This paper contributes to the debate on how nanosized objects negotiate membrane barriers inside biological cells. The uptake of peptide-modified gold nanoparticles by HeLa cells has been quantified using atomic emission spectroscopy. The TAT peptide from the HIV virus was singled out as a particularly effective promoter of cellular uptake. The evolution of the intracellular distribution of TAT-modified gold nanoparticles with time has been studied in detail by TEM and systematic image analysis. An unusual trend of particles disappearing from the cytosol and the nucleus and accumulating massively in vesicular bodies was observed. Subsequent release of the particles, both by membrane rupture and by direct transfer across the membrane boundary, was frequently found. Ultimately, near total clearing of particles from the cells occurred. This work provides support for the hypothesis that cell-penetrating peptides can enable small objects to negotiate membrane barriers also in the absence of dedicated transport mechanisms.

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Spectrophotometric monitoring of 4-Nitrophenol (4-NP) reduction by Sodium borohydride (NaBH 4) using Gold nanoparticles (GNPs) as a catalyst has been extensively studied, but the stability of GNPs in terms of change in the surface plasmon resonance (SPR) at different temperatures has not been explored. In the present investigation, our aim was to evaluate the SPR stability of GNPs as a catalyst during the reduction of 4-NP at different elevated temperatures i.e., 30-60 °C, and sodium borohydride concentrations. Sensitivity of this degradation process towards concentration of GNPs at a range of temperatures is also evaluated. The spectrophotometric results reveal that up to 45 °C, 12 ± 1.5nm catalyst has a consistent optical density (OD) during whole 4-NP reduction process, which is related to the surface 2 integrity of catalyst atoms. As the temperature approached 50 °C, the OD gradually decreases and shows a blue shift as the reaction proceed which can be related to decrease in particle size or surface dissolution of gold atoms. Present study can find its applications in catalyst designing for the reduction of organic pollutants in industrial waste waters at a range of temperatures.

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