Important Considerations for Immunoassay Selection

Selecting the right immunoassay is a critical step in any research, drug development, or diagnostic workflow. However, with a vast array of immunoassay formats and commercial kits available, choosing the most suitable option for your needs can be challenging. In this article, we explore the most important factors to consider when selecting an immunoassay to help you make an informed decision that aligns with your experimental goals and resources.

What’s your research question

Clearly defining your research question is crucial. Are you measuring a single analyte or multiple analytes? Do you need quantitative, semi-quantitative, or qualitative data? Some immunoassays are designed for absolute quantification, while others provide relative or categorical results. Additionally, consider whether you are interested in the abundance of a protein, its cellular localization, or its interaction with other molecules. The type of information you require will guide your choice of assay format.

Sample type

One of the first things to consider when selecting an immunoassay is the sample type. Different immunoassays are optimized for specific sample types, such as serum, plasma, cell lysates, or cell media. For instance, an assay validated for serum may not perform optimally with cell culture media, and vice versa. It is essential to confirm compatibility between your sample matrix and the chosen immunoassay to avoid issues with matrix interference or inaccurate results. If your sample is limited or precious, you may also need to consider assays that require small sample volumes.

Sensitivity

Sensitivity refers to the lowest concentration of an analyte that can be accurately differentiated from background. Highly sensitive assays are essential for detecting low-abundance targets, such as cytokines or biomarkers present in trace amounts. Techniques like chemiluminescent ELISA or ultra-sensitive ELISA, fluorescence-based assays, and xMAP bead-based assays are known for their excellent sensitivity. Always match the assay’s sensitivity to the expected concentration range of your target analyte.

Type of readout

Immunoassays can provide different types of readouts. Quantitative assays deliver precise numerical values, semi-quantitative assays give relative measurements, and qualitative assays simply indicate the presence or absence of an analyte. Techniques that are considered semi-quantitative or qualitative include western blot, IHC, and lateral flow immunoassays. Your choice should reflect the level of detail required for your application. For regulatory or clinical purposes, quantitative results are often necessary, while qualitative assays may suffice for screening or initial discovery.

Dynamic range

Assays with a broad dynamic range are preferable when the expected analyte concentration varies widely between samples. If the dynamic range is too narrow, samples may need to be diluted or concentrated, adding complexity and potential for error.

Throughput

The number of samples you need to process and the frequency of your experiments will influence your choice of immunoassay. High-throughput assays, such as those compatible with 96- or 384-well plates, are ideal for large-scale studies. Automation-friendly formats can significantly reduce hands-on time and minimize human error. Consider whether the assay can be automated and whether your laboratory has the necessary equipment.

Expert tip: Advantages of homogeneous immunoassays

In research settings where time and throughput are critical, homogeneous immunoassays offer a distinct advantage over traditional formats, explains Hicham Zegzouti, Sr Research Scientist at Promega. These assays eliminate the need for wash steps, relying instead on a streamlined add-mix-read protocol that simplifies execution and reduces total assay time to under two hours. In addition to giving results faster, the no-wash protocol reduces variability introduced by manual steps, which improves consistency across plates and between runs.

Fast turnaround is especially valuable in high-throughput screening environments where researchers are processing hundreds or thousands of samples in parallel. Perhaps most importantly, homogeneous assays seamlessly scale to 384-well plates and are readily compatible with automated liquid handlers, making them ideal for labs aiming to increase efficiency without sacrificing data quality.

For projects where reproducibility, speed and scalability are top priorities, no-wash immunoassays such as the Lumit^® platform from Promega, are a highly effective solution, Zegzouti adds.

Multiplexing

Multiplex immunoassays can save time, reduce sample consumption, and provide a more comprehensive view of biological processes. However, multiplex assays may be more complex to optimize and interpret, and not all analytes can be measured together due to potential cross-reactivity or interference.

Expert tip: Planar or suspension multiplexing assays?

If a multiplex assay is the right choice for your research needs, then you still have a decision to make: which type of multiplexing technology is the best fit? These tools fall into two types—planar or suspension arrays. We asked Dr. Sherry Dunbar, Senior Director of Scientific Affairs Programs at Luminex, to explain the differences. Here’s what she had to say.

Planar multiplex assays bind capture molecules to a solid substrate, such as a microscope slide. Planar options can have very high density for nucleic acids, which are more amenable to this kind of approach. With their complex folding structure, proteins aren’t as well-suited to being immobilized on a solid plane, so multiplex planar array assays tend to be more limited in the number of proteins they can query at once.

Suspension arrays typically rely on binding capture molecules to individual beads, which are then combined and suspended in liquid for the duration of the reaction. The suspension microarray is more flexible for custom multiplexing, allowing the user to query very high numbers of proteins or nucleic acids in a single reaction. They also enable faster binding due to their near-liquid-based kinetics.

Ease of use

Ease of use is an important consideration, especially in laboratories with limited technical expertise or resources. Simple, user-friendly assays with minimal hands-on steps are less prone to user error and require less training. Pre-configured kits with clear protocols and all necessary reagents included can streamline the process and improve reliability.

Time-to-result

The time required to complete an immunoassay can vary from less than an hour to overnight or longer. Some assays require multiple incubation and wash steps, while others are designed for rapid results. Consider your timeline and whether a faster assay would improve your workflow efficiency.

Data analysis and interpretation

Modern immunoassays can generate large and complex datasets, especially in multiplex formats. It is important to consider how easy it will be to analyze and interpret the results. Some assays require specialized software or statistical expertise, while others provide straightforward, user-friendly outputs. Be honest about your team’s data analysis capabilities and the availability of appropriate tools before committing to a particular assay.

Reproducibility

High reproducibility is essential for reliable data. Factors affecting reproducibility include antibody quality, assay conditions, and operator technique. Always perform validation studies and include appropriate controls to monitor assay performance.

Total cost

The total cost of an immunoassay includes not only the price of reagents and kits but also the time and labor required for sample preparation, assay execution, and data analysis. Some assays may be more expensive upfront but save resources in the long run by reducing hands-on time or improving data quality.

Continuous availability of the antibodies or immunoassay kit

Ensuring the long-term availability of critical reagents is essential, particularly for ongoing or multi-year projects. Commercial kits and antibodies should be sourced from suppliers with a track record of consistent product quality and supply. For in-house assays, consider using recombinant antibodies or those available from multiple vendors to mitigate the risk of discontinuation.

Need for specialized equipment

Many immunoassays require specialized equipment, such as plate readers, washers, or automated liquid handlers. Assess whether your laboratory has access to the necessary instruments and whether the cost of acquiring or maintaining this equipment is justified by your experimental needs. Some assays, such as those based on fluorescence or luminescence, can be performed using standard plate readers, while others may require more advanced or proprietary systems.

In summary, selecting the right immunoassay requires a careful evaluation of multiple interrelated factors. With careful consideration, you can choose an assay that delivers reliable, reproducible, and meaningful results for your specific application.

References

Biocompare, Choosing an Immunoassay

Biocompare, Choosing the Right Immunoassay for Your Research

Bio-techne, Immunoassay Selection Guide

GenScript, Optimizing Sensitivity in Antibody-Based Immunoassays: Key Strategies for Reliable Diagnostics

NIH, Immunoassay Methods

Promega, Guide to Immunoassays

Quanterix, Immunoassay Technologies: Past, Present, and Future