A novel approach for in situ monitoring of Zn in citrus plants using two-step square-wave anodic stripping voltammetry
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Research Letter
A novel approach for in situ monitoring of Zn2+ in citrus plants using two-step square-wave anodic stripping voltammetry Jared Church and Woo Hyoung Lee, Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, Florida 32816, USA Address all correspondence to Woo Hyoung Lee at [email protected] (Received 9 February 2018; accepted 2 April 2018)
Abstract This study presents in situ detection of Zn2+ using a novel two-step square-wave anodic stripping voltammetry (SWASV)-based needle-type microsensor for citrus plant applications. A double-barrel bismuth/platinum (Bi/Pt) microelectrode was fabricated with a solid metal tip (∼110 µm), which was durable enough to penetrate the thick skin of the citrus leaves and sensitive enough to detect ppb changes in Zn2+ concentration using SWASV. The microelectrode tip size was also determined to reduce mass transport limitation and improve limit of detection. Overall, the developed Bi/Pt microelectrode successfully measured Zn2+ concentrations within the vascular bundle of citrus plants.
Introduction In the span of 10 years, Huanglongbing (HLB) has devastated Florida’s over the 10-billion-dollar citrus industry.[1] Recent works on greenhouse canker infiltration assays showed the local systemic activity of Zn-chelate[2]; however, there is no clear understanding of how the Zn-chelate moves in citrus trees. Although there are many analytical methods available for detecting Zn in aqueous solutions [e.g., inductively coupled plasma mass spectrometry and atomic absorption spectroscopy (AAS)], in situ monitoring of the movement of Zn-chelate in citrus trees has not been fully explored due to lack of experimental tools.[3] There is an urgent need to develop a reliable Zn2+ monitoring tool, capable of tracking its systemic activity directly in plants. Successful in situ Zn2+ detection will lead to a better understanding of its potential fate in plants by estimating spatial and temporal phloem concentrations of Zn2+ between successive spray applications, which will benefit the assessment of spray rate and timings for effective HLB management. Microelectrodes are needle-type electrochemical microsensors that have been used for in situ monitoring of chemical compounds of interest in biofilm and corrosion processes in drinking water distribution systems[4–6] and can be used to measure intracellular free-ion activities by inserting their tip into plant tissues. Previous studies have shown the usefulness of applying ion-selective microelectrodes to track the movement + [7–10] of H+, K+, NO− ; however, it was 3 , and Na in plants 2+ found that Zn ion-selective electrodes show interference to Cu2+,[3] a common micronutrient found in plants. Furthermore, ion-selective microelectrodes are difficult to manufacture and can be easily broken when the glass tip comes in contact
with hard surfaces. The microelectrode tip must be microscale to impale the phloem, but durable enough to penetrate the plant without breaking. Miller et al.[7] r
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