Therapeutic drug monitoring: how electrochemical sensors measure drugs in serum
When a doctor prescribes a medicine, the dose is usually based on factors such as body weight or age. Yet two patients given the same dose can end up with very different drug levels in their blood. For drugs with a narrow therapeutic window, including several anticancer drugs, that difference can decide whether a treatment works, fails or causes serious side effects. This is where therapeutic drug monitoring (TDM) comes in, and where electrochemical sensors may help.
What is therapeutic drug monitoring?
TDM means measuring the concentration of a drug, usually in blood, serum or plasma, and using that value to adjust the dose for an individual patient. It is most useful when the gap between an effective and a toxic concentration is small and when people handle the drug very differently.
In clinical practice, immunoassays are used as routine methods and liquid chromatography–tandem mass spectrometry (LC-MS/MS) is accepted as the reference method (Ates et al., 2020). Both need central laboratories and trained staff, and LC-MS/MS has a lower throughput than immunoassay platforms (Ates et al., 2020). This has driven interest in on-site and point-of-care TDM.
How an electrochemical sensor reads a drug in serum
Many drug molecules contain groups that can be oxidised or reduced at an electrode. An electrochemical sensor applies a controlled potential and records the resulting current; within the working range, that current increases with the drug concentration. A typical measurement looks like this:
A small volume of serum, often diluted with buffer, is placed on the electrode, for example a disposable screen-printed strip.
The potential is scanned with a sensitive technique such as differential pulse or square-wave voltammetry.
The drug is oxidised or reduced at its characteristic potential and produces a current peak.
The peak height is converted into a concentration using a calibration curve.
A useful analogy is a fuel gauge. Once calibrated with known standards, the signal rises with the amount of drug present. Current research aims to make these sensors sensitive enough for the low drug levels found in patient samples (Florescu, 2024).
Why serum is a demanding sample
Serum is not a clean solution. Proteins such as albumin can adsorb onto the electrode and block it (fouling), and other electroactive compounds can give signals close to the drug's peak. Two strategies are widely used to deal with this:
Nanomaterials: carbon nanomaterials and metal nanoparticles increase the active surface area and speed up electron transfer, which improves sensitivity.
Molecularly imprinted polymers (MIPs): a polymer layer with cavities shaped like the target drug lets the drug bind while larger or differently shaped molecules are kept out, which improves selectivity. MIP-based sensors and nanosensors for anticancer drugs are reviewed by Samancı et al. (2025).
Key takeaways
TDM adjusts doses based on measured drug levels, which matters most for drugs with a narrow therapeutic window.
Electrochemical sensors turn the oxidation or reduction of a drug into a current that can be calibrated against concentration.
In serum, selectivity and resistance to fouling are as important as sensitivity; nanomaterials and MIPs address these needs.
Therapeutic drug monitoring at SAOnS Lab
At SAOnS Lab, we develop electrochemical and molecularly imprinted polymer-based sensors for the determination of drugs, including anticancer agents, in pharmaceutical and biological samples. Our group's review on the electrochemical analysis of anticancer drugs with MIP-based sensors and nanosensors (Samancı et al., 2025) gives an overview of this field.
Are you working on a drug that would benefit from faster monitoring? We would be glad to hear from you through our website.
References
Ates, H. C., Roberts, J. A., Lipman, J., et al. (2020). On-site therapeutic drug monitoring. Trends in Biotechnology, 38(11), 1262–1277. https://doi.org/10.1016/j.tibtech.2020.03.001
Florescu, M. (2024). Ultrasensitive electrochemical (bio)sensors for therapeutic drug monitoring. Current Opinion in Electrochemistry, 46, 101501. https://doi.org/10.1016/j.coelec.2024.101501
Samancı, S. N., Ozcelikay, G., & Özkan, S. A. (2025). A review: electrochemical analysis and application of anticancer drugs with MIP-based sensors and nanosensors. Essential Chem, 2(1), 1–19. https://doi.org/10.1080/28378083.2025.2459262
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