The invention relates to a microfluidic device (100) comprising at least one sheath fluid inlet channel (1, 2) and a sample fluid inlet channel (3), and a common channel (4) configured to guide the sample fluid (20), with hydrodynamic focusing, and the at least one sheath fluid (21, 22) in the direction of at least two outlet channels (11, 12, 13).

According to the invention, the microfluidic device comprises heating means arranged to transmit over a short period of time an amount of heat localised in the at least one sheath fluid flow (21, 22) in the common channel (4) upstream of a junction between the at least two outlet channels (11, 12, 13) and the at least one sheath fluid having a thermal variation in viscosity suitable for diverting or extracting a portion (120, 130, 220) of the sample fluid selectively towards a given outlet channel.

A reaction container for a nucleic acid amplification reaction of a biological sample. The reaction container comprises a wall having an inner surface and an outer surface. The inner surface defines a cavity for containing the biological sample. At least part of the wall comprises an inductively heatable susceptor material for heating the biological sample.