Table 1.

Summary of common fluorescent imaging probes for optical tumor imaging.

Category	Examples	Excitation/Emission	Properties	Phase	Pros	Cons	Refs
Small molecules	Indocyanine green (ICG)	805/835 nm (in whole blood)	Negatively charged; hydrophobic; always-ON	FDA-approved	Easy tissue penetration; fast systemic clearance	Low tissue accumulation; limited imaging payload; non-specific binding	[49–53]
	Methylene blue (MB)	665/686 nm	Positively charged; hydrophilic; always-ON	FDA-approved			[46–48]
	5-ALA	407/635 and 705 nm (protoporphyrin IX)	Responsive to reduced activity of ferrochelatases in tumor microenvironment	FDA-approved			[64.68,126]
	γ-glutamyl-hydroxymethyl rhodamine green	502/527 nm	Responsive to overexpressed in TME	Pre-clinical			[24]
Fluorescent proteins	IFP2.0 and miRFP709	690/711 nm (IFP2.0); 683/709 nm (miRFP709)	NIR fluorescent proteins that can be endogenously expressed; always-ON	Pre-clinical	High specificity and low signal background	May not be translatable into human	[127,128]
	cpYFP, HyPer and roGFP	420/516 nm (cpYFP); 500/516 nm (HyPer); 405 and 488/510 nm (roGFP)	Fluorescent proteins that are ROS sensitive and can be endogenously expressed	Pre-clinical			[129–132]
Biomolecule-conjugates	cRGD-ZW800–1 conjugate	772/788 nm	Targeting αvβ3; always-ON	Phase I	Active targeting; standard Manufacturing process	Long bloodcirculation time; limited imaging payload	[70,71]
	Panitumumab-IRDye 800 C W conjugate	774/789 nm	Targeting EGFR; always-ON	Phase I			[77]
	Folate-FITC	495/519 nm	Targeting folate receptor α; always-ON	Phase I			[80] [82],
	CH1055-anti-EGFR affibody	808/1055 nm	Targeting EGFR; NIR-II window; always-ON	Pre-clinical			[72]
	Trastuzumab conjugated with aniline-BODIPY-based fluorophores	493/503 nm (BODIPY)	Targeting EGFR; pH-responsive	Pre-clinical			[15]
	pHLIP™-Cy5.5/ICG	684/710 nm (Cy5.5); 805/835 nm (ICG)	pH-responsive	Pre-clinical			[110] [111]
Nanoparticulate agents	CdTe/CdSe type-II QDs and alloyed semiconductor QDs	Declining absorption/up to 850 nm	NIR window; can be conjugated with targeting ligands; always-ON	Pre-clinical	Tunable size; high imaging payload	Long bloodcirculation time; non-specificbinding; safety concerns	[91]
	Single-walled carbon nanotubes	550–1000/950–1800 nm	NIR II window; can be conjugated with targeting ligands; always-ON	Pre-clinical			[98–100,133,134]
	Enzyme-activatable copolymers	Dependent on conjugated fluorophores	Responsive to overexpressed proteases in tumor microenvironment	Pre-clinical	Tunable size; high imaging payload; active targeting		[22]
	pH-responsive conjugated copolymers	Dependent on conjugated fluorophores	Responsive to acidic pH in tumor microenvironment	Pre-clinical			[113,114,117]
	Semiconducting polymer conjugated with ROS- and RNS-sensitive dyes	580/680 or 820 nm (Fluorescence resonance energy transfer, RNS-sensitive); NA/680–820 nm (Chemiluminescence resonance energy transfer, ROS-sensitive)	Applicable to high ROS and RNS levels in TME	Pre-clinical			[125]
	Hypoxia-responsive iridium (III) complex conjugated polymer	510/565 and 710 nm	Responsive to increased oxygen consumption in TME; water-soluble	Pre-clinical			[21]