinc oxide nanorods for potassium detection. J. Colloid Interface Sci. 518, 277–283 (2018)View ArticleGoogle Scholar
- R. Ahmad, N. Tripathy, M.-S. Ahn, J.-Y. Yoo, Y.-B. Hahn, Preparation of a highly conductive seed layer for calcium sensor fabrication with enhanced sensing performance. ACS Sens. 3, 772–778 (2018)View ArticleGoogle Scholar