Low cost aluminium foil platforms for rapid mass spectrometric differentiation of the fungal pathogen Aspergillus niger mycelium and spores by in situ gold nanosphere accelerated microwave digestion

Abstract

Fungal analysis involving filamentous pathogens is usually a challenging task. The present work uses aluminium foils as MALDI MS platforms for microwave digestion of whole fungal mycelium and spores belonging to the pathogen, A. niger. The 10 mm² aluminium foil platforms cut from a 2 USD worth 80 m commercial foil pack, costs about 0.000008 USD per platform. The home made aluminium target holder on which we mount these foils costs only 100 USD, compared to the 600 USD of conventional stainless steel MALDI MS target plates. Hence a 6-times reduction in cost has been achieved using our system. Our results and optimization experiments concluded that a 3 min microwave digestion could lead to significant signals both in the case of mycelium and spores. The signals obtained were reliable and could help in the differentiation between the non-infecting mycelium and the highly infective and contagious sporulation phase. We further used the homemade Au nanospheres, known for their high heat absorption ability, for accelerating the microwave digestion on the Al foil platforms. The fungal analyte (mycelium/spores) when sandwiched between the Al foil on the ventral side and the Au nanospheres on the dorsal side led to significant reduction in the microwave time from 3 min to 30 s.