3 research outputs found
Label-Free Optical Method for Quantifying Molecular Transport Across Cellular Membranes In Vitro
We demonstrate a nonlinear optical
method for the label-free quantification
of membrane transport rates of small/medium size molecules in living
cells. Specifically, second-harmonic generation (SHG) laser scattering
permits surface-specific characterization of transport across membranes.
Unfortunately, most biologically relevant molecules are SHG-inactive.
In the interest of extending this methodology for characterizing transport
of any molecule, we monitor the SHG produced from an SHG-active reference
molecule, in the presence of an SHG-inactive target molecule-of-interest
as both molecules compete to cross a membrane. Of significance, the
SHG-inactive target transport rate can be deduced as a perturbation
in the measured transport rate of the reference. As proof-of-principle,
we examine competitive transport of the strongly SHG-active cation,
malachite green (MG), in the presence of a weakly SHG-active dication,
propidium (Pro), across the outer-membrane protein channels in living
bacteria. Comparison of the extracted and directly measured Pro transport
rates validates the effectiveness of the method
Azithromycin-Induced Changes to Bacterial Membrane Properties Monitored <i>in Vitro</i> by Second-Harmonic Light Scattering
We present a nonlinear light scattering
method for monitoring,
with real-time resolution and membrane specificity, changes in molecular
adsorption, and transport at bacterial membranes induced by an antimicrobial
compound. Specifically, time-resolved second-harmonic light scattering
(SHS) is used to quantify azithromycin-induced changes to bacterial
membrane permeability in colloidal suspensions of living <i>Escherichia
coli</i>. Variations in membrane properties are monitored through
changes in the adsorption and transport rates of malachite green,
a hydrophobic cation that gives SHS signal. Regardless of concentration,
instantaneous treatment with azithromycin showed no significant changes
in membrane permeability. However, 1 h pretreatment with subminimum
inhibitory concentrations of azithromycin induced an order-of-magnitude
enhancement in the permeability of both the outer membrane and, through
facilitation of a new transport mechanism, the cytoplasmic membrane
of the bacteria as well. This study illustrates SHS as a novel tool
for monitoring antimicrobial-induced changes to membrane properties
in living bacteria
Mitigation of Thin-Film Composite Membrane Biofouling via Immobilizing Nano-Sized Biocidal Reservoirs in the Membrane Active Layer
This work investigates the use of
a silver-based metal–organic
framework (MOF) for mitigating biofouling in forward-osmosis thin-film
composite (TFC) membranes. This is the first study of the use of MOFs
for biofouling control in membranes. MOF nanocrystals were immobilized
in the active layer of the membranes via dispersion in the organic
solution used for interfacial polymerization. Field emission scanning
electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy
(XPS) characterization results showed the presence of the MOF nanocrystals
in the active layer of the membranes. The immobilization improved
the membrane active layer in terms of hydrophilicity and transport
properties without adversely affecting the selectivity. It imparted
antibacterial activity to the membranes; the number of live bacteria
attached to the membrane surface was over 90% less than that of control
membranes. Additionally, the MOF nanocrystals provided biocidal activity
that lasted for 6 months. The immobilization improved biofouling resistance
in the membranes, whose flux had a decline of 8% after 24 h of operation
in biofouling experiments, while that of the control membranes had
a greater decline of ∼21%. The better biofouling resistance
is due to simultaneous improvement of antiadhesive and antimicrobial
properties of the membranes. Fluorescence microscopy and FE-SEM indicated
simultaneous improvement in antiadhesive and antimicrobial properties
of the TFN membranes, resulting in limited biofilm formation