Self-supporting hydrogel stamps for the microcontact printing of proteins

In this work we explore a new hydrogel stamp material obtained from polymerizing 2-hydroxyethyl acrylate and poly(ethylene glycol) diacrylate in the presence of water for the microcontact printing of proteins directly on gold substrates and by covalent coupling to self-assembled monolayers of alkanethiols. At high cross-link density, the hydrogel is rigid, hydrophilic, and with a high buffer holding capacity to enable the unsupported printing of protein patterns homogeneously and reproducibly, with micrometer-range precision. The stamps were used to print antibodies to human parathyroid hormone, which were shown using immunoassay tests to retain their biological function with binding capacities comparable to those of solution-adsorbed antibodies.

On the response of a label-free interferon-γ immunosensor utilizing electrochemical impedance spectroscopy

The research on our flow-injection, label-free, non-faradaic impedimetric immunosensor for interferon-gamma (IFN-gamma) has been extended. The sensor is prepared by immobilization of anti-IFN-gamma antibodies on a self-assembled monolayer (SAM) of acetylcysteine, deposited on polycrystalline gold. A multi-frequency impedance method is described, which allows time-resolved measurement of Nyquist plots. To these plots, an equivalent circuit was fitted, which is discussed in terms of a two-layer structure (inner and outer layer) of the interfacial region. Because binding of IFN-gamma mainly causes a decrease of Q (a constant-phase element), this element is considered as the outer layer. Several aspects of the impedimetric sensor response are studied, including the dependence on detection frequency, target concentration and applied dc potential. For quantitative detection of IFN-gamma, an optimum of the signal-to-noise (S/N) ratio of the out-of-phase impedance component (Z'') was found at about 100 Hz. At a dc-potential of +0.2 V versus a saturated calomel reference electrode, the sensor response is higher than at 0.0 V. Logarithmic dose-response curves of IFN-gamma in the concentration range of 10(-18) to 10(-9) M were obtained using two procedures: by successive injections over a single electrode, and by using freshly prepared electrodes for each measurement. Using the latter method, the repeatability is impaired. The need for in situ complementary techniques for a correct interpretation of the studied parameters is discussed.

Light-harvesting ionic dendrimer porphyrins as new photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising therapeutic modality for treatment of solid tumors. In this study, third-generation aryl ether dendrimer porphyrins (DPs) with either 32 quaternary ammonium groups (32(+)DPZn) or 32 carboxylic groups (32(-)DPZn) were evaluated as a novel, supramolecular class of photosensitizers for PDT. DPs showed a different cell-association profile depending on the positive or negative charge on the periphery, and both DPs eventually localized in membrane-limited organelles. In contrast, protoporphyrin IX (PIX), which is a hydrophobic and relatively low molecular weight photosensitizer used as a control in this study, diffused through the cytoplasm except the nucleus. Confocal fluorescent imaging using organelle-specific dyes indicated that PIX induced severe photodamage to disrupt membranes and intracellular organelles, including the plasma membrane, mitochondrion, and lysosome. On the other hand, cells treated with DPs kept the characteristic fluorescent pattern of such organelles even after photoirradiation. However, notably 32(+)DPZn achieved remarkably higher (1)O(2)-induced cytotoxicity against LLC cells than PIX. Furthermore, both dendrimer porphyrins had far lower dark toxicity as compared with PIX, demonstrating their highly selective photosensitizing effect in combination with a reduced systemic toxicity.