A method comprising: mounting a substrate comprising a biological sample on a base of a substrate holder, the substrate holder comprising: the base configured to receive a substrate, the base comprising non-movable tabs extending from at least two of its sidewalls; and a cover configured to mateably engage with the base, the cover defining an opening configured to receive a removable insert, the cover comprising movable tabs configured to engage with the non-movable tabs of the base, wherein each movable tab comprises first and second contacting surfaces configured to engage with a corresponding non-movable tab of the base, the first contacting surface configured to engage with the corresponding non-movable tab such that the cover and the base are engaged in an unlocked state, and wherein the second contacting surface is configured to engage with the corresponding non-movable tab such that the cover and the base are engaged in a releasably locked state, inserting the removable insert in the opening of the cover; engaging the first contacting surface of the movable tab with a surface of the non-movable tab while placing the cover on the base such that the cover and the base are engaged in the unlocked state; and adjusting a position of the removable insert. mounting a substrate comprising a biological sample on a base of a substrate holder, the substrate holder comprising: the base configured to receive a substrate, the base comprising non-movable tabs extending from at least two of its sidewalls; and a cover configured to mateably engage with the base, the cover defining an opening configured to receive a removable insert, the cover comprising movable tabs configured to engage with the non-movable tabs of the base, wherein each movable tab comprises first and second contacting surfaces configured to engage with a corresponding non-movable tab of the base, the first contacting surface configured to engage with the corresponding non-movable tab such that the cover and the base are engaged in an unlocked state, and wherein the second contacting surface is configured to engage with the corresponding non-movable tab such that the cover and the base are engaged in a releasably locked state, the base configured to receive a substrate, the base comprising non-movable tabs extending from at least two of its sidewalls; and a cover configured to mateably engage with the base, the cover defining an opening configured to receive a removable insert, the cover comprising movable tabs configured to engage with the non-movable tabs of the base, wherein each movable tab comprises first and second contacting surfaces configured to engage with a corresponding non-movable tab of the base, the first contacting surface configured to engage with the corresponding non-movable tab such that the cover and the base are engaged in an unlocked state, and wherein the second contacting surface is configured to engage with the corresponding non-movable tab such that the cover and the base are engaged in a releasably locked state, inserting the removable insert in the opening of the cover; engaging the first contacting surface of the movable tab with a surface of the non-movable tab while placing the cover on the base such that the cover and the base are engaged in the unlocked state; and adjusting a position of the removable insert. <EOS>