Table 1. Protein Biosensors in Gas Sensing.

	Protein	VOCs	Support	Transducer	LoD/measureda	Source	Expression system	Refs
Olfactory receptors	OR-10	Diacetyl	Gold	QCM	1 x 10–12 M	C. elegans	E. coli	[32]
				SAW	1.2 x 10–11 mM		MCF-7 cells	[34]
	hOR 17–40 hOR3A1	Helional	CNT	Interdigitated microelectrode array, Current-voltage	0.02 ppt	Homo sapiens	MC18 (Saccharomyces cerevisiae) HEK-293T cells	[36]
	mOR174-9 mOR203-1 mOR256-17	Acetophenone, Others	CNT	CNT transistors, Current-gate Voltage	1–10 μM	Mus musculus	S. cerevisiae	[35]
Odorant-binding proteins	AaegOBP22	N,N-diethyl-meta-toluamide (DEET)	Gold	ZnO film bulk acoustic resonators	–	A. aegypti	E. coli	[55]
	pOBP	Ethanol; methanol	Si	Si-substrate with interdigitated electrodes (EIS)	20 ppma; 10 ppma	Sus scrofa	Pig nasal tissue	[46]
	pOBP	(R)-(−)-1-octen-3-ol(octenol); (R)-(−)-carvone (carvone)	Gold	SAW	0.48 ppm; 0.72 ppm	S. scrofa	Pig nasal tissue	[47]
	wtbOBP	(R)-(−)-1-octen-3-ol(octenol); (R)-(−)-carvone (carvone)		SAW	0.2–0.23 ppm (carvone); 0.18–0.21 ppm (octenol)	Bos taurus	BL21-DE3 E. Coli	[49]
	pOBP wtbOBP dmbOBP	(R)-(−)-1-octen-3-ol(octenol); (R)-(−)-carvone (carvone)	Gold	SAW	wtpOBP: 25.9 (octenol), 7.0 (carvone) Hz/ppm; wtbOBP: 3.5 (octenol), 5.4 (carvone) Hz/ppm; dmbOBP: 6.0 (octenol), 9.2 (carvone) Hz/ppm;	S. scrofa; B. Taurus	Pig nasal tissue; BL21-DE3 E. Coli	[51]
	pOBP wtbOBP dmbOBP	(R)-(−)-1-octen-3-ol(octenol); (R)-(−)-carvone (carvone)	Gold	SAW	0.48 ppm (octenol); 0.74 ppm (carvone)	S. scrofa; B. Taurus	Pig nasal tissue; E. coli	[52]
	wtbOBP	(R)-(−)-1-octen-3-ol (octenol)	Gold	Solidly mounted resonator	7 ppm	B. taurus	BL21-DE3 E. coli	[48]
	wtbOBP	(R)-(−)-1-octen-3-ol(octenol); (R)-(−)-carvone (carvone)	Gold	SAW	0.18 ppm; 0.2 ppm	B. taurus	BL21-DE3 E. Coli	[49]
	wtbOBP	(R)-(−)-1-octen-3-ol (octenol)	Gold	SAW	2 ppm	B. taurus	BL21-DE3 E. coli	[50]
	wtbOBP, dmbOBP	DMMP	Silicon nitrate	Photonic ring resonator	6.8 ppb	B. taurus	BL21-DE3 E. coli	[53]

^aIndicates when the detected concentration was not the LoD, but the “measured” in that paper.