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Malkiat
S. Johal |
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Welcome to our
Nano-Materials Research Page
Chemistry Department, Seaver North, Room 23 Laboratory phone: (909) 607-7959 The Johal Research Group From
left to right:
Ellen Yang (’11), Michael Gormally (’11), Ted
Zwang (’11), Will Fletcher (’12). Jake
Schual-Berke (’11), Mal Johal, Michael
Haber (’13), Alex Polizzotti (’11), Lucille
Sun (’11), and Natalie Chung (’11).
CLICK ON ONE
OF THE FOLLOWING LINKS
·
List of Past Undergraduate
Thesis Students
·
Partnerships
and Collaborations
The underlying theme of our research program is to
take advantage of molecular self-assembly processes to construct functional nano-materials
for optical and biosensing applications. Our research program primarily
explores the electrostatic self-assembly (ESA) of novel polyelectrolytes,
biological macromolecules, and ionic surfactants. We use a variety of
layer-by-layer (LbL) methods, including direct adsorption and spin-assembly, to
fabricate well-defined multilayer assemblies. Current projects in our
laboratory include the immobilization of biomolecules (enzymes, proteins,
microbes) on polyelectrolyte surfaces,
the fabrication of organic photovoltaic devices, the complexation of
polyelectrolytes and ionic surfactants, the fabrication of high quantum yield
polyelectrolyte films, the asymmetric assembly of non-linear optically (NLO)
active materials, and the spin-assembly of charge alternating polyelectrolytes.
Our
laboratory specializes in adsorption phenomena and is equipped with some of the
modern instruments used to obseve real-time binding events. Our suit of surface
science capabilities include:
Dual-Beam Polarization
Interferometry (DPI)
Quartz Crystal
Microbalance with Dissipation monitoring (QCM-D)
X-Ray
Reflectivity
Ellipsometry
(multi-wavelength)
Surface
Tension, Wettability, and Contact Angle Instruments
Spectroscopy
(ATR-FTIR, Absorption, and Fluorescence methods)
DPI is a non-invasive optical technique that uses a
waveguide interferometer to determine the effective refractive index (RI) of a
thin film from both s and p polarized light. Both of these polarization modes generate
evanescent fields that extend into the sensing region of the waveguide, but the
fields produced by each mode are of different intensities and decay at
different rates. Therefore, each
polarized mode will generate its own interference pattern and consequently will
provide a separate calculation of the effective RI. Only one unique pair of
absolute RI and thickness values will generate the observed effective RI for
both polarized modes and this pair represents the value of the absolute RI and
thickness of the film on the sensing waveguide surface. Therefore, by using two
different polarized modes of light and by calculating the unique solution pair,
DPI can be used to determine the RI and thickness of thin films to within a
fraction of an angstrom simultaneously and in real-time. Furthermore, since RI
can yield the film density, DPI can be used to calculate the mass of the film.
We are using Farfield’s AnaLight Flex Bio200 for observing
real-time binding events.
QCM-D measures both the dissipation
and the resonance frequency of a quartz crystal. We use QCM-D to investigate
the formation of thin films containing proteins, polyelectrolytes and bacteria
onto well-defined surfaces in the liquid phase. In liquid, adsorbed films
typically contain trapped water molecules, which is sensed as a mass uptake by
all QCMs. We measure several frequencies and the dissipation making it possible
to determine whether the adsorbed film is rigid or water-rich (soft). The
measurement of frequency and dissipation at multiple overtones allows us to use
viscoelastic models to obtain insight into the mechanical properties of the
films. This information is particularly important when assembling lipid
membranes or immobilizing proteins on polyelectrolytes. We are using Q-Sense’s next
generation E4 system made for the rapid characterization of
bio-interfaces. Interestingly, the mass value of an assembly obtained using QCM
is usually greater than the corresponding value obtained using DPI. This is due
to the fact that QCM measures the mass of the film including coupled water,
unlike DPI which measures the mass of the “dry” film under water. The
difference between these values provides a measure of the water content in the
assembly.
In addition to DPI and QCM-D, we are also using multi-wavelength
ellipsometry (544 nm and 633 nm) to measure the refractive index and film
thickness down to a few angstroms. This data in combination with the DPI and
QCM-D measurements provides a powerful characterization (e.g. binding events,
kinetics, phase transitions) of films adsorbed at the solid-liquid and
solid-air interfaces.