Electrochemical aptamer-based, or EAB, sensors work by tethering a redox-labeled aptamer, a short single-stranded nucleic acid folded to bind a specific target, to an electrode. When the target molecule binds, the aptamer changes shape, altering the distance between the redox reporter, typically methylene blue, and the electrode surface. That distance change modulates electron transfer, producing a measurable current shift without any reagents or labels. Because the binding is reversible, the same sensor can be interrogated repeatedly, making the platform uniquely suited to real-time tracking in living bodies. The concept dates to work by Fan, Plaxco and Heeger in 2003, and the field has since demonstrated sensors for chemotherapeutics, antibiotics, cocaine, glucose, lactate, phenylalanine and inflammatory cytokines.

The pharmacological applications are the most mature. A landmark system called MEDIC tracked the chemotherapy drug doxorubicin in whole human blood for over four hours with deviations below 0.06 micromolar, then reproduced the feat in live rats, keeping drift below two percent through a signal-processing trick known as kinetic differential measurement. Later work extended the approach to awake, freely moving animals, achieving second-scale pharmacokinetic measurements of antibiotics. More recently, flexible nanoporous gold electrode arrays implanted into melanoma tumors in mice revealed striking differences between drug concentrations in plasma and in tumor tissue, a disparity that conventional blood sampling simply cannot see. In the brain, aptamer-functionalized probes have resolved cocaine dynamics with sub-five-second temporal resolution.

But the review, which synthesizes progress across chemistry, materials science and electronics, is candid about the central obstacle: most EAB sensors survive only hours in the body, not the weeks or months that clinical deployment would demand. The degradation is multifactorial. Repeated voltammetric scanning itself damages the sensor, because potentials more negative than about minus 0.2 volts drive oxygen reduction and generate locally destructive hydrogen peroxide, while potentials above plus 0.2 volts oxidize the gold electrode. Studies using scanning electrochemical microscopy measured peroxide concentrations reaching 320 micromolar near the surface, enough to corrode the self-assembled monolayer that anchors the aptamers.

Even without electrical stress, the sensors fall apart. The gold-sulfur bonds holding the molecular layer degrade thermally at body temperature, with defect-rich regions of the monolayer acting as initiation sites for detachment. At 37 degrees Celsius in serum, conventional mercaptohexanol-based sensors lost their signal within three days, while identical sensors held at 4 degrees Celsius remained robust for at least a week. Endogenous thiols such as cysteine and glutathione compound the problem by chemically displacing the gold-bound molecules, and adsorbing serum proteins restrict the aptamer’s freedom to fold, blunting the signal. Notably, nuclease digestion, long suspected as the primary culprit, turns out to be context-dependent: in vitro, nuclease-resistant mirror-image DNA degraded at nearly the same rate as natural DNA, suggesting fouling and monolayer loss dominate early signal decay, whereas in vivo experiments show enzymatic cleavage becomes significant once interfacial degradation is controlled.

The most compelling recent advance comes from xenonucleic acids, synthetic nucleic acid analogues whose modified backbones evade nuclease recognition. When researchers replaced DNA aptamers with 2′-O-methyl RNA, sensors implanted in rat jugular veins lost only about seven percent of their signal over five hours, compared with roughly forty-eight percent for DNA-based controls, a sevenfold reduction in drift. Building on that foundation, a separate team achieved continuous, seconds-resolved drug measurements over a full week in vivo, tracking circulating tobramycin across multiple dosing events without any protective coating or nanoengineered electrode. After seven days, the sensor still retained about forty percent of its initial current with well-defined voltammetric peaks.

Materials strategies are advancing in parallel. Hydrogel coatings form hydrated barriers that exclude cells and proteins while allowing small molecules to diffuse through; a combinatorially screened polyacrylamide hydrogel kept implanted sensors responsive with only about twenty-four percent signal loss after five days in rat veins. Zwitterionic polymers, whose balanced positive and negative charges bind water exceptionally tightly, resist protein adsorption and have been shown in mice to prevent fibrotic capsule formation for months. Nanostructured electrodes add another layer of protection: nanoporous gold physically shelters aptamers inside nanocavities too small for proteins and nucleases to enter, and when combined with a hyperbranched polyethylene glycol coating, such sensors retained over seventy percent of their signal after twenty-eight days in human serum and remained functional after a week implanted in freely moving rats.

System integration is also maturing rapidly. Application-specific integrated circuits such as the Analog Devices AD5940 now provide miniaturized, low-noise electrochemical front ends, while Bluetooth Low Energy microcontrollers handle wireless data transmission. Fully integrated platforms have been demonstrated across nearly every form factor: a skin-mounted wearable patch that measures the hormone estradiol in induced sweat with a detection limit of 0.14 picomolar, a microneedle array for interstitial fluid metabolites, a battery-free implantable catecholamine sensor, and an ingestible capsule that monitored serotonin, glucose and pH in the gut for over twenty hours. Most strikingly, a first-in-human pilot study reported a wearable EAB patch for continuous vancomycin monitoring in dermal interstitial fluid, delivering five-minute-resolved measurements for more than a day, though signal degradation limited the highest-quality data to the first twelve hours.

An emerging frontier is bioresorbability, the idea that sensors should safely dissolve after their useful life rather than require surgical retrieval. Printed electrochemical glucose monitors built from zinc, molybdenum and tungsten pastes on biodegradable polymer substrates have been shown to disappear completely within eight weeks in rats, leaving no residue or inflammation. A newly reported programmable system goes further, using an electronic suture to connect a bioresorbable microneedle implant to external electronics, with an applied electrical trigger commanding when the implant begins to degrade, enabling multimodal monitoring of deep-organ physiology without permanent hardware.

The review’s authors distill the remaining challenges into a clear agenda: extending operational lifetimes from days to months, quantitatively deciphering how degradation mechanisms interact in vivo, combining stabilization strategies that have so far been deployed in isolation, building fully integrated and eventually fully bioresorbable devices, and pushing the platform toward difficult targets such as low-abundance proteins, whose slow diffusion and tight binding kinetics complicate reversible sensing. If those hurdles fall, the payoff could be transformative: continuous troponin monitoring for earlier heart attack detection, real-time chemotherapy dosing guided by tumor microenvironments, and round-the-clock cytokine tracking for autoimmune disease. The field has proven that aptamer sensors can see molecules no enzyme-based monitor can. The task now is to make them last long enough to matter.

Subject of Research: Electrochemical aptamer-based sensors for long-term in vivo continuous molecular monitoring

Article Title: Continuous Molecular Monitoring Using Electrochemical Aptamer‐Based Sensors: Remaining Challenges for Long‐Term In Vivo Deployment

Article References: Liu, S., Li, X., & Ouyang, W. (2026). Continuous Molecular Monitoring Using Electrochemical Aptamer‐Based Sensors: Remaining Challenges for Long‐Term In Vivo Deployment. Advanced Science, Article e77896. https://doi.org/10.1002/advs.77896

Image Credits: AI Generated

DOI: 10.1002/advs.77896

Keywords: aptamers, electrochemical biosensors, continuous monitoring, xenonucleic acids, biofouling, drug monitoring, wearable sensors, implantable devices, bioresorbable electronics, nanoporous gold, zwitterionic coatings, precision medicine