Table 3.

Summary for QCM gas sensors

Piezoelectric materials	Device frequency (MHz)	Sensing layer	Target	LOD (ppm)	Frequency shift (Hz/ppm)	Response time (s)	Recovery time (s)	Temp	Year	Ref
AT-CUT	25	PAAM/MWCNTs.	Formaldehyde.	0.5	3	80	100	RT	2021	[331]
AT-CUT	10	Cu-doped ZnO NRs.	H2S	6.6	68	n/g	n/g	RT	2020	[175]
AT-CUT	10	rGO	${\text{CO}}_2$	50–500	50	26	10	RT	2021	[176]
AT-CUT	10	MOF	${\text{CO}}_2$	400–500	n/g	n/g	n/g	RT	2018	[179]
AT-CUT	9	(ZIF-8)	${\text{CO}}_2$	1.000.000	217	10	n/g	RT	2018	[215]
AT-CUT	9	Graphene oxide	Formaldehyde	1.7	22.9	60	n/g	RT	2016	[332]
AT-CUT	9	ZIF	${\text{CO}}_2$	n/g	n/g	n/g	n/g	RT	2018	[333]
AT-CUT	8	PEI/MWCNTs	Formaldehyde	6	0.82	114	127	RT	2015	[334]
AT-CUT	8	SnO${}_2$/Polydopamine	Formaldehyde.	0.5-50	12.2	25	38	RT	2021	[335]
AT-CUT	5	polymer/GNR.	NH3	70	106	1800	n/g	RT	2021	[169]
AT-CUT	n/g	GO/Cu${}_2$O.	Trimethylamine.	5	15.2	20	n/g	RT	2018	[177]

n/g $=$ Not Given