Page 180 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Reactive Oxygen Species Generation on Nanoparticulate Material 165

TABLE 5.2 A Brief Summary of ROS Detection Methods

difficult to detect low concentrations of ROS when compared with
EPR methods (Table 5.2).
Chemical or biochemical quenchers can also be added to target spe-
cific ROS. For example, superoxide dismutase is routinely used to
quench superoxide in a reaction medium [7]. Beta carotene and azide

ion (N 3 ) are known quenchers for singlet oxygen [12]. These compounds
serve to eliminate the response seen from any of the above detection
methods. If a response is eliminated by the addition of a quencher, it is
easier to assume that the specific ROS generated the signal. However,
most quenchers lack complete specificity for a single ROS component.
For example, superoxide dismutase seems to have an effect on singlet
oxygen production despite its supposed specificity [13] for superoxide.
Alternative methods for detection of ROS include fingerprinting of
reaction products and direct chemiluminescence detection (e.g., singlet
oxygen luminescence can be quantified at 1270 nm [14]).

Nanoparticulate Semiconductor Particles
and ROS Generation

Semiconducting metal oxides and metal chalcogenides have been used
as catalysts for a wide variety of chemical reactions in the gas-solid
phase and liquid-solid reactions over a broad range of temperatures
o
from < 0 to 500 C [15]. Semiconducting oxides and sulfides can be acti-
vated by an applied electrical potential, by the absorption of photons,
or by elevated temperatures. The energies required for activation of
some common metal oxide and metal chalocogenide semiconductors are
given in Tables 5.3 and 5.4, respectively.