Table 3.

Comparative account of probes other than antibodies for single cell identification

Method	Target	Type of probe	Applications	Advantages	Limitations
Molecular beacons (MBs)	DNA/RNA	DNA/RNA	Pathogen detection	Sensitive, high signal to background ratio	It needs a reagent to introduce MBs to living cell
			Stem cell isolation		Endonucleases cleave MBs, limiting live cell application
			Cancer detection		Affected by temperature and pH shift
Aptamers	Inorganic molecules	DNA/RNA	Diagnostics	Wide range of targets	SELEX protocol is time consuming and laborious
	Toxins Metabolites		Therapy	High affinity binding to targets	Probes selected in vitro condition do not work well under physiological condition
	Nucleic acids			Modifications possible	Relatively unstable in biological fluids
	Carbohydrates			Synthesis is cheaper and reproducible	SELEX protocol varies with target
	Amino acids			No immunogenicity
	Peptides			Aptamers may not require reagents to introduce to living cells
	Proteins
	Complex biological structures
Peptide nucleic acid probes (PNPs)	Nucleic acids miRNA	PNA	Diagnostics	High specificity	Cannot cross cell membranes, limiting live cell application
			Therapy	Not detected by nucleases or proteases
				Stable over a wide pH range
Targeting cell-penetrating peptides (targeting CPPs)	Proteins	Peptides	Translational medicine	Easy to synthesis	Degradation by proteases
			Therapy	Easy to modify	Limited to targets, whose interacting partners and interacting regions are known
				High affinity binding to targets
				Less immunogenicity