Reagent well having a retention feature for retaining a lyophilized reagent

An article for performing a reaction comprising:

• a reagent well including a side wall, a bottom wall, and an open upper end defined by a top surface;
• a lyophilized reagent disposed within the reagent well;
• and
• a retention feature that is not integral with the reagent well, the retention feature comprising a fingered collar fixed to the side wall at or proximal to the open upper end and comprising one or more flexible fingers extending into the well, wherein each of the one of more fingers extends toward an axial center of the well, wherein the retention feature is inserted into the open upper end of the well and fixed to the side wall above the lyophilized reagent, wherein the retention feature defines an opening that is smaller than the diameter of the lyophilized reagent, such that the retention feature retains the lyophilized reagent within the reagent well, and wherein the opening is sized to permit an end of a pipette tip to be inserted into the well.