The present invention provides integrated sample preparation systems and stabilized enzyme mixtures. In particular, the present invention provides microfluidic cards configured for processing a sample and generating DNA libraries that are suitable for use in sequencing methods (e.g., next generation sequencing methods) or other suitable nucleic acid analysis methods. The present invention also provides stabilized enzyme mixtures containing an enzyme (e.g., an enzyme used in whole genome amplification), BSA, and a sugar. Such enzyme mixtures may be lyophilized and stored at room temperature without significant loss of enzyme activity for months.