Effect of Surface Modification on Protein Deposition in Desiccated Droplets

Detection of fluorescent signals from desiccated droplets is a useful tool for the analysis of microarray devices. This investigation presents an optical method for the observation of physical structures and protein deposition in desiccated droplets. Greyscale images of droplets containing red fluorescent protein solutions in water were recorded after desiccation. Images were obtained under both white and fluorescent light for droplets desiccated on glass and Teflon. Spots desiccated on glass were twice the size of those desiccated on Teflon. As such, average physical deposition and protein concentration was higher for Teflon spots. The average fluorescence intensity for spots desiccated on Teflon were four times greater than those desiccated on glass. For spots desiccated on glass, physical deposition and protein concentration increased with radial position, consistent with a coffee-ring pattern. The local maximum fluorescence intensity was highest at the center of the droplet. Protein deposition then decreased with increasing radius before increasing again toward the edge of the spot. These results suggest that desiccation of protein laden droplets on hydrophobic coatings, such as Teflon, may increase sensitivity of fluorescent protein detection while improving the uniformity of the fluorescent signal measured from the droplet.