Schematic illustration of the fabrication for glass/PDMS microchip: (a) PDMS layer fabricated by replica moulding; (b) part of SPE channel in PDMS layer was cut off; (c) PDMS layer was sealed with the thin glass cover slip; (d) MISPE monolithic capillary column was coupled with glass/PDMS chip to form the final chip. A, B, C, D: holes, E: sample reservoir, F: buffer reservoir, G: sample waste reservoir, H: buffer waste reservoir, I: separation channel, J: SPE channel, K: MISPE monolithic capillary column and L: epoxy glue. Reprinted with permission from reference [115]. Copyright 2020 Elsevier.