Abstract
Volatile organic compounds (VOCs) released by plants are closely associated with plant metabolism and can serve as biomarkers for disease diagnosis. Huanglongbing (HLB), also known as citrus greening or yellow shoot disease, is a lethal threat to the multi-billion-dollar citrus industry. Early detection of HLB is vital for removal of susceptible citrus trees and containment of the disease. Gas sensors are applied to monitor the air quality or toxic gases owing to their low-cost fabrication, smooth operation, and possible miniaturization. Here, we report on the development, characterization, and application of electrical biosensor arrays based on single-walled carbon nanotubes (SWNTs) decorated with single-stranded DNA (ssDNA) for the detection of four VOCs—ethylhexanol, linalool, tetradecene, and phenylacetaldehyde—that serve as secondary biomarkers for detection of infected citrus trees during the asymptomatic stage. SWNTs were noncovalently functionalized with ssDNA using π–π interaction between the nucleotide and sidewall of SWNTs. The resulting ssDNA-SWNT hybrid structure and device properties were investigated using Raman spectroscopy, ultraviolet (UV) spectroscopy, and electrical measurements. To monitor changes in the four VOCs, gas biosensor arrays consisting of bare SWNTs before and after being decorated with different ssDNA were employed to determine the different concentrations of the four VOCs. The data was processed using principal component analysis (PCA) and neural net fitting (NNF).
Highlights
Citrus huanglongbing (HLB), commonly called yellow shoot disease or citrus greening disease, is a lethal disease of citrus [1], which has become one of the most devastating diseasesSensors 2019, 19, 4795; doi:10.3390/s19214795 www.mdpi.com/journal/sensorsSensors 2019, 19, 4795 threatening citrus trees worldwide [2]
We propose a novel biosensor array using single-walled carbon nanotubes (SWNTs) functionalized with single-stranded DNA (ssDNA) through π-stacking, which improved the sensitivity of bare SWNTs
Electrical sensor arrays were fabricated using SWNTs decorated with ssDNA with a facile Electricalmethod
Summary
Citrus huanglongbing (HLB), commonly called yellow shoot disease or citrus greening disease, is a lethal disease of citrus [1], which has become one of the most devastating diseases. Due to the lengthy incubation and latent period of the pathogen, it has been shown that the infected trees can remain asymptomatic for extended periods of time [10,11] Visual symptoms, such as yellowing or asymmetrical yellow spots, start to display on parts of single shoot or branch [12], progressing to sparse yellow foliage, twig dieback, stunting, and reduced fruit yield [13,14] to half of their peak value. This renders early-stage diagnosis of HLB very challenging. To obtain the changes in VOCs, different mathematical models were employed to distinguish the species and contents of VOCs
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