Nanoparticle-based biosensors and bioassays - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 450

orders of magnitude lower than that obtained by a conventional immunoassay using the
same gold nanoparticle labels.
Recently, a particle-based renewable electrochemical magnetic immunosensor was
developed in our group by using magnetic beads and gold nanoparticle labels [61].
Anti-IgG antibody-modifi ed magnetic beads were attached to a renewable carbon paste
transducer surface by a magnet that was fi xed inside the sensor. Gold nanoparticle
labels were capsulated to the surface of magnetic beads with a sandwich immunoassay
(Fig. 14.4). Highly sensitive electrochemical stripping analysis offers a simple and fast

(i) (ii) (iii) (iv)

Stripping
analysis

Anti-IgG attached magnetic beads IgG

Carbon paste

(a) Gold nanoparticle modified secondary antibody

Magnets

(i) (ii)

(b)

FIGURE 14.4 (a) Particle-based electrochemical immunoassay protocol: (i) introduction of antibody-
modifi ed magnetic beads to magnet/carbon paste electrochemical transducer surface; (ii) binding of the IgG
antigen to the antibodies on the magnetic beads; (iii) capture of the gold nanoparticle-labeled secondary anti-
bodies; (iv) electrochemical stripping detection of gold nanoparticles. (b) TEM images of magnetic beads-
gold nanoparticles assembly resulting from the sandwich immunoreaction of 0.2 µg mL 1 IgG analyte (i)
and an expanded view of the particle assembly (ii) (reproduced from [61] with permission).