The progress of nanotechnology has developed nanofluidic devices utilizing nanochannels with a width and/or depth of sub-100 nm (101 nm channels), and several experiments have been implemented in ultra-small spaces comparable to DNAs and proteins. However, current experiments utilizing 101 nm channels focus on a single function or operation; integration of multiple analytical operations into 101 nm channels using nanofluidic circuits and fluidic control has yet to be realized despite the advantage of nanochannels. Herein, we report the establishment of a label-free molecule detection method for 101 nm channels and demonstration of sequential analytical processes using integrated nanofluidic devices. Our absorption-based detection method called photothermal optical diffraction (POD) enables non-invasive label-free molecule detection in 101 nm channels for the first time, and the limit of detection (LOD) of 1.8 μM is achieved in 70 nm wide and deep nanochannels, which corresponds to 7.5 molecules in the detection volume of 7 aL. As a demonstration of sampling in 101 nm channels, aL-fL volumetric sampling is performed using 90 nm deep cross-shaped nanochannels and pressure-driven fluidic control from three directions. Finally, the POD and volumetric sampling are combined with nanochannel chromatography, and separation analysis in 101 nm channels is demonstrated. The experimental results reported in this paper will contribute to the advances in 101 nm fluidic devices which have the potential to provide a novel platform for chemical/biological analyses.