Enzymatic Biosensors: Why the Biggest Hurdle Is Not New Materials

Enzymatic biosensors have quietly become one of the workhorses of modern analytical science, converting the exquisite specificity of biological catalysts into measurable signals for clinical, environmental and industrial applications. Ever since Clark and Lyons described the first enzyme electrode in 1962, holding glucose oxidase against an oxygen electrode behind a semipermeable membrane, the field has promised rapid, selective detection of biologically significant molecules. Yet a new review published in Frontiers in Sensors argues that the path to better devices runs not primarily through exotic new materials, but through a reckoning with how the field measures and reports its own performance.

The review, written by researchers at the Universidad Autónoma de Nuevo León and collaborators in Mexico, examines the kinetic and thermodynamic foundations of enzymatic sensing, the engineering of enzyme immobilization, signal amplification strategies and the full range of transduction architectures, from electrochemical and optical platforms to semiconductor devices and emerging in-sensor computing. Its central claim is provocative: the most consequential unresolved problem is not a shortage of new materials or immobilization chemistries, but the absence of standardized, quantitative benchmarking that would allow fair comparison between competing strategies.

At the heart of the argument lies a distinction that is easy to state and easy to overlook. Classical Michaelis–Menten kinetics describes an enzyme freely dissolved in a well-mixed solution, where the Michaelis constant reflects enzyme–substrate affinity and the maximum velocity sets the ceiling of the response. Almost no biosensor operates in that regime. Once an enzyme is confined to an electrode surface, a porous carrier or a polymer film, the measured response becomes a convolution of catalysis, substrate partitioning between phases and diffusion through the immobilization layer and the adjacent boundary layer. The parameters extracted from such a device are therefore apparent values that reflect the complete sensing architecture rather than the enzyme itself.

The magnitude of this effect is far from marginal. For lactate oxidase immobilized by the same chemistry on two different carbon matrices, apparent Michaelis constants of 73.7 millimolar and 8.25 millimolar were reported, a spread approaching an order of magnitude arising solely from the choice of electrode matrix. Laccase covalently attached to a lignocellulosic support through glutaraldehyde showed its constant rising from 0.53 to 0.72 millimolar after immobilization, an increase attributed to diffusional limitation within the porous carrier, steric hindrance near the active site and conformational constraint from multipoint attachment. Nor does the shift always run in one direction: horseradish peroxidase immobilized on magnetic hybrid nanoflowers showed its apparent constant falling from 15.55 to 7.67 millimolar while its maximum velocity dropped roughly eighteen-fold, demonstrating that apparent affinity and catalytic throughput can move independently.

These transport effects can be diagnosed rather than assumed. Dimensionless treatments based on the Damköhler number, which compares the characteristic reaction rate to the characteristic transport rate, together with current-control coefficients, have been applied directly to enzyme electrodes, while the Thiele modulus and effectiveness factor serve the same role for entrapped systems. The numbers can be sobering: effectiveness factors between 6 and 14 percent have been reported for enzymes trapped in printed hydrogel carriers, and counterintuitively, the effectiveness factor decreased as the absolute activity of the entrapped enzyme increased, because a faster enzyme exhausts its local substrate supply sooner. The practical consequence is that a quoted apparent constant without the accompanying immobilization chemistry, layer thickness, loading and hydrodynamic conditions is difficult to interpret and cannot be reliably compared across studies.

Immobilization strategy itself emerges as a field of trade-offs rather than a ladder of progress. Physical entrapment in sol–gel silica, hydrogels or polysaccharide matrices preserves the native enzyme structure but invites diffusion limitations and leakage. Covalent attachment through glutaraldehyde, EDC/NHS or epoxy-silane chemistry reduces leaching and survives harsh conditions, but rigid attachment can compromise catalytic efficiency if orientation is uncontrolled. Oriented strategies, including affinity tags and site-directed chemistry, can deliver striking gains: a glucose dehydrogenase wired site-specifically through an unnatural amino acid showed more than fifteen times higher catalytic current and ten-fold higher sensitivity than the same enzyme wired non-specifically. But the review is emphatic that these advantages are conditional. Adding a routine His-tag can be enough to compromise an enzyme, and a twenty-fold activity decrease has been reported for an azoreductase depending on where the fusion partner sat. Site-directed attachment through an unsuitable site can even fare worse than random immobilization, retaining only 10 percent of functionality in one systematic comparison against 50 percent for a randomly oriented control.

Nanoengineered platforms add further promise and further caveats. Metal–organic frameworks can encapsulate enzymes and shield them from denaturation: glucose oxidase immobilized on ZIF-7-III retained 98 percent of its relative catalytic activity, stayed stable up to 80 degrees Celsius and preserved 66 percent of activity after 60 days of storage. Co-immobilizing laccase with its mediator in a doped framework improved catalytic efficiency 2.6-fold over the free enzyme. Carbon nanomaterials, meanwhile, cut both ways: in a structure–function comparison, multi-walled carbon nanotubes induced conformational change and reduced glucose oxidase activity by 7 percent, whereas bio-graphene preserved function and yielded sensors with 1.33-fold higher sensitivity. The review stresses that the benefits of nanostructuring come with greater fabrication complexity, and that reproducibility across batches remains less well documented than reported peak performance.

On the transduction side, the survey spans amperometric, potentiometric and impedimetric electrochemical devices, optical platforms, enzymatic field-effect transistors and wearable formats. A photoelectrochemical solution-gated graphene transistor functionalized with an acetylcholinesterase–nanozyme cascade reported a thousand-fold current gain and a detection limit of 0.05 picomolar for organophosphates, with a companion quantum-dot configuration reaching 0.21 picomolar. Wearable sweat patches have demonstrated simultaneous glucose and alcohol determination with minimal drift over 30 hours, and a microneedle glucose sensor reported a sensitivity of 137.7 nanoamperes per milligram per deciliter with interferent currents below 4 percent in artificial interstitial fluid. Yet the review identifies three recurring constraints that it considers more limiting than sensitivity: sweat metabolite concentrations correlate imperfectly with blood values, on-body operation exposes enzymes to mechanical deformation and a dehydrating microenvironment, and calibration drift over multi-day wear remains poorly characterized because lifetimes are usually reported in hours rather than days of realistic use.

Perhaps the most striking section is the case study of gas-phase enzymatic detection of volatile organic compounds, which the authors treat as a stress test for every design principle. The subfield turns out to be far smaller and more chemically constrained than commonly implied: their searches returned on the order of tens of records against a liquid-phase literature numbering in the tens of thousands, and nearly all verified devices come from a single research group sharing one architecture, an NAD(P)-dependent dehydrogenase held in a hydrated polymer on a porous membrane with fluorometric detection of NADH autofluorescence. Reported analytes are largely short-chain alcohols, aldehydes and ketones, and the authors identified no verified enzymatic gas-phase biosensor for benzene, toluene, ethylbenzene or xylenes. Crucially, every device operates with the enzyme in a hydrated condensed phase, meaning gas-phase biosensing is more accurately described as vapor partitioning into a thin wet layer followed by conventional aqueous biocatalysis. Extending the field to aromatic volatiles, they conclude, is primarily an enzyme-discovery and enzyme-engineering challenge, not a materials problem.

The review closes with five priorities, chief among them the benchmarking gap. The authors call for future studies to report apparent kinetic parameters together with the architectural and hydrodynamic conditions that determine them, and to describe stability as retained performance over a defined period rather than an isolated figure of merit. They also urge validation in realistic matrices rather than buffered solutions, and integrated, application-specific design in which enzyme selection, immobilization, mass transport, nanomaterial architecture and transduction are optimized as a coupled system. Emerging in-memory and in-sensor computing architectures, including memristive transducers that perform threshold sensing within the device, could eventually address drift and reproducibility locally, but the authors are careful to frame this as an aspiration rather than a demonstrated capability for enzymatic devices. Their broader message is that performance trade-offs are unavoidable and should be reported openly: stabilization restricts the very conformational motions that catalysis requires, and reviews that celebrate only performance gains offer an incomplete picture. Closing the benchmarking gap, they argue, may matter as much for advancing the field as the next generation of sensing architectures themselves.

Subject of Research: A review of enzymatic biosensor design, covering enzyme kinetics, immobilization strategies, signal amplification, transduction platforms and gas-phase volatile organic compound sensing.

Article Title: Enzymatic biosensors: biocatalytic mechanisms, immobilization strategies, and signal amplification approaches

Article References: Arvizu-De León, I. C., Quintanilla-Villanueva, G. E., Cedillo-González, E. I., Muñoz-Benítez, J., Villarreal-Chiu, J. F., & Rodríguez-Delgado, M. M. (2026). Enzymatic biosensors: biocatalytic mechanisms, immobilization strategies, and signal amplification approaches. Frontiers in Sensors, 7, Article 1933492. https://doi.org/10.3389/fsens.2026.1933492

Image Credits: AI Generated

DOI: 10.3389/fsens.2026.1933492

Keywords: enzymatic biosensors, enzyme immobilization, Michaelis-Menten kinetics, signal amplification, nanomaterials, field-effect transistors, wearable biosensors, volatile organic compounds, direct electron transfer, benchmarking, cofactor regeneration, metal-organic frameworks