S-Layer Protein Coated Carbon Nanotubes

Abstract

Carbon nanotubes (CNTs) have already been considered for medical applications due to their small diameter and ability to penetrate cells and tissues. However, since CNTs are chemically inert and non-dispersible in water, they have to be chemically functionalized or coated with biomolecules to carry payloads or interact with the environment. Proteins, although often only randomly bound to the CNT surface, are preferred because they provide a better biocompatibility and present functional groups for binding additional molecules. A new approach to functionalize CNTs with a closed and precisely ordered protein layer is offered by bacterial surface layer (S-layer) proteins, which have already attracted much attention in the functionalization of surfaces. We could demonstrate that bacterial S-layer proteins (SbpA of Lysinibacillus sphaericus CCM 2177 and the recombinant fusion protein rSbpA31-1068GG comprising the S-layer protein and two copies of the IgG binding region of Protein G) can be used to disperse and functionalize oxidized multi walled CNTs. Following a simple protocol, a complete surface coverage with a long-range crystalline S-layer lattice can be obtained. When rSbpA31-1068GG was used for coating, the introduced functionality could be confirmed by binding gold labeled antibodies via the IgG binding domain of the fusion protein. Since a great variety of functional S-layer fusion proteins has already been described, our new technology has the potential for a broad spectrum of functionalized CNTs.

Scalable biomimetic sensing system with membrane receptor dual-monolayer probe and graphene transistor arrays

“…S-layer proteins guided receptor orientations and forced exposure of their functional sites to enhance signal-to-noise ratio as well as provided antifouling for the device underneath. The construct is naturally multimodal ( 49 – 51 ), which overcomes one of the fundamental challenges to ultrasensitive bioelectronic detections in obtaining well-defined sensing structures on device surfaces ( 4 ). The dual monolayer was then introduced to a GFET array integrated with more than 200 transistors to mimic the redundancy in natural systems and provide statistically significant electrical readouts ( 25 ).…”

Morphological Investigation of Protein Crystals by Atomic Force Microscopy

“…S-layer properties can moreover be changed due to environment chemical modifications, emphasizing the versatility and significance of S-layers as a building block for constructing supramolecular complex structures that involve proteins, lipids, glycans, and nucleic acids [143][144][145][146][147]. Considering their unique structural and physicochemical properties, S-layers have shown great potential in various fields of application including nano(bio)technology, design of vaccines, diagnostics, and drug delivery [148][149][150][151][152].…”

Electrochemical Biosensors Based on S-Layer Proteins

“…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] S-layer proteins have so far suggested to mediate a broad range of specific biological functions, including protection against (e.g., bdellovibrios, bacteriophag...…”