An integrated ion-selective optode sensor cartridge for directly detecting electrolyte ions in blood plasma without pretreatment to adjust pH

•An integrated ion-selective optode sensor cartridge that directly detects ions in blood plasma without pretreatment to adjust pH was developed.•The optode sensor consisted of two separate layers, the optode and dried buffer, which work by introducing blood plasma.•The ion concentrations measured from the optode sensors corresponded well with those from a commercial system (cobas® 8000; Roche).•This sensing platform can be useful as a point-of-care diagnostic device.