The protein resistance of poly(N-isopropylacrylamide) brushes grafted from silicon wafers was investigated as a function of the chain molecular weight, grafting density, and temperature. Above the lower critical solution temperature (LCST) of 32°C, the collapse of the water swollen chains, determined by ellipsometry, depends on the grafting density and molecular weight. Ellipsometry, radio assay, and fluorescence imaging demonstrated that, below the lower critical solution temperature, the brushes repel protein as effectively as oligoethylene oxide terminated monolayers. Above 32°C, very low levels of protein adsorb on densely grafted brushes, and the amounts of adsorbed protein increase with decreasing brush grafting densities. Brushes that do not exhibit a collapse transition also bind protein, even though the chains remain extended above the LCST. These findings suggest possible mechanisms underlying protein interactions with end-grafted PNIPAM brushes.
Excess iron is found in brain nuclei from neurodegenerative patients (with Parkinson's, Alzheimer's and Huntington's diseases) and also in the liver and spleen of cirrhosis, hemochromatosis and thalassaemia patients. Ferritin, the iron-storing protein of mammals, is known to darken T(2)-weighted MR images. Understanding NMR tissue behavior may make it possible to detect those diseases, to follow their evolution and finally to establish a protocol for non-invasive measurement of an organ's iron content using MRI methods. In this preliminary work, the MR relaxation properties of embalmed iron-containing tissues were studied as well as their potential correlation with the iron content of these tissues. Relaxometric measurements (T(1) and T(2)) of embalmed samples of brain nuclei (caudate nucleus, dentate nucleus, globus pallidus, putamen, red nucleus and substantia nigra), liver and spleen from six donors were made at different magnetic fields (0.00023-14 T). The influence of the inter-echo time on transverse relaxation was also studied. Moreover, iron content of tissues was determined by inductively coupled plasma atomic emission spectroscopy. In brain nuclei, 1/T(2) increases quadratically with the field and depends on the inter-echo time in CPMG sequences at high fields, both features compatible with an outer sphere relaxation theory. In liver and spleen, 1/T(2) increases linearly with the field and depends on the inter-echo time at all fields. In our study, a correlation between 1/T(2) and iron concentration is observed. Explaining the relaxation mechanism for these tissues is likely to require a combination of several models. The value of 1/T(2) at high field could be used to evaluate iron accumulation in vivo. In the future, confirmation of those features is expected to be achieved from measurements of fresh (not embalmed) human tissues.
Oligo(ethylene glycol) films are known to be very efficient at reducing the nonspecific adsorption of biomacromolecules on surfaces, but they often show a tendency to decrease drastically the rate of heterogeneous electron transfer at the modified surface, making them unsuitable for electrochemical biosensing. In this work, the heterogeneous electron transfer across the self-assembled monolayer of a short thiolated oligo(ethylene glycol) is investigated using four redox systems: [Fe(CN) 6 ] 3−/4− , [Ru(NH 3 ) 6 ] 3+/2+ , Fc(MeOH) 2 +/0 , and [IrCl 6 ] 2−/3− . Fast electrontransfer kinetics are evidenced in all cases except the ferri/ferrocyanide couple, for which the electron transfer is completely suppressed. Interfacial characterizations by means of spectroscopic ellipsometry, electrochemical desorption experiments, and capacity measurements indicate that the film consists of a fairly hydrated single monolayer with a surface concentration of 4.1 × 10 −10 mol cm −2 . The peculiar behavior of [Fe(CN) 6 ] 3−/4− is discussed in terms of the hydration properties of both the monolayer and the electroactive anions. Interestingly, the self-assembled monolayer exhibits the desired antifouling properties against protein adsorption, tested with bovine serum albumin, making this system a promising platform for the development of electrochemical biosensors.
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