NanoLuc is a small, engineered luciferase enzyme that produces light roughly 150 times brighter than the firefly and Renilla luciferases that dominated biology labs for decades. Derived from a deep-sea shrimp and refined through extensive protein engineering, it has become one of the most versatile bioluminescent tools in biomedical research. Its compact size, intense glow, and chemical simplicity have opened doors in drug discovery, virus research, protein interaction studies, and live-animal imaging that older luminescent reporters struggled to reach.
A Glowing Enzyme From the Deep Ocean
The story starts with Oplophorus gracilirostris, a deep-sea shrimp that produces light using a multi-subunit luciferase. The native enzyme is built from two large subunits (each about 35 kDa) and two smaller ones (each about 19 kDa). Researchers found that the bioluminescent activity depends entirely on the smaller subunit, but when they tried producing that subunit on its own in the lab, it was unstable and poorly soluble.1Nature Communications. Illuminating the mechanism and allosteric behavior of NanoLuc luciferase It glowed, but barely enough to be useful.
To fix this, researchers at Promega carried out extensive protein engineering on the 19 kDa subunit while simultaneously designing a new chemical substrate called furimazine. The combined effort improved luminescence in mammalian cells by roughly 2.5 million-fold compared to the wild-type subunit, producing the enzyme they named NanoLuc. In glow-type assay configurations, where you want steady light output rather than a brief flash, NanoLuc’s specific activity exceeded that of both firefly and Renilla luciferases by more than 150-fold.2PubMed Central. Engineered luciferase reporter from a deep sea shrimp utilizing a novel imidazopyrazinone substrate The signal half-life exceeded two hours, meaning the light output stays usable for a long time rather than fading away in minutes.3ACS Chemical Biology. Engineered Luciferase Reporter from a Deep Sea Shrimp Utilizing a Novel Imidazopyrazinone Substrate
What Makes It Better Than Older Luciferases
Firefly luciferase and Renilla luciferase were workhorses for years, but they come with trade-offs. Firefly luciferase is a relatively large protein (about 61 kDa) that requires ATP to produce light, which means any assay measuring luminescence is also sensitive to changes in cellular energy metabolism. That can be a confounding factor. Renilla luciferase is smaller but still larger than NanoLuc, and neither enzyme matches NanoLuc’s combination of brightness, stability, and compact size.4PubMed Central. NanoLuc: A Small Luciferase Is Brightening Up the Field of Bioluminescence
NanoLuc’s small size matters practically because when you fuse a reporter enzyme onto a protein of interest to track it, a big tag can interfere with how that protein folds, moves, or interacts with partners. At 19 kDa, NanoLuc is less likely to disrupt normal protein behavior. Its reaction also does not need ATP or any other cofactor beyond furimazine and oxygen, which simplifies assay design and removes a variable. The furimazine substrate itself shows lower background activity than the substrates used by older luciferases, which means less noise in your data.
In a head-to-head comparison using bacteria labeled with either NanoLuc or firefly luciferase, the NanoLuc-labeled cells produced about 15 times higher signal than firefly-labeled cells at comparable bacterial numbers.5Biotechnology Letters. Comparison of firefly luciferase and NanoLuc luciferase for biophotonic labeling of group A Streptococcus That kind of signal advantage translates directly into better sensitivity: you can detect fewer cells, lower concentrations of a target, or earlier time points in an experiment.
Watching Proteins Interact in Real Time
One of NanoLuc’s most impactful applications takes advantage of the fact that the enzyme can be split into two pieces. The system, called NanoBiT (NanoLuc Binary Technology), divides NanoLuc into a large fragment (18 kDa, called LgBiT) and a tiny peptide tag (1.3 kDa, called SmBiT). On their own, these two pieces barely stick together. But when you fuse LgBiT to one protein and SmBiT to another, the fragments are brought close enough to reassemble into a working luciferase only when the two proteins interact. More interaction means more light; less interaction means less light.6ACS Chemical Biology. NanoLuc Complementation Reporter Optimized for Accurate Measurement of Protein Interactions in Cells
The beauty of this design is that it works inside living cells without disrupting normal cellular processes. Because SmBiT and LgBiT do not strongly self-associate, the luminescent signal genuinely reflects whether the two target proteins are binding to each other, rather than being forced together by the reporter fragments. Researchers have used this to detect even weak and transient protein interactions that are difficult to catch with other methods.7PubMed Central. Split NanoLuc technology allows quantitation of interactions between PII protein and its receptors with unprecedented sensitivity and reveals transient interactions
Measuring Whether a Drug Hits Its Target
A persistent challenge in drug development is knowing whether a candidate molecule actually binds its intended target inside a cell, not just in a test tube. NanoLuc has been adapted for this through bioluminescence resonance energy transfer, or BRET. In a typical NanoBRET setup, the target protein is fused to NanoLuc, and a fluorescent tracer molecule that binds the same target is added to the cells. When the tracer sits on the target protein, NanoLuc’s blue light energy transfers to the tracer, which emits at a different wavelength. A drug candidate that successfully displaces the tracer reduces that energy-transfer signal, providing a direct, quantitative readout of drug binding in living cells.8Nature Communications. Target engagement and drug residence time can be observed in living cells with BRET
This approach goes beyond just confirming binding. It also reveals how long a drug stays on its target (residence time), which can matter as much as binding strength for predicting how a drug performs in the body. The method has been applied to a range of target classes. In one recent example, researchers fused NanoLuc to a lipid transfer protein called CERT and used a fluorescently labeled ceramide as the energy-transfer partner, creating a system to screen for inhibitors of lipid transport inside living cells.9PubMed Central. Live-Cell Identification of Inhibitors of the Lipid Transfer Protein CERT Using Nanoluciferase Bioluminescence Resonance Energy Transfer (NanoBRET) BRET offers a general solution when researchers need quantitative measurements or kinetic analyses of how compounds engage their targets inside cells.10PubMed. Quantitative, Real-Time Measurements of Intracellular Target Engagement Using Energy Transfer
Tracking Gene Activity as It Happens
Reporter genes have long been used to monitor when and how strongly a gene is switched on. You place the reporter under the control of whatever genetic switch (promoter) you want to study, and then measure reporter activity as a stand-in for gene expression. The problem with older reporters like beta-galactosidase (LacZ) is that the reporter protein hangs around long after gene activity drops, obscuring the timing of events.
NanoLuc, especially in a destabilized form tagged for rapid degradation (called NlucPEST), solves this. In yeast, researchers found that the NlucPEST signal closely tracked actual mRNA levels during both the activation and the shutdown of a heat-shock gene, something LacZ failed to capture.11PubMed Central. Luciferase NanoLuc as a reporter for gene expression and protein levels in Saccharomyces cerevisiae In mammalian cells, a destabilized NanoLuc reporter driven by an inflammation-related promoter showed the fastest and largest response to stimulation, reaching peak signal within six to eight hours and then declining, while other luciferase reporters accumulated signal and stayed elevated.12Scientific Reports. Reporter gene comparison demonstrates interference of complex body fluids with secreted luciferase activity That rapid rise-and-fall pattern is exactly what you want when studying gene regulation dynamics.
Speeding Up Virus Research
Virologists have embraced NanoLuc for building reporter viruses, where the gene for NanoLuc is inserted into the viral genome so that infected cells glow. This turns slow, labor-intensive assays into fast, plate-reader-friendly ones. The approach proved especially valuable during the COVID-19 pandemic. Researchers engineered a SARS-CoV-2 strain carrying NanoLuc and used it to develop a neutralization assay that could be completed in about five hours, compared to days for the traditional plaque-reduction method. The NanoLuc assay correctly distinguished all positive and negative patient sera, and it detected neutralizing antibodies with higher sensitivity than the conventional approach.13PubMed Central. A nanoluciferase SARS-CoV-2 for rapid neutralization testing and screening of anti-infective drugs for COVID-19
Similar strategies have been applied to other pathogens. A NanoLuc-based microneutralization assay for Rift Valley fever virus showed strong agreement with traditional plaque assays across a range of antibody levels.14MethodsX. NanoLuc-based microneutralization assay for high-throughput detection of neutralizing antibodies against rift valley fever virus For HIV research, pseudotyped particles carrying NanoLuc instead of firefly luciferase produced roughly 100-fold brighter luminescence, enabling detection of single infection events in a 96-well plate format.15bioRxiv. Measuring SARS-CoV-2 neutralizing antibody activity using pseudotyped and chimeric viruses When you can detect a single infected cell, you can measure very low levels of viral entry or very potent neutralizing antibodies that leave only a few cells infected.
Screening Thousands of Drug Candidates at Once
High-throughput screening campaigns test tens of thousands of compounds against a target to find a handful worth pursuing. NanoLuc’s brightness and the flexibility of NanoBiT make it well suited for this. In one campaign targeting the c-Myc oncoprotein, which has been notoriously difficult to drug, researchers built a Myc-NanoLuc fusion and screened over 108,000 compounds. The assay correctly flagged known Myc-downregulating molecules and identified 14 novel hits after confirmation and dose-response testing.16PubMed Central. Cell-based high-throughput screening using a target-NanoLuc fusion construct to identify molecular glue degraders of c-Myc oncoprotein
NanoBiT-based assays have also been adapted for screening protein-protein interaction inhibitors. A screen for compounds that block the interaction between two neuronal signaling proteins achieved a signal-to-background ratio exceeding 240-fold and identified 19 validated hits from a library of over 10,000 compounds.17PubMed. Development of a NanoBiT based high throughput screening assay for discovery of NOS1-NOS1AP interaction inhibitors That signal-to-background ratio matters in practice: the wider the gap between your real signal and your noise floor, the fewer false positives you chase through expensive follow-up chemistry. However, screening teams do need to be aware that certain metal ions can interfere with NanoLuc’s signal, just as they can with firefly and Renilla assays, so compound libraries containing metal-chelating scaffolds require careful controls.18PubMed Central. Interference of metal ions on the bioluminescent signal of firefly, Renilla, and NanoLuc luciferases in high-throughput screening assays
Imaging in Living Animals
NanoLuc’s native emission peaks at around 460 nm, which is blue light. Blue light does not penetrate mammalian tissue well because it gets absorbed by hemoglobin and scattered by tissue. For imaging inside living animals, this is a genuine limitation. Furimazine also has poor water solubility, which limits how much substrate you can deliver and therefore how bright the signal is in deep tissues.
Both problems have been tackled through chemistry and protein engineering. On the substrate side, researchers developed hydrofurimazine and fluorofurimazine, two analogues with much better water solubility.19Nature Methods. Novel NanoLuc substrates enable bright two-population bioluminescence imaging in animals Fluorofurimazine proved about nine times brighter than furimazine when delivered intravenously in mice, and roughly three times brighter when given by the more common intraperitoneal route.20PubMed. Evaluation of NanoLuc substrates for bioluminescence imaging of transferred cells in mice In influenza A virus tracking, fluorofurimazine substantially improved detection sensitivity in both respiratory organs and brain tissue, allowing more precise monitoring of viral replication over time.21PubMed Central. Fluorofurimazine, a novel NanoLuc substrate, enhances real-time tracking of influenza A virus infection without altering pathogenicity in mice
On the color side, chemists have synthesized furimazine analogues that push the emission toward red wavelengths. By modifying the chemical core of the substrate, one group achieved emission near 600 nm, deep into the orange-red range, which passes through tissue far more effectively than blue light.22PubMed. Coelenterazine analogues emit red-shifted bioluminescence with NanoLuc An alternative strategy fuses NanoLuc to a fluorescent protein so that NanoLuc’s blue light excites the fluorescent partner through BRET, and the partner emits at a longer wavelength. The Antares2 reporter takes this approach and offers improved signal from deep tissues compared to the original Antares design.23PubMed Central. Red-shifted luciferase-luciferin pairs for enhanced bioluminescence imaging
Running Two Reporters in the Same Experiment
Because NanoLuc uses a different substrate than firefly luciferase, researchers can pair the two in a single experiment to track two biological events simultaneously. You read one signal by adding furimazine, and the other by adding luciferin (firefly’s substrate). This dual-reporter strategy has been used to quantify two steps in the same signaling pathway in both cultured cells and living mice.24Molecular Imaging. NanoLuc Reporter for Dual Luciferase Imaging in Living Animals Multiplexing like this gives a richer picture than measuring one readout at a time: you can see whether a drug affects one step in a pathway without affecting another, or whether two events are coordinated in time.25PubMed Central. Dual Reporter Bioluminescence Imaging with NanoLuc and Firefly Luciferase
Furimazine Toxicity and Newer Substrates
For all its advantages, furimazine is not biologically inert. Cell culture experiments have shown that its toxicity varies considerably by cell line. In one study, the breast cancer cell line SK-BR-3 was quite sensitive, with half the cells dying at a furimazine concentration of about 25 micrograms per milliliter, while another breast cancer line (BT-474) showed only minimal effects even at the highest doses tested. In mice, intravenous furimazine at 60 micrograms per day caused liver damage including cell death in hepatocytes. Lower doses still caused some damage, though splitting the daily dose into three smaller injections reduced the liver impact substantially.26Russian Journal of Bioorganic Chemistry. A Highly Specific Substrate for NanoLUC Luciferase Furimazine Is Toxic in vitro and in vivo
This toxicity profile is worth keeping in mind for any experiment involving repeated substrate dosing or long-term imaging in animals. The newer substrates like fluorofurimazine not only produce brighter signals but also show reduced toxicity at the concentrations needed for effective imaging, partly because their improved solubility means lower doses can achieve the same brightness.21PubMed Central. Fluorofurimazine, a novel NanoLuc substrate, enhances real-time tracking of influenza A virus infection without altering pathogenicity in mice For cell-based assays at standard working concentrations, furimazine toxicity is generally not a concern. It becomes a factor primarily in longitudinal animal studies where substrate is administered repeatedly at high doses.
Building Biosensors for Clinical Samples
Beyond lab-focused assays, NanoLuc is being engineered into biosensors that could work with human clinical samples. One approach uses a circularly permuted version of NanoLuc whose activity depends on whether a specific analyte is present. When the analyte binds a recognition domain built into the sensor, the enzyme folds into its active shape and produces light. Without the analyte, it stays inactive. Researchers have demonstrated sensors with sensitivity down to 50 picomolar concentrations and dynamic ranges up to 16-fold, and they successfully measured target molecules in human fluids.27Nature Communications. Engineering and exploiting synthetic allosteric of NanoLuc luciferase These sensors can also be tuned to emit at different wavelengths, raising the possibility of reading multiple analytes from a single sample. The work is still at the proof-of-concept stage, but the picomolar sensitivity and compatibility with complex biological fluids like blood are features that point toward point-of-care diagnostic applications in the future.