Just What Is an RLU (Relative Light Unit)?

This post was contributed by guest blogger, Scott Messenger, Technical Support Scientist 2 at Promega Corporation.

It’s always an exciting time in the lab when you find a new assay to answer an important research question. Once you get your hands on the assay, it is always good to confirm it will work for your experimental setup. Repeating the control experiment shown in the technical manual is a great way to test the assay in your hands.

After running that first experiment of your assay, it looks pretty good. The trends of control and treatment are consistent. Time to get on with the experiments…but wait—the RLUs (Relative Light Units) are two orders of magnitude lower than the example data! I can’t show this data to my colleagues; it doesn’t match. What did I do wrong?

This is a concern that we in Technical Services hear frequently. The concern is real, and I had this same thought when doing some of my first experiments using luminescence. When a question like this comes in, a Technical Service Scientist will make sure the experiment was performed as we described, and in most cases it is. We then start talking about RLUs (Relative Light Units).

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Increasing Testing Efficiency with Multiplexed Detection of SARS-CoV-2 and Influenza A and B

It is almost November, and in the Northern hemisphere the cold and flu season is about to start. Most years that means people schedule flu shots, dust off chicken soup recipes and stock up on tissues. If they start to feel sick, they stay home for a day or two, drink hot tea, eat warm soup and—for the most part— go on with their lives. 

This is not, however, most years. This year the world is battling a pandemic virus, SARS-CoV-2. Symptoms of COVID-19, the disease caused by this virus, mirror those of the flu and common cold, and that overlap in symptoms is going to make life more complicated. Most years, a mild cough or minor body aches wouldn’t even warrant a call to the doctor. This year these, and other undiagnosed cold- and flu-like symptoms, won’t be easily ignored. They could mean kids have to stay home from school, and adults have to self-quarantine from work, for up to 2 weeks. In years past people might have been comfortable treating their symptoms at home, this year people will want answers: Is it the flu? Or is it COVID-19?

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How Does Human Papillomavirus (HPV) Infection Drive the Progression of Cervical Cancer?

Cervical cancer is a major health problem for women, and it is currently the fourth most common cancer in women globally (1). A worldwide analysis of cancer estimates from the Global Cancer Observatory 2018 database showed that cervical cancer disproportionally affects lower-resource countries, on the basis of their Human Development Index; it was the leading cause of cancer-related death in women in many African countries (1).

Global cervical cancer incidence 2018
Estimated cervical cancer global incidence rates from the GLOBOCAN 2018 database; image generated using IARC (http://go.iarc.fr/today).

Infection by human papillomavirus (HPV), a double-stranded DNA virus, is the leading cause of cervical cancer. Many types of HPV have been identified, and at least 14 high-risk HPV types are cancer-causing, according to a World Health Organization (WHO) fact sheet. Of these types, HPV-16 and HPV-18 are responsible for 70% of cervical cancers and pre-cancerous cervical lesions. HPV infection is sexually transmitted, most commonly by skin-to-skin genital contact. Although the majority of HPV infections are benign and resolve within a year or two, persistent infection in women, together with other risk factors, can lead to the development of cervical cancer [reviewed in (2)].

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New Bioluminescent Sensor Can Detect Multiple Antibodies in a Single Drop of Blood

nanoluc invivo imaging

Antibody tests are often used to determine whether individuals have been exposed to certain bacteria or viruses. For most existing antibody tests, the process goes something like this: A vial of blood is drawn from the individual, the vial is sent to a lab, then a trained technicians performs the antibody test and sends back the results. The current process is less than ideal for a few reasons. For one, blood draws are invasive and can be painful. Also, getting results could take days, due to the time required to deliver and process the sample. Lastly, costs can be high, since the need for trained professionals and specialized instruments in laboratory settings adds to the cost of each test.

What if all you needed to do for an antibody test was apply a single drop of blood onto a thin piece of film, and you would get results on the spot within five minutes? Scientists have recently developed an antibody test based on bioluminescent technology that could make this a reality. They describe their findings in a recent study published in ACS Sensors.

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iGEM in a Pandemic: Reflecting on Human Practices

Today’s blog is written by the University of Copenhagen iGEM Team.


The International Genetically Engineered Machine (iGEM) competition has 257 teams of students competing this year. Despite all of the unique difficulties we’re all facing in 2020, the University of Copenhagen is competing once again. This year’s project involves a unique approach to Chronic Inflammatory Diseases (CIDs).

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A Closer Look at C. difficile Biology with Luminescent Tagging

Clostridium difficile is a bacterium that infects around half a million people per year in the United States. The infection causes symptoms ranging from diarrhea to severe colitis, and it’s one of the most common infections contracted while staying in the hospital. As the global incidence of C. diff infection has risen over the past decade, so has the pressure to develop novel therapeutic strategies. This requires a thorough exploration of all aspects of C. difficile biology.

Two recent papers published by researchers at the University of Leiden have shed light on C. difficile physiology using HiBiT protein tagging. The HiBiT system allows detection of proteins in live cells using an 11 amino acid tag. The HiBiT tag binds to the complementary LgBiT polypeptide to reconstitute the luminescent NanoBiT® enzyme. The resulting luminescence is proportional to the amount of HiBiT-tagged protein that is present.

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Rapid COVID-19 Testing, International Collaboration, and a Family Favor

When the COVID-19 pandemic descended on New York in March 2020, Christopher Mason, PhD, knew he was in a unique position to contribute. The Mason Lab specializes in sequencing and computational methods in functional genomics – valuable expertise for addressing an emerging infectious disease. Within days, Chris and his team were helping to analyze patient data, as well as developing new tests and detection methods for the SARS-CoV-2 virus.

3d model of coronavirus covid-19

The Mason Lab developed protocols for a simple COVID-19 detection test that requires less time and equipment than common PCR methods. Their subsequent preprint detailing these methods quickly gained widespread attention, and Chris found himself fielding an endless stream of questions and requests.

During the frenzy, Chris received a call from his older brother. Cory Mason is the mayor of Racine, Wisconsin, the brothers’ hometown.

“He said he saw me tweeting about our new test,” Chris says. “Then he asked me, ‘What if we set it up here in Wisconsin?’’

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Screen Media in the Time of COVID-19: Should You Be Reading this Blog?

Screen Media. Cell phones. Social media accounts. If you are a parent, you have probably discussed rules of engagement with your children about these things. All of our modern social media platforms are designed to keep us engaged with them by showing us the latest post, the next video or the people now online. Work emails give us notifications when something arrives in our Inbox. Business software platforms like Microsoft Teams send us notifications whenever someone comments in a conversation we have ever been part of. There are many siren signals pulling us toward our screens.

Enter COVID-19, the flu-like illness caused by the SARS-CoV-2 virus that has already claimed the lives of 210,000 people in the United States, and leaving countless others permanently affected by other long-term health consequences. Spread by aerosol, COVID-19 is most dangerous in places where lots of people congregate in a small area, particularly if they are talking to each other. Consequently, office buildings are empty as many of us work or go to school remotely.

Before COVID-19, if I had a day full of meetings at work, I was running from conference room to conference room, two miles, uphill, in the snow between buildings. Now, a day full of meetings means sitting in front of a computer monitor, trying to figure out how I will get any kind of break between calls. The average number of steps recorded by my pedometer has decreased markedly since March when our remote work started.

Technology has been an incredible blessing during this pandemic—allowing us to continue to work and stay connected with friends and family. Technology is the only way that some people can connect with loved ones in long-term care facilities. It allows students to continue learning through remote classrooms and chats.

But what has been the effect of the increased time spent on screens during this pandemic?

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Maximize Your Time in the Lab: Improve Experimental Reproducibility with Thaw-and-Use Cells

Many cell biology researchers can name their department’s  or institutions’s “cell culture wizard”—the technician with 20+ years of experience whose cell cultures are always free from contamination, exhibit reliable doubling rates and show no phenotype or genotype weirdness. Cell culture takes skill and experience. Primary cell culture can be even more difficult still, and many research and pharmaceutical applications require primary cells.

Yet, among the many causes of failure to replicate study results, variability in cell culture stands out (1). Add to the normal challenges of cell culture a pandemic that shut down cell culture facilities and still limits when and how often researchers can monitor their cell culture lines, and the problem of cell culture variability is magnified further.

Treating Cells as Reagents

A good way to reduce variability in cell-based studies is to use the thaw-and-use frozen stock approach. This involves freezing a large batch of “stock” cells, then performing quality control tests to ensure they respond appropriately to treatment. Then whenever you need to perform an assay, just thaw another vial of cells from that batch and begin your assay—just like an assay reagent! This approach eliminates the need to grow your cells to a specific stage, which could take days and introduce more variability.

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The Impact of Positive Self-Talk: A Next-Level Story

Today’s blog is written by Malynn Utzinger, Director of Integrative Practices, and Tim Weitzel, ESI Architect.

Last month in this series, we posed to you that the most important decision you’ll ever make is the one about how to respond to the circumstances of your life – the story you tell yourself when the rough patches of life show up. Because of our brains’ wiring, we tend to spin self-defensive and blaming stories as a first line of defense until we learn to pause, check in with ourselves, and cultivate a narrative of more generative possibilities.
This month, we promised you a next-level story that shows the outer impact that happened when one person changed his self-talk.

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