Purposeful identification,
selection, and collection of particles
are of great significance in environmental research. Microscopy is
the common technique used in previous studies of particle identification.
However, the microscopic technique was intricate and time-consuming.
To conduct an intensive analysis of targeted particles, there is a
need for the development of a simple method that can differentially
abandon the nontargeted particles and only retain the targeted particles
on the surface of a substrate. In the study, three methods were attempted
for differential removal of nontargeted nanoparticles on the surface,
including air jet, nanobubble, and ultrasonic methods. Acidic particles
were taken as the targeted particles, while nonacidic particles were
regarded as nontargeted particles. The results showed that regardless
of methods, acidic particles were retained on the surface due to the
strong particle–surface interaction. As for nonacidic particles,
air jet treatment and nanobubble treatment were not able to completely
remove nonacidic particles from the surface with the removal efficiencies
of 5.1 ± 3.4 and 89.3 ± 4.1%, respectively, while the nonacidic
particles were entirely removed in the ultrasonic treatment. Ethanol
rather than deionized (DI) water was the proper solution in the ultrasonic
treatment to avoid contamination. In conclusion, ultrasonic by ethanol
was fully efficient for differential removal of nonacidic particles
on the surface. The principle of differential removal of particles
is the differences in the particle–surface interaction force
between nonacidic particles (i.e., physically attached particles)
and acidic particles (i.e., chemically formed particles). Nonacidic
particles are removed from the surface through cavitation to form
bubbles in the gap between a nonacidic particle and the surface in
the ultrasonic treatment. In contrast, the space between an acidic
particle and the surface is filled by the reaction, and thus bubbles
cannot enter the crevice to remove the acidic particle. The developed
method is useful for aerosol research.