nanoparticles deposited electrochemically on colloidal gold assembled on a glass/
SnO 2 electrode are found to be reasonably good substrates for SERS studies. Ag
particles deposited on Pt electrodes by a chemical method show excellent potentialdependent SERS spectra for pyridine [24].
20.6
Nanosensors
20.6.1
Biosensors
Electrode surfaces can be modified with metal nanoparticles and such surfaces
have found numerous applications in the field of bioelectrochemistry, particularly
in biosensors [7, 155]. Gold nanoparticles are often utilized in such studies since
they are known to retain the activity of the biomolecule with electrochemical activity intact as well [15]. It has also been observed that these nanoparticles can act as
conduction centers facilitating the transfer of electrons. In addition, they provide
large catalytic surface areas.
A vast amount of literature exists on enzyme-modified metal nanoparticles.
Crumbliss and co-workers pioneered the use of metal nanoparticles for enzymatic
sensors for various analytes such as H 2 O 2 , glucose, xanthine and hypoxanthine
[156–158]. GCE or Pt electrodes are modified with enzyme-capped Au colloids,
either by simple evaporation or electrodeposition. The nanoparticles act as mediators, transferring electrons between the redox-active site on the immobilized biomolecule and the electrode and thus eliminating the need for external mediators.
These sensors are classified as ‘‘third generation biosensors’’.
Carbon paste as an electrode has been well studied for biosensing applications.
It has the advantage of ease of preparation, desired level of loading and good
conductivity. Celej and Rivas developed a sensor for the determination of glucose
using gold-dispersed carbon paste electrodes containing glucose oxidase (GOx)
[159]. The gold particles catalyze the electrooxidation and reduction of the H 2 O 2
generated during the enzymatic catalysis. This sensor can also be used in flow
injection systems.
Natan and co-workers have demonstrated the reversible electrochemistry of
cytochrome-c at gold colloid-modified SnO 2 electrodes. The voltammetric behaviour depends strongly on the nanoscale morphology. Surfaces composed of isolated
12 nm Au particles give rise to reversible voltammetry while aggregates of particles
of the same size result in irreversible behavior [160a]. Ju and co workers [160b]
prepared similar nanoparticle-modified carbon paste electrodes and incorporated
horse-heart cytochrome-c using a polishing procedure to detect micromolar (mM)
concentrations of H 2 O 2 . More recently, tyrosinase–colloidal gold-modified carbon
paste electrodes have been used for the detection of nanomolar (nM) concentrations of phenol [161]. The immobilized tyrosinase efficiently catalyzes the reaction
20 Electrochemistry with Nanoparticles
670
SnO 2 electrode are found to be reasonably good substrates for SERS studies. Ag
particles deposited on Pt electrodes by a chemical method show excellent potentialdependent SERS spectra for pyridine [24].
20.6
Nanosensors
20.6.1
Biosensors
Electrode surfaces can be modified with metal nanoparticles and such surfaces
have found numerous applications in the field of bioelectrochemistry, particularly
in biosensors [7, 155]. Gold nanoparticles are often utilized in such studies since
they are known to retain the activity of the biomolecule with electrochemical activity intact as well [15]. It has also been observed that these nanoparticles can act as
conduction centers facilitating the transfer of electrons. In addition, they provide
large catalytic surface areas.
A vast amount of literature exists on enzyme-modified metal nanoparticles.
Crumbliss and co-workers pioneered the use of metal nanoparticles for enzymatic
sensors for various analytes such as H 2 O 2 , glucose, xanthine and hypoxanthine
[156–158]. GCE or Pt electrodes are modified with enzyme-capped Au colloids,
either by simple evaporation or electrodeposition. The nanoparticles act as mediators, transferring electrons between the redox-active site on the immobilized biomolecule and the electrode and thus eliminating the need for external mediators.
These sensors are classified as ‘‘third generation biosensors’’.
Carbon paste as an electrode has been well studied for biosensing applications.
It has the advantage of ease of preparation, desired level of loading and good
conductivity. Celej and Rivas developed a sensor for the determination of glucose
using gold-dispersed carbon paste electrodes containing glucose oxidase (GOx)
[159]. The gold particles catalyze the electrooxidation and reduction of the H 2 O 2
generated during the enzymatic catalysis. This sensor can also be used in flow
injection systems.
Natan and co-workers have demonstrated the reversible electrochemistry of
cytochrome-c at gold colloid-modified SnO 2 electrodes. The voltammetric behaviour depends strongly on the nanoscale morphology. Surfaces composed of isolated
12 nm Au particles give rise to reversible voltammetry while aggregates of particles
of the same size result in irreversible behavior [160a]. Ju and co workers [160b]
prepared similar nanoparticle-modified carbon paste electrodes and incorporated
horse-heart cytochrome-c using a polishing procedure to detect micromolar (mM)
concentrations of H 2 O 2 . More recently, tyrosinase–colloidal gold-modified carbon
paste electrodes have been used for the detection of nanomolar (nM) concentrations of phenol [161]. The immobilized tyrosinase efficiently catalyzes the reaction
20 Electrochemistry with Nanoparticles
670