A carrier for holding a biological sample includes a substrate. The substrate is configured to engage a first sample chamber comprising a first opening characterized by a first opening diameter or a second sample chamber comprising a second opening characterized by a second opening diameter that is greater than the first opening diameter. The substrate includes an upper portion, a lower portion, and an intermediate portion disposed between the upper portion and the lower portion. The lower portion is disposed below the upper portion and comprises a bottom surface configured to receive a biological sample. The intermediate portion is characterized by a first substrate diameter and the lower portion is characterized by a second substrate diameter that is less than the first substrate diameter.