BIRD-Seq: B2 Protein Integrated End-to-End Pipeline for dsRNA Detection and Nanopore Sequencing for Virus Monitoring

Abstract

Double-stranded RNA (dsRNA) is a near-universal hallmark of active viral infection. Despite its role as a pan-viral replication intermediate, dsRNA-centred technologies for virus monitoring remain scarce and largely rely on monoclonal antibody-based approaches that, while highly sensitive, are costly and difficult to engineer, scale, or integrate with downstream assays. Here, we present a modular and antibody-free pipeline for quantitative and qualitative dsRNA analysis built around an engineered B2 protein from Flock House virus with nanomolar-range binding affinity. The pipeline is compatible with absorbance- or luminescence-based measurement formats. In a sandwich assay configuration (Sand-BIRD), sub-ng mL-1 quantification of dsRNA is achieved, comparable to the gold standard J2 monoclonal antibody, directly from crude biological samples without RNA extraction. Sand-BIRD reliably detects viral infection in both plant samples (Tomato bushy stunt virus and Grapevine fanleaf virus) and mosquitoes (West Nile virus and Dengue virus) with commercial-grade reliability. dsRNA eluted from positive samples were further processed directly by Oxford Nanopore direct sequencing, enabling identification of virus species without prior sequence knowledge or total RNA extraction. Together, this work establishes an end-to-end, sequence-agnostic workflow for direct RNA-duplex quantification and sequencing (BIRD-Seq), which has compelling potential for emerging infectious disease surveillance and next-generation point-of-care (PoC) diagnostics. Technology ReadinessBIRD-Seq is an integrated pipeline for agnostic dsRNA detection and sequencing designed for broad-spectrum virus monitoring. A Technology Readiness Level (TRL) 5 under NASAs classification framework has been reached as BIRD-Seq has been validated in laboratory-relevant environments using real-world samples, including virus-infected plants and mosquitoes. The ELISA-based sensing platform employs engineered variants of the B2 protein (from Flock House virus) in a sandwich assay format for dsRNA capture and detection, achieving sensitivity comparable to the gold-standard J2 monoclonal antibody. Unlike traditional antibody-based methods, the B2 protein offers key practical advantages: straightforward production in bacterial expression systems, high versatility, and reduced manufacturing costs, as well as direct compatibility with crude extract monitoring, eliminating the need for RNA extraction. Captured B2/RNA duplexes can then be directly eluted from the ELISA microplates and subjected to downstream nanopore direct RNA sequencing, providing both quantitative and qualitative information on the underlying virus infection, a capacity enabled by the near-universal nature of dsRNA as a pathogen-associated molecular pattern. That said, further validation on large-scale field-collected and clinical samples will be essential before widespread deployment can be envisioned. While the B2 sandwich assay offers favorable cost-efficiency over antibody-based alternatives, the relatively high cost of Oxford Nanopore direct RNA sequencing remains an important economic constraint. Nevertheless, the growing importance of dsRNA detection across virus sensing, mRNA vaccine development, innate immunity research, and human disease diagnostics, combined with the increasing role of portable long-read sequencing in emerging infectious disease (EIDs) surveillance, positions BIRD-Seq as an innovative and competitive diagnostic platform. Highlights- Double-stranded RNA (dsRNA) is one of the critical pathogen-associated molecular patterns for viral invasion in the host. A protein-based sandwich assay for dsRNA detection in crude biological samples with a sub-ng mL-1 order detection limit was developed, achieving similar sensing efficiency in comparison to expensive and proprietary monoclonal antibody-based ELISA methods. - The quantitative detection of RNA duplex is coupled with an Oxford nanopore direct dsRNA sequencing method for virus species identification and qualitative analysis. - This is one of the very first dsRNA-centered end-to-end workflows for virus monitoring and sequencing, validated for both infected plant and animal samples.