Table 1.

Summary of the biosensor-relevant properties of S-layer proteins and lattices Reference.

Molecular weight of S-layer protein subunits: 40–200,000 Da	[7,23,24,25,26,27,28]
Reactive groups (e.g., carboxyl- and amino-residues) occur on each protomer in identical position and orientation	[7,23,24]
Two-dimensional (glyco)protein crystal composed of identical subunits	[7,25]
Oblique (p2), square (p4) or hexagonal (p6) space group symmetry	[7,16,26,27]
Center-to-center spacing of unit cells (= morphological units) of crystalline lattice: 3.5–35 nm	[7,27]
Layer thickness: 5–10 nm	[7,8]
High porosity (30%-70%) with pores of identical size (2–8 nm), morphology, and physicochemical properties	[7,24]
Topography: Inner surface smooth, outer surface more corrugated	[7,8,26]
Anisotropic charge distribution between outer and inner face: Outer face charge neutral due to an equal number of carboxyl- and amino groups. Inner face net negatively charged due to an excess of carboxyl groups	[7,8,24]
Antifouling, non-sticky outer surface	[7,11,28]
Self-assembly capability in aqueous media, on the air/water interface, on lipid films, and on solid surfaces like metals (gold, silver, platinum, stainless steel), glass, silicon, silicon oxide and nitride, mica, polymers (e.g., polystyrene, polyester, cellulose, polydimethylsiloxane (PDMS), indium tin oxide (ITO), highly oriented pyrolytic graphite (HOPG), and carbon nanotubes	[7,9,28,29,30]