Applications of Carbon Nanotubes in Biotechnology and Biomedicine

Abstract

Due to their electrical, chemical, mechanical and thermal properties, carbon nanotubes are one of the most promising materials for the electronics, computer and aerospace industries. Here, we discuss their properties in the context of future applications in biotechnology and biomedicine. The purification and chemical modification of carbon nanotubes with organic, polymeric and biological molecules are discussed. Additionally we review their uses in biosensors, assembly of structures and devices, scanning probe microscopy and as substrates for neuronal growth. We note that additional toxicity studies of carbon nanotubes are necessary so that exposure guidelines and safety regulations can be established in a timely manner.

Fig. 1

TEM micrographs of (a) MWNTs and (b) SWNTs (c) TEM micrograph showing bundles of SWNTs. The dark spots are catalyst particles used for nanotube growth. (d, e) Schematics of (d) MWNT and (e) SWNT. The TEM micrographs shown in (a) and (b) were kindly provided by Sumio Iijima, NEC, Japan and reproduced with the permission of Nature Publishing Group.

Fig. 2

(a) Two-dimensional graphene sheet. A carbon nanotube is formed by rolling up the graphene sheet, superimposing the two ends, OA, of the chiral vector (C_h). The chiral vector is defined as C_h = na₁ + ma₂, where a₁ and a₂ are unit vectors in the two-dimensional hexagonal lattice, and n and m are integers. The pair of integers (n= m) and the chiral angle (θ—the angle between C_h and a₁) define the nanotube type: armchair (n = m, and θ = 30°), zig-zag (n or m = 0, and θ = 0°) and chiral (θ between 0 and 30°). The diagram is constructed for a (5, 2) carbon nanotube. T is the basic translation vector for the tubule and the unit cell of this tubule is defined by OABB′. (b) Schematic models for the three types of SWNTs; courtesy of Riichiro Saito, Tohoku University, Japan.

Fig. 3

Mass balance of the normalized weight percent of all components including SWNT, metal, carbonaceous impurities, and weight loss of the SWNT samples under various nitric acid treatment conditions. The treatment conditions are given above the columns as xM/yh, where xM denotes x molar HNO₃ and yh indicates the time of treatment in hours. AP is as-prepared SWNTs.

Fig. 4

(a) Absorption spectra of as-prepared (AP-SWNTs) and purified SWNTs after controlled heating in oxygen. The insets illustrate the density of state (DOS) in SWNTs contributing to the near-IR absorption: M₁₁ is the first metallic transition in metallic SWNTs; S₁₁ and S₂₂ are the first and second interband transitions in semiconducting SWNTs. M₀₀ is the curvature induced energy gap in metallic SWNTs. (b and c) Absorption spectrum of (b) reference, R2, and (c) arc-produced SWNTs, S1, in the range of the S₂₂ interband transition before (bottom frame) and after (top frame) baseline subtraction. The relative carbonaceous purity of a SWNT sample is estimated from the ratio of the integral absorptions under the curves in the top and bottom frames, AA(S₂₂, S1)/AA(T, S1) related to the same ratio of integral absorbances for the reference sample AA(S₂₂, R2)/AA(T, R2). Thus, the relative purity RP(X) =[AA(S, S1)/AA(T, S1)]/[AA(S, R)/AA(T, R)].

Fig. 5

(a) A solution of SWNTs, chemically functionalized with octadecylamine (ODA) by a general functionalization scheme illustrated in (b).

Fig. 6

(a) SEM image of SWNT-PABS showing fibrous morphology and (b) Atomic force microscopy (AFM) image illustrating good dispersion of small bundles of SWNT-PABS. (c) A bundle of functionalized SWNTs, red arrowhead. (d) The cross-section of the bundle imaged in (c), has a height of 3.5 nm (red arrowheads) corresponding to the bundle diameter. (e) Scheme of the SWNT-PABS chemical structure.

Fig. 7

(a) Differential interference contrast and (b) immunofluorescent images of a SWNT-fiber functionalized with bovine serum albumin.

Fig. 8

(a) Schematic of a carbon nanotube wrapped with single stranded DNA. (b) Absorption spectra of two different fractions (f47 and f49) of SWNTs wrapped with DNA after chromatographic ion exchange separation. Fraction 47 has a more pronounced absorption in the metallic interband transition, M₁₁ (400 to 600 nm), with weaker absorption in the semiconducting interband transition, S₁₁ (900 to 1600 nm) indicating that f47 is enriched in metallic nanotubes. Data courtesy of Ming Zheng, DuPont. Reproduced with permission of Nature Publishing Group.

Fig. 9

Schematic of biosensing with modified carbon nanotubes. (A) Binding of the alkaline phosphatase (ALP)-loaded CNTs to streptavidin-modified magnetic beads, MB, by (a) sandwich DNA hybridization or (b) antibody-antigen-antibody interaction. (B) Enzymatic reaction. (C) Electrochemical detection of the product of the enzymatic reaction. P—DNA probe 1; T—DNA target; P2—DNA probe 2; A1—antibody attached to the magnetic bead; Ag—antigen; A2—antibody conjugated to ALP-CNT; S and P—substrate and product, respectively, of the enzymatic reaction; GC—glassy carbon electrode; CNT—carbon nanotube layer. Data reproduced with permission from Ref. [90], J. Am. Chem Soc.

Fig. 10

Proposed SWNT array for detection of neurotransmitter release from individual presynaptic terminals.

Fig. 11

(a) Assembly of a DNA-templated FET. (i) Polymerization of RecA monomers on a ssDNA molecule. (ii) Homologous recombination reaction binding the nucleoprotein filament to an aldehyde-derivatized scaffold dsDNA molecule. (iii) Localization of the streptavidin-functionalized SWNT on the scaffold dsDNA using a primary antibody to the bound RecA and a biotin-conjugated secondary antibody. (iv) Formation of silver clusters on the segments unprotected by RecA by incubation in an AgNO₃ solution. (v) Gold deposition to form two DNA-templated gold wires contacting the SWNT. (b) SEM image of an individual SWNT contacted by self-assembled DNA-templated gold wires. Scale bar, 100 nm. Data courtesy of Erez Braun, Technion-Israel Institute of Technology, Israel. Reproduced with permission from Science.

Fig. 12

AFM images of neurites (~500 nm in diameter) containing a varicosity. (a) Deflection mode AFM image; imaging force, 12 nN. Artifact at neurite varicosity is due to delay in the feedback loop. The box in (b) indicates the area that was scanned at 72 nN after acquisition of (a) in order to remove a portion of the neurite. (b) Image of neurites after excision; imaging force, 12 nN.

Fig. 13

(a) Schematic of a SWNT tip with attached carboxylic acid groups. (b–d) Chemical mapping with functionalized SWNT tip. (b) Schematic of a patterned substrate consisting of a self-assembled monolayer (SAM) region terminated with methyl groups and surrounded by carboxylic acid-terminated SAM. (c) Tapping mode phase image of the patterned SAM in (b) imaged with a carboxylic acid-terminated SWNT tip, and (d) phase image of a similar substrate imaged with C₆H₅-terminated SWNT tip. Courtesy of Charles M. Lieber, Harvard University, USA.

Fig. 14

(A) SEM image of a neuron grown on as-prepared MWNTs. (b) Fluorescent image showing a live neuron on as-prepared MWNTs, which accumulated the vital stain, calcein. Arrow indicates a growth cone. Scale bar, 20 μm. (c) Drawing summarizing the effects of MWNT charges on growth cones, neurite outgrowth and branching. Modified from Ref. .

Scheme 1

Schematic illustration of procedures for covalent functionalization of SWNTs with biological molecules.