Counting particles using an electrical differential counter
This disclosure relates to methods and devices to count particles of interest, such as cells. The methods include obtaining a fluid sample that may contain particles of interest; counting all types of particles in a portion of the sample using a first electrical differential counter to generate a first total; removing any particles of interest from the portion of the fluid sample; counting any particles remaining in the portion of the fluid sample using a second electrical differential counter after the particles of interest are removed to generate a second total; and calculating a number of particles of interest originally in the fluid sample by subtracting the second total from the first total, wherein the difference is the number of particles of interest in the sample. These methods and related devices can be used, for example, to produce a robust, inexpensive diagnostic kit for CD4+ T cell counting in whole blood samples.
1. A device comprising:
a microfluidic chip defining a channel including an inlet and an outlet;
a capture chamber arranged along the channel between the inlet and the outlet, wherein the capture chamber comprises a surface functionalized or coated with binding agents or binding moieties selected to specifically bind to a first type of particle of interest from fluid flowing through the channel;
a first electrical differential counter arranged to count all types of particles in a fluid flowing into the capture chamber and to count all types of particles remaining in the fluid flowing out of the capture chamber, wherein a portion of the channel defines a flow path that extends in a loop from the first electrical differential counter through the capture chamber and back to the first electrical differential counter; and
a computer in electronic communication with the first electrical differential counter, wherein the computer calculates a number of the first type of particle of interest based on a difference between signals from the first electrical differential counter.
2. The device of claim 1 , further comprising a pump system in fluid communication with the channel, wherein the pump system is operable in a first mode to cause fluid to flow in a first direction in the channel past the first electrical differential counter and
operable in a second mode to cause fluid to flow in a second direction in the channel opposite the first direction and back to the first electrical differential counter.