Table 2.

Examples of fluorescent probes (FP) for other metabolites visualization.

Type	Name	Target	Detection mechanism	Reference
Small molecule FP	EOS	Glutamate	Glutamate binds of AMPA causes a fluorescence increase of small molecule dye;	[40]
	PTMs	H2O2	Based on the oxidation of boronate esters;	[16,41]
	PFBS		Based on C–S bond cleavage of perfluoro-benzyl sulfonates;	[42]
	NBzF		Based on oxidation-induced C–C bond cleavage of benzils;	[43]
	SO3 H-APL		Based on C–N bond cleavage of anilines;	[44]
	DPPEA-HC		Based on oxidation of phosphorous	[45]
	ANRP	CO	Anchored to cell membrane and sense the CO by a metal palladium-catalysed reaction;	[46]
	DAF	NO	Based on the reaction with NO to furnish fluorescent triazole derivatives;	[47]
Nanomaterial based FP	C3N4 Nanoribbons	Citrate	Quenched by Cu2+ and then recovered by the addition of citrate;	[48]
Genetically encoded FP	FICRhR	cAMP	Based on the dissociation of purified regulatory and catalytic subunits of PKA;	[49–57]
	ICUE1		Form Epac1-cyan-YFP sandwich when it binds with cAMP;	[58]
	cADDis		cAMP binding of the regulatory region causes a large conformational change in EPAC 2;	[59, 60]
	cdiA		cdiA riboswitches fused with Spinach2 aptamer;	[61]
	cGES	cGMP	cGMP binding domain from PDEs;	[62, 63]
	cGi		cGMP binding domains from PKG and from PDEs;	[64]
	CGY		cGMP binding of PKGs induced fluorescent change;	[65]
	c-di-GMP-I	c-di-GMP	c-di-GMP riboswitches fused with Spinach aptamer	[66–68]
	Bc RNA		c-di-GMP riboswitches fused with two FP genes;	[69]
	DNB sensor		c-di-GMP binding aptamer fused into DNB, Broccoli as the;	[70]
	Frex	NADH	NADH binds to Rex subunit causes the conformational change of cpFP;	[71]
	Peredox	[NAD+]/[NADH]	The competition between NADH and NAD+ for binding to Rex subunit causes the conformational change of two FP;	[72, 73]
	Rex YFP		Different binding affinity of NAD+ and NADH to nucleotide-binding domains of each Rex subunit;	[74]
	SoNar		Binding of NAD+ or NADH to Rex subunit both induces changes in protein conformation and fluorescence;	[75, 76]
	GluSnFR/FLIPE	Glutamate	Glutamate binds to GltI causes the conformational change of two FP;	[77–82]
	FLIPQ-TV	Glutamine	Glutamate binds to GlnH causes the conformational change of two FP;	[82]
	FLIP family	Sugar	Sugar binds to PBPs causes an increase in FRET between two FP;	[83–89]
	roGFP/roGFP2	ROS	ROS binds to the surface-exposed cysteine;	[90]
	CY-RL5	Redox state	Binds to redox linker 5 (RL5) causes an increase in FRET between two FP;	[91]
	COSer	CO	CO binds to CO sensitive heme protein causes the conformational change of cpYFP;	[92]
	sGC	NO	Combining endogenously expressed guanylate cyclase with a FRET-based cGMP indicator;	[93]
	OGsor	2OG	Binds to 2OG-binding domain GAF causes an increase in FRET between two FP;	[94]
	CIT	Citrate	Binds to citrate-binding domain CitA causes an increase in FRET between two FP;	[95]
	Lactate sensor	Lactate	Binds to lactate-binding domain of bacterial transcription factor LldR causes an increase in FRET between two FP;	[88]
	Lapronic	Lactate/pyruvate	Different binding affinity of lactate and pyruvate to the binding domains of transcriptional factor LutR subunit;	[96]