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Silicion nitride is normally used as a sensitive surface for silicon-based transducers like ISFETs or light-addressable potentiometric sensors (LAPS), because of its capability to sense preferentially H+ions. We have investigated Si/SiO2/Si3N4heterostructures and studied the surface layers via an atomic force microscope (AFM) and a PAB (potentiometric alternating biosensor) system; in particular, the latter method allows the investigation of the temporal behaviour after input pH steps. A suitable experimental set-up has been installed in order to optimize the pH changes in the measuring chamber; data have been acquired corresponding to unit pH steps. The resulting time constants are calculated and the data related to the surface layer images acquired by the AFM. A correlation between different observed responses and the corresponding surfaces characteristics has been established.

The macronuclear chromatin of the ciliate Blepharisma japonicum was studied by electrophoretic and immunological techniques as well as by micrococcal nuclease digestion and circular dichroism spectroscopy. Under these experimental conditions the macronuclear chromatin of B. japonicum was compared to that of Tetrahymena pyriformis. Data obtained through this analysis showed that the macronuclear chromatin of B. japonicum is structurally more relaxed than that of T. pyriformis. A perchloric acid soluble polypeptide, referred to as P3, is the only polypeptide of B. japonicum chromatin to appear immunologically related to the H1 histone of T. pyriformis. It is suggested that this P3 polypeptide in B. japonicum should be considered functionally equivalent to the T. pyriformis H1 histone, even though it differed from it both in terms of molecular mass and relative concentration.