open three - dimensional network , microporous hydrogels containing substrates attached to binding molecules is disclosed . the hydrogel is comprised of a hydrated gel matrix containing substrates embedded in the matrix . the substrates are attached to binding molecules that selectively bind specific molecules that encounter the hydrogel . thus the hydrogel serves to selectively bind out target molecules from an aqueous environment or sample that the hydrogel comes in contact with and concentrates them within the hydrogel .