Polymeric based (SC-µ-ISEs) Established Equilibrium Elaboration and Characterization of Solid-Contact micro-Electrodes for the Indirect Detection of Zinc by Subtracting Interfering Signal Cody M. Autrey1, Stephanie M. Armas1, Percy Calvo-Marzal1, Karin Y. Chumbimuni-Torres1 1Department of Chemistry, University of Central Florida, Orlando, Florida 32816. MOTIVATION CONCLUSION Figure 1. Areas of the world that are affected by HLB. PROPOSED SOLUTION 𝑰 𝒂𝒒 𝒛+ + 𝒏𝑳 𝒐𝒓𝒈 + 𝑴 𝒐𝒓𝒈 + 𝑹 𝒐𝒓𝒈 − ⇌ 𝑰𝑳 𝒏 𝒐𝒓𝒈 𝒛+ + 𝑴 𝒂𝒒 + + 𝑹 𝒐𝒓𝒈 − Easy miniaturization Portable, Simple Construction Ability to perform in-situ analysis Polymeric based (SC-µ-ISEs) Versatile Non-destructive Selective (complex matrix analysis) Established Equilibrium 𝑬 = 𝑬 𝟎′ + 𝟐.𝟑𝟎𝟑𝑹𝑻 𝒛 𝑰 𝑭 𝒍𝒐𝒈( 𝒂 𝑰 𝒂𝒒 ) Nernst Equation To develop a reliable, sensitive, and selective tool for monitoring ionic concentrations in plants and bactericides. High rates of Huanglongbing (HLB) infected citrus crops are affected worldwide. HLB is known to be linked to ionic deficiencies within the phloem and xylem bundles of citrus crops2. Focus will be geared towards zinc ionic efficiencies. Well established tools for plant analysis such as Atomic Absorption Spectroscopy (AAS), X-Ray Fluorescence3, among other methods are costly, non-portable and destructive. A main issue that we have encountered is the effect of copper (Cu2+) interference. In plants, copper abundance is significant in relation to zinc. Due to the ionic radius of the two ions being close in size, the ionophore begins to lose selectivity towards the Zn2+ ion. The ionic radius of a Zn2+ ion is 0.74 Å, while the ionic radius for a Cu2+ ion is 0.73 Å.4 This seemingly minor difference in size characteristics causes a problem in the detection of zinc ions in plant systems. The ion-selective electrodes that we are created are the solution to this problem. SC-µ-ISEs were developed from scratch and characterization showed high reliability and consistency. We have characterized these ion-selective electrodes so that they respond to both Zn2+ and Cu2+ in a Nernstian fashion. The selectivity studies that we conducted showed that Zinc Ionophore I actually favored copper over zinc – attributing to a significant amount of interference when using this ionophore to detect zinc. The pH stability studies that were conducted revealed that the ISEs were most reliable when the pH ranged from 4-7. This is optimal, as we are working with phloem and xylem bundles within citrus crops and the pH falls within this range. Further optimization of the Zn2+ and Cu2+ SC-µ-ISEs and multiplex analysis of these ions will come in the future. Figure 2. A. HLB infected citrus crops. B. Vector of transmission of the bacterial disease HLB. A B EXPERIMENTAL RESULTS 0.73 Å Cu2+ 0.74 Å Figure 3. Ionic radii of both Cu2+ (0.73Å) and Zn2+ (0.74Å). Zn2+ FUTURE/ONGOING WORK We plan on creating a multiplex sensor that can be used to detect both copper and zinc in plants. Once we are able to measure the copper interference, we can then subtract that interfering signal from the zinc signal, thus allowing us to determine the amount of zinc that is in the phloem and xylem bundles. Figure 5. SC-µ-ISE containing Copper (II) Ionophore I and NaTFPB response to Cu2+ in DI water. Slope 27.11±0.97 mV decade-1 LOD 7.17x10-7 of mol L-1. Figure 6. SC-µ-ISE containing Zinc Ionophore I and KTFPB response to Cu2+ in DI water. Slope 28.88±0.95mV decade-1 LOD 2.18x10-7 of mol L-1. Figure 7. SC-µ-ISE containing Zinc Ionophore I and KTFPB response to Zn2+ in DI water. Slope 32.28±1.29 mV decade-1 LOD 2.83 x10-7 of mol L-1. METHODOLOGY Zn2+ SC-µ-ISE Cu2+ SC-µ-ISE Table 1. Selectivity Studies of Zinc Ionophore I based on the separate solutions method.1 ZINC IONOPHORE I COPPER (II) IONOPHORE I NaTFPB KTFPB Ionophore: Selectivity Ion-Exchanger Electroneutrality & Permselectivity Plasticized polymer Mechanical stability PVC o-NPOE Figure 9. Schematic Diagram of the future multiplex analysis sensors that are to be tested simultaneously. ACKNOWLEDGEMENTS Plastic Pipette Polymeric Membrane POT Coated Gold Wire Gold Wire Adhesive (1) (2) (3) The authors of this project would like to thank the Department of Chemistry and the Office of Undergraduate Research at the University of Central Florida. This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number USDA Grant 2016-70016-24828. We also thank the NanoScience Technology Center for the shared facilities. Figure 8. pH stability studies with a working pH range of 4-7.1 REFERENCES (1) Church, J*.; Armas, S. M*.; Patel, P. K.; Chumbimuni-Torres, K.; Lee, W. H. Electroanalysis 2017. (2) Batool, A.; Iftikhar, Y.; Mughal, S. M.; Khan, M. M.; Jaskani, M. J.; Abbas, M.; Khan, I. A. Horticultural Science 2007, 34, 159-U153. (3) Kalra, Y. P. Handbook of reference methods for plant analysis; CRC Press: Boca Raton, 1998. (4) http://www.cgl.ucsf.edu/chimera/1.1700/docs/UsersGuide/midas/vdwtables.html (5) Bakker, E.; Buehlmann, P.; Pretsch, E. ChemInform 2010, 29 (11) Figure 4. Electrochemical cell set-up. (1) Reference Electrode (2) pH Electrode (3) SC-µ-ISEs Schematic 1. Schematic diagram SC-µ-ISE