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ANALYTICAL CURRENTS Modified AFM cantilevers en masse Qi Ye and colleagues at the NASA Ames Research Center, Integrated Nanosystems, and Charles Evans and Associates have fabricated a wafer of cantilevers, each modified with a carbon nanotube tip (CNT). CNTs are attractive for atomic force microscopy (AFM) because they permit high-resolution imaging of deep surface features with sharp edges. Previous cantilever modification methods often involved attaching CNTs to pre-existing cantilevers one by one, which was time-consuming and tedious. Attempts to mass-fabricate modified silicon cantilevers by growing CNTs on the cantilevers using thermal chemical vapor deposition resulted in poor yields, and the quality of the CNTs was difficult to control. To overcome these limitations, Ye and colleagues fabricated a wafer of >100 silicon cantilevers, each carrying a CNT with a defined orientation. The cantilevers were first formed in a silicon
wafer by traditional fabrication (a) (b) techniques. The locations and diameters of the CNTs were marked on the cantilevers by e-beam lithography before the cantilevers were etched out and formed. Subsequent to cantilever formation, the CNTs were directly grown on the marked positions by plasma-enhanced chemical vapor deposition. The CNTs had diameters (a) A transmission electron micrograph of a CNT on a canof 40–80 nm and lengths tilever. (b) The CNT is 60 nm in diameter and 5 µm in length. of 2–6 µm. They required ble of stable AFM imaging. Ye and colno shortening to appropriate lengths leagues found that the cantilevers could or any other post-fabrication treatwithstand continuous imaging on a hard ments. The yield of CNT growth surface, without showing significant deon cantilevers was 85–90%, although gradation of the CNT. They also found the investigators predict that it will inthat the CNT could trace the outlines of crease with improvements in the fabrisurface features and the walls and bottoms cation process. of 1-µm trenches. (Nano Lett. 2004, 4, Initial trials with the CNT-modified 1301–1308) cantilevers showed that they were capa-
Routine monitoring of drugs in water As part of a larger study aimed at determin-
usage estimates. They only chose com-
ed drugs. The most difficult drugs to analyze
ing the prevalence of organic wastewater
pounds from the 20 most commonly pre-
were the highly polar and amphoteric com-
contaminants in primary drinking water
scribed drugs and the most commonly sold
pounds. Method detection limits averaged
sources, Edward Furlong and colleagues
nonprescription drugs. The list included
0.022 µg/L, which is sufficient for detecting
at the U.S. Geological Survey and the Uni-
antibiotics, analgesics, and drugs for heart
the presence of pharmaceuticals at ambient
versity of Colorado at Denver have devel-
disease, hypertension, and lowering cho-
concentrations. The researchers plan to fur-
oped a routine method for monitoring a host
lesterol, just to name a few. As a result,
ther develop SPE to include the use of tan-
of commonly used pharmaceuticals in sur-
the researchers needed a method that
dem or mixed modes of extraction sorbents.
face- and groundwater samples. The method,
could handle a diverse number of chemical
This improvement would allow better re-
which relies on solid-phase extraction (SPE)
classes. In addition, the method had to be
covery of multiple classes of compounds.
and HPLC/electrospray ionization (ESI) MS,
sensitive enough to detect compounds in
In addition, the introduction of new phases
was recently used in a national reconnais-
the low-ng/L range.
with ion-exchange capability could lead to
sance of prescription and over-the-counter drugs in U.S. surface waters. The researchers selected which pharmaceuticals to evaluate on the basis of
304 A
According to the researchers, the HPLC/ ESI-MS method performed well for most of
better isolation of diverse compounds and eliminate interferences from dissolved or-
the pharmaceuticals that were evaluated,
ganic matter. (J. Chromatogr. A 2004, 1041,
and recoveries were >60% for 12 of the test-
171–180)
A N A LY T I C A L C H E M I S T R Y / S E P T E M B E R 1 , 2 0 0 4
