A glass slide, silicon wafer, or glass bead on which are deposited biomolecules or other material in a regular micro-scale pattern to enable automated simultaneous multiple assays of target substances or activities. Microarrays are powerful analytical tools with wide-ranging applications, including the analysis of gene expression and of genetic variation. They can be designed to carry small DNA molecules (see dna microarray), proteins (e.g. antibodies or antigens), carbohydrates or other organic molecules, or even individual living cells. These reagents are applied to the substrate in a regular microscopic grid pattern, each being identified by its unique coordinate, or address, on the grid. Interaction of a target substance (e.g. an antibody or a complementary nucleic acid) with a particular address on the microarray activates or attaches a label (e.g. a fluorescent dye). The microarray can then be ‘read’ by a scanner, which automatically assesses the amount of label at each address, and hence the amount of target substance. Even smaller-scale nanoarrays have been developed, to increase further the scope and speed of this technology. These are made using a form of high-precision lithography, and employ atomic force microscopy to detect direct interactions between individual molecules with nanometre resolution. No label is required, although some applications do use reporter labelling. Advances in next-generation DNA sequencing mean that it is replacing microarray analysis for some applications, particularly where sensitivity and accuracy are at a premium, e.g. for assessing rare or previously unknown sequence variants (see RNA sequencing). See Feature.