Detection of quiescent fungi in harvested fruit using CMOS biosensor: A proof of concept study.

Postharvest fruit decay is caused by fungal pathogens and leads to major losses. In this study, specific mRNA sequences that are upregulated in the fungus Colletotrichum gloeosporioides during its quiescent stage in fruits, were identified using a CMOS sensor. The identification process was based on sandwich approach, where strands complementary to the C. gloeosporioides mRNA sequences (quiescent stage-specific) were immobilized on the CMOS surface, and exposed to the target complementary reporter strands. In the presence of a target sequence, the reporter strand (linked to the enzyme horseradish peroxidase (HRP)) was left in the system and a measurable light signal was produced. The complementary strands specifically anneal to the mRNA in the sample. The sensitivity of the technology was assessed by mRNA sequences isolated from C. gloeosporioides, and identified as 10 nM RNA. The effect of the pathogenicity state on the sensor performance was also evaluated. The CMOS sensor could detect quiescent fungi, which are barely detectable by other means. The unique capability of the proposed system to detect and recognize the fungus during both pathogenic and quiescent stages, will allow the development of new sensors that can monitor the amount of undetectable quiescent fungi in harvested fruit, enabling improved food management.