What to Consider When Selecting a Dynamic Light Scattering (DLS) Instrument?

The physical features and components of a dynamic light scattering (DLS) instrument together with the technical specifications of the instrument are significant considerations when buying a new system. However, written specifications can be puzzling, misleading and maybe even have little bearing on the instrument's actual performance.

Specifications on paper do not essentially translate into advantages or disadvantages when it comes to performing measurements on users’ samples. The world’s best components and technical specifications do not matter if the instrument is not optimized or assembled in a way that they translate into real improvements in data quality when the user is making measurements on the samples.

This article looks at some questions that need to be asked before evaluating dynamic light scattering instruments.

What Type of Samples Will Be Analyzed?

This sounds so rudimentary that it is easily ignored and too frequently dismissed as a silly question. If the user's requirement is a DLS instrument then surely they know it is for measuring something.

But not always.

Researchers frequently know their specific application and samples fairly well, they typically understand exactly what data they need from a DLS instrument. The purchase of a light scattering system, however, sometimes needs a number of researchers or several labs to work in unison to find an instrument that matches the needs of everyone involved. It is in these situations where the answer to the, "What type of samples will I be analyzing?" question becomes complex. As, not only must users understand their own samples but they must also understand the needs of others who will be sharing the instrument. At times these differing requirements start to compete with each other.

All DLS instrument models have their own strengths and weaknesses. There are usually trade-offs involved when considering a broad range of sample types or applications.

Sometimes what works best for one lab’s samples might not be ideal for those samples from the neighboring lab. Some might be at low concentrations, others at high concentrations. Some researchers might have many samples available for DLS analysis, while others might only have a few microliters of precious sample. Some might want to quantify trace quantities of aggregation in pure protein solutions and others might need to establish if final formulations are remaining stable over a variety of temperatures, several freeze/thaw cycles or for a prolonged shelf life. Others yet might be characterizing inks, novel nanoparticles, quantum dots, pigments or broad range of other types of samples. An instrument enhanced for one application might not be suitable for the other applications.

It is recommended to define the types of samples that are to be measured most often and make sure the instrument chosen excels in those measurements first. After gaining confidence that an instrument's strengths apply to the types of samples that need to be measured most often, then the next step would be to ensure how flexible the instrument is in terms of applicability to a variety of other sample types whose significance might be secondary.

What Are the Main Differences between Instruments?

Each DLS instrumentation vendor uses their own jargon and specific trademarked names and approaches that they will attempt to tout as "must haves". However all considerations regarding light scattering instruments must begin with an understanding of the users’ application requirements.

The actual hardware that light scattering manufacturers use to construct their instruments is pretty much irrelevant unless these components are assembled and configured in a way that offers required performance.

A high power laser, for example, does not essentially represent a complete improvement in performance if its wavelength is beyond the optimal response range for the detector or if it induces heating of the samples. Sometimes, the specifications that vendors put on paper to suggest an advantage do not really translate into real-world performance benefits because of other mitigating factors.

So rather than asking about hardware, users can enquire about the performance of the instrument because even the same hardware can provide different performance outputs if configured in a different way.

The key differences that should be understood are: the largest and smallest size molecules or particles that can be measured, the size range for which the instrument is enhanced, the concentration ranges possible, how the instrument deals with intensity spikes from agglomerates or aggregates, whether the instrument is susceptible to number fluctuations from large particles or dust, whether or not the optics are highly susceptible to effects from multiple scattering and whether or not the instrument uses good temperature control of the sample being measured.

What Typical Volume of Sample Do I Have for Analysis?

Currently-available commercial dynamic light scattering instruments have sample volume necessities ranging from 2 µL to 3 mL or more. It is important to understand the minimum sample requirement that each instrument needs and what is the maximum quantity of sample it can handle. If users only have a few microliters of sample then the otherwise best performing instrument they can find doesn't matter if it needs milliliters of sample.

How User-Friendly Is the Instrument and Software?

The instrument’s user-friendliness and its associated software are very important, but user-friendliness depends upon the eye of the beholder.

Certain scientists want an instrument that is very easy for any operator to use with basic training and as little user-intervention as possible. Others require data interpretation to be simple and as non-subjective as possible. Other scientists want to know that they can access and alter just about every parameter that goes into a measurement, export the raw data to conduct their own analyses or otherwise make the most of the instrument as a true research tool.

The only way to get a perfect understanding of the user-friendliness of instruments is to have them demonstrated in the lab scenario, so that the instrument can be seen in operation with actual samples before a purchase decision is made.

Performing measurements on standards in a vendor's lab is not going to tell much when the vendor is in control of the total situation.  Experiments are most likely pre-optimized and pre-set in the software before the user arrives to ensure they give ideal results. Only when the instrument is used with users’ own samples in the users’ own lab will they have a true test of how easy it is to work the instrument and interpret data. Just being shown data reports from earlier run standard samples will not enlighten users much either. Users must ask to use the software and work an experiment or two from start to finish during the demo in the lab. It will be worth it as only then will they have a true understanding of how user-friendly the instrument and software are according to their own definition of "user-friendliness."

Do I Just Want to Know the Size of My Particles or Molecules?

This is another question that sounds simple but it can frequently become complex.

DLS instruments should be able to measure the size of particles or molecules in solution repeatedly and accurately, of course, but often the distribution or Polydispersity Index of those particles and the ability for the deconvolution algorithms to resolve a number of components within the sample is just as vital.

Users must ask vendors to provide data about how their instruments report and quantify data. At the very least, the instrument should accurately and reproducibly be able to establish the size and distribution of the users’ samples and include at least two or three deconvolution algorithms to allow the users to resolve multi-component distributions accurately.

Some DLS instruments also have extra capabilities to offer zeta potential, molecular weight, and Aggregation Index information. So, a clear understanding of the information users are trying to gain beyond just the average particle size is very helpful before users start assessing different instruments.

How Will I Operate the Instrument?

Most commercial DLS instruments can be operated in batch mode, but several can also be operated in flow mode along with size exclusion chromatography. In SEC-DLS mode, molecules are measured for absolute hydrodynamic size as peaks elute and then good estimates of molecular weight are offered to eliminate the need to run molecular weight standards for SEC column calibration. A clear understanding of the users’ current and future requirements is important before choosing an instrument such as an online-only instrument or an instrument that can be operated in different or additional modes, such as combined batch and flow, attached with an autotitrator, automated micro plate sampling or just operated in batch analysis mode.

How Confident Can I Be in the Result?

Some dynamic light scattering instruments are very much "black box" machines that offer masses of data output for the user to then subjectively qualify and interpret. It is important to find out if and how many "behind the scenes" measurement parameters are available and how they can be used to gain confidence in the results.

Some dynamic light scattering instruments automatically qualify data and "grade" it based on rigid criteria and generally-accepted data tolerance ranges. In order to guarantee that the instrument returns statistically-significant results, from measurements that reflect good light scattering practices and good science.

When making vital decisions based on the data assurance of the quality of that data is very important, including confidence both in the results and in the decisions taken.

How Good Is the Manufacturer or Vendor?

With many companies developing low cost dynamic light scattering instruments and rushing to make them commercial, it is vital to judge the reputation of the manufacturer or vendor users choose.

Selecting a DLS instrument is not like choosing a bench top centrifuge or pipette where all options are very good and they will all get the job done. DLS instruments must be fabricated using high standards and designed by solid, technology leading companies so as to yield publication-quality or decision-making results.

Look for a manufacturer that has not lately embraced dynamic light scattering technology, but has an appropriate history of being at the lead of developing and optimizing these instruments. Such companies have been through the learning curve and users will benefit greatly as a result. These companies are much more likely to have the experience, expertise and support resources to not only build great instruments but also to support them appropriately.

Users should also be cautious of manufacturers or companies that just re-label somebody else's instrument, who have a short history with dynamic light scattering technologies, or who have not invested in keeping their instruments up-to-date to take advantage of the latest advances in technology. These practices specify a lack of lasting commitment to the science and should cause users to become concerned and cautious.

What About Post-Sale Service and Support?

Once the instrument is bought, the user's experience is really just starting so it is vital to purchase a system from a company that provides acceptable service and post-sale support.

Find a company that can offer ongoing training opportunities aswel as, telephone, in-person and email support; field-based service and expert level support. Some also offer 24/7 support via their websites by offering extensive on-demand application notes, training sessions or pre-recorded seminars and ongoing live educational/training seminars.

Before purchasing an instrument, users should ask about what support is offered and maybe even ask to try some of these before a decision is made, so that they can get a feel for the quality and depth of support that can be expected once they have their new instrument installed in their lab.

Dealing with small, family-run, or thinly resourced companies can frequently make the support and service processes tough, complex or very frustrating. Larger suppliers typically offer depth and stability of resources so users can get the support, answers and services from local experts when and how it is needed.

Shouldn't I Just Buy the Instrument with the Lowest Price Because They are all Pretty Much the Same on Paper?

Absolutely not.

Dynamic light scattering instruments can differ significantly in their quality, design and performance.

Although a number of different instruments may have specifications that look similar on paper (often done so purposefully by unprincipled vendors who are out to just win bids from people who have not assessed actual performance), instruments differ significantly in real-life performance, longevity and quality. It has been reported that some instruments available today cannot actually even meet their own stated performance specifications, so just comparing prices and specifications on paper does not ensure users of anything.

Instruments that have unique capabilities or that come with tested and well-established performance specifications, warrantees, free software updates, training and re-training opportunities, superior support and excellent service might cost a little more up front but they can considerably reduce the user's recurring costs.  They can also guarantee actual instrument performance and decrease the total ownership cost over the lifetime of the instrument. The low-price choice frequently leads to hidden costs, unanticipated surprises and unwanted headaches.

As with many things in life, the most economical option available is usually not the best long-term value and generally winds up costing users the most in the long-run.

This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical.

For more information on this source, please visit Malvern Panalytical.

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