A barrel defines a channel, and has an opening into the channel, and an outlet from the channel. A porous carrier disposed within the channel carries an albumin. A cellulosic stationary phase is disposed within the channel between the carrier and the distal region of the barrel. A lateral flow platform is coupled to the barrel such that a sample pad of the lateral flow platform is in fluid communication with the outlet. A sponge, coupled to a plunger, is configured to hold saliva. The plunger is dimensioned to compress the sponge within the channel such that the saliva is driven (i) out of the sponge and through the carrier, dissolving at least some of the albumin, (ii) with the dissolved albumin, into the stationary phase, and (iii) as an eluate, out of the stationary phase, through the outlet, and onto the sample pad. Other embodiments are also described.