NexaTag^® qIPCR ELISA

The Next Generation of Ultrasensitive Protein Quantification

RayBiotech NexaTag^® technology is a bead-based quantitative immuno-PCR (qIPCR) platform that delivers ultrasensitive protein quantification by combining the specificity of sandwich-based ELISA, the amplification power of real-time PCR, and the versatility of magnetic bead handling. With detection limits in the femtogram per milliliter (fg/mL) range from as little as 5 µL of diluted sample, NexaTag kits achieve a level of sensitivity rivaling digital immunoassays like Simoa—without the need for dedicated capital equipment.

Because each detection antibody carries its own DNA barcode paired with its own sequence-specific probe, multiplex panels enable simultaneous quantification of up to 5 proteins in a single reaction without sacrificing sensitivity.

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NexaTag_ultrasensitive ELISA standard curve

How NexaTag Works

NexaTag leverages the principles of quantitative immuno-PCR (qIPCR) in a bead-based sandwich assay format:

Assay Procedure

Mix – Magnetic beads pre-coated with capture antibodies are mixed with detection antibodies that are conjugated to a unique DNA oligonucleotide (barcode).
Incubate – The samples and standards are added and incubated for 2.5 hours with shaking. If the target antigen is present, it binds to both the capture and detection antibodies to form a sandwich immunocomplex.
Wash – Assay diluent is added and the beads are washed using a magnetic plate separator (automated plate washer compatible but not required).
Amplify – The DNA barcodes are eluted and amplified via real-time PCR.
Quantify – Fluorescent signals from dsDNA-binding dyes are measured, with signal intensity proportional to the target protein concentration.

Choosing your format: Singleplex or Multiplex

Both formats use the same technology, the same 4-hour workflow, and similar instrumentation. The choice comes down to how many targets you need and how much sample you have.

	Singleplex	Multiplex
Targets per well	1	Up to 5
Sample volume per well	5 μL (diluted)	5 μL (diluted)
Sample volume per target	5 μL	1 μL
qPCR channels required	1	5
Sensitivity	As low as fg/mL (target-dependent)	As low as fg/mL (target-dependent)
Assay time	~4 hours	~4 hours
Best for	Single validated biomarker; deep dose-response; instruments with limited channel capacity	Panel-level profiling; precious or volume-limited samples; multi-analyte screening with minimal sample draw

**Figure 1. Singleplex vs. multiplex standard curves for five representative targets.** Serially diluted standards were run in parallel in both formats with concentration decreasing along the x-axis. Ct values (y-axis) track together across the full standard series for all five targets confirming equivalent sensitivity and dynamic range in both formats.

NexaTag brings together the best of ELISA and qPCR — no trade-offs, just results you can trust.

Key Advantages

Ultrasensitive Detection	Limits of detection down to femtogram/mL — up to 1000 times more sensitive than standard ELISA
Low Sample Volume	Requires as little as 5 μL per replicate of diluted sample per well (1 µL per target in a 5-plex panel) — ideal for precious samples (e.g., CSF)
High Specificity	Sandwich-based format ensures dual recognition of the target antigen, reducing false positives
Fast Protocol	Complete processing in ~4 hours, with antibodies mixed prior to sample incubation for streamlined workflow
Multiplex Advantage	Five targets quantified simultaneously in a single well using sequence-specific probes across five discrete fluorescence channels — with sensitivity matching singleplex

Applications

Inflammation and immune profiling — resolve cytokine networks rather than single mediators, from one small-volume sample
Biomarker discovery and validation — screen panels of low-abundance candidates in plasma, serum, and complex matrices
Neuroscience and neurodegeneration — multi-analyte CSF profiling where sample volume is the binding constraint
Oncology and immuno-oncology — coordinated readouts across immune signaling axes
Longitudinal and preclinical studies — repeated sampling from small animals without exhausting the specimen
Translational and clinical research — panel-level data with ELISA-grade specificity

Considerations

While NexaTag delivers unmatched sensitivity, it requires:

Magnetic plate separator (Catalog #BIQ-MPS or similar)
Exceptional pipetting precision
Triplicate sample measurements to account for small-volume variability

With good lab technique, NexaTag enables highly precise quantification with just 7.5 µL of sample using a 2X dilution.

See What Ultrasensitivity Can Do For Your Research

Browse NexaTag™ Kits

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Maximize operational efficiency while receiving data you can depend on when you trust your ELISA service needs to the experienced scientists at RayBiotech.

Choosing your format: Singleplex or Multiplex

Both formats use the same technology, the same 4-hour workflow, and similar instrumentation. The choice comes down to how many targets you need and how much sample you have.

	Singleplex	Multiplex
Targets per well	1	Up to 5
Sample volume per well	5 μL (diluted)	5 μL (diluted)
Sample volume per target	5 μL	1 μL
qPCR channels required	1	5
Sensitivity	As low as fg/mL (target-dependent)	As low as fg/mL (target-dependent)
Assay time	~4 hours	~4 hours
Best for	Single validated biomarker; deep dose-response; instruments with limited channel capacity	Panel-level profiling; precious or volume-limited samples; multi-analyte screening with minimal sample draw

Featured Products

NexaTag^® qIPCR ELISA

The Next Generation of Ultrasensitive Protein Quantification