CO detection LTCC side via MEMS UV irradiation ZnO amperometric array optimization bad breath capacitive micromachined ultrasonic transducers (CMUT) combinatorial and high-throughput technique core/shell nanostructure efficiency electronic nose electrospray environmental monitoring gas sensing gas sensor halitosis hydrogen sulfide indirect packaging indium oxide laser ablation low temperature co-fired ceramic (LTCC) metal-oxide-semiconductor array sensor packed gas chromatographic column semiconductor sensitive material ultrathin carbon layer