Surface plasmon resonance (SPR) is one of the most widely used techniques for measuring biomolecular binding, from proteins and antibodies to small molecules. It has real strengths, and real limitations. This guide covers both, with practical ways to work around each limitation, so you can decide whether SPR fits your experiment.
What are the advantages and disadvantages of surface plasmon resonance?
Surface plasmon resonance measures binding in real time without labels, using small sample volumes and reusable sensors, and works in opaque matrices such as serum. Its main disadvantages are that one partner must be immobilized, small analytes give small signals, and results depend on careful surface chemistry, referencing and data fitting.
SPR works by immobilizing one binding partner (the ligand) on a thin gold film and detecting the change in refractive index within roughly 200–300 nm of the surface as the other partner (the analyte) binds. Both the strengths and the weaknesses below follow from that principle.
What are the advantages of surface plasmon resonance?
The main advantages of surface plasmon resonance are real-time binding data, label-free detection, small sample volumes, reusable sensor chips, compatibility with complex samples such as serum and cell lysate, and fewer hands-on steps than plate assays such as ELISA. Depending on the setup, the same sensorgrams report affinity (KD), kinetics and analyte concentration.
1. Real-time binding data
SPR follows association and dissociation as they happen, plotted as a sensorgram (signal vs. time). End-point methods such as ELISA or co-immunoprecipitation tell you whether binding occurred; a sensorgram also shows how fast it happens and how stable the complex is. In flow (kinetic) mode, SPR gives on- and off-rates (kon, koff) as well as the dissociation constant (KD); in static mode, it gives KD from steady-state responses.
2. Label-free detection
SPR reads a change in refractive index at the sensor surface, so neither partner needs a fluorescent, radioactive or enzyme label. That removes a labeling step, and the risk that a label masks or alters the binding site you are trying to measure.
3. Small sample volumes
Each injection uses microlitres of sample, which matters when a protein purification gives a low yield or a reagent is scarce. You can often characterize an interaction with material that would be too little for many other biophysical methods.
4. Reusable sensor chips
When a regeneration solution can remove the bound analyte without damaging the immobilized ligand, the same sensor surface can be reused for many binding cycles, unlike single-use ELISA wells. That reduces consumables and waste. Regeneration has to be tested for each interaction, though: conditions that are too harsh gradually destroy ligand activity.
5. Works in complex samples
The light excites surface plasmons on the far side of the gold film and never passes through the sample, so opaque or coloured matrices such as serum, plasma and cell lysate can be measured. In practice these samples still need a reference channel and a surface that resists non-specific adsorption (see limitation 3 below).
6. Fewer steps, faster answers
There are no plate washes, secondary antibodies or substrate development: buffer and sample are simply injected over the surface. An SPR experiment typically takes minutes to a few hours, compared with hours to days for an ELISA. For a side-by-side, see the advantages of SPR over ELISA.
What are the disadvantages of surface plasmon resonance?
The main disadvantages of surface plasmon resonance are that one binding partner must be immobilized, small analytes produce small signals, non-specific binding and bulk refractive-index effects must be referenced out, and kinetic fits are easy to get wrong. Flow-based systems can clog, and conventional instruments are large, centralized and need trained operators.
None of these rules SPR out for most experiments, but each one needs a plan. Here is what goes wrong, and how to work around it.
1. One partner must be immobilized, and may lose activity
SPR detects binding at the sensor surface, so one partner has to be attached to it. Coupling can block the binding site, orient the ligand poorly or partly denature it, leaving part of the surface inactive. Repeated regeneration can erode activity further.
How to work around it: use a capture strategy (His-tag, biotin, Fc) for oriented presentation instead of random amine coupling, scout the coupling pH, and confirm the surface still binds a known partner. Where it makes sense, swap which partner is immobilized. Our surface chemistry troubleshooting guide covers low immobilization levels and surfaces that couple but barely bind.
2. Small analytes give small signals
The SPR response scales with the mass bound at the surface, so a small molecule binding a large protein produces a much smaller signal than an antibody binding the same protein. Low-molecular-weight analytes, fragments and weak binders can sit close to the noise.
How to work around it: immobilize the larger partner and inject the small one, raise the ligand density within limits (see mass transport below), match buffers carefully, and rely on reference subtraction and replicate channels. SPR is still generally more sensitive than BLI for small analytes; compare SPR and BLI.
3. Non-specific binding and bulk refractive-index effects
SPR responds to anything that changes the refractive index near the surface, not only specific binding. Sticky proteins, serum components and a mismatch between sample and running buffer (for example in DMSO or glycerol content) all add signal that can look like binding.
How to work around it: subtract a reference channel (same surface, no ligand), match the sample and running buffer composition, add Tween 20 (typically 0.005–0.05%) to the running buffer, block unused surface groups, and for serum or lysate use a low-fouling surface such as AffiCoat. See how to reduce non-specific binding.
4. Mass transport and fitting pitfalls
Kinetic constants are only as good as the data and model behind them. If analyte reaches the surface more slowly than it binds (mass transport limitation), the association phase looks linear and fitted rates are wrong. Heterogeneous surfaces, incomplete regeneration or aggregation produce curves that do not fit a simple 1:1 model.
How to work around it: lower the ligand density and, in flow mode, increase the flow rate; extend the contact time if the signal has not plateaued; fit a full concentration series; and fix the surface or concentration range rather than forcing a more complex model. Our guide to measuring KD with SPR and the sensorgram troubleshooting cheat sheet show what good and bad curves look like.
5. Flow systems can clog and need clean samples
Conventional kinetic SPR pumps sample through narrow microfluidic channels. Particulates, aggregates and bubbles can block channels or disturb the baseline, so crude samples usually have to be filtered or clarified first, and the fluidics need regular cleaning.
How to work around it: centrifuge or filter samples, degas buffers and let them reach room temperature before injecting. If you mainly need affinity or concentration rather than full kinetics, static-mode SPR removes the pump and tubing: the sample is injected and binds by diffusion, so there is nothing to clog.
6. Conventional systems are large and need training
Traditional SPR instruments are large systems, often shared in core facilities with booked time and run by trained specialists. That limits how often individual researchers can use SPR, and how quickly they can iterate on an assay.
How to work around it: compact SPR instruments that sit on a standard bench, or a service provider that runs the experiments for you, bring SPR closer to the question. Read more about the advantages of a portable SPR instrument.
7. Throughput is limited by channels
Most SPR instruments read a handful of channels at a time, extended by autosamplers. If you need to screen hundreds of samples a day in 96- or 384-well plates, plate-based methods such as BLI or ELISA are built for that.
How to work around it: use a plate-based method to triage large sample sets and SPR to characterize the shortlist in detail. Many labs use exactly this combination.
How does SPR compare with BLI and ELISA?
SPR, BLI and ELISA answer different questions. ELISA is an end-point, labeled plate assay that is good for high sample numbers. BLI is label-free and plate-based, with no fluidics, but weaker for small analytes. SPR generally offers higher sensitivity than BLI and richer kinetic information than either, at the cost of lower throughput.
For a criterion-by-criterion view, use our technique comparison tool. For a real example, see how SPR and BLI compared in human serum.
Is SPR right for your experiment?
SPR is a strong fit when you need to know how tightly and how fast two molecules bind, want to avoid labels, have limited sample, or must measure in serum or plasma. It is a weaker fit for screening thousands of samples, for analytes too small to resolve, or when neither partner can be immobilized without losing activity.
SPR is likely a good choice if you:
- need affinity (KD), kinetics (kon, koff) or concentration, not just a yes/no answer;
- want to avoid labels that could change the interaction;
- have limited amounts of purified protein or other reagent;
- need to measure in serum, plasma or other opaque matrices.
Consider another technique first if you:
- need to screen hundreds or thousands of samples a day in plate format;
- are working with an analyte too small or too weakly binding to resolve above noise;
- cannot immobilize either partner without losing its activity.
If SPR fits, the next question is whether you need full kinetics. Static-mode SPR (sample injected, no pump) gives affinity (KD) and concentration; flow-based SPR adds on- and off-rates. The P4SPR 2.0 is a static-mode SPR instrument: samples are injected by syringe, with no pump or flow system and no clogging risk. The P4PRO with AffiPump runs both static and kinetic experiments. The static vs kinetic SPR cheat sheet helps you choose.
The bottom line
The advantages of surface plasmon resonance are real: label-free, real-time binding data from small volumes, even in complex samples. So are its disadvantages. Almost all of them come down to three things: the surface, the reference and the fit. Plan those carefully and SPR delivers some of the most informative binding data available.