Depending on the purpose of the analysis, RNA-seq can be performed using different approaches:
* Ion Torrent sequencing: NGS technology based on the use of a semiconductor chip where the sample is loaded integrated with an ion-sensitive field-effect transistor able to sensitively detect reductions of the pH value due to the release of one or more protons after the incorporation of one or more dNTPs during sequencing by synthesis: the signal is, then, transmitted to a machine composed of an electronic reading board to interface with the chip, a microprocessor for signal processing and a fluidics system to control the flow of reagents over the chip. 
* Illumina sequencing: it offers a good method for small RNA sequencing and it is the most widely used approach. After the library preparation and amplification steps, the sequencing (based on the use of reversible dye-terminators) can be performed by using different systems, such as Miseq System, Miseq Series, NextSeq Series and many others, according to the applications