Frequently Asked Questions
Fundamental Questions
Size range
What is the largest size of particles that can be analysed?
The upper size limit is approximately 1000 nm. The NanoSight NTA technique analyses the movement of a particle undergoing Brownian motion by tracking the spot of light it scatters. For large particles:
1. The diffusion of the particle reduces making the accurate determination of its mean displacement progressively less accurate.
2. For dense particles, sedimentation rates become significant compared to the limited Brownian motion.
3. The spot of light becomes so large and its edges variable between frames, thus identifying its centre becomes increasingly difficult, leading to centring errors which are as large as the particle's movement.
These effects get progressively larger as particle size increases so there is no specific limit to our upper size range. This upper limit will depend on the nature of the system. In practice, for low density and low Ri particles such as polystyrene micro-spheres their buoyancy and weaker scattering allow them to remain Brownian movers with easily identifiable centres and the upper size limit is 1000 nm or above.
For dense, high Ri particles such as gold, their rapid sedimentation rate and excessive scattering restricts the upper size at which they can be analysed to approx <200 nm.
What is the smallest particle that can be analysed?
The minimum size of particle that is detectable depends on the scattering being sufficiently strong. To understand this question better see 'How much light is scattered by a particle?'. As a general guide:
1. Low Ri (e.g. biological/polymer) will be detectable down to approximately 40-50 nm.
2. Higher refractive particles (e.g. ceramics, metal oxides) will be detectable down to approximately 10-25 nm.
3. Exceptionally high Ri particles (e.g. Ag sol, Au colloid) can be detected at diameters as low as approximately 10 nm.
How does a larger particle (such as an advanced agglomerate or contaminant) affect the measurement?
Unlike other light scattering techniques we are not strongly affected by large contaminants. This is because we visualise individual particles. Whilst an unusually large particle will scatter far more than the primary particles, its scattered light will be confined to and tracked in a region of the image.
Light scattering
How much light is scattered by a particle?
The particles that we size are generally in the Rayleigh or Rayleigh-Debye-Gans scattering regime. As an approximation briefly the Rayleigh regime will be discussed. In this case the efficiency of light scattering is given by:
Therefore the factors affecting the amount of light scattered are:
d = the particle diameter. If you double the particle size you increase the power of light scattered by a factor of 64.
λ = the wavelength of light. If you half the wavelength of light you increase the scattering by a factor of 16.
n = the ratio of the particle refractive index to the solvent refractive index.
For example for latex particles (ref. ind. 1.59) in water (ref. ind. 1.33), n is 1.195 and the factor 
is 0.0157.
However for the case of gold (ref. ind. 0.2-3.37i) in water n is 0.15+ 2.53i and is 2.78, a factor of 177 greater than for the latex particles.
The amount of light scattered is also directly proportional to the intensity of incident illumination.
2D observation
The particles are only being imaged in two dimensions, but they must be moving in three dimensions. Is this a problem?
No, the Stokes-Einstein theory that is used to calculate the particles size from the particle motion can take into account whether two or three dimensions are tracked (see equations below).
Concentration
What is the best particle concentration to use?
Between 107-109 particles per ml.
Twinkle effect
Why do my particles twinkle and appear to diffuse asymmetrically?
Whilst currently we cannot quantitatively answer this, our understanding is that this is due to the particles being oblate (non spherical).
Validity of Method
Accuracy
How accurately can particle size be determined?
For samples in which an adequate number of particles are present in the sample (typically >109/ml), the determination of particles size can be as accurate as that of equivalent dynamic light scattering techniques such as Photon Correlation Spectroscopy. For samples in which solvent viscosity and temperature is correctly entered, the diameter of a well prepared, monodisperse, calibration polystyrene micro-sphere can, for instance, be accurately measured to within 1-2 percent of nominal. Increasing analysis time (e.g. 1 to 2 minutes) will increase accuracy of measurement.
Polydispersity
How accurately can particle size be determined?
For polydisperse samples, the NanoSight system exhibits significant advantages over PCS in that the size distribution profile obtained is based on the separate but simultaneous analysis of each and every particle seen during the analysis period. This is in stark contrast to the data obtained by PCS in which a large ensemble of particles are measured and from which an intensity weighted (z-average) is obtained.
The NanoSight system can distinguish between a bimodal system if the particles are 50% different in size (for example 80 nm and 120 nm particles).
Reproducibility
How reproducible is the result?
Given the statistical nature of analysis of a population of particles, reproducibility is a function of the numbers of particles measured over the period of analysis. For optimum concentrations of monodisperse samples containing no contaminating aggregates, results reproducible to within approx 2-3% can be achieved in a comparatively short time (e.g. 10-20 seconds). Clearly, for low concentrations of particles exhibiting a range of particle sizes, extended analysis periods will be required to obtain reproducibility of results. Note that analysis times need to be increased for larger particle diameters to achieve similar reproducibilities.
Specification Questions
Dimensions
What are the space requirements of the system?
The LM10 system requires room for a desktop PC and (in addition) approximately 400 x 400 mm of bench space.
The LM20 system requires the desktop PC plus 130 x 380 mm of bench space.
What are the dimensions of the sample chamber?
Cell volume: Approximately 0.5 ml
Cell depth: 0.9mm
Laser lifetime
What is the life time of laser source in the NanoSight instrument?
10,000 hours specified by manufacturer.
Safety
Is the system safe?
Yes. Providing the samples that you are analysing are safe. The system is a class one laser product as it has a fail-safe mechanism.
Constituent Materials
What is the unit made of?
The parts of the NanoSight Viewing Unit in contact with the sample are made of glass, '316' stainless steel, nylon 66 and fluorocarbon.
PC & Software
What is the current latest version of the software?
The current version is NanoSight NTA 2.0 (build 128). The version you are using can be found by clicking help -> about in NTA. If you are an existing user of NTA but have not been issued with a user log-in, please contact support@nanosight.com.
Computer Specifications:
The recommended specifications for running NTA 2.0 (build 128) are 2Gb of RAM, and ideally a 2GHz dual-core processor and a hard drive with a minimum speed of 5400rpm (7200rpm+ optimal).
Does the PC used matter, can I use my own?
Experience shows that specification of a computer to guarantee function with NanoSight software is outside of our control. Here are some recent reasons:
1. Hardware performance such as rotation speed of hard drives is a critical performance variable in writing video to disc.
This measure is not a usual part of a computer specification.
2.Different national and local versions of Microsoft Windows have differing dll files and Microsoft change these as they see fit. Language pack differences inevitably cause problems.
3. Camera drivers are proprietary and the set we use has to be prioritised over the Microsoft Windows defaults. If there are further camera drivers on a computer the problems are increased.
4. Models change so fast that we cannot maintain instructions on how to install on a system and machine specific basis.
5. Networking a computer running NanoSight software always gives problems, hence we always use computers as dedicated control machines.
For these reasons we receive computers here, install software and bench test it before it leaves. We can then support these machines, with the supplier's input.
Temperature control
Can the unit be temperature controlled?
A temperature control accessory is available for the NanoSight LM20 system. Currently there is no temperature control available on the LM10.
Fluorescence
Can the device be used in fluorescence experiments?
The system currently uses a red laser and hence fluorescence experiments would probably not be feasible. If this is an area that is of great interest to you, do contact us about it so we can discuss your individual application further.
Microscope
Does the microscope have an effect on getting a good image, can I use my own microscope?
As we are not imaging the particles, a better microscope will not in general give an improvement. The LM10 microscope has been customised to allow ease of manipulation of viewing unit and allowing attachment of camera.
In addition the fixed field of view must be very accurately set. This cannot be carried out off-site and the tube length/configuration is unlikely to be compatible with our adapter. Therefore we do not offer this as an option, we offer no hardware technical support for systems used with non-standard microscopes and would expect such systems not to work. The LM10 is supplied as a complete system including the microscope and camera.
Sales Questions
Quotations
What is the cost of the system?
For a quote for the system contact NanoSight Ltd, or your local distributor. Instruments are sold as complete systems including the computer and software.
Requesting a call back
Our technical team is on hand to answer your questions. If you prefer you can request we call you when it's convenient.
If you want to get in touch with our team email them here: enquiries@nanosight.com
Or for more information about us why not head over to our contact page for a full detail list.