Page 391 - Book Hosokawa Nanoparticle Technology Handbook

6.5 ELECTROCHEMICAL PROPERTIES FUNDAMENTALS
Thus the coupling condition for the surface plas- plasmon resonance. If the nanoparticles smaller
mon resonance is remarkably sensitive to change of than the wavelength of light are irradiated, the exci-
the dielectric constant near the metal surface. tation of plasmon named as a localized surface plas-
Therefore, as shown in Fig. 6.5.12, a sensor can be mon resonance will occur resulting in absorption
composed of a prism and a metal thin-film support- and scattering of the light of a specific wavelength.
ing receptors which selectively bind with specific Therefore, the detection of the nanoparticle sensor
molecule to detect. Schematics of signal changes of is based on the change of transmission and/or scat-
the sensor using the surface plasmon resonance are tering of light. Since the sensing system needs no
shown in Fig. 6.5.13. If the supported receptor binds optical system with a prism, the sensor has an
with the molecule, the dielectric constant near the advantage that the whole sensing system can be
metal surface will change, and the absorption angle made compact compared with the thin-film sensor.
will shift. The detection of the specific molecule is Theoretically, a single metal nanoparticle can be
performed based on the incident angle dependence of used as a detection medium. For example, a sensor
the reflected intensity. Moreover, if the incident angle can be made by attaching the nanoparticle on the
is fixed near the absorption angle, real-time meas- end of an optical fiber.
1
urement will be realized as shown in Fig. 6.5.13b. Fig. 6.5.14 shows the plasmon scattering from a
The metal nanoparticles as well as a metal thin- single gold nanoparticle in various solvents measured
film are applicable to the sensor using surface through a optical fiber [5]. The nanoparticle with
50–100 nm in diameter was attached on the tip of an
axicon microlens fabricated on the end of an optical
fiber. The position of the peak changes in the various
Evanescent wave
solvent, implying that the nanoparticle is sensitive to
the deference of the solvent. Since the peak change is
attributed to the change of the dielectric constant near
Molecule to detect the metal surface, it is expected that the single
nanoparticle can be used for chemical and biological
Receptor
sensors of a nanometer scale.
The chemical sensor using surface plasmon
Metal thin-film
resonance is indispensable in the field of the present
biochemistry or biotechnology because of the follow-
ing reasons:
Prism
1. The real-time measurement for a small quantity
of specimen is possible.
Incident light Reflected light
2. Labeling substances, such as a fluorescent mate-
rial, are not required.
Figure 6.5.12
Schematic diagram of surface plasmon resonance 3. The manufacturing cost of a sensor is low.
sensor. 4. Disposable use is possible.

Reflected intensity Reflected intensity

Time
Incident angle
Δθ
θ 1 (b)
(a)
Figure 6.5.13
Schematic of detection characteristics of surface plasmon resonance sensor. (a) Change in the absorption angle that the
surface plasmon resonance takes place. (b) Change in reflected light intensity with time.

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