7 Considerations When Purchasing a Microvolume UV-Vis Instrument

Microvolume UV-Vis spectrophotometers are essential tools for quantifying and qualifying nucleic acids and proteins in molecular biology research. It all started with the Thermo Scientific NanoDrop 1000 as the first microvolume UV-Vis spectrophotometer, and now they're everywhere. How do you choose the instrument that’s right for your lab?

Here’s some practical advice – broken down into 7 key factors – to help you decide.

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A wide dynamic range means you spend less time measuring samples and more time on experiments.

Researchers find microvolume UV-Vis spectrophotometers useful in molecular biology labs due to their minimal volume requirements and their ability to measure highly concentrated samples without dilution. These benefits result from using light pathlengths shorter, sometimes much shorter, than traditional cuvette-based spectrophotometers. 

Recall the Beer-Lambert equation can be rearranged to calculate sample concentration using the formula below where ɛ is the wavelength-specific extinction coefficient and l is the light pathlength in cm.

c=  𝐴
ɛ∗𝑙
There is an inverse relationship between concentration and light pathlength. As the light pathlength decreases, the concentration, which can be accurately quantified, increases. 

Wide detection limits are preferred because they minimize sample preparation time in two ways 1) there is no need to dilute samples prior to measuring the absorbance and 2) the researcher does not have to estimate sample concentration ahead of time to properly dilute it. Dilution is generally not beneficial as technical errors can increase the error in the final measurement, sample is wasted for the measurement, and unnecessary time is spent on sample preparation. 

Question to ask: How reliable is the underlying technology used to achieve wide detection limits?

NanoDrop spectrophotometers introduced advanced auto-pathlength technology to achieve high detection limits. The NanoDrop instruments use a highly reliable digital stepper motor to achieve precise control. The pedestal of the Thermo Scientific NanoDrop One/OneC Microvolume UV-Vis Spectrophotometers can measure samples using pathlengths ranging from 1.0 mm to 0.03 mm, which yields the table of detection limits below. This wide detection range means researchers can spend more time preparing experiments and less time quantifying samples.

Pedestal absorbance limits
(10 mm equivalent)
dsDNA
(ng/µL)
RNA
(ng/µL)
Protein – IgG
(mg/mL)
Protein – BSA
(mg/mL)
0.04 2 1.6 0.03 0.06
550 27,500 22,00 402 825

Laboratory needs change and people have different preferences. Instrument flexibility lets users customize their experience.

Each laboratory configuration is as unique as the people working in it. Many labs house various instruments and reagents across benches, cabinets, and drawers. In these situations, an instrument which can be controlled using on-board software is ideal. Other spaces don’t require users to be concerned about footprint, or researchers prefer to use computers.

When considering a new instrument, you want one that is versatile - one that will adapt with the laboratory in which it’s located and provide users with an experience that suits their needs and preferences.

Question to ask: Does the instrument support multiple user scenarios and accessibility needs (e.g., color blind friendly)?

The NanoDrop One/OneC Spectrophotometer only needs 20 x 25 cm of benchtop space and is fitted with a 7-inch high definition touch screen that runs the instrument software and is glove-compatible. Data measurement, archiving & exporting, and printing can all be accomplished without the need of a computer. In addition, free PC Control software is available that lets users enter sample names, obtain measurements, and save and store data directly on a computer. The software user interface follows the latest Material Design language developed by Google to ensure an easy experience for everyone.

Maintaining accurate data records is important for all laboratories, not just for those that comply with 21 CFR Part 11.

Beyond compliance with regulations, the concept of data integrity is relevant when data-driven decisions are made. Simply put, integrity of data requires that records are protected from modification by unauthorized individuals and changes to the records are captured in a traceable system. These practices need to be implemented across the lifetime of a piece of datum – from creation, to processing, reviewing, reporting, and ultimately preservation.

The US FDA Code of Regulations Title 21 Part 11 provides guidance on systems that should be in place to ensure data integrity. Such guidance calls for limited user account access, electronic signatures, and audit trails. In addition to labs regulated by the FDA, these systems can help all groups that make data-driven decisions ensure their data is free from error and manipulation.

Question to ask: Does the software allow me to ensure the integrity of my data?

The optional software, Thermo Scientific Security Suite for NanoDrop One/OneC Spectrophotometers, provides users with a simple way of managing user accounts, electronically signing for data, and maintaining an audit trail. The software suite populates usernames from your company’s domain. Within this application the IT administrator can manage who has access to the software, who can make measurements, and who can edit details such as experiment names. All absorbance data are collected, recorded, and saved directly on the PC controlling the instrument. NanoDrop One software utilizes a database driven backend providing a high reliability platform. The IT administrator can implement mandatory electronic signatures after data acquisition or sample name changes. Lastly, the software suite tracks all creation, modification, and deletion events related to the NanoDrop software. The Security Suite for NanoDrop One/OneC spectrophotometers works to make data integrity simple.

The NanoDrop PC control software is developed following the latest Agile development principles. This development philosophy allows quick iterations of software which in turn allows users to stay current with latest and greatest features. Thermo Fisher Scientific’s extensive experience with pharmaceutical compliance means users can rest assured that the NanoDrop software will keep-up with changing regulatory and compliance requirements.

Sample concentration and sample purity are the two most important considerations; both should be measured quantitatively by the instrument system before downstream activities begin.

It is standard for a life science focused UV-Vis spectrophotometer to calculate A260/A280 and A260/A230 purity ratios. By comparing the ratio values for a given sample to the expected ranges for pure samples, one can qualitatively assess the purity of the sample. For example, pure DNA generally has an A260/A280 value of ~ 1.8 and pure RNA a value of ~ 2.0.

Sample purity is the second-most important consideration of a sample, the first being concentration. Quality downstream assay results, such as qPCR, rely in part on quality starting material. Contamination of a nucleic acid sample may falsely elevate the reported concentration or impede subsequent reactions. Researchers measure samples to determine whether there are offending contaminants in the preparation and so they use the correct amount in their next assay. One limitation of purity ratios is that contaminant concentrations, especially for protein, need to be relatively high before the purity ratio falls out of range. A small number of modern UV-Vis spectrophotometers employ advanced spectral processing algorithms that not only indicate that a sample is impure, but also identify the offending contaminant and provide a corrected sample concentration.

Question to ask: Does the instrument software provide deep enough insight into sample composition?

NanoDrop software is constantly evolving to incorporate the newest and most advanced software algorithms to make it easy for your analysis to be successful. NanoDrop One instruments have built-in software that quantitatively analyzes contaminants in a sample and reports predicted analyte concentrations. The software uses mathematical models trained using thousands of spectra of known concentrations. With these models, the software can predict the identity of a contaminant, the absorbance of the contaminant, and the predicted concentration of the sample. The contaminants that can be identified include DNA and RNA, phenol, protein, and guanidine salts. The specificity to be able to differentiate DNA from RNA is a feature typically only available in fluorescence measurements; however, software advancements built into the NanoDrop One/OneC can distinguish between the subtle differences of DNA and RNA.

Ideally a spectrophotometer allows the user to assess instrument performance for GLP or data integrity regulations without requiring routine calibration.

A lab’s microvolume UV-Vis spectrophotometer is typically used by several people throughout the day. It needs to measure the sample quickly and accurately and without requiring constant maintenance or service. Because the results from these instruments are critical to future success, users should be able to assess how the instrument is performing with internal or external standards. If service is needed in the form of a repair or preventive maintenance, it should be available in a timely manner to limit downtime in the lab.

Question to ask: How easy is it to validate my instrument, and how quickly can service be rendered to the instrument?

NanoDrop products are manufactured in compliance with ISO 9001:2015 quality systems. That means they are developed, tested, manufactured, and serviced following the most rigorous standards. NanoDrop One instruments do not require recalibration at standard intervals, but if a service is ever requested, the turnaround time in North America is 48 hours door-to-door. For example, if you ship an instrument for service on a Monday, you can expect to have it back on Wednesday. If that is still too long to be without your instrument, a loaner instrument can be sent for you to use in the meantime.

As part of good laboratory practices and compliance with 21 CFR Part 11, there are multiple, easy ways that you can confirm the performance of NanoDrop One instruments. The first is by using a standard solution, PV-1, to confirm the accuracy of pedestal measurements. Another diagnostic allows you to verify the wavelength accuracy and flashlamp performance, while the third and final diagnostic activity assesses the digital image sensor performance. All three tests provide evidence that your sample results are accurate to within the instrument specifications.

Choosing a proven name with many users over time means an instrument is more likely meet your expectations and be supported for years to come.

You want to be sure that a new instrument is going to work and do its job well. Choosing a supplier with a proven history gives you piece of mind that the manufacturer knows what they’re doing and that you’re not piloting a first-generation instrument. In addition, a long-term manufacturer can generally be counted on to provide support for spectrophotometers throughout the many years of ownership.

Reputation and presence offer another opportunity for users to gain confidence in their purchase. Instruments with a large user base mean the manufacturer already understands the concerns of users, and likely is working constantly to address those concerns via software updates and advanced generation systems. You want to know that others in your field are using the same piece of equipment and it successfully meets their needs. Using something other than the standard in a field can call your work into question. The number of citations attributed to an instrument is just one method used to assess how many researchers rely on it.

Question to ask: Does the instrument manufacturer have a long history of delighting users? Has the instrument been proven by other scientists?

The instrument side of Thermo Fisher Scientific was founded in 1956 and has been producing industry-leading instruments since its inception. NanoDrop spectrophotometers have been used by scientists around the world since 2001 when the NanoDrop 1000 was introduced. To date NanoDrop instruments have been cited in over 55,000 peer-review publications – the most of any microvolume UV-Vis spectrophotometer. Even after sales of a particular instrument platform are discontinued, Thermo Fisher Scientific typically continues support of that NanoDrop system for a further 7 years. Users of NanoDrop instruments stand with thousands of other users around the world in knowing their instrument will be supported for years to come.

System downtime impacts business revenue directly not to mention lab productivity and morale, so ask ahead of time about support availability and response times in your area.

Researchers rely on quality results from the same microvolume UV-Vis spectrophotometer for many years. Inevitably questions will arise about the data generated, how to maintain the instrument, optimizing the instrument for custom use, and servicing the instrument. It’s important for a customer support and technical support team to not only understand the end-user perspective but to also know the science behind the experiment, how the software and hardware integrate, and the urgency with which questions need to be addressed. These qualities will get the researcher back up-and-running in the shortest time possible.

Question to ask: Does the technical support team have the scientific and instrumentation background to understand and address questions and issues quickly?

Members of the NanoDrop technical support team have over 28 years combined experience supporting microvolume UV-Vis instruments. All team members are trained scientists who have worked in the molecular biology field for over 43 combined years. They have a proven track record of supporting customers and giving them a world-class experience.

The team’s depth of knowledge about the science of UV-Vis and the field of molecular biology is further demonstrated by their publications. Team members have authored over 150 technical notes to educate users and lead them toward experimental success.