Miniature particulate matter counter and analyzer based on lens-free imaging of light scattering signatures with a holed image sensor

•Etching an air channel in the detection area of a CMOS image sensor in possible.•Detection of calibrated particles down to 320 nm is demonstrated.•Lens-free imaging of scattering signature efficiently differentiate particles.•Stray-light protection is easily achievable using a 3D printed ‘cloaker’.•We show significant progress toward full CMOS fabrication of PM sensors.