Kinetics of Antibody Release from Gelatine Layers for On-chip Sample Preparation

On-chip sample preparation is essential for an easy, robust and accurate operation of point-of-care (POC) diagnostic devices. We recently demonstrated a simple cell-counting device realised by controlled antibody release from a gelatine layer implemented on a microfluidic chip. However, little is known about the release kinetics from this gelatine layer with sub-micrometre(μm)-scale thickness. In this work, we have realised real-time and in situ monitoring of antibody release from sub-μm thick gelatine layers on second to minute timescale. The measured antibody release kinetics comply with diffusion controlled release. Release times between ~20 s and ~840 s are obtained from dry layers with the thicknesses between 0.25 μm and 1.5 μm. The estimated diffusion coefficient in equilibrium swelling gelatine layer is 0.4 μm/s. Higher drying temperatures result in a lower degree of physical crosslinking and further lead to shorter release time. In addition, we observe a considerably faster release from an inkjet-printed gelatine layer compared with the release from a cast layer prepared under comparable conditions. Moreover, the ionic strength of the medium is found to have a significant impact on release kinetics.