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Biomedical subjects

Susan Daniel

Publications and source records attributed to Susan Daniel.

7 recordsLinked to original sources
PubMed2006

Ionic conductivity of the aqueous layer separating a lipid bilayer membrane and a glass support.

The in-plane ionic conductivity of the approximately 1-nm-thick aqueous layer separating a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer membrane and a glass support was investigated. The aqueous layer conductivity was measured by tip-dip deposition of a POPC bilayer onto the surface of a 20- to 75-microm-thick glass membrane containing a single conical-shaped nanopore and recording the current-voltage (i-V) behavior of the glass membrane nanopore/POPC bilayer structure. The steady-state current across the glass membrane passes through the nanopore (45-480 nm radius) and spreads radially outward within the aqueous layer between the glass support and bilayer. This aqueous layer corresponds to the dominant resistance of the glass membrane nanopore/POPC bilayer structure. Fluorescence recovery after photobleaching measurements using dye-labeled lipids verified that the POPC bilayer maintains a significant degree of fluidity on the glass membrane. The slopes of ohmic i-V curves yield an aqueous layer conductivity of (3 +/- 1) x 10(-3) Omega(-1) cm(-1) assuming a layer thickness of 1.0 nm. This conductivity is essentially independent of the concentration of KCl in the bulk solution (10-4 to 1 M) in contact with the membrane. The results indicate that the concentration and mobility of charge carriers in the aqueous layer between the glass support and bilayer are largely determined by the local structure of the glass/water/bilayer interface.

Electric Conductivity↗
PubMed2006

Supported lipopolymer membranes as nanoscale filters: simultaneous protein recognition and size-selection assays.

A technique for size-selective discrimination of protein analytes was developed by incorporating poly(ethylene glycol) (PEG) lipopolymers into supported lipid bilayers. The membranes also contained biotinylated lipids, which recognized both streptavidin and anti-biotin IgG. By employing various PEG lipopolymer concentrations, clear discrimination against anti-biotin (Mw = 150 000 Da) binding could be observed, which became more pronounced at higher polymer densities. On the other hand, streptavidin (Mw = 52 800) binding to the membrane remained unaffected even at PEG concentrations that were well into the mushroom-to-brush phase transition. These observations were exploited to create an on-chip ligand-receptor binding assay that favored streptavidin binding over anti-biotin by several orders of magnitude in the presence of the lipopolymer. Control experiments revealed that the two proteins are bound to similar extents from a multi-protein analyte solution in the absence of PEG.

Binding, Competitive↗
PubMed2005

Vibration-actuated drop motion on surfaces for batch microfluidic processes.

When a liquid drop is subjected to an asymmetric lateral vibration on a nonwettable surface, a net inertial force acting on the drop causes it to move. The direction and velocity of the drop motion are related to the shape, frequency, and amplitude of vibration, as well as the natural harmonics of the drop oscillation. Aqueous drops can be propelled through fluidic networks connecting various unit operations in order to carry out batch processing at the miniature scale. We illustrate the integration of several unit operations on a chip: drop transport, mixing, and thermal cycling, which are precursor steps to carrying out advanced biological processes at microscale, including cell sorting, polymerase chain reaction, and DNA hybridization.

Journal Article↗
PubMed2004

Ratcheting motion of liquid drops on gradient surfaces.

The motions of liquid drops of various surface tensions and viscosities were investigated on a solid substrate possessing a gradient of wettability. A drop of any size moves spontaneously on such a surface when the contact angle hysteresis is negligible; but it has to be larger than a critical size in order to move on a hysteretic surface. The hysteresis can, however, be reduced or eliminated with vibration that allows the drop to sample various metastable states, thereby setting it to the path of global energy minima. Significant amplification of velocity is observed with the frequency of forcing vibration matching the natural harmonics of drop oscillation. It is suggested that the main cause for velocity amplification is related to resonant shape fluctuation, which can be illustrated by periodically deforming and relaxing the drop at low frequencies.

Journal Article↗
PubMed2002

Guadeloupean parkinsonism: a cluster of progressive supranuclear palsy-like tauopathy.

An unusually high frequency of atypical Parkinson syndrome has been delineated over the last 5 years in the French West Indies. Postural instability with early falls, prominent frontal lobe dysfunction and pseudo-bulbar palsy were common and three-quarters of the patients were L-dopa unresponsive. One-third of all patients seen had probable progressive supranuclear palsy (PSP). This new focus of atypical parkinsonism is reminiscent of the one described in Guam and may be linked to exposure to tropical plants containing mitochondrial complex I inhibitors (quinolines, acetogenins, rotenoids). Two hundred and twenty consecutive patients with Parkinson's syndrome seen by the neurology service at Pointe à Pitre, Guadeloupe University Hospital were studied. Currently accepted operational clinical criteria for Parkinson's syndromes were applied. The pathological findings of three patients who came to autopsy are reported. Fifty-eight patients had probable PSP, 96 had undetermined parkinsonism and 50 had Parkinson's disease, 15 had amyotrophic lateral sclerosis with parkinsonism and one had probable multiple system atrophy. All three PSP patients in whom post-mortem study was performed had early postural instability, gaze palsy and parkinsonian symptoms, followed by a frontolimbic dementia and corticobulbar signs. Neuropathological examination showed an accumulation of tau proteins, predominating in the midbrain. There was an exceptionally large accumulation of neuropil threads in Case 1. Biochemical studies detected a major doublet of pathological tau at 64 and 69 kDa in brain tissue homogenates. All cases were homozygous for the H1 tau haplotype, but no mutation of the tau gene was observed. Clinical, neuropathological and biochemical features were compatible with the diagnosis of PSP, although some unusual pathological features were noted in Case 1. A cluster of cases presenting with atypical parkinsonism is reported. Guadeloupean parkinsonism may prove to be a tauopathy identical or closely related to PSP.

Aged↗