Biophotonics_Concepts_to_Applications

11.4 Single Nanoparticle Detection

Clinical techniques that exhibit a high sensitivity to specific allergens, a large
dynamic range to detect all clinically relevant concentrations of various biomarkers,
and the ability to simultaneously assess multiple biomarkers are in high demand for
disease diagnostics. Of particular interest is the ability to detect and analyze natural
nanoparticles such as viruses and pollutants, which can have a major impact on
human health. The detection of single nanoscale particles has been demonstrated
using a method namedinterferometric reflectance imaging sensor(IRIS) [ 27 – 29 ].
The IRIS technique does not require complex micro-fabricated detector surfaces
but instead employs a simple and inexpensive silicon-silicon dioxide (Si-SiO 2 )
substrate, commercially available LEDs, and a CCD detector. This method can
detect single nanoparticles that are captured across a sensor surface by means of
interference between an incident opticalfield that is scattered from the captured
nanoparticles and a reference reflection from the sensor surface.
The basic concept of single-particle IRIS (SP-IRIS) is illustrated in Fig.11.5.
First a natural nanoparticle, such as a virus, is captured on a specially prepared
sensor surface consisting of a silicon dioxide layer deposited on a silicon substrate.
To detect these viral nanoparticles and to determine their size, visible LED light is
used to illuminate the surface and a CCD camera captures a bright-field reflection
image. In this image the particles of interest appear as diffraction-limited dots. The
contrast of the dots can be used to determine their sizes and shapes.

CCD camera

Microscope

objective

Si substrate

SiO 2 layer

Dichroic

beamsplitter

Nanoparticle

Visible

LED

Fig. 11.5 Illustration of the
single-particle IRIS imaging
technique

11.4 Single Nanoparticle Detection 333