Abstract: Microporous solid phase materials that are suitable for lateral flow and other assays for detecting the presence of analytes in test samples, that are stable under variations in humidity and, even after storage for extended periods of time, can form stable covalent bonds with molecules containing a free primary or secondary amine group or sulfhydryl group are described. The invention further concerns chemically derivatized solid phase materials, and conjugates comprising such materials. Examples of lateral flow devices for the quantitative or semi-quantitative determination of an analyte in a biological sample are described.