Highly sensitive interleukin 6 detection by employing commercially ready liposomes in an LFA format

Abstract

Recent years have confirmed the ubiquitous applicability of lateral flow assays (LFA) in point-of-care testing (POCT). To make this technology available for low abundance analytes, strategies towards lower limits of detections (LOD), while maintaining the LFA’s ease of use, are still being sought. Here, we demonstrate how liposomes can significantly improve the LOD of traditional gold nanoparticle (AuNP)–based assays while fully supporting a ready-to-use system for commercial application. We fine-tuned liposomes towards photometric and fluorescence performance on the synthesis level and applied them in an established interleukin 6 (IL-6) immunoassay normally using commercial AuNP labels. IL-6’s low abundance (< 10 pg mL−1) and increasing relevance as prognostic marker for infections make it an ideal model analyte. It was found that liposomes with a high encapsulant load (150 mmol L−1 sulforhodamine B (SRB)) easily outperform AuNPs in photometric LFAs. Specifically, liposomes with 350 nm in diameter yield a lower LOD even in complex matrices such as human serum below the clinically relevant range (7 pg mL−1) beating AuNP by over an order of magnitude (81 pg mL−1). When dehydrated on the strip, liposomes maintained their signal performance for over a year even when stored at ambient temperature and indicate extraordinary stability of up to 8 years when stored as liquid. Whereas no LOD improvement was obtained by exploiting the liposomes’ fluorescence, an extraordinary gain in signal intensity was achieved upon lysis which is a promising feature for high-resolution and low-cost detection devices. Minimizing the procedural steps by inherently fluorescent liposomes, however, is not feasible. Finally, liposomes are ready for commercial applications as they are easy to mass-produce and can simply be substituted for the ubiquitously used AuNPs in the POCT market. Graphical abstract

Liposome-based high-throughput and point-of-care assays toward the quick, simple, and sensitive detection of neutralizing antibodies against SARS-CoV-2 in patient sera

“…Liposomes were developed to bear the unique property of offering a highly sensitive fluorescent and a rapid, simple colorimetric read-out. This was accomplished using the encapsulation of SRB as previously demonstrated [25,31,33]. Key assay development points described here were the investigation of RBD, ACE2 and liposome concentration, ACE2 immobilization, and the optimization of SRB liposomes with respect to signaling strength.…”

“…Here, we investigated the use of sulforhodamine B (SRB) encapsulating liposomes conjugated to RBD as a signaling alternative. In previous work, SRB liposomes were shown to surpass gold nanoparticles in sensitivity in a lateral flow assay [25]. Additionally, the encapsulated SRB enables the use of the liposomes in fluorescence-based microplate assays.…”

Progression of Paper-Based Point-of-Care Testing toward Being an Indispensable Diagnostic Tool in Future Healthcare

“…Quite promising are also strategies that use embedding methods or nanocontainers. These methods can maximize the density of the signal molecule per reporter probe with sensitivity enhancement of over 1 order of magnitude up to an about 250-fold sensitivity increase . Multifunctional nanocomposite probes are of interest as they typically combine features, for example, magnetic enrichment and separation, paired with their detection properties or allow detection with low- and high-sensitivity modes (see next paragraph).…”

Can classical surface plasmon resonance advance via the coupling to other analytical approaches?

“…A LFA commonly is based on sandwich immunoassay where the analyte is captured by an antibody and its presence is reported through a labelled reporter antibody. The most common labels are colloidal gold, latex beads or liposomes (Rink et al, 2022) (Figure 6A). The result of an LFA is almost always related to an optical signal generated at the test line which can be read off by the naked eye or a smart phone (Joshi et al, 2017)].…”