  Label-free detecting multiple analytes in a high-throughput fashion has been
one of the long-sought goals in biosensing applications. Yet, for all-optical
approaches, interfacing state-of-the-art label-free techniques with
microfluidics tools that can process small volumes of sample with high
throughput, and with surface chemistry that grants analyte specificity, poses a
critical challenge to date. Here, we introduce an optofluidic platform that
brings together state-of-the-art digital holography with PDMS microfluidics by
using supported lipid bilayers as a surface chemistry building block to
integrate both technologies. Specifically, this platform fingerprints
heterogeneous biological nanoparticle populations via a multiplexed label-free
immunoaffinity assay with single particle sensitivity. Herein, we first
thoroughly characterise the robustness and performance of the platform, and
then apply it to profile four distinct ovarian cell-derived extracellular
vesicle populations over a panel of surface protein biomarkers, thus developing
a unique biomarker fingerprint for each cell line. We foresee that our approach
will find many applications where routine and multiplexed characterisation of
biological nanoparticles is required.
