Methods of cross-linking polypeptide molecules are provided, where such methods include combining a cross-linking agent and polypeptide molecules in a solution under conditions suitable for a cross-linking reaction to occur. Also provided are preparations of cross-linked polypeptide molecules, where the polypeptide molecules are cross-linked by essentially unbranched cross-linking groups of at least 40 contiguous atoms. Further provided are test chemistry matrices and methods of making the same, where the matrices include a redox cofactor, an agent capable of eliciting a change in at least one measurable property of an indicator reagent in the presence of redox equivalents, an indicator reagent, and a preparation of cross-linked polypeptide molecules as described herein. Test elements and methods of using the same to diagnose diseases such as diabetes also are provided, where the test elements include a test chemistry matrix as described herein.
