NOVELTY - Production of a porous nanoscale membrane comprises applying a nanoscale film to one side of a substrate, the nanoscale film comprising a semiconductor material; masking an opposite side of the substrate; etching the substrate, beginning from the masked opposite side of the substrate, and continuing until a passage is formed through the substrate, exposing the film on both sides to form a membrane; and simultaneously forming spaced pores in the membrane.    USE - The method is for production of a porous nanoscale membrane or nanoporous semiconductor membrane for use in a filter device useful for a microfluidic flow device and a dialysis machine; a fuel cell; and filtering nanoscale products from proteins, viruses, bacteria, a cell line, an isolated cell, a protoplast, a fungus, a parasite, colloidal nanoparticles, organic molecular systems, inorganic nanoparticles, dissolved ions, drugs, dyes, sugars, aqueous salts, metals, semiconductors, or pharmaceutical compounds, where product to be filtered is a charged species. The porous nanoscale membrane is used for a bioreactor device for carrying out a biological reaction for use in screening an agent for its activity on a cell (claimed). It is used as electron microscopy substrates, and useful in macromolecular filtration.    ADVANTAGE - The method provides porous nanoscale membrane having smooth surfaces, high pore densities (between 106-1012 cm-2), and high aspect ratio dimensions (a lateral length to thickness aspect ratio that is more than 10000-1). It is reproducible and cost-effective.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a nanoporous semiconductor membrane exposed on its opposite sides, and having an average thickness of less than 500 nm;    (2) a filter device comprising a nanoscale membrane(s);    (3) a microfluidic flow device comprising the filter device;    (4) a dialysis machine comprising the filter device;    (5) a fuel cell comprising the nanoscale membrane, which selectively passes positively charged species;    (6) a method of filtering nanoscale products comprising providing nanoscale membrane(s); and passing a fluid, containing product(s) to be filtered, through the membrane, where objects larger than a maximum pore size are precluded from passing through pores of the membrane;    (7) a bioreactor device for carrying out a biological reaction comprising a substrate comprising well(s), each having a bottom and sidewall(s), where bottom comprises nanoscale semiconductor membrane having pores extending between its opposite sides; and a biological reaction medium in the well(s), and greater than or equal to2 reactants individually from compounds or organisms;    (8) a method of performing a biological reaction comprising providing a bioreactor device; carrying out the biological reaction in the well(s) forming an end product; and passing spent biological reaction medium from the well(s) through the nanoscale membrane, where end product is passed through the nanoscale membrane or retained in the well(s); and    (9) a method of screening an agent for its activity on a cell, comprising providing an agent; performing biological reaction by introducing the agent into the biological reaction medium comprising the cell; and analyzing the cell or the end product to identify the activity of the agent on the cell.    DESCRIPTION OF DRAWING(S) - The figure schematically illustrates the manufacture of a porous nanoscale semiconductor membrane.