Whilst larger nanoparticles represent greater assay sensitivity in theory, their benefit in practice is offset by poor kinetics. As modelled by Zhan et al., large particle complexes (>100 nm) were shown to have slower diffusion rates which limited LFA sensitivity due to poor test line capture. Authors also noted that larger particles were associated with increased non-specific binding, limiting their effective concentrations in assays. To demonstrate this in the context of our work, a high concentration of HER2 antigen (500 ng/mL) was detected across test strips -printed with a capture area of 9 PSA test lines -using 20, 40, and 150 nm FluoroPerAuNPs (Figure ). Particles were prepared using identical physisorption conditions and similar antibody per surface area loading ratios (12.6 nm 2 / Ab), whilst test lines were printed using a high receptor density of PSA (1 mg/mL). When normalising the signal intensity at each test line, we observed that assays deploying 150 nm FluoroPerAuNPs yielded a more even distribution of signal across the capture area. By comparison, the use of smaller FluoroPerAuNPs (20 and 40 nm) resulted in signal distributions which instead tended sharply towards the front of the capture area, further indicating the trade-off between particle size and capture affinity.