Nanoparticle Tracking Analysis (NTA) It is a method of tracking and analyzing individual nanoparticlesBrownian motionA technique for measuring particle size and concentration. Although NTA can provide information on the particle size distribution and concentration of nanoparticles, it cannot provide traditional LOD due to the following reasons:

NTA relies on light scattering to detect particles, and the scattering intensity of different particles varies greatly, especially when there is polydispersity in the sample. The scattering intensity of large particles often blocks the signal of small particles, resulting in larger particle size and lower concentration. Therefore, particles of different sizes may produce different signal intensities, making it difficult to define a unified LOD.

2. Influence of particle concentration：

The detection range of NTA is limited by particle concentration. When the concentration is too high, the mutual interference between particles of different sizes can lead to inaccurate analysis; When the concentration is too low, the inability to detect a sufficient number of particles can also cause sampling errors and random errors. Therefore, it is difficult to determine a low concentration detection limit that is applicable to all samples (the LOD of different samples may vary). Meanwhile, even for clear samples such as purified extracellular vesicles, their linear concentration range is usually only concentrated in one order of magnitude^[1][2].

3. Limitations of Optical Systems：

The detection sensitivity of NTA also depends on the resolution and parameter settings of the optical system, especially when detecting small-sized nanoparticles. The limitations of optical resolution make it difficult to define a unified LOD for NTA technology.

Due to these factors, NTA provides a relatively quantitative result in characterizing particle size and concentration, rather than an absolute low detection limit.

Dynamic Light Scattering (DLS) Essentially, it is a method for measuring the fitted particle size of nanoparticles or macromolecules in suspension. Due to the dependence of DLS on the intensity of particle scattered light, there are usually certain limitations in determining the detection limit LOD

1. Dependence of scattering intensity：

DLS measures the average Brownian motion of all particles in the sample, therefore, the scattered signals generated by smaller particles or low concentration particles may be overwhelmed by background noise and difficult to accurately detect. Generally speaking, the LOD of DLS requires higher particle concentration and particle size range than commonly understood.

2Multi dispersibility and concentration effects：

In multi dispersed systems or samples with low concentrations, DLS is difficult to distinguish particles of different sizes, making it difficult to accurately provide a unified LOD. Specifically, the principle of DLS assumes that the samples have a monodisperse size distribution (PDI<0.1 or even smaller), which is not suitable for polydisperse samples (such as most biological samples); In addition, although the DLS principle cannot calculate concentration data, DLS measurement requires concentration, and inappropriate sample concentrations can lead to significant deviations in particle size, which are easily overlooked.

The Resistive Pulse Sensing (RPS) method can provide a definite LOD in characterizing the particle size and concentration of nanoparticles.RPS measures the size and quantity of particles by detecting the resistance changes caused by individual particles passing through micropores.Because it is a single particleThe detection method, RPS, can provide very low detection limits under certain conditions, especially suitable for detecting low concentration particles in diluted samples.LOD is usually associated with the size of micropores or nanopores and the level of noise in the sample.

Dependent on aperture size：

LOD is usually associated with the size of micropores and the level of noise in the sample. A smaller aperture can detect smaller particles, but it may also increase background noise, thereby affecting the accuracy of LOD.

Dependent on noise level：

The conductivity of the sample, the surface characteristics of the pores, and the stability of the background current all affect the detection limit. If the background noise is low, RPS can detect very small and low concentration particles, thereby achieving lower LOD.

Generally speaking, if background noise can be well controlled and appropriate aperture and measurement conditions can be selected in RPS testing experiments, lower LOD can be achieved.This makes RPS technology significantly advantageous in certain fields, such as detecting diluted biological particles or nanoparticles.