Biological Applications of Diamond

8.1 PROPERTIES OF DIAMOND FOR BIOLOGICAL APPLICATIONS

The following superior properties of diamond make it a special and promising material that can be widely applied to biological fields:

(A) Diamond is a type of superhard material. Table 8.1 shows some physical properties of diamond compared to Titanium and stainless steel. The hardness of diamond is about 50 times of Titanium and stainless steel. The toughness of diamond makes it suitable in applications in biomedical fields such as implant, cutting tools for surgeries, etc.

(B) Chemical inertness is an important factor for diamond to be applied in biology, since the biological environment is corrosive. Azevedo and coworkers' corrosion tests (Fig. 8.1) of diamond films grown on Ti6Al4V alloy show that the diamond films have a very good chemical resistance to the corrosive liquid.2

(C) Biocompatibility cannot be ignored when diamond is applied to biology. Yu and coworkers investigated the biocompatibil-ity of fluorescent nanodiamond (FND) powder with size of 100 nm in cell culture and found low cytotoxicity in kidney cells.3 Further, Schrand and coworkers4 showed that nanodiamond (ND) with small size of 2-10 nm are not toxic to a variety of cells through mitochondrial function (MIT) and luminescent ATP production assays. Figure 8.2 shows that after the

Diamond Nanotechnology: Synthesis and Applications by James C Sung & Jianping Lin

Copyright © 2009 by Pan Stanford Publishing Pte Ltd

www.panstanford.com

978-981-4241-36-6

Table 8.1. Comparison of properties of chemical vapor deposited (CVD) diamond, titanium and 316 stainless steel

Properties

CVD

Titanium

316 Stainless

Diamond

Steel

Hardness (kg mm-2)

10000

230

210

Young's modulus (GPa)

1000

120.2

215.3

Bulk modulus (GPa)

442

108.6

166

Thermal conductivity

20

0.21

0.16

0-100°C (Wm-1K-1)

Thermal expansion

1.1

8.8

17.2

(x10-8K-1)

Source: From Ref. 1 and references therein.

Source: From Ref. 1 and references therein.

tym : Mag- 5.M K K

Figure 8.1. Scanning electron microscopy (SEM) images of diamond films deposited on Ti6Al4V alloy after (a) 1-month immersion in an isotonic NaCl solution, (b) 1 month immersion in a Ringer's physiological solution, and (c) 2 months in the 2% HCl. Source: From Ref. 2.

Properties of Diamond for Biological Applications 165

Properties of Diamond for Biological Applications 165

Figure 8.2. Incubation of cells with two types of ND after 24 h viewed by light microscopy: (A) control; (B) 100 ^g/ml ND-raw; (C) 100 ^g/ml ND-COOH. Scale bars are 20 ^m. Source: From Ref. 4.

incubation of cells with NDs, cell morphology is unaffected by the presence of NDs while NDs are seen surrounding the cell borders and attached to neurite extensions.

(D) Excellent optical property is necessary for diamond to be applied as a biomarker or a biolabel. There are impurity sites within core, defects in the diamond or sp2 clusters on the ND surface. With the light excitation, the ND will emit light with different frequency due to different type of impurity sites. Figure 8.3 shows some of these processes.5 Raman spectrum of diamond also exhibits a sharp peak located at 1332 cm-1 for phonon mode of the sp3 bonding carbons.19

(E) Chemical modification of diamond surface is essential for diamond to be applied as potential biosensor or biochip,7 or a diamond conduction band hv

<400 ran blue hv

red hv

560 nm

700 am W

cure defects surface sp- clusters core (N-V) centres diamond valence hand

Figure 8.3. Schematic of energy levels within the diamond band gap capable of undergoing excitation and photoluminescence. Grey wave arrows represent light absorption or emission; black wave arrows is for non-radiative energy loss. Source: From Ref. 5.

substrate to immobilize biological molecules. Diamond surface can be hydrogen-terminated by exposing the surface to a 13.5-MHz inductively coupled hydrogen plasma (15 torr) at 800°C.6 With the hydrogen-terminated nanocrystalline diamond, Yang and coworkers successfully designed a chemical procedure to attach DNA onto the diamond surface.8 Figure 8.4 shows the schematic diagram of the attachment. Recently, Chang and coworkers9 carboxylated the ND with the size of 5-100 nm in diameter using the following method: The diamonds were heated in a 9:1 mixture of concentrated H2SO4 and HNO3 at 75°C for 3 days, and subsequently in 0.1 M NaOH aqueous solution at 90°C for 2 h, and finally in 0.1 M HCl aqueous solution at 90°C. In Fig. 8.5, Holt showed various surface modifications of ND starting from carboxylated nanodiamond.5 Chemically modified diamond has good physical aborption properties including hydropho-bic and hydrophilic interaction, which can be used to immobilize biomolecules (see, e.g. Section 7.3). Figure 8.6 shows the physical properties on hydrogen- and oxygen-terminated diamond.26

The following sections will introduce the applications of diamond including diamond film, nanodiamond, nanocrystalline diamond film, and diamond-like carbon in biological fields.

8.2 DIAMOND IN BIOMEDICAL APPLICATIONS

Due to its hardness, chemical intertness, thermal conductivity, and low cytotoxicity, diamond could be applied as coating materials of implants, other surgery tools, etc. in biomedical fields.

In 1995, for the first time, Zolyinski and coworkers implanted orthopedic screws, coated with nanocrystelline diamond film (NCD) to a patient with a complex fracture of femoral bone.10 Figure 8.7 shows the implanted screws in an X-ray radiogram.11 After surgery, no ejection was observed, whereas the standard metal implants were rejected twice.

Another implantation application of diamond is that an endo-prothesis of hip joint, coated with NCD film was successfully implanted to a living organism (Fig. 8.8),11 after positive results

Figure 8.4. Sequential steps in DNA attachment to diamond thin films. Source: From Ref. 8.

FWH,

NH2(CH^2KH:Py

NH2(CH^2KH:Py

bciriiiie /THI-

acetone. 43 htrt

prorecied amino acids

Figure 8.5. Schemes for the chemical modification of carboxylated nan-odiamond ND. Source: From Ref. 5.

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