Virus Counter® & Virotag® Reagents

Virus Counter® Platform for Rapid Virus Quantification

Products from ViroCyt, now part of Sartorius Stedim Biotech, are leading the field of rapid virus quantification. Our goal is to provide the tools that deliver meaningful improvements to mission-critical processes where viruses play a significant role. The Virus Counter® platform is purpose build to rapidly and precisely quantify total virus particles in process development and manufacturing processes.

The Virus Counter® platform and Virotag® reagents were specially developed to quantify viruses rapidly and with high specificity utilizing the Virus Counter® instrument. The reagents offer a biologically relevant readout with versatility to address unique quantification needs. Virus samples stained with Virotag® reagents are quantified after a 30-minute incubation.

  • Accelerate time-to-result and time-to-market for vaccines and viral therapies
  • Speed up development times with real-time titer insights
  • Increase product safety and quality by in-depth sample characterization

Virus Counter® Platform

Meet The Virus Counter® Platform: The Powerful Tool for Rapid Virus Quantification

The Virus Counter® Platform is in use by leading companies, regulatory agencies, and research agencies around the world. Why? A growing body of evidence demonstrates that noninfective particles are of biological importance and can impact both in vitro and in vivo studies. Infectivity and total particle concentration are essential for in-depth sample characterization.

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Simple, No-Wash Assay

The Virotag® labeling system uses a rapid, no wash-assay workflow.

With the Virus Counter® 3100 platform, use this rapid, no wash labeling procedure and take virus quantification to new levels of accuracy, speed and simplicity.

Virotag® Reagents

Our Virotag® Reagents – The Right Quantification Solution for Everyone

Virotag® reagents utilize a simple, no-wash protocol for optimal staining of your virus of interest. This allows for rapid, direct, and precise quantification of viruses using the Virus Counter® platform.

Antibody-Based Detection

Virotag® AB Reagent

The Virotag® detection system provides mission-critical data in real-time. This novel technology enables direct, biologically specific quantification of viruses. by utilizing a fluorescently-labeled, high-affinity antibody that binds to a unique epitope expressed by your virus of interest.

Use the Virotag® reagents to label your virus samples and analyze on the Virus Counter® instrument.

  • High specificity due to antibody-based labeling system
  • Enables detection of viruses and virus like particles
  • Ready-to-use reagent with a simple no-wash protocol 

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Universal Detection

Virotag® DY Reagent

The Virotag® DY detection system is a ready-to-use, simple, and universal approach for virus quantification. This reagent is compatible with all enveloped viruses, with single or double-stranded DNA or RNA genome. This universal reagent is based on a dual strain approach that identifies intact virus particles by simultaneous detection of protein and nucleic acid signals. The use of fluorogenic dyes eliminates the need to wash.

  • Universal detection method for enveloped viruses
  • Detect and identify virus particles with a dual signal approach
  • Ready-to-use reagent with a simple no-wash protocol

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Choose the Optimal Reagent for Every Virus Sample

Enveloped Virus

Virotag® DY Reagent

Virotag® AB Reagent

Enveloped Virus (universal)





  (Virotag BCVB)

Influenza A


  (Virotag INVA)

Influenza B


  (Virotag INVB)



  (Virotag VSVG*)

Non-Enveloped Virus

Adeno-associated Virus 2


  (Virotag AAV2-3)

Adeno-associated Virus 3


  (Virotag AAV2-3)

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Non-Enveloped Virus

Virotag Reagent

Adeno-associated Virus 2

Virotag AAV2-3

Adeno-associated Virus 3

Virotag AAV2-3

* for VSV-G pseudotyped Lentivirus

If your sample is compatible with the universal Virotag® DY reagent and an antibody-based Virotag® reagent, please consult a specialist about your specific needs to choose the optimal reagents for your sample.

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Learn More About Virus Quantification

Highlight Assets


Virus Counter Platform

Accelerate Vaccine Development With Rapid Total Particle Quantification

Watch Webinar Online

The Impact of Rapid Virus Quantification - BPI Webcast

Learn more about the impact of rapid virus quantification in the development and manufacture of advanced therapies.

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Related Assets

Application Note

Rapid, Real Time Quantification of Lentivirus Particles Using Antibody-Based Detection on the Virus Counter® 3100 Platform

PDF | 113.4 KB

Meet the Virus Counter® Platform - Rapid, Direct, Biologically Relevant Virus Quantitation

PDF | 1.3 MB

Rapid Total Particle Quantification for Viral Families With High Potential for Pathogenic Emergence

PDF | 949.7 KB

Rapid, Real Time Quantification of Adeno-Associated Virus Particles Using Antibody-Based Detection on the Virus Counter® 3100

PDF | 1.4 MB

Q&A: Quantifying Viruses? Here’s What Matters Most

PDF | 174.8 KB

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