Observations of Tunable Resistive Pulse Sensing for Exosome Analysis: Improving System Sensitivity and Stability

Abstract

Size distribution and concentration measurements of exosomes are essential when investigating their cellular function and uptake. Recently, a particle size distribution and concentration measurement platform known as tunable resistive pulse sensing (TRPS) has seen increased use for the characterization of exosome samples. TRPS measures the brief increase in electrical resistance (a resistive pulse) produced by individual submicrometer/nanoscale particles as they translocate through a size-tunable submicrometer/micrometer-sized pore, embedded in an elastic membrane. Unfortunately, TRPS measurements are susceptible to issues surrounding system stability, where the pore can become blocked by particles, and sensitivity issues, where particles are too small to be detected against the background noise of the system. Herein, we provide a comprehensive analysis of the parameters involved in TRPS exosome measurements and demonstrate the ability to improve system sensitivity and stability by the optimization of system parameters. We also provide the first analysis of system noise, sensitivity cutoff limits, and accuracy with respect to exosome measurements and offer an explicit definition of system sensitivity that indicates the smallest particle diameter that can be detected within the noise of the trans-membrane current. A comparison of exosome size measurements from both TRPS and cryo-electron microscopy is also provided, finding that a significant number of smaller exosomes fell below the detection limit of the TRPS platform and offering one potential insight as to why there is such large variability in the exosome size distribution reported in the literature. We believe the observations reported here may assist others in improving TRPS measurements for exosome samples and other submicrometer biological and nonbiological particles.

Urinary Extracellular Vesicles: Potential Biomarkers of Renal Function in Diabetic Patients

“…Principles of the technique were described in [15–18]. To detect particles in the range 60–480 nm the pores labeled NP150 were used.…”

Extracellular Vesicles: Isolation Methods

“…Label-free characterization techniques are preferred when the analysis has to be done on the entire EV population independently of their surface biomarkers. The most common label-free methods applied to the characterization of isolated EVs in solution are nanoparticle tracking analysis (NTA), [70] resistive pulse sensing (RPS), [71] surface plasmon resonance (SPR), [72] and Raman spectroscopy. [73] Emerging techniques enable the characterization of single EV like surface enhanced Raman spectroscopy.…”

Single particle analysis: Methods for detection of platelet extracellular vesicles in suspension (excluding flow cytometry)

“…For example, it was recently used as the standard method to evaluate different isolation procedures on exosome yield and size, 37 and has been highlighted as an accepted characterization method in a ISEV position paper dating to 2012 38 . Nevertheless, as with all techniques, TRPS has its own limitations that have been called out by several studies, such as minimum detectable size 32 and maximum throughput 35 that should be kept in mind. At higher throughputs (or with particles larger than the pore diameter), pore clogging can occur at unacceptable rates.…”