Resistive pulse sensing

Resistive pulse sensing (RPS) is the generic, non-commercial term given for the well-developed technology used to detect, and measure the size of, individual particles in fluid.

Resistive pulse sensing is also known as the electrical zone sensing technique, reflecting its fundamentally electrical nature, which distinguishes it from other particle sizing technologies such as the optically-based dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA).

[2] The basic design principle underlying resistive pulse sensing is shown in Fig.

The fluids most commonly used are water containing some amount of dissolved salts, sufficient to carry an electrical current.

The change in the electrical resistance as a particle passes through a constriction is shown schematically in Fig.

is a factor that depends on the detailed geometry of the constriction and the electrical conductivity of the working fluid.

The original Coulter counter was originally designed using a special technology to fabricate small pores in glass volumes, but the expense and complexity of fabricating these elements means they become a semi-permanent part of the analytic RPS instrument.

There was therefore significant interest in applying the fabrication techniques developed for microfluidic circuits to RPS sensing.

This translation of RPS technology to the microfluidic domain enables very small constrictions, well below effective diameters of 1 micron; this therefore extends the minimum detectable particle size to the deep sub-micron range.

Using microfluidics technology also allows the use of inexpensive cast plastic or elastomer parts for defining the critical constriction component, which also become disposable.

The use of a disposable element eliminates concerns about sample cross-contamination as well as obviating the need for time-consuming cleaning of the RPS instrument.

Fig. 1. Schematic diagram for resistive pulse sensing, in which particles, suspended in a weakly conducting fluid, flow through a nanoconstriction, and are sensed electrically by electrodes placed on either side of the nanoconstriction.
Fig. 2. Line drawing of resistive pulse sensing time-based schematic data. A single particle passing through a constriction causes a momentary change in the electrical resistance, proportional to the particle volume.