It is challenging to convert redox metabolites present inside fungi into measurable signals via permeabilization because of the fungi's thick and rigid cell walls. We report that Aspergillus niger (A. niger) can be detected via the electrochemical measurement of redox metabolites excreted by a low level of permeabilization of the cell wall of A. niger, when incubated in tris buffer containing hydrazine. Electrochemical signals of redox metabolites are amplified by electrochemical-chemical redox cycling, in which hydrazine acts as a reductant for rapid redox cycling. The detection method is specific to A. niger among the major three fungi causing aspergillosis. The calculated detection limit for A. niger is $2 Â 10 2 CFU/ml despite the incubation period being only 5 min, indicating that the detection method is highly sensitive and rapid. The detection method does not require a wash step, specific affinity binding, or pretreatment step, indicating that it is a simple method.

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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 ~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.