A system for treating a biological sample, comprising: a. at least one dispenser for dispensing a liquid reagent; b. at least one dispense detector locatable along a dispense path between an outlet of the at least one dispenser and the biological sample, the dispense detector comprising at least two arrays of emitters and corresponding receivers, the space between the emitters and corresponding receivers of at least one array forming a first detection region of the at least one dispense detector, wherein the at least two arrays of emitters and corresponding receivers form the first detection region and a second, different detection region of the dispense detector, wherein the at least two arrays of emitters are each positioned such that light paths between the emitters and corresponding receivers of the at least two arrays are non-parallel to each other, wherein the at least two arrays of emitters are each positioned such that light paths between the emitters and corresponding receivers of the at least two arrays are at about 90 degrees relative to each other, wherein the first and second array of emitters and corresponding receivers are positioned at different locations along the dispense path between the outlet of the dispenser and the biological sample; and c. a dispense detection unit configured to receive a signal from the at least one dispense detector during a dispensing event and output a detected dispense volume of the liquid reagent, wherein the dispense detection unit is configured to calculate the detected dispense volume by integrating over time the product of the signal and a velocity of the liquid reagent passing through the dispense detector during the dispensing event to generate the detected dispense volume for the liquid reagent delivered to the biological sample, wherein the dispense detector provides at least two different signals, one signal from the at least first array of emitters and corresponding receivers and one signal from the at least second array of emitters and corresponding receivers, that are utilized by the dispense detection unit to determine the velocity of the dispensing event. a. at least one dispenser for dispensing a liquid reagent; b. at least one dispense detector locatable along a dispense path between an outlet of the at least one dispenser and the biological sample, the dispense detector comprising at least two arrays of emitters and corresponding receivers, the space between the emitters and corresponding receivers of at least one array forming a first detection region of the at least one dispense detector, wherein the at least two arrays of emitters and corresponding receivers form the first detection region and a second, different detection region of the dispense detector, wherein the at least two arrays of emitters are each positioned such that light paths between the emitters and corresponding receivers of the at least two arrays are non-parallel to each other, wherein the at least two arrays of emitters are each positioned such that light paths between the emitters and corresponding receivers of the at least two arrays are at about 90 degrees relative to each other, wherein the first and second array of emitters and corresponding receivers are positioned at different locations along the dispense path between the outlet of the dispenser and the biological sample; and c. a dispense detection unit configured to receive a signal from the at least one dispense detector during a dispensing event and output a detected dispense volume of the liquid reagent, wherein the dispense detection unit is configured to calculate the detected dispense volume by integrating over time the product of the signal and a velocity of the liquid reagent passing through the dispense detector during the dispensing event to generate the detected dispense volume for the liquid reagent delivered to the biological sample,