Real-Time Colorimetric and Fluorescent Imaging in Live Cells


Description of Technology


Innovators at Michigan State University (MSU) have developed a novel method for dynamic tracking of proteins in living cells. MSU's novel method tags proteins with a wide variety of colors, enabling several different proteins to be detected and tracked simultaneously. Using this method, multiple color variants are genetically tagged onto a protein expressed in cells, allowing proteins to be visualized over a very broad light spectrum -- including bright fluorescents -- as soon as they are synthesized.


Unlike green fluorescent protein (GFP), which is expensive and requires significant activation time, MSU's low-cost technology allows proteins to be detected instantaneously. The ability to track specific proteins as they are expressed can provide critical tools for pharmaceutical research and development, genetic engineering as well as a myriad of cell and molecular biology experiments.


Unlike GFP, which requires several hours to manifest fluorescence, this protein fusion is fluorescent within minutes after the fluorophore has been added, meaning that proteins can be visualized as soon as they are synthesized. Furthermore, their visualization can be temporally controlled (i.e. proteins present at a single time point can be specifically visualized). MSU's technology is also remarkably stable, retaining its fluorescence at room temperature for several days in normal light. Because this method produces fluorescent proteins that are excited and emit over a broad range, several proteins can be detected simultaneously. This same system can be used for colorimetric and fluorescent detection of pH over a wide range. In addition, the method can be used in scenarios where GFP may be unsuitable (e.g., low intracellular oxygen environments, pulse-chase type experiments, low pH environments).


Key Benefits

  • Unlimited color variants: Virtually all colors and fluorescent properties can be obtained and co-expressed with a gene of interest. Absorbance and light transmission of the chromophore ligand can be modulated across the visible range to near-infrared range (425 - 644 nm).
  • Extremely fast: Colors become visible within minutes.
  • Excellent biochemical properties: The fusion domain has an excellent combination of properties, including small size and compact domain (~16 kD), high affinity for ligands (nm dissociation constant), highly stable chromophore (>1 week at room temperature), and very high recombinant expression. Protein variants are available that are stable at pH levels lower than 1.8.
  • Allows for temporal control of visualization: Since the fusion protein is only fluorescent upon the addition of the fluorophore, and the fusion binds the fluorophore within seconds, proteins present within a narrow time window can be specifically visualized.
  • Multi-purpose: This technology can simultaneously tag different proteins and measure pH in one cell in different cellular locations, indicating protein location and environment. Proteins have been developed covering a broad range of pH (1.5 - 8.8 pH units).
  • Functions in anaerobic environments: Unlike GFP, this technology does not require molecular oxygen to become fluorescent.



  • Pharmaceutical: Developing new drugs (e.g., high-throughput and high-content screening assays)
  • Medical: Pursuing new treatments and diagnostics for a variety of diseases
  • Agriculture: Developing transgenic organisms and new crops
  • Brain research: Analyzing brain circuitry
  • Infectious disease: Researching viral entry and infection of viruses
  • Cell and molecular biology: 
    • Viral infection
    • Intra/Extracellular receptor-mediated binding
    • Protein expression, trafficking, post-translational modifications, and targeted degradation
    • Cellular movement, attachment, growth, programmed death, and homeostasis


Patent Status


Patent pending


Additional Information


Article by the inventors, "Tuning the Electronic Absorption of Protein-Embedded All-Trans-Retinal," Science, December 2012, 338(6112):1340-1343.




Babak Borhan, James Geiger, Wenjing Wang, Chrysoula Vasileiou, Kin Sing Lee, Tetyana Berbasova


Tech ID




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