Wash-Free Digital Detection of Tumor Extracellular Vesicles via Plasmonic Droplet Microfluidics.

Early detection of tumor-derived extracellular vesicles (EVs) enables noninvasive cancer diagnostics, but current assays often require wash steps and suffer from limited sensitivity. Here, we developed PlasDroplex, a wash-free digital plasmonic assay that detects tumor-derived extracellular vesicles via droplet-confined binding between EVs and antibody-functionalized gold nanoparticles (Ab-AuNPs), eliminating washing and multistep labeling processes. Plasma (10 μL) is coencapsulated with Ab-AuNPs targeting CD9, EpCAM, PSA, PSMA, and PD-L1 in picoliter droplets. Target binding induces AuNP clustering into plasmonic networks that generate bright "On" droplets, while "Off" droplets remain dark, enabling a wash-free optical readout within 1 h. Limits of detection were 2500-6700 EVs/mL with high reproducibility (CV < 3%). In 63 clinical samples, PSA- and PSMA-positive EVs yielded AUCs of 0.926 and 0.932 for prostate cancer, respectively, while PD-L1 EVs achieved an AUC of 0.998 for lung cancer. PlasDroplex enables rapid, marker-specific, digital droplet-based EV profiling from minimal plasma volumes.