9 research outputs found
Label-Free Impedance Detection of Cancer Cells
Ovarian cancer cells, SKOV3, have been immobilized onto
platinum
microelectrodes using anti-EPCAM capture antibodies and detected with
high sensitivity using electrochemical impedance. The change in impedance
following cell capture is strongly dependent on the supporting electrolyte
concentration. By controlling the concentration of Dulbecco’s
phosphate buffered saline (DPBS) electrolyte, the double layer thickness
can be manipulated so that the interfacial electric field interacts
with the bound cells, rather than simply decaying across the antibody
capture layer. Significantly, the impedance changes markedly upon
cell capture over the frequency range from 3 Hz to 90 kHz. For example,
using an alternating-current (ac) amplitude of 25 mV, a frequency
of 81.3 kHz, and an open circuit potential (OCP) as the direct-current
(dc) voltage, a detection limit of 4 captured cells was achieved.
Assuming an average cell radius of 5 μm, the linear dynamic
range is from 4 captured cells to 650 ± 2 captured cells, which
is approximately equivalent to fractional coverages from 0.1% to 29%.
An equivalent circuit that models the impedance response of the cell
capture is discussed
RGD Labeled Ru(II) Polypyridyl Conjugates for Platelet Integrin α<sub>IIb</sub>β<sub>3</sub> Recognition and as Reporters of Integrin Conformation
The
ability of two novel ruthenium(II) polypyridyl-Arg-Gly-Asp
(RGD) peptide conjugates to act as molecular probes for reporting
on the presence and conformation of integrin α<sub>IIb</sub>β<sub>3</sub> in solution and in live cells was described.
The compounds are [Ru(bpy)<sub>2</sub>PIC-RGD]<sup>2+</sup>, bpy-RGD,
and [Ru(dpp)<sub>2</sub>PIC-RGD]<sup>2+</sup>, dpp-RGD, where dpp
is 4,7-diphenyl-1,10-phenanthroline, bpy is 2,2′-bipyridine,
and PIC is 2-(4-carboxyphenyl)imidazo[4,5-<i>f</i>][1,10]phenanthroline.
Bpy-RGD is hydrophilic, whereas dpp-RGD is comparatively hydrophobic.
Both probes exhibited good affinity and high specificity for purified
α<sub>IIb</sub>β<sub>3</sub> in solution. Binding of either
complex to the resting integrin resulted in an approximately 8-fold
increase of emission intensity from the metal center with dissociation
constants (<i>K</i><sub>d</sub>) in the micromolar range
for each complex. The <i>K</i><sub>d</sub> for each conjugate/α<sub>IIb</sub>β<sub>3</sub> assembly were compared following treatment
of the integrin with the activating agents, Mn<sup>2+</sup> and dithiothreitol
(DTT), which are commonly used to induce active-like conformational
changes in the integrin. For bpy-RGD/α<sub>IIb</sub>β<sub>3</sub> <i>K</i><sub>d</sub> showed relatively little variation
with integrin activation, presenting the following trend: denatured
α<sub>IIb</sub>β<sub>3</sub> > resting α<sub>IIb</sub>β<sub>3</sub> = pretreated DTT = pretreated Mn<sup>2+</sup>. <i>K</i><sub>d</sub> for dpp-RGD/ α<sub>IIb</sub>β<sub>3</sub> showed greater variation with integrin
activation
and the following trend was followed: denatured α<sub>IIb</sub>β<sub>3</sub> > resting α<sub>IIb</sub>β<sub>3</sub> > pretreated Mn<sup>2+</sup> = pretreated DTT. Time resolved
luminescence
anisotropy was carried out to obtain the rotational correlation time
of bpy-RGD and dpp-RGD bound to resting or nominally activated integrin.
The rotational correlation times of bpy-RGD and dpp-RGD, too fast
to measure unbound, decreased to 1.50 ± 0.03 μs and 2.58
± 0.04 μs, respectively, when the complexes were bound
to resting integrin. Addition of Mn<sup>2+</sup> to bpy-RGD/α<sub>IIb</sub>β<sub>3</sub> or dpp-RGD/α<sub>IIb</sub>β<sub>3</sub> reduced the rotational correlation time of the ruthenium
center to 1.29 ± 0.03 μs and to 1.72 ± 0.03 μs,
respectively. Following treatment, the rotational correlation time
decreased to 1.04 ± 0.01 μs and 1.29 ± 0.03 μs
for bpy-RGD/α<sub>IIb</sub>β<sub>3</sub>, and dpp-RGD/α<sub>IIb</sub>β<sub>3</sub>, respectively. The large relative changes
in rotational correlation times observed for Mn<sup>2+</sup> or DTT
activated integrin indicates significant change in protein conformation
compared with the resting integrin. The results also indicated that
the metal complex itself affects the final conformational and/or aggregation
status of the protein obtained. Furthermore, the extent of conformational
change was influenced by whether the probe was bound to the integrin
before or after activator treatment. Finally, in vitro studies indicated
that both probes selectively bind to CHO cells expressing the resting
form of α<sub>IIb</sub>β<sub>3</sub>. In each case the
probe colocalized with α<sub>IIb</sub> specific SZ22 antibody.
Overall, this work indicates that bpy-RGD and dpp-RGD may be useful
peptide-probes for rapid assessment of integrin structural status
and localization in solution and cells
Peptide-Bridged Dinuclear Ru(II) Complex for Mitochondrial Targeted Monitoring of Dynamic Changes to Oxygen Concentration and ROS Generation in Live Mammalian Cells
A novel mitochondrial localizing
ruthenium(II) peptide conjugate
capable of monitoring dynamic changes in local O<sub>2</sub> concentrations
within living cells is presented. The complex is comprised of luminescent
dinuclear ruthenium(II) polypyridyl complex bridged across a single
mitochondrial penetrating peptide, FrFKFrFK-CONH<sub>2</sub> (r = d-arginine). The membrane permeability and selective uptake
of the peptide conjugate at the mitochondria of mammalian cells was
demonstrated using confocal microscopy. Dye co-localization studies
confirmed very precise localization and preconcentration of the probe
at the mitochondria. This precision permitted collection of luminescent
lifetime images of the probe, without the need for co-localizing dye
and permitted semiquantitative determination of oxygen concentration
at the mitochondria using calibration curves collected at 37 °C
for the peptide conjugate in PBS buffer. Using Antimycin A the ability
of the probe to respond dynamically to changing O<sub>2</sub> concentrations
within live HeLa cells was demonstrated. Furthermore, based on lifetime
data it was evident that the probe also responds to elevated reactive
oxygen species (ROS) levels within the mitochondria, where the greater
quenching capacity of these species led to luminescent lifetimes of
the probe at longer Antimycin A incubation times which lay outside
of the O<sub>2</sub> concentration range. Although both the dinuclear
complex and a mononuclear analogue conjugated to an octaarginine peptide
sequence exhibited some cytotoxicity over 24 h, cells were tolerant
of the probes over periods of 4 to 6 h which facilitated imaging.
These metal-peptide conjugated probes offer a valuable opportunity
for following dynamic changes to mitochondrial function which should
be of use across domains in which the metabolic activity of live cells
are of interest from molecular biology and drug discovery
Peptide-Mediated Platelet Capture at Gold Micropore Arrays
Ordered
spherical cap gold cavity arrays with 5.4, 1.6, and 0.98 μm
diameter apertures were explored as capture surfaces for human blood
platelets to investigate the impact of surface geometry and chemical
modification on platelet capture efficiency and their potential as
platforms for surface enhanced Raman spectroscopy of single platelets.
The substrates were chemically modified with single-constituent self-assembled
monolayers (SAM) or mixed SAMs comprised of thiol-functionalized arginine–glycine–aspartic
acid (RGD, a platelet integrin target) with or without 1-octanethiol
(adhesion inhibitor). As expected, platelet adhesion was promoted
and inhibited at RGD and alkanethiol modified surfaces, respectively.
Platelet adhesion was reversible, and binding efficiency at the peptide
modified substrates correlated inversely with pore diameter. Captured
platelets underwent morphological change on capture, the extent of
which depended on the topology of the underlying substrate. Regioselective
capture of the platelets enabled study for the first time of the surface
enhanced Raman spectroscopy of single blood platelets, yielding high
quality Raman spectroscopy of individual platelets at 1.6 μm
diameter pore arrays. Given the medical importance of blood platelets
across a range of diseases from cancer to psychiatric illness, such
approaches to platelet capture may provide a useful route to Raman
spectroscopy for platelet related diagnostics
Fibrinogen Motif Discriminates Platelet and Cell Capture in Peptide-Modified Gold Micropore Arrays
Human blood platelets
and SK-N-AS neuroblastoma cancer-cell capture
at spontaneously adsorbed monolayers of fibrinogen-binding motifs,
GRGDS (generic integrin adhesion), HHLGGAKQAGDV (exclusive to platelet
integrin α<sub>IIb</sub>β<sub>3</sub>), or octanethiol
(adhesion inhibitor) at planar gold and ordered 1.6 μm diameter
spherical cap gold cavity arrays were compared. In all cases, arginine/glycine/aspartic
acid (RGD) promoted capture, whereas alkanethiol monolayers inhibited
adhesion. Conversely only platelets adhered to alanine/glycine/aspartic
acid (AGD)-modified surfaces, indicating that the AGD motif is recognized
preferentially by the platelet-specific integrin, α<sub>IIb</sub>β<sub>3</sub>. Microstructuring of the surface effectively
eliminated nonspecific platelet/cell adsorption and dramatically enhanced
capture compared to RGD/AGD-modified planar surfaces. In all cases,
adhesion was reversible. Platelets and cells underwent morphological
change on capture, the extent of which depended on the topography
of the underlying substrate. This work demonstrates that both the
nature of the modified interface and its underlying topography influence
the capture of cancer cells and platelets. These insights may be useful
in developing cell-based cancer diagnostics as well as in identifying
strategies for the disruption of platelet cloaks around circulating
tumor cells
Enhanced electrochemiluminescence and charge transport through films of metallopolymer-gold nanoparticle composites
Water-soluble 4-(dimethylamino) pyridine (DMAP) stabilized gold nanoparticles (DMAP-AuNP) were synthesized by ligand exchange and phase transfer (toluene/water). The DMAP-AuNPs are positively charged with the core diameter of 4 +/- 1 nm. Metallopolymer-gold nanocomposites were prepared by mixing gold nanoparticles and [Ru(bpy)(2)PVP(10)](ClO(4))(2), in water at different mole ratios: bpy is 2,2'-bipyridyl and PVP is poly (4-vinylpyridine). The photoluminescence emission intensity of the metallopolymer decreases with increasing AuNP loading and approximately 57% of the emission intensity is quenched when the Au NP:Ru mole ratio is 14.8 x 10(-2). The rate or homogeneous charge transfer through thin layers of the nanocomposite deposited oil glassy carbon electrodes increases with increasing nanoparticle loading. The homogeneous charge transport diffusion coefficient, D(CT)., for the composite (AuNP:Ru mole ratio 13.2 x 10(-2)) is (2.8 +/- 0.8) X 10(-11) cm(-2) s(-1) and is approximately 3-fold higher than that found for the pure metallopolymer. Significantly, despite the ability of the metal nanoparticles to quench the ruthenium-based emission, the electrochemiluminescence of the nanocomposite with a AuNP:Ru mole ratio of 4.95 x 10(-2) is approximately three times more intense than the parent metallopolymer. This enhancement arises from the increased rate of charge transport that leads to it greater number of excited states per unit time while minimizing lie quenching effects. The implications of these findings for the design of electrochemiluminescent sensors are discussed
Evaluating Metabolite-Related DNA Oxidation and Adduct Damage from Aryl Amines Using a Microfluidic ECL Array
Damage to DNA from
the metabolites of drugs and pollutants constitutes
a major human toxicity pathway known as genotoxicity. Metabolites
can react with metal ions and NADPH to oxidize DNA or participate
in S<sub>N</sub>2 reactions to form covalently linked adducts with
DNA bases. Guanines are the main DNA oxidation sites, and 8-oxo-7,8-dihydro-2-deoxyguanosine
(8-oxodG) is the initial product. Here we describe a novel electrochemiluminescent
(ECL) microwell array that produces metabolites from test compounds
and measures relative rates of DNA oxidation and DNA adduct damage.
In this new array, films of DNA, metabolic enzymes, and an ECL metallopolymer
or complex assembled in microwells on a pyrolytic graphite wafer are
housed in dual microfluidic chambers. As reactant solution passes
over the wells, metabolites form and can react with DNA in the films
to form DNA adducts. These adducts are detected by ECL from a RuPVP
polymer that uses DNA as a coreactant. Aryl amines also combine with
Cu<sup>2+</sup> and NADPH to form reactive oxygen species (ROS) that
oxidize DNA. The resulting 8-oxodG was detected selectively by ECL-generating
bis(2,2′-bipyridine)-(4-(1,10-phenanthrolin-6-yl)-benzoic acid)Os(II).
DNA/enzyme films on magnetic beads were oxidized similarly, and 8-oxodG
determined by LC/MS/MS enabled array standardization. The array limit
of detection for oxidation was 720 8-oxodG per 10<sup>6</sup> nucleobases.
For a series of aryl amines, metabolite-generated DNA oxidation and
adduct formation turnover rates from the array correlated very well
with rodent 1/TD<sub>50</sub> and Comet assay results
Electrochemiluminescent Array to Detect Oxidative Damage in ds-DNA Using [Os(bpy)<sub>2</sub>(phen-benz-COOH)]<sup>2+</sup>/Nafion/Graphene Films
Reactive
oxygen species (ROS) oxidize guanosines in DNA to form
8-oxo-7,8-dihydro-2-deoxyguanosine (8-oxodG), a biomarker for oxidative
stress. Herein we describe a novel 64-microwell electrochemiluminescent
(ECL) array enabling sensitive multiplexed detection of 8-oxodG in
ds-DNA without hydrolysis. Films of Nafion and reduced graphene oxide
containing ECL dye [Os(bpy)<sub>2</sub>(phen-benz-COOH)]<sup>2+</sup> (OsNG, {bpy= 2,2′-bipyridine and phen-benz-COOH = (4-(1,10-phenanthrolin-6-yl)benzoic
acid)}) were assembled into microwells on a pyrolytic graphite wafer
to detect 8-oxodG in oligonucleotides by electrochemiluminescence
(ECL). DNA oxidation by Fenton’s reagent or by ROS formation
during redox cycles involving NADPH, Cu<sup>II</sup>, and model metabolites
was monitored. UPLC-MS/MS of oxidized DNA samples were used for calibration.
Detection limit for the fluidic arrays was one 8-oxodG per 670 intact
nucleobases, or 0.15%. The method is sensitive enough to evaluate
DNA oxidation from biologically relevant ROS-generating reactions
of Cu<sup>II</sup>, NADPH, and model metabolites
Galectin‑3 Binding to α<sub>5</sub>β<sub>1</sub> Integrin in Pore Suspended Biomembranes
Galectin-3 (Gal3)
is a β-galactoside binding lectin that
mediates many physiological functions, including the binding of cells
to the extracellular matrix for which the glycoprotein α5β1 integrin is of critical importance. The
mechanisms by which Gal3 interacts with membranes have not been widely
explored to date due to the complexity of cell membranes and the difficulty
of integrin reconstitution within model membranes. Herein, to study
their interaction, Gal3 and α5β1 were purified, and the latter reconstituted into pore-suspended
lipid bilayers comprised eggPC:eggPA. Using electrochemical impedance
and fluorescence lifetime correlation spectroscopy, we found that
on incubation with low nanomolar concentrations of wild-type Gal3,
the membrane’s admittance and fluidity, as well as integrin’s
lateral diffusivity, were enhanced. These effects were diminished
in the following conditions: (i) absence of integrin, (ii) presence
of lactose as a competitive inhibitor of glycan–Gal3 interaction,
and (iii) use of a Gal3 mutant that lacked the N-terminal oligomerization
domain (Gal3ΔNter). These findings indicated that WTGal3 oligomerized
on α5β1 integrin in a glycan-dependent
manner and that the N-terminal domain interacted directly with membranes
in a way that is yet to be fully understood. At concentrations above
10 nM of WTGal3, membrane capacitance started to decrease and very
slowly diffusing molecular species appeared, which indicated the formation
of protein clusters made from WTGal3−α5β1 integrin assemblies. Overall, our study demonstrates the
capacity of WTGal3 to oligomerize in a cargo protein-dependent manner
at low nanomolar concentrations. Of note, these WTGal3 oligomers appeared
to have membrane active properties that could only be revealed using
our sensitive methods. At slightly higher WTGal3 concentrations, the
capacity to generate lateral assemblies between cargo proteins was
observed. In cells, this could lead to the construction of tubular
endocytic pits according to the glycolipid–lectin (GL–Lect)
hypothesis or to the formation of galectin lattices, depending on
cargo glycoprotein stability at the membrane, the local Gal3 concentration,
or plasma membrane intrinsic parameters. The study also demonstrates
the utility of microcavity array-suspended lipid bilayers to address
the biophysics of transmembrane proteins