Page 15 - Shimadzu Journal vol.9 Issue1

Clinical Research

15
appropriate biological conditions . The effects of these new ma- stainless-steel cylinder approximately 30 cm in height and 20 cm in
terials on the morphological and chemical structures of metallic diameter. The thermal evaporation source is located at the bottom
nanostructures has not been the topic of sufficient investigation in of the chamber, approximately 25 cm from the slides. The slides are
the literature. As such, observed differences and claims of detec- oriented at an incident angle of 87° relative to the source normal to
tion of biological materials, like SARS-CoV-2, may be observa- achieve a glancing angle condition. The chamber is evacuated using
tions of changes to the metallic nanostructures caused by buffers a mechanical roughing pump and turbomolecular pump until a
-5
and additives rather than the target molecule itself. For example, vacuum level of 5 x 10 Torr is reached and maintained for an hour
an extensive review of the literature shows that there has been no to remove excess adsorbed water from the chamber. Evaporation
investigation into the effects of something as simple as the pres- is performed from a tungsten boat using 99.99% Ag pellets (Kurt J.
ence of dissolved gases in the water used in sensing experiments Lesker Co.). The deposition rate is monitored via quartz crystal mi-
o
o
with metallic nanostructures, like Ag nanorods. However, it is well crobalance and controlled to 10 A /s +/- 2 A /s to a total film thick-
known in the literature and industry that dissolved oxygen in water ness of 500 nm. The samples are then held under low to medium
16
can rapidly corrode silver . vacuum and only removed prior to subsequent experiments.
In this technical Letter, a representative study, the authors
demonstrate that significant differences exist in the optical reflec-
tion and Raman signals of rhodamine-6G (R6G), a classical organic Degassing of Water
target molecule, absorbed onto the surfaces of Ag nanorods when
the samples were exposed to deionized water versus the same High purity deionized water is obtained and half is degassed
water that had been degassed via boiling. Through investigation through boiling. To degas, the water is placed into a glass jar with
using scanning electron microscopy (SEM), post operation and in- a vacuum tight lid, removed during boiling, and heated to rapid
situ UV-Vis spectroscopy, scanning probe microscopy (SPM), and boiling on a laboratory hot plate. The water is vigorously boiled for
Raman spectroscopy the authors determine that significant chem- 15 minutes and then immediately sealed with the vacuum tight lid.
ical and morphological changes occur when Ag nanorods are ex- The sealed container is then allowed to return naturally to room
posed to water that has not been degassed, compared to negligible temperature. The boiling method has been shown to produce
17
measured changes when they have been exposed to appropriately water with as little as 1 ppm of dissolved oxygen .
degassed water.

Electron Microscopy
Experimental
SEM is performed on a Tescan Mira scanning electron microscope
Prior to presenting the results we will briefly describe the exper- equipped with an Oxford energy dispersive spectroscopy (EDS).
iments performed in this investigation. The experiments involve Samples are imaged using secondary electrons at magnifications
the fabrication of Ag nanorods using glancing angle physical vapor up to 100k X under beam voltages of 10kV and working distances
deposition (GLAD PVD), preparation of components and mate- of 10 mm. Samples are imaged immediately after removal from
rials used in the study, and then the characterizations carried out vacuum and immediately after removal from exposure to degassed
using SEM, SPM, UV-Vis spectroscopy, and Raman spectroscopy. and non-degassed water with subsequent drying under a gentle
flow of dry nitrogen.

Nanorod fabrication
SPM
Ag nanorods are fabricated using GLAD PVD in a custom-built
high vacuum chamber and thermal evaporation 13,18,19 . First, Corning SPM is performed on a Shimadzu SPM-9700 HT equipped with
glass slides are cleaned sequentially through sonication in acetone, the 10-micron scanner attachment, fiber optic light source, and the
ethanol, and deionized water for five minutes at each stage. The high magnification CCD optical microscope unit. The SPM was
cleaned slides are then dried under a gentle flow of high purity performed on samples grown onto 12.7 x 12.7 mm corning glass
nitrogen. After drying, the slides are placed onto a substrate holder substrates with the evaporated silver nanorod films. The rate of
at the top of the vacuum chamber. The vacuum chamber is a raster scanning was set to 1.00 Hz and the pixel setting was ran with

Shimadzu Journal vol.9 Issue1 14