Table 1.

Detection of protein biomolecules

Tool or technique	Read-out	Illustration	Detection limit*	Molecules per drop (60 μl)	In clinical use
Colorimetry	Visual		150 pM	109	Yes
Carbon nanotubes	Electrical		100 pM	109	No
Chemiluminescence	Luminescence		30 pM	109	Yes
ELISA	Luminescence		1–10 pM	107	Yes
Quantum dots	Fluorescence		500 fM	107	No
Silicon nanowires	Electrical		1 fM	104	No
Metal nanoparticles (bio-barcode)	Scanometric and/or light scattering		30 aM	900	Yes
Immuno-PCR	Fluorescence		20 aM	700	Yes

^*Detection limits are best-case examples from the literature and can vary substantially depending on the target and the assay conditions.