Simple and rapid detection of Alternaria alternata using an excreted redox-active species

Airborne fungi pose a serious threat to public health. Alternaria alternata (A. alternata) is a fungus that has been associated with the development of asthma. Detection using redox-active species excreted from fungi is an effective method for a simple electrochemical fungal biosensor. The achievable electrochemical signal in most fungi, however, is exceptionally low because of the low amount of excreted redox-active species and their slow excretion rates. Herein, we report that A. alternata excretes an exceptionally large amount of a redox-active species that can be used for sensitive and selective detection of A. alternata. The excretion rate is enhanced in Tris buffer, and the electrochemical-chemical redox cycling involving excreted redox-active species significantly increases the electrochemical signals. Only A. alternata among five common airborne fungi provides large electrochemical signals, which allows selective detection of A. alternata. The calculated detection limit for A. alternata is similar to 20 spores/mL with an incubation period of 10 min, indicating that the detection method is highly sensitive and rapid. The detection method does not require complicated procedures or harsh pretreatment and is optimal for point-of-care testing of A. alternata.