Devices and methods are provided for precise production of arrays of microspots. A pulse jetting device is employed having a capillary of micron dimensions, with a portion of the capillary proximal to the jetting orifice circumferentially surrounded by a piezoelectric transducer. By appropriate design of the capillary, orifice and piezoelectric transducer, droplets can be formed on a surface, separated by as little as 80 microns center-to-center, and having at least about a 15 micron spacing at the border. The subject substrate arrays can be used for providing miniaturized arrays of reagents, such as nucleic acids, for detecting the presence of homologous sequences in a sample.