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Polymerization-based signal amplification (PBA) is a material-based approach to improving the sensitivity of paper-based diagnostic tests. Eosin Y is used as an assay label to photo-initiate free-radical polymerization to produce colored hydrogels in the presence of target analytes captured by bioactive paper. PBA achieves high-contrast and time-independent signals, but its nanomolar detection limit makes it impractical for early diagnosis of many diseases. In this work, we demonstrated efficient localization of large quantities of eosin Y per captured target analyte by incorporating eosin Y-loaded liposomes into PBA. This new "materials approach" allowed 30-fold signal enhancement compared to conventional PBA. To further improve the detection limit of liposome-enhanced PBA, we used a continuous flow-through assay format with 100 μL of analyte solution, achieving sub-nanomolar detection limits with high-contrast signals that were easily discernible to the unaided eye.

Lipid packing is a crucial feature of cellular membranes. Quantitative analysis of membrane lipid packing can be achieved using polarity sensitive probes whose emission spectrum depends on the lipid packing. However, detailed insights into the exact mechanisms that cause the changes in the spectra are necessary to interpret experimental fluorescence emission data correctly. Here, we analysed frequently used polarity sensitive probes, Laurdan and di-4-ANEPPDHQ, to test whether the underlying physical mechanisms of their spectral changes are the same and, thus, whether they report on the same physico-chemical properties of the cell membrane. Steady-state spectra as well as time-resolved emission spectra of the probes in solvents and model membranes revealed that they probe different properties of the lipid membrane. Our findings are important for the application of these dyes in cell biology.

The use of electrospun nanofibers as functional material in paper-based lateral flow assays (LFAs) was studied. Specific chemical features of the nanofibers were achieved by doping the base polymer, poly(lactic acid) (PLA), with poly(ethylene glycol) (PEG) and polystyrene8K-block-poly(ethylene-ran-butylene)25K-block-polyisoprene10K-Brij76 (K3-Brij76) (KB). The LFAs were assembled such that the sample flowed through the nanofiber mat via capillary action. Initial investigations focused on the sustainable spinning and assembly of different polymer structures to allow the LFA format. Here, it was found that the base polymer poly(vinyl alcohol) (PVA), which was shown to function well in microfluidic biosensors, did not work in the LFA format. In contrast, PLA-based nanofibers enabled easy assembly. Three relevant features were chosen to study nanofiber-based functionalities in the LFA format: adsorption of antibodies, quantification of results, and nonspecific binding. In particular, streptavidin-conjugated sulforhodamine B (SRB)-encapsulating liposomes were captured by anti-streptavidin antibodies adsorbed on the nanofibers. Varying the functional polymer concentration within the PLA base enabled the creation of distinct capture zones. Also, a sandwich assay for the detection of Escherichia coli O157:H7 was developed using anti-E. coli antibodies as capture and reporter species with horseradish peroxidase for signal generation. A dose-response curve for E. coli with a detection limit of 1.9 × 10(4) cells was achieved. Finally, functional polymers were used to demonstrate that nonspecific binding could be eliminated using antifouling block copolymers. The enhancement of paper-based devices using functionalized nanofibers provides the opportunity to develop a broad spectrum of sensitive and specific bioassays with significant advantages over their traditional counterparts.

Self assembled poly diacetylene (PDA) based blue vesicles LS-Terpy, LS-DPA, LS-DP and LS-DEA with metal chelating sites have been prepared and characterized. Their response to the presence of metal cations in buffered aqueous solution has been investigated by monitoring changes of colour, UV-Vis absorption and emission. The addition of zinc, manganese, cadmium, mercury or silver salts to solutions of the vesicles induces a colour change from blue to red observable by the naked eye, while the addition of other metal salts, containing ions like Li(+), Na(+), K(+), Mg(2+), Ca(2+), Cr(2+), Ni(2+), Fe(2+), Co(2+), Cu(2+) or Pb(2+), failed to show any changes. The metal ion coordination selectivity of the ligands is slightly different for the vesicle surface immobilized ligands compared to the reported metal cation binding of the corresponding ligands in solution, which may be due to the special environment at the lipid-solution interface. The vesicles aggregate upon metal ion coordination to the embedded ligands as shown by dynamic light scattering (DLS) particle size analysis. The functionalized PDA vesicles retain their response to the presence of aqueous solutions of metal ions if immobilized in transparent polyvinyl alcohol films or on paper.