Controlled particle self-assembly in an evaporating droplet

It is well known that particulate matter is drawn to the periphery of evaporating droplets, hence once evaporation is complete a ring of dried matter can be deposited (depending on the wetting conditions of the original drop). The focus of this work is the alteration of the natural process, such that the advantages of simplicity and low cost are not lost, however additional control is gained over the resulting depositions. Timely interventions allow control over the geometrical features of the ring, and allow the deposition of a second particulate matter on top of the first in two ways. Firstly without destruction of the original ring, for biosensing, and secondly with destruction of the original ring to create self-supporting thin chains of particles for flagella construction.

Graphical abstractBy using extraction and deposition of fluid in a timely manner, structures can be designed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Control of the coffees stain process is demonstrated. ► Timely intervention can be used to tailor the ring profile. ► Biosensors can be fabricated and kept intact for optimal analysis. ► Self-supporting structures can be released from the substrate.