By Dr. David Rubert, Xpedite Diagnostics · 7 min read
The bottleneck in decentralized testing
Most discussion of Point-of-Care molecular testing focuses on the readout, the sequencer, the qPCR, the isothermal assay. In the field, the step that actually limits things is upstream. Conventional column- and bead-based extractions depend on chaotropic salts, centrifugation, and cold-chain reagents: requirements that “do not travel” to a rural clinic, a mobile laboratory, or an operating room.
Dr. Johannes Graf, R&D scientist at Xpedite, framed the work around three application areas: human health (infectious-disease screening, chronic-disease monitoring); veterinary and food safety (pathogen detection, antimicrobial-resistance surveillance); and remote or resource-limited settings, which connects directly to the portable-laboratory work of the preceding talk of the webinar. All three impose the same constraint.
'Nucleic acid extraction has be extremely fast, and testing needs to happen close to the patient' — Dr. Johannes Graf, Xpedite Diagnostics
Reverse purification: keeping the target, removing the noise
The core method inverts the conventional binding logic. For low-complexity samples (swabs, plasma, serum), the sample is incubated with heat and a lysis buffer containing no chaotropic salts, together with proprietary paramagnetic particles. In the step Xpedite terms reverse purification, the particles bind cell debris and inhibitory substances rather than the nucleic acid; these are removed magnetically, and the cleared lysate proceeds to downstream qPCR or NGS.
Two consequences matter in a field setting. Because DNA and RNA are never bound to the solid phase, extraction losses are minimal and total nucleic acid is retained. And because the chemistry carries no chaotropic salts, the reagents present a lower transport and regulatory burden, a point that connects directly to the cold-chain and customs constraints that limited the most field deployments.
Complex and diluted samples: cell capture
Reverse purification alone is not sufficient for complex, low-target matrices such as whole blood or sputum, where the target is heavily diluted by host material. Here an upstream cell-capture step is added: paramagnetic beads bind intact target cells directly from the liquid and are magnetically separated before lysis and reverse purification. The capture chemistry is configurable for pan-bacterial and pan-fungal binding, or for host cells. The overall process is modular: lysis alone, capture upstream, mechanical grinding, or a downstream clean-up can be included or omitted by sample type.
'Can that actually work?'
In its minimal configuration the extraction needs only sample, beads, lysis buffer, optional proteinase K, and heat. Heat inactivates nucleases and disrupts particulate material; reverse purification removes inhibitors; the output is total nucleic acid. Instrumentation is limited to a heat block and a magnetic separator.
'You might think, this one-step DNA extraction, how does that work? Can that actually work? I hope I can convince you that it really does. The fastest protocol that we can do is around six minutes.' — Dr. Johannes Graf, Xpedite Diagnostics
Johannes was explicit about the trade-offs: the one-step method operates on smaller input volumes; it dilutes rather than enriches, lowering analytical sensitivity; and difficult matrices (stool, wastewater, veterinary samples, whole blood) can retain residual inhibitory potential. Those constraints are the reason the extraction is paired with a purification step.
Pure elutes, ready for NAAT and NGS: ClassiX™ CleanUp
The clean-up is a solid-phase reversible immobilisation (SPRI) chemistry, an established, bead-based, size-selective purification. Polyethylene glycol and salt concentration set the fragment-length threshold at which DNA binds the particles, and the bead-to-sample ratio tunes that cut-off: 0.8× retains fragments ≥400 bp while removing smaller fragments and inhibitors; 1.0× gives a standard PCR/NGS library clean-up (≥250 bp); and 1.8× recovers small amplicons down to ≥100 bp. One reagent, one adjustable ratio, from primer removal to small-amplicon rescue. This is what makes a fast, chaotrope-free extraction compatible with long-read chemistries, where input fragment length determines achievable read length.
Example 1: a fast molecular answer during surgery
The first application targets intra-operative solid-tumour classification: a workflow from tissue sampling to data analysis fast enough to inform a procedure, using non-chaotropic reagents and yielding fragments long enough (target ≥4 kb) for structural-variant analysis. The clinical rationale is well established, molecular and methylation-based classification conventionally takes days to weeks, whereas intra-operative nanopore sequencing with a deep-learned classifier (Sturgeon) has been shown to return a CNS-tumour subclass within ~40 minutes of sequencing and to guide neurosurgical decisions in real cases [1].
In the Xpedite proof-of-concept run, the complete workflow ran in ≈60 minutes: ~20 minutes of sample preparation (tissue lysis with beads, proteinase K, and metal-bead grinding; reverse purification; ClassiX™ CleanUp at a 0.35× bead ratio to retain high-molecular-weight fragments), ~10 minutes of library preparation on a transposase-based nanopore rapid sequencing kit (V14), and 30 minutes of sequencing to approximate an intra-operative window. Reported metrics: pore health 99.6% (assessed between consecutive runs, after flow-cell washing); pore occupancy 57.5%, which Graf identified as sub-optimal; and an N50 read length of ~14 kb, versus ~8.5 kb for the reference method, the fragment-length gain that a structural-variant or methylation classifier depends on. A first step forward for the field and with potential incoming improvements.
Example 2: skipping the blood culture in Sepsis diagnostics
The second application targets fungaemia and bacteraemia (e.g. sepsis), where the objective is to reduce time-to-result and remove the blood-culture step. The clinical stakes are quantified: in septic shock, each hour of delay in effective antimicrobial therapy after the onset of hypotension is associated with a measurable increase in mortality [2]. Yet blood culture, the standard of care, can take one to five days, and the analytical obstacle is extraction: in early infection the pathogen load is low and swamped by host cells.
The workflow adds up to 10 mL of whole blood to a capture buffer and beads that bind pathogens preferentially over the host background; magnetic separation provides a first concentration step. After washing to remove blood components, lysis proceeds by mechanical grinding, proteinase K digestion at 65 °C, and heat lysis at 95 °C, followed by a further magnetic separation to remove debris and inhibitors. The crude lysate can feed a nucleic acid amplification test directly, or be taken through ClassiX™ CleanUp (~15–20 minutes). Concentration and lysis run in ≈40 minutes, with full sample preparation under two hours, reducing 10 mL of input to 50–100 µL.
On analytical performance, Johannes presented limit-of-detection (LoD) data from internal laboratory-developed tests (LDTs), single-copy targets, on spiked whole blood, across Gram-negative (E. coli, K. pneumoniae, P. aeruginosa), Gram-positive (S. aureus, E. faecalis, S. pneumoniae), and fungal (C. albicans) organisms. Most targets were detected at 10 CFU/mL; the lowest LoDs were 3 CFU/mL (E. coli) and 5 CFU/mL (E. faecalis). Multi-target or multi-copy assays could lower these further. The decisive point is the removal of the blood culture step, recovering intact pathogens directly from whole blood and therefore enabling a faster and more precise antibiotic treatment at the Point-of-Care.
From bench to field: automation
The whole-blood workflow runs end-to-end on the SwiftXtractor™ SL as a two-step automated process: ~50 minutes for capture and lysis (10 mL input), then ~25 minutes for ClassiX™ CleanUp, yielding ~100 µL of eluted DNA/RNA for qPCR, dPCR, ddPCR and NGS, approximately 75 minutes total. The instrument accepts inputs from 0.2 to 40 mL, operates on AC or DC power, provides two heating zones with active mixing/grinding, and uses standard 2, 5, and 50 mL tubes rather than proprietary cartridges. It is specified as IVD-R ready (open and closed configurations), and Xpedite's quality system is certified to EN ISO 13485:2016. In validation of the manual workflow, the combined metal-bead and paramagnetic-bead lysis recovered ~95% of input, with no measurable bead damage at standard vortex speeds.
Johannes was clear that field robustness is developed with, not for, the end user:
'It's quite important that you work quite closely with people who are going into the field, because in a laboratory environment it's always difficult to get hands-on the actual, difficult samples.' — Dr. Johannes Graf, Xpedite Diagnostics
From breakthrough to system change
The through-line across both examples is consistent: decentralized molecular testing depends on rapid nucleic acid extraction; rapid methods carry both advantages and limitations; and most real workflows therefore integrate a purification step, reverse purification to remove inhibitors, or SPRI-based clean-up to control fragment-size distribution for NGS. The same chemistry that supports an intra-operative tumour readout or a culture-free sepsis workflow in a hospital is the chemistry that lets a genetics laboratory operate from three suitcases in Dakar, as seen in the previous talk of the same webinar. Moving a capable, chaotrope-free, automatable sample-prep step out of the central laboratory is what makes the rest of the decentralized workflow possible.
Related Xpedite products
The workflows above correspond to three Xpedite products: ClassiX™ CleanUp (SPRI-based size selection and clean-up), the SwiftX™ Sepsis Kit (cell-capture extraction of microbial nucleic acid from whole blood), and the SwiftXtractor™ SL (automated extraction, 0.2–40 mL input).
About the speaker. Dr. Johannes Graf (PhD, biochemistry) is R&D scientist at Xpedite Diagnostics, working on rapid, infrastructure-independent nucleic acid extraction for decentralized molecular diagnostics.
Data shown are proof-of-concept and analytical (LoD) results from internal laboratory-developed tests. SwiftX™ Sepsis and Xpedite extraction kits are for research use only (RUO); the SwiftXtractor™ SL is specified as IVD-R ready.
References
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Vermeulen C, et al. Ultra-fast deep-learned CNS tumour classification during surgery. Nature. 2023;622:842–849. DOI: 10.1038/s41586-023-06615-2.
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Kumar A, et al. Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock. Critical Care Medicine. 2006;34(6):1589–1596. DOI: 10.1097/01.CCM.0000217961.75225.E9.