The last years have witnessed a link between the COVID-19 pandemic with increasing numbers of
vulnerable patients and globally emerging incidences of severe drug-resistant fungal infections, thus,
calling for rapid, reliable, and sensitive diagnostic tools for fungal infections. However, despite strong
warnings from health authorities, such as the World Health Organization, concerning the fatal consequences
of the global spread of drug-resistant pathogenic fungi, progress in fungal infection diagnosis and therapy
is still limited. Today, gold standard methods for revealing resistance and susceptibility in pathogenic fungi,
namely antifungal susceptibility testing (AFST), require several days for completion, and thus this lengthy
process can adversely affect antifungal therapy and further promote the spread of resistance.
In this work, the use of photonic silicon chips consisting of micropatterned diffraction gratings as sensitive
sensors for rapid AFST of clinically relevant fungal pathogens is investigated. These photonic chips provide
a surface for the colonization of microbial pathogens at a liquid-solid interface and serve as the optical
transducer element for label-free monitoring of fungal growth by detecting real-time changes in the white
light reflectance. These sensor elements are used to track morphological changes of fungi in the presence
of clinically relevant antifungals at varying concentrations to rapidly determine the minimum inhibitory
concentration (MIC) values that help to classify pathogens as resistant or susceptible. We show that by
careful design of the chip dimensions, this optical method can extend from bacteria, through yeasts, to
filamentous fungi for accelerated AFST, which is at least three times faster than current gold standard
methods and can provide same-day results.
Moreover, a 3D-printed microfluidic gradient generator was designed to complement the assay and provide
an integrated system, which can potentially be employed in point-of-care settings. This gradient generator
produces the two-fold dilution series of clinically relevant antimicrobials in an automated manner and is
interfaced with the photonic silicon chips to include a complete, on-chip, label-free, and phenotypic assay.
Using the bacterial species Escherichia coli and ciprofloxacin as a model pathogen-drug combination, MIC
values can be expeditiously determined within 90 minutes compared to current clinical practices, which
typically require up to 24 h for bacterial species.
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