A stack of fluidics layers of a microfluidic cartridge for sequencing nucleic acid molecules includes a sequencing chamber layer having a sequencing chamber area configured for carrying out clustering and sequencing reactions, and a sequencing chamber bottom layer disposed under the sequencing chamber layer. The sequencing chamber bottom layer has an opening configured to hold an image sensor with the image sensor having an active area disposed under the sequencing chamber area. The sequencing chamber area spans substantially all of the active area of the image sensor. The stack of fluidics layers includes a flexible printed circuit board (PCB) layer under the sequencing chamber bottom layer, and a fluidics channels layer disposed under the flexible PCB layer. The fluidics channels layer includes fluidics channels that are configured to deliver reactants to the sequencing chamber area. The fluidics channels do not substantially overlap with the active area of the image sensor.