Label-free detection of Staphylococcus aureus captured on immutable ligand arrays

The rapid capture and label-free detection of Staphylococcus aureus, an opportunistic bacterium that can infect upon contact, can be performed using periodic microarrays of ligand-protein conjugates created by noncontact (inkjet) printing, darkfield imaging conditions, and a FFT-based readout method. Ink solutes were prepared using bovine serum albumin (BSA) conjugated to a glycan with high affinity for bacterial adhesins and printed as dot-matrix arrays with periodicities of 80-120 μm using a thermal injection method. Upon exposing the glycan-BSA microarrays to live strains of S. aureus, patterns emerge that can be detected under optical darkfield conditions. These patterns can be decoded by fast Fourier transform (FFT) analysis to generate fault-tolerant readout signals that correspond to the capture of S. aureus, with a limit of detection between 10² and 10³ cfu/mL. Inkjet printing provides independent control over array periodicity, enabling FFT signals to be assigned to specific frequencies in reciprocal k-space.