Citrus Huanglongbing (HLB) is incurable, so it is necessary to develop an accurate and timely detection method for citrus HLB. Volatile organic compounds (VOCs) of plants can be used as an indicator of their health status. Based on the difference of VOCs between healthy and HLB citrus leaves, we designed the polyethyleneimine (PEI)-modified carboxylic multi-walled carbon nanotubes (CNT-COOH) gas sensor and used it in the diagnosis of citrus HLB. Our PEI/CNT-COOH sensor showed significant impedance responses to four citrus HLB biomarkers VOCs (ethylhexanol, phenylacetaldehyde, linalool and methyl salicylate) with sensitivity up to single-digit ppm. We then used the sensor to detect the VOCs in citrus leaves, and found that the diseased citrus can be distinguished from the healthy citrus according to the different response values of the sensor, successfully identified HLB-infected citrus. Compared with the conventional qPCR method, PEI/CNT-COOH sensor not only has higher accuracy, but also can be used in real time field detection of citrus leaves due to its less stringent operating condition and portability.

柑橘黄龙病（HLB）是无法治愈的，因此有必要开发一种准确及时的柑橘HLB检测方法。植物的挥发性有机化合物（VOCs）可作为其健康状况的指标。基于健康和HLB柑橘叶片VOCs的差异，我们设计了聚乙烯亚胺（PEI）修饰的羧基多壁碳纳米管（CNT-COOH）气体传感器，并将其用于柑橘HLB的诊断。我们的 PEI/CNT-COOH 传感器对四种柑橘 HLB 生物标志物 VOC（乙基己醇、苯乙醛、芳樟醇和水杨酸甲酯）显示出显着的阻抗响应，灵敏度高达个位数 ppm。然后我们用传感器检测柑橘叶片中的VOCs，发现根据传感器响应值的不同，可以区分患病柑橘和健康柑橘，成功鉴定出感染 HLB 的柑橘。与传统的qPCR方法相比，PEI/CNT-COOH传感器不仅具有更高的精度，而且由于其操作条件不那么严格和便携性，可用于柑橘叶片的实时现场检测。