Most biomarkers in biological fluids are present in very low quantities—for this reason, identifying and dosing them often requires them to be concentrated. To do so, a droplet of the sample must be deposited and evaporated before analysis. This step introduces flaws in terms of homogeneity within the deposit and in terms of reproducibility from one deposit to another. Microfluidics has led to advances on both issues.

The principle consists in producing a series of calibrated "microdroplets" by introducing a drop of analyte at the entrance of a T-shaped microchannel filled with oil. The microdroplets are carried away in the form of an oil-water emulsion, ultimately reaching a drying spot. There, an ultraviolet laser focused on the microdroplet vaporizes it, and ionizes the condensate which is then analyzed using a time-of-flight mass spectrometer.

In this way, the scientists developed a technique called DMF-MALDI (Droplet Microfluidic – Matrix Assisted Laser Desorption Ionization) interfacing a microfluidic digital chip to a time-of-flight mass spectrometer MALDI-TOF (MALDI – Time of Flight). Applied to peptides, this process strongly increases the detection sensitivity, and makes it possible to analyze solutions with initial sub-nanomolar concentrations (10^-9 mole/l).