Carbon nanofiber (CNF)-nanocatalyst hybrids hold great promise in fields such as energy storage, synthetic chemistry and sensors. Current strategies to generate such hybrids are laborious and utterly incompatible with miniaturization and large-scale production. Instead, this

Laser-induced graphene’s (LIG) inherent graphene-like and highly porous characteristics and its simple, scalable, and inexpensive fabrication render it a desirable electrode material for bio- and chemosensors. The best LIG electrodes are made in polyimide foils using a CO2 laser scriber, which unfortunately limits their integration into more sophisticated analytical devices due to polyimide’s inertness. The transfer of LIG electrodes onto standard polymer substrates used in microfluidic systems and their use in microfluidic assays were therefore studied and the resulting electrodes characterized morphologically, chemically, and electroanalytically. It was found that a direct pressure-driven transfer produces highly functional transfer-LIG (tLIG) electrodes. tLIG differed from LIG electrodes with respect to a much smoother surface and hence a lower active surface area, a loss of the graphene characteristic Raman 2D peak, and a slight decrease in electron transfer rates. However, their performance in amperometric detection strategies were comparable also when used in adhesive-tape-enabled microfluidic channels for the detection of p-aminophenol. tLIG outperformed LIG electrodes in their ability to be integrated into more advanced microfluidic channel systems made of an all-polymethyl methacrylate (PMMA) substrate for the biosensing detection of alkaline phosphatase, commonly used as a biomarker and as a biosensor amplification system. LIG and tLIG have hence the potential to change electroanalytical sensing in diagnostic systems as their fabrication requires minimal resources, is highly scalable, and allows their integration into simple and, as tLIG, also sophisticated analytical systems.

The emergence of severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) in 2019 caused an increased interest in neutralizing antibody tests to determine the immune status of the population. Standard live-virus-based neutralization assays such as plaque-reduction assays or pseudovirus neutralization tests cannot be adapted to the point-of-care (POC). Accordingly, tests quantifying competitive binding inhibition of the angiotensin-converting enzyme 2 (ACE2) receptor to the receptor-binding domain (RBD) of SARS-CoV-2 by neutralizing antibodies have been developed. Here, we present a new platform using sulforhodamine B encapsulating liposomes decorated with RBD as foundation for the development of both a fluorescent, highly feasible high-throughput (HTS) and a POC-ready neutralizing antibody assay. RBD-conjugated liposomes are incubated with serum and subsequently immobilized in an ACE2-coated plate or mixed with biotinylated ACE2 and used in test strip with streptavidin test line, respectively. Polyclonal neutralizing human antibodies were shown to cause complete binding inhibition, while S309 and CR3022 human monoclonal antibodies only caused partial inhibition, proving the functionality of the assay. Both formats, the HTS and POC assay, were then tested using 20 sera containing varying titers of neutralizing antibodies, and a control panel of sera including prepandemic sera and reconvalescent sera from respiratory infections other than SARS-CoV-2. Both assays correlated well with a standard pseudovirus neutralization test (r = 0.847 for HTS and r = 0.614 for POC format). Furthermore, excellent correlation (r = 0.868) between HTS and POC formats was observed. The flexibility afforded by liposomes as signaling agents using different dyes and sizes can hence be utilized in the future for a broad range of multianalyte neutralizing antibody diagnostics. Graphical abstract