A Sample-to-Answer Compact Optical System for On-Site Detection of Candidatus Liberibacter Asiaticus

摘要

Candidatus Liberibacter asiaticus (Las) is a main causal agent of huanglongbing (HLB), a destructive disease that has greatly reduced citrus yields and quality. Instruments with high sensitivity and portability are urgently required for on-site testing. In this study, a novel sample-to-answer optical system for on-site detection of Las was developed. Three major functions, including DNA extraction, amplification, and detection, are integrated into a portable case. This system mainly consists of (1) aspecially designed 3D printed box for on-site reagent storage that can maintain low temperature (below 4°C) for 7.5 h at ambient temperature (35°C); (2) a custom device, called the IF-Device, for DNA amplification and detection of HLB, with an optimized optical structure, a sensitive signal processing circuit, and a precise temperature control algorithm with an accuracy of ±0.1°C; and (3) a battery-based power supply for the whole system. In a typical test using sodium fluorescein as a standard model, the results showed that the sensitivity of this system (1.0 nM) could easily meet the requirements of fluorescence biosensors. The feasibility of this homemade system was evaluated with samples extracted from infected citrus leaves based on the loop-mediated isothermal amplification (LAMP) method, and the limit of detection (LOD) was approximately 1.0 x 10~(-4) ng muL~(-1). The whole detection process for eight samples could be simultaneously accomplished within 40 min, and the results could be displayed on a smartphone in real-time. Moreover, the portable case is anti-interference, low cost, and only 2 kg in weight. Considering its sensitivity, stability, and portability, this highly integrated system possesses promising prospects for in-field detection.