Nanoparticle analysis methods do not all measure the same thing. In biological applications, four approaches are often compared: NTA, TRPS, DLS and ILM. However, these technologies do not answer the same questions and are not suited to the same sample constraints.
Before choosing an instrument, it is therefore essential to understand what each method actually measures: size, concentration, surface charge, fluorescence, analysis speed, sample volume or level of preparation required. This distinction helps avoid misleading comparisons and supports the selection of a technology that is truly adapted to laboratory use.
Nanoparticle analysis methods : Understanding what each technology measures
The first distinction concerns the ability to measure particles individually. Some methods analyze a population as a whole, while others track or count particles one by one.
DLS, or dynamic light scattering, measures fluctuations in light scattered by the entire illuminated volume. It provides an intensity-weighted average size. This method is fast, requires little preparation and is well suited to clean, monodisperse samples.
Its main limitation is that it does not provide particle concentration. It is also strongly influenced by larger particles or aggregates. A few larger elements can be enough to significantly shift the result.
NTA, TRPS and ILM, on the other hand, work at the single-particle level. They can therefore provide particle counting and concentration, but with different physical principles, constraints and uses.
Comparing the four analysis approaches
| Method | Measurement principle | Particle counting | Charge | Fluorescence | Typical volume | Measurement time | Main constraint |
| DLS | Scattered light fluctuations across the whole volume | No | No | No | Low preparation | Fast | Average biased by large particles |
| NTA | Brownian motion and scattered light | Yes | On equipped platforms | Yes, on equipped platforms | Hundreds of µL | A few minutes, with preparation | Dilution and acquisition settings |
| TRPS | Ionic current drop through a nanopore | Yes | Yes | No | Tens to hundreds of µL | A few minutes, depending on the pore | Pore clogging and electrolyte required |
| ILM | Interference between scattered and incident light | Yes | No | No | 5 to 10 µL | Less than one minute | Around 80 nm threshold, no charge or fluorescence |
This table shows that selection cannot be based on a single criterion. One technology may offer good resolution but require more preparation. Another may be faster but unable to provide charge or fluorescence information.
Lower limits should also be interpreted carefully. For optical methods, the detection threshold depends not only on diameter, but also on refractive index and particle type. A reference bead does not necessarily scatter light like a biological particle of the same size.
Choosing a method according to the question
The choice of an analysis method should start from the scientific or operational question.
If the goal is simply to determine the average size of a clean and monodisperse preparation, DLS may be sufficient. It is fast, economical and well suited to this type of use. However, it does not provide the number of particles per milliliter.
If the laboratory needs concentration and size distribution, a single-particle method is required. NTA, TRPS and ILM can meet this need, but the final choice will depend on size range, available volume and workflow.
If the priority is surface charge, TRPS becomes relevant, as do some NTA platforms equipped for zeta potential measurement. If the objective is to identify particles carrying a marker, a fluorescence-capable solution is required, such as an equipped NTA platform or a nano-flow cytometry technology.
When the critical population is below 80 nm, ILM is not suitable. NTA or TRPS should then be considered. Conversely, when many samples need to be processed quickly during a process, ILM may be useful because of its speed, low volume and lack of complex parameter settings.
Adapting the instrument to biological constraints
Biological nanoparticles do not always behave like reference particles. Extracellular vesicles, viral vectors, viruses or debris present in a sample can have very different optical properties.
This is why a published detection threshold should never be read in isolation. An instrument capable of detecting a highly scattering reference particle will not necessarily deliver the same performance with a more weakly scattering biological particle.
Polydispersity is another important point. When a sample contains several populations of different sizes, some technologies can better reveal aggregates, debris or smaller particles. A method that images or tracks individual particles can sometimes provide a clearer view of what is actually present in the sample.
Preparation also plays a major role. Dilution, acquisition settings, pore selection, electrolyte use or handling a static droplet do not require the same time or the same level of expertise.
Combining several methods in one laboratory
No technology dominates across all criteria. The most detailed methods may be slower or more demanding. The fastest methods may provide less information.
In many laboratories, the most realistic solution is therefore to combine two instruments. A fast method can absorb routine analyses, while a more complete method can be reserved for more specific questions: charge measurement, fluorescence, fine resolution or subpopulation identification.
The choice depends on the main bottleneck. If the issue is throughput, it may be logical to start with a fast and simple technology. If the difficulty lies in resolution, particle identity or charge, a more complete platform will take priority.
This combination avoids using a heavy instrument for simple and repetitive measurements, while keeping a more advanced solution available for analyses that require it.
Nanoparticle analysis methods : Selecting a method according to real use
The choice between NTA, TRPS, DLS and ILM should be driven by the laboratory’s real needs. The first step is to define whether the objective is average size, concentration, surface charge, fluorescence information or fast process monitoring.
DLS may be sufficient for a monodisperse preparation when particle concentration is not required. NTA is relevant when individual particle tracking is needed and, depending on equipment, fluorescence or zeta potential may be required. TRPS is useful for single-particle measurements with access to charge, but it involves nanopore-related constraints. ILM enables fast counting on low sample volume, but remains limited by its detection threshold and the absence of charge or fluorescence.
Nanoparticle analysis methods should therefore be compared according to samples, expected parameters, throughput and acceptable limitations. This technical reading makes it possible to select a coherent solution instead of comparing instruments as if they all measured the same thing.
