Rapid and sensitive detection of Aspergillus niger using permeabilization based on tris buffer containing hydrazine

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 × 10² 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.