nanoparticles - Carbon Nanotubes and Graphene

Types of Nanoparticles:
  - Organic Nanomedicines:
    - Liposome
    - Carbon Nanotube
    - Polymer-based nanoparticles
  - Inorganic Nanomedicines:
    - Gold Nanoparticle
    - Iron Oxide Nanoparticle
    - Quantum Dots
    - Nonporous Silica Nanoparticle
Conjugates:
  - Drug-Polymer Conjugate
  - Protein-Polymer Conjugate
  - Dendrimers
  - Micelles
  - Hollow/Porous Nanoparticles
Applications:
- Chemotherapeutic or diagnostic probes
- References: Tang L, Cheng J (2013) Nonporous Silica Nanoparticles for Nanomedicine Application. Nano Today.

What are Carbon Nanotubes?
  - Long, thin cylinders of carbon discovered by Japanese scientist S. Iijima in 1991.
  - Unique properties include:
    - High electrical conductivity, up to 100 times more conductive than copper over distances around a micron.
    - Thermal conductivity that matches diamond.
    - Very high melting temperature (~3600 °C).
    - Chemically inert but can be functionalized to modify characteristics.
    - Approximately 100 times stronger than steel.
Types of Carbon Nanotubes:
  - Single-Wall Carbon Nanotubes (SWCNTs):
    - Composed of a single layer of graphene.
    - Require a catalyst for synthesis.
    - Bulk synthesis is difficult.
    - Higher defects during functionalization.
    - Purity is generally poor.
    - Less accumulation in the body, easier characterization.
    - Twisting is easy.
  - Multi-Wall Carbon Nanotubes (MWCNTs):
    - Composed of multiple layers of graphene.
    - Can be produced without a catalyst.
    - Bulk synthesis is easier.
    - Fewer defects, difficult to improve purity.
    - More accumulation in the body, difficult characterization and evaluation.
    - Difficult to twist.

Methods:   - Non-covalent functionalization:
    - Proteins anchored on the surface using pyrene π–π stacking.
      - Visual example: Transmission Electron Microscopy (TEM) image of SWNT conjugated with proteins.
    - Single-stranded DNA can coat SWNTs via similar π–π stacking.
    - SWNT functionalized with PEGylated phospholipids, using both linear and branched PEG.
π–π stacking:
- Noncovalent attractive force between two aromatic rings due to electrostatic interactions.

Production Issues:
- Limited control over growth and connections between nanotubes.
High Cost:
- Market pricing poses barriers to widespread use.
Manipulation Difficulties:
- Challenges arise due to insolubility in many solvents.
Efficacy Concerns:
- Uncertain advantages over established therapies.
Risks:
- Potential for long-term accumulation and toxicity associated with structural similarities to asbestos fibers.
- Long-term deposits may result in side effects.

What is Graphene?
- A single atom-thick sheet of carbon atoms arranged in a honeycomb lattice structure.
Unique Properties:
  - Enhanced electrical conductivity.
  - High mechanical strength and thermal conductivity.
  - High impermeability to gases and optical transparency.
Historical Context:
- First isolated in 2004; Nobel Prize awarded in Physics to Geim and Novoselov in 2010.

Key Intermediates:
- Graphite oxide significantly facilitates production, primarily via oxidative treatment that increases interlayer distances.
- Top-down synthesis allows for large-scale production through exfoliation of graphite sheets.

Target Functionalizations Include:**
- Biotin-avidin interactions, nucleic acids, proteins, peptides, small molecules, and bacteria through both physical and chemical conjugation.
Report Link: Trends in Biotechnology, Volume 29, Issue 5 (2011).

Overview of Applications:
  - Drug and gene delivery.
  - Cancer therapies.
  - Biosensing and bioimaging capabilities.
  - Graphene oxide (GO)-based antibacterial materials and scaffolds for cell culture.
Reference: Sheng-Tao Yang et al. (2012) for pharmacokinetics, metabolism, and toxicity investigations.

Surface Area:
- Graphene sheets have a larger surface area compared to single-walled carbon nanotubes (SWCNTs).
Efficacy in Tumor Targeting:
- 2D graphene has a more effective passive tumor target compared to 1D SWCNTs.
Complexity in Functionalization:
- 2D graphene sheets allow for easy complexation with various nanoparticles, unlike 1D nanotubes, which have complex modifications.
Biosensing:
- Graphene devices showcase better reproducibility compared to those made from SWCNTs due to uniform structural characteristics.

Variability in Properties:
- Different forms and modifications of graphene yield various biological effects.
Toxicology Paradigms:
- Graphene's flat structure might not trigger adverse inflammatory responses similar to fibrous materials like asbestos, but research is ongoing regarding biodegradability and toxicity.
Biodegradability Evidence:
- Some graphene types may be enzymatically degraded through specific biological processes.