A method and apparatus for using arrays of polymers each having a pattern of features over a corresponding array region on a surface of a flexible elongated web. In this method each array region may be exposed to a corresponding continuous volume of a sample fluid. A method and apparatus are also provided for reading arrays disposed along a surface of a flexible elongated web. In one such method the web with the arrays thereon may be transported in a lengthwise direction past a reading location at which a characteristic of the features is read, while restraining the web on both surfaces on either side of the reading location to assist in maintaining the reading location flat.