Substrates coated with a precious-metal salt KAuCl4 have been found to be useful for detecting hydrazine vapors in air at and above a concentration of the order of 0.01 parts per million (ppm). Upon exposure to air containing a sufficient amount of hydrazine for a sufficient time, the coating material undergoes a visible change in color

Dee, Louis A.

Greene, Benjamin

NASA Technical Reports Server

Nanocarpets — that is, carpets of car-
bon nanotubes — are undergoing devel-
opment as means of trapping micro-
scopic particles for scientific analysis.
Examples of such particles include inor-
ganic particles, pollen, bacteria, and
spores. Nanocarpets can be character-
ized as scaled-down versions of ordinary
macroscopic floor carpets, which trap
dust and other particulate matter, albeit
not purposefully. Nanocarpets can also
be characterized as mimicking both the
structure and the particle-trapping be-
havior of ciliated lung epithelia, the car-
bon nanotubes being analogous to cilia
(see figure).
Carbon nanotubes can easily be chem-
ically functionalized for selective trap-
ping of specific particles of interest. One
could, alternatively, use such other
three-dimensionally-structured materi-
als as aerogels and activated carbon for
the purposeful trapping of microscopic
particles. However, nanocarpets offer
important advantages over these alterna-
tive materials:
• Nanocarpets are amenable to nonin-
trusive probing by optical means; and
• Nanocarpets offer greater surface-to-
volume ratios.
This work was done by Flavio Noca, Fei
Chen, Brian Hunt, Michael Bronikowski,
Michael Hoenk, Robert Kowalczyk, and
Daniel Choi of Caltech for NASA’s Jet
Propulsion Laboratory. Further informa-
tion is contained in a TSP (see page 1).
In accordance with Public Law 96-517,
the contractor has elected to retain title to this
invention. Inquiries concerning rights for its
commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
(818) 354-2240
E-mail: iaoffice@jpl.nasa.gov
Refer to NPO-30659, volume and number
of this NASA Tech Briefs issue, and the
page number.
NASA Tech Briefs, December 2004 13
Materials
Nanocarpets for Trapping Microscopic Particles
Properties of nanocarpets can be tailored for selective trapping.
NASA’s Jet Propulsion Laboratory, Pasadena, California
Microscopic Particles (Bacillus pumilis spores) were trapped on a nanocarpet by immersing the
nanocarpet in a spore-containing solution, then drying the nanocarpet.
Substrates coated with a precious-
metal salt KAuCl4 have been found to
be useful for detecting hydrazine va-
pors in air at and above a concentra-
tion of the order of 0.01 parts per mil-
lion (ppm). Upon exposure to air
containing a sufficient amount of hy-
drazine for a sufficient time, the coat-
ing material undergoes a visible
change in color. Although the color
change is only a qualitative indication,
it can serve as an alarm of a hazardous
concentration of hydrazine or as advice
of the need for a quantitative measure-
ment of concentration. Detection of
hydrazine vapors by this technique
costs much less and takes less time than
does laboratory analysis of sorbent
tubes using high-performance liquid
chromatography, which is the tech-
nique used heretofore to detect hy-
drazines at concentrations down to
0.01 ppm.
A substrate for use in this technique
should be made of a chemically inert
material (e.g., fiberglass filter paper).
The substrate is uniformly coated with
1 to 10 weight percent of the precious-
metal salt in a solvent (e.g., dilute HCl)
that does alter the physical characteris-
Precious-Metal Salt Coatings for Detecting Hydrazines
Colors change upon exposure to hydrazines and perhaps other hazardous gases.
Lyndon B. Johnson Space Center, Houston, Texas
https://ntrs.nasa.gov/search.jsp?R=20110020444 2019-08-30T17:59:37+00:00Z
14 NASA Tech Briefs, December 2004
tics of the substrate. After driving off
the solvent by gentle heating and/or by
use of a vacuum, the coated substrate is
packed into an inert tube with open-
ings at each end. (The dried precious-
metal coating is somewhat sensitive to
light; the dried coated substrate should
be handled accordingly and stored in
the dark.)
The coated substrate is held in place
with small quantities of inert wadding
(i.e., borosilicate glass wool). A gas suc-
tion pump is attached to one end of the
tube, and the air or other gas suspected
to contain hydrazine vapor is drawn
through the tube at a specified pump-
ing rate for an amount of time sufficient
to obtain a sufficient chemical change
(and thus an observable color change)
in the coating material. A semiquantita-
tive relationship between the degree of
chemical change and the quantity of
vapor sampled can be established from
observations of intensities of color
changes and/or areas of color change in
tests on similarly prepared substrates and
tubes using known concentrations of hy-
drazine vapors.
In experiments, tubes containing
KAuCl4-coated substrates prepared as
described above were exposed to 40-
liter flows of air containing, variously,
hydrazine, monomethylhydrazine, or
unsymmetrical dimethylhydrazine at
concentrations of the order of 0.01 ppm.
These exposures caused the colors of
the substrates to change from yellow to
various purplish colors and, in one case,
to black.
No such color changes were observed
upon exposure of the KAuCl4-coated
substrates to flows of air that contained
other gases (ammonia, isopropyl alco-
hol, NO2, and H2). Whether or not other
precious-metal coating materials could
be used as color-change indicators of
these or other nonhydrazine gases re-
mains to be determined.
This work was done by Louis A. Dee and
Benjamin Greene of Allied-Signal Aerospace Co.
for Johnson Space Center. For further infor-
mation, contact the Johnson Commercial Tech-
nology Office at (281) 483-3809.
MSC-22870
Amplifying Electrochemical Indicators
Reporter compounds can be formulated for high sensitivity and miniaturization of sensor units.
Ames Research Center, Moffett Field, California
Dendrimeric reporter compounds have
been invented for use in sensing and am-
plifying electrochemical signals from mol-
ecular recognition events that involve
many chemical and biological entities.
These reporter compounds can be for-
mulated to target specific molecules or
molecular recognition events. They can
also be formulated to be, variously, hy-
drophilic or amphiphilic so that they are
suitable for use at interfaces between (1)
aqueous solutions and (2) electrodes con-
nected to external signal-processing elec-
tronic circuits. The invention of these re-
porter compounds is expected to enable
the development of highly miniaturized,
low-power-consumption, relatively inex-
pensive, mass-producible sensor units for
diverse applications, including diagnoses
of infectious and genetic diseases, testing
for environmental bacterial contamina-
tion, forensic investigations, and detec-
tion of biological warfare agents.
The multiple functionality of a reporter
compound of this type is achieved
through integration of a variety of chemi-
cal moieties into each molecule. The
structure and composition of such a mol-
ecule is depicted schematically in the fig-
ure and represented by the general for-
mula ALBn. As used here, A signifies a
targeting group, L signifies a linking
group, and B signifies an active group.
The targeting group (A) can include
nucleic-acid intercalators or other or-
ganic functional subgroups. It is designed
to interact directly with a targeted mole-
cule or molecular recognition event; that
is to say, it is designed to bring itself and
the rest of the reporter molecule into the
vicinity of the target. Hence, the collec-
tive effect of the targeting groups of mul-
tiple reporter molecules is to concentrate
the reporter compound in the region of
the target compound or molecular recog-
nition events that one seeks to detect.
An active group (B) is, more specifi-
cally, either (1) electroactive in a manner
that enables detection of an electro-
chemical signal or (2) hydrophilic to en-
hance solubility. It is preferable that the
number (n) of B groups exceed 1. The
linking group (L) comprises two moi-
eties: (1) a linker between the targeting
(A) group and the B groups and (2) an
amplifying moiety, through which the B
groups are connected in series, parallel,
or a combination of series and parallel
connections in a dendritic structure.
The active (B) groups can also be char-
acterized as indicator groups because these
are the ones that generate the desired elec-
tronic sensory signals. Because they are
linked to the targeting group, the active
groups are concentrated in the vicinity of
the target, and the probability that each
will generate a signal is correspondingly in-
creased. The multiple active groups, con-
nected together in the dendritic molecular
structure, contribute to an aggregate signal
much greater than that generated by a sin-
gle-indicator reporter molecule. Depend-
ing upon the specific formulation of a re-
porter molecule according the invention,
the primary signal could be as little as two
B
A
L
A Reporter Compound according to the invention can have any of a wide variety of dendritic struc-
tures. The A, B, and L groups contribute synergistically to the overall effect of generating a highly am-
plified primary electrochemical sensory signal.


Precious-Metal Salt Coatings for Detecting Hydrazines

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