Fig. 3: rHEALTH base device with detail of subsystems.

a Transparent image of the device, showing the location of the optical module in the unit. The 532 nm laser and associated copper heat sinks are directly in the path of the fan. b The fluidics module is located on the opposite side of the optical module. It is a microfluidic assembly with a bank of five low-power latching valves and a motorized pressure regulator. c Main PCB that controls the device and sends data to the USB-attached PCB. The valve drivers are on the side of the fluidics module. Supercapacitors allow for additional power for valve switching. A field-programmable gate array (FPGA)-based system on a chip (SmartFusion) provides computing. Wires lead to a door sensor. A flat flex connector (FFC) provides data and power between the main PCB and the detector PCB. d The back of the optical module has an integrated detector PCB with attached flex boards with preamplifiers, powered by the high-voltage (HV) supply. The detector PCB has a separate microprocessor (dsPIC33) to provide counters for photon counting. Additional features are labeled in the figure. e Preamplifier circuit schematic. Photons captured by the SiPM result in a detectable signal after the op-amp. HV, ground (GND) provides power input and the photon counting signal is the Out. f Inside the optical module showing the locations of the 532 and 405 nm lasers, bandpass filters, dichroic filters (DC), lenses, and overall layout. g Left: detail of the flow cell showing the retaining ring, flow cell top (with burp, sample, and sheath inlets), and fused silica flow cell with integrated lens. Right: fused silica flow cell image with epoxied brass flow cell top as in the graphic.