A method of chemical analysis that includes: a) introducing an analyte fluid having a flow to a surface of a sample chip through a microfluidic device comprising i) a fluid inlet having a semi-circular groove and ii) a flow chamber comprising an inner wall having an inlet end, where the fluid inlet is in communication with the flow chamber and where the inner wall at the inlet end is curved and has a radius similar to the radius of semi-circular groove; b) maintaining the flow of the analyte fluid such that the analyte fluid forms a pattern on the surface of the sample chip, the pattern approximating the semi-circular groove; c) maintaining the flow of the analyte fluid so that a linear fluid front forms on the surface of the sample chip at the inlet end; and d) maintaining the flow so that the linear fluid front moves along the surface of the sample chip.