A paper-based immunoassay may detect SARS-CoV-2 signals associated with long COVID.
Evidence
Proof-of-concept platform experiment tested dendrimer-amplified paper immunoassay detection and applied it to 20 plasma samples, 10 from long COVID patients and 10 healthy controls.
Caveat
The human sample set was very small and used healthy controls with no SARS-CoV-2 history, so diagnostic performance for real-world long COVID screening is unresolved.
Simplified
Long COVID is characterized by persistent symptoms, including fatigue, cognitive impairment, and respiratory issues, affecting a considerable number of individuals post-infection. The underlying mechanism is not fully understood, but it has been proposed to involve the reactivation of virus, which subsequently induces immune dysregulation. In this proof-of-concept study, we developed a paper-based immunoassay for the detection of nucleocapsid (N) protein, which, due to its stability and low mutation rate, is a valuable biomarker for detecting the presence of residual virus. By utilizing reporter antibodies conjugated to cleavable ionic probes through dendrimer chemistry, we were able to analyze the immunoassay results with ambient using on-chip paper spray ionization. The used dendrimer enhanced mass spectrometry sensitivity by enabling the attachment of multiple ionic probes to a single reporter antibody. The method presented here achieved a limit of detection of 2.4 pM for N protein detection from paper. Unlike traditional sensitive COVID tests that are only accessible to hospitalized individuals, our paper-based assay has potential to enable long COVID to be detected under resource-limited settings. Our method was applied to analyze 20 human plasma samples, including 10 from individuals with long COVID and 10 from healthy controls with no history of SARS-CoV-2 infection. We observed a significantly higher MS signal-by up to two orders of magnitude-for samples collected from long COVID patients compared to controls. The ability to use the paper device in remote locations was tested by evaluating the stability of the assay, which showed that after 30 days of storage at room temperature, the device retained sufficient analytical performance. Given its robustness, we believe that our platform will be suitable for direct-to-consumer testing, enabling individuals with low viral loads to be screened in a timely fashion.
Key numbers
2.4 pM
Limit of Detection
Sensitivity of the paper-based immunoassay for
up to 100×
Signal Increase
Comparison of MS signal from long COVID patients vs. healthy controls
30 days
Stability Duration
Duration the assay maintained performance at room temperature
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Long Covid