Cytokine
storm, known as an exaggerated hyperactive immune response
characterized by elevated release of cytokines, has been described
as a feature associated with life-threatening complications in COVID-19
patients. A critical evaluation of a cytokine storm and its mechanistic
linkage to COVID-19 requires innovative immunoassay technology capable
of rapid, sensitive, selective detection of multiple cytokines across
a wide dynamic range at high-throughput. In this study, we report
a machine-learning-assisted microfluidic nanoplasmonic digital immunoassay
to meet the rising demand for cytokine storm monitoring in COVID-19
patients. Specifically, the assay was carried out using a facile one-step
sandwich immunoassay format with three notable features: (i) a microfluidic microarray patterning technique for high-throughput,
multiantibody-arrayed biosensing chip fabrication; (ii) an ultrasensitive nanoplasmonic digital imaging technology utilizing
100 nm silver nanocubes (AgNCs) for signal transduction; (iii) a rapid and accurate machine-learning-based image
processing method for digital signal analysis. The developed immunoassay
allows simultaneous detection of six cytokines in a single run with
wide working ranges of 1–10,000 pg mL–1 and
ultralow detection limits down to 0.46–1.36 pg mL–1 using a minimum of 3 μL serum samples. The whole chip can
afford a 6-plex assay of 8 different samples with 6 repeats in each
sample for a total of 288 sensing spots in less than 100 min. The
image processing method enhanced by convolutional neural network (CNN)
dramatically shortens the processing time ∼6,000 fold with
a much simpler procedure while maintaining high statistical accuracy
compared to the conventional manual counting approach. The immunoassay
was validated by the gold-standard enzyme-linked immunosorbent assay
(ELISA) and utilized for serum cytokine profiling of COVID-19 positive
patients. Our results demonstrate the nanoplasmonic digital immunoassay
as a promising practical tool for comprehensive characterization of
cytokine storm in patients that holds great promise as an intelligent
immunoassay for next generation immune monitoring.