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Gold nanoparticles of 20-100 nm diameter were synthesized within HEK-293 (human embryonic kidney), HeLa (human cervical cancer), SiHa (human cervical cancer), and SKNSH (human neuroblastoma) cells. Incubation of 1 mM tetrachloroaurate solution, prepared in phosphate buffered saline (PBS), pH 7.4, with human cells grown to approximately 80% confluency yielded systematic growth of nanoparticles over a period of 96 h. The cells, stained due to nanoparticle growth, were adherent to the bottom of the wells of the tissue culture plates, with their morphology preserved, indicating that the cell membrane was intact. Transmission electron microscopy of ultrathin sections showed the presence of nanoparticles within the cytoplasm and in the nucleus, the latter being much smaller in dimension. Scanning near field microscopic images confirmed the growth of large particles within the cytoplasm. Normal cells gave UV-visible signatures of higher intensity than the cancer cells. Differences in the cellular metabolism of cancer and noncancer cells were manifested, presumably in their ability to carry out the reduction process.

Creation of affordable materials for constant release of silver ions in water is one of the most promising ways to provide microbially safe drinking water for all. Combining the capacity of diverse nanocomposites to scavenge toxic species such as arsenic, lead, and other contaminants along with the above capability can result in affordable, all-inclusive drinking water purifiers that can function without electricity. The critical problem in achieving this is the synthesis of stable materials that can release silver ions continuously in the presence of complex species usually present in drinking water that deposit and cause scaling on nanomaterial surfaces. Here we show that such constant release materials can be synthesized in a simple and effective fashion in water itself without the use of electrical power. The nanocomposite exhibits river sand-like properties, such as higher shear strength in loose and wet forms. These materials have been used to develop an affordable water purifier to deliver clean drinking water at US $2.5/y per family. The ability to prepare nanostructured compositions at near ambient temperature has wide relevance for adsorption-based water purification.hybrid | green | appropriate technology | frugal science | developing world S afe drinking water is a significant, but simple indicator of development. Its availability at point of use can save over 2 million human lives (1) (of the 3.575 million deaths caused by water, sanitation, and hygiene issues, 42.6% are due to diarrhea alone: 3.575 million × 0.426 = 1.523 million lives), can avoid over 2 billion diarrheal infections (2), and can contribute over $4 billion to the global gross domestic product (3) (formula used: Σ (number of deaths attributed to diarrhea in each country × corresponding country's per capita gross domestic product). Considering the challenges associated with traditional disinfectants (4), solutions based on state-of-the-art science and technology hold the key for safe drinking water (5) and novel approaches are being looked at (6, 7). It has been long known that silver, especially in nanoparticle form, is an effective disinfectant and works for a wide spectrum of bacteria and viruses (8, 9). Numerous approaches are available for the synthesis of biocidal silver nanoparticles or colloids, including the use of matrices (10-12). The biocidal property of silver nanoparticles, usually in the size range of 10-20 nm, is attributed to the release of trace quantities of silver ions in water (13-16), which, although being sufficient for microorganism killing, does not exhibit toxicity to humans (17,18). [Toxicity due to silver nanoparticles themselves is also known (16)]. Although a number of silver-based biocidal compositions have been synthesized, those have not been able to reach the masses in large volumes (e.g., silver nanoparticleloaded ceramic candles) (19). Massive deployment has been hampered due to the following reasons: (a) Drinking water contains many species (e.g., inorganic ions and organics) that anchor on the sur...