Endotoxin detection is critical for both clinical management of sepsis and the safety evaluation of pharmaceutical products. The source reports a peptide-based digital enzyme-linked immunosorbent assay (dELISA) implemented on a single-molecule array platform that enables antibody-free, ultrasensitive, and specific detection of endotoxin directly in complex matrices such as plasma and pharmaceutical formulations.
This platform integrates two high-affinity peptides identified by phage display as capture and detection binders and couples them with digital readout on single-molecule arrays to achieve high sensitivity while avoiding limitations associated with antibody reagents.
The assay replaces conventional antibodies with two phage-displayed peptides that exhibit high affinity for endotoxin. These peptides were incorporated into a single-molecule array workflow to capture and report individual binding events on magnetic beads, enabling digital counting of endotoxin molecules without relying on antibody-based capture.
Using peptide binders targets the specific advantage of smaller, synthetic molecular recognition elements that can be selected and deployed to improve stability, reduce lot-to-lot variability, and potentially lower cost relative to antibodies. The source emphasizes the integration of these peptides into a dELISA format rather than providing the peptide sequences or selection details.
Bead surface chemistry was specifically optimized for the peptide-based dELISA. Carboxylated magnetic beads were activated using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) at 10 °C to enable stable conjugation of peptides to the bead surface.
During optimization, L-lysine (Lys) was identified as an effective blocking agent. L-lysine preserved bead monodispersity through electrostatic repulsion, a property important for uniform bead behavior in single-molecule arrays and for minimizing aggregation that can confound digital readout.
Under the optimized conditions described, the peptide-based dELISA achieved a limit of detection of 0.2 pg mL-1 for endotoxin. The assay displayed a linear dynamic range spanning 0–200 pg mL-1, enabling quantification across a clinically and pharmaceutically relevant concentration window.
Analytical precision was reported as robust, with coefficients of variation (CV) below 15%. These performance metrics indicate reproducible measurement suitable for applications that require low-level endotoxin quantification.
The assay was applied to common pharmaceutical formulations to assess interference and recovery. Tested matrices included saline, 5% dextrose, and commercial ophthalmic solutions. Recovery rates in these formulations ranged from 76.9% to 110.1%, demonstrating resistance to matrix effects and suggesting applicability for endotoxin testing in diverse product types.
These results support the potential use of the peptide-based dELISA for batch-release testing or investigational quality control when traditional assays may be limited by matrix interference or antibody availability.
Clinical validation involved quantifying endotoxin in plasma samples from septic and non-septic patients. The platform successfully detected and quantified endotoxin in these clinical plasma samples, indicating utility for patient-derived specimens.
In whole blood spiking experiments, the method produced an overall recovery of 78.0% when exogenous endotoxin was added to whole blood, demonstrating the assay's ability to operate in more complex cellular and protein-rich matrices beyond plasma.
Key advantages highlighted in the source include the combination of single-molecule array digital sensitivity with peptide binders to enable ultrasensitive, antibody-free endotoxin detection. The assay's low detection limit (0.2 pg mL-1), acceptable precision (CV < 15%), and measured recoveries in pharmaceutical and clinical matrices indicate strong analytical performance.
By eliminating antibody-related constraints—such as limited availability, stability issues, and batch variability—the peptide-based dELISA is positioned as a robust, translational tool for direct endotoxin detection in complex biological samples and pharmaceutical products.
The source does not provide complete operational details such as peptide sequences, full assay protocol, throughput, run time, or comparative performance against established endotoxin assays in head-to-head format. Those details were not reported in the source abstract and would be needed for full implementation or regulatory adoption.
Overall, the reported platform expands options for ultrasensitive endotoxin measurement with potential applications in critical care diagnostics and pharmaceutical quality control, pending further methodological and regulatory validation.