Table 1 Single-cell functional proteomics tools

Flow cytometry methods

Fluorescence flow cytometry

Around 15 proteins (mostly membrane proteins, a few cytoplasmic proteins)

10⁴ cells s^-1

500 copies per cell

90% phenotyping accuracy; relative protein abundance

Standard for sorting and enumeration of cellular phenotypes. Secretion blocked and cells fixed for cytoplasmic proteins

[5, 6]

Mass flow cytometry

Around 35 membrane and intracellular proteins, likely expandable

10³ cells s^-1

>10³ copies per cell

Good cell counting statistics; relative protein abundance

Cells handled in bulk prior to analysis. Secretion blocked and cells fixed for cytoplasmic proteins

[8]

Surface methods

ELISpot

1-3 secreted proteins

6 spots per 10⁵ cells

Quantitative for percentage active cells

Cells secrete proteins onto antibody coated surfaces; secretion activity correlated with cell location

[9]

Microfluidics technologies

Image cytometry

3-4 membrane or intracellular proteins and cell size

10³-10⁴ cells per chip

10⁵ fluoro-phores per μm²

Good cell counting statistics; relative protein abundance

Cells are fixed and stained (in bulk) with fluorescent antibodies; protein assay and cell location spatially correlated

[19, 20]

Cell array

1 intracellular protein

<10³ cells per chip

Good cell counting statistics; relative protein abundance

Single cells separated and imaged on chip; continuous monitoring of cell physiology

[12–15]

Micro-droplet

1 membrane or intracellular protein

10² μdrops s^-1

Not defined

Good cell sampling statistics

Cells entrained in microdroplets; microdroplet composition control permits screening cells

[16–18]

Micro-engraving

3 secreted or 3 membrane proteins

10⁴-10⁵ cells per chip

Not available

Very good cell number statistics; relative protein abundance

Cells isolated in miocrowells; surface immunoassays; proteins colorimetrically detected; secretome kinetics from single cells; proteomeic and functional assays from same cell

[21–23, 37]

Single cell barcode chips

About 20 secreted, membrane, or cytoplasmic proteins, expandable

10³-10⁵ cells per chip

10² copies

Good cell counting statistics, absolute quantification, 10% measurement error per protein per cell

Cells isolated in microchambers, miniature antibody arrays yield spatial separation of specific protein assays; proteomeic and functional assays from same cell; single cells or defined small cell populations accessed.

[4, 5, 26–30]