Microneedle-based sampling of dermal interstitial fluid biomacromolecules: transport constraints, design principles, and diagnostic translation

1 Introduction

Dermal interstitial fluid (ISF) is an extracellular fluid surrounding the cells within skin tissue and serves as the immediate biochemical environment through which cells acquire nutrients, exchange metabolites, and communicate via molecular signals (Friedel et al., 2023; Tran et al., 2018; Fogh-Andersen et al., 1995; Miller et al., 2018; Nilsson et al., 2019; Samant and Prausnitz, 2018; Ming et al., 2022). The molecular composition of dermal ISF is shaped by both systemic input from the vasculature and local tissue activity, including immune surveillance, inflammation, extracellular matrix remodeling, and cell turnover (Friedel et al., 2023). As a result, ISF contains diverse classes of biomolecules, including metabolites, soluble proteins and peptides, immunoglobulins (Ig), nucleic acids, and extracellular vesicles (EV), many of which are directly involved in disease mechanisms rather than being downstream correlates (Friedel et al., 2023; Fogh-Andersen et al., 1995; Liu et al., 2025; Merzougui et al., 2025; Saifullah and Faraji Rad, 2023; Wu et al., 2024; Ribet et al., 2023; Bao et al., 2022; Al Sulaiman et al., 2019). Among these, biomacromolecules-proteins, nucleic acids, and EVs represent critical classes of diagnostic biomarkers. Soluble proteins and peptides-including cytokines, chemokines, enzymes, immunoglobulins (Ig) and peptide hormones-influence immune signalling, inflammation, and metabolic regulation and constitute the foundation of many clinically established blood-based assays. (Friedel et al., 2023; Ribet et al., 2023). Ig serve as integrated indicators of immune status, infection, vaccination response, allergy, and autoimmunity and are therefore central to serological diagnostics (Friedel et al., 2023; Bao et al., 2022; Sjöbom et al., 2020). Extracellular nucleic acids, particularly microRNAs and other cell-free RNA species, provide sequence-specific insight into gene regulation, cellular stress, and disease-associated transformation, supporting their emergence as highly specific molecular biomarkers (Liu et al., 2025; Al Sulaiman et al., 2019). EV including exosomes, constitute a higher-order biomarker class by encapsulating proteins and nucleic acids within lipid bilayers, thereby preserving cell-of-origin information and enabling multiplex molecular readouts from a single nanoscale entity (Tran et al., 2018; Miller et al., 2018; Smith et al., 2025).

Accessing dermal ISF for biomarker analysis has been enabled by a range of sampling approaches, including suction blistering, microdialysis, open-flow microperfusion, reverse iontophoresis, and, more recently, microneedle-based techniques (Friedel et al., 2023). Collectively, these methods have demonstrated good correlation between biomarkers measured in blood and ISF, supporting the potential of ISF as an alternative diagnostic sample (Friedel et al., 2023; Saifullah and Faraji Rad, 2023). In several studies, ISF biomarker profiles show substantial overlap with plasma while also capturing tissue-proximal signals that may be diluted or obscured in circulation (Friedel et al., 2023; Tran et al., 2018; Miller et al., 2018). Each ISF sampling strategy presents distinct advantages and limitations. Established techniques such as suction blistering and microdialysis can yield analytically rich samples but are time-consuming, invasive, and poorly suited for routine or repeated use (Rao et al., 2025). In contrast, microneedle-based approaches offer minimally invasive, scalable access to dermal ISF and are compatible with both laboratory-based analyses and emerging point-of-care formats, albeit with constraints related to sampled volume, analyte recovery, and potential sampling-induced discomfort (Friedel et al., 2023).

Microneedle (MN) technologies enable minimally invasive access to dermal interstitial fluid by breaching the stratum corneum while largely avoiding vascular penetration (Samant and Prausnitz, 2018; Samant et al., 2020; Zhou et al., 2023). MNs typically comprise micron-scale projections (∼250–1,000 μm) that form transient microchannels into the viable epidermis or superficial dermis, supporting either in situ sensing or localized ISF extraction depending on device architecture (Friedel et al., 2023; Miller et al., 2018; Ming et al., 2022; Liu et al., 2025; Merzougui et al., 2025; Hung et al., 2025; Ma et al., 2023; Heikenfeld et al., 2019; Alkasem and Can, 2025). Clinically, MN-based ISF sensing has achieved its greatest success in continuous glucose monitoring, which employs a single solid, flexible polymer filament (>5 mm length, ∼200–400 μm diameter) implanted in the dermal or subcutaneous ISF rather than microneedle arrays or bulk extraction devices (Heikenfeld et al., 2019). This diffusion-based, enzyme-coupled electrochemical architecture is well suited to small, rapidly equilibrating analytes. Beyond glucose, MN-enabled lactate monitoring has been evaluated in human clinical and translational studies, demonstrating correlation with blood lactate trends, but remains at the clinical trial or advanced prototype stage (Ming et al., 2022). More broadly, MN-based ISF platforms have been extensively explored for small ions and low–molecular-weight drugs, which are favorable targets due to their rapid diffusion, fast blood–ISF equilibration, and limited interaction with the dermal extracellular matrix (Ming et al., 2022; Alkasem and Can, 2025).

While dermal ISF contains a regulated and protein-rich extracellular compartment distinct from plasma and lymph, effective access to these biomacromolecules depends critically on the sampling interface. Unlike small-molecule sensing, the extraction and detection of proteins, nucleic acids, and extracellular vesicles require device architectures that account for molecular size, binding interactions, extracellular matrix hindrance, and limited accessible volume. Consequently, the design of microneedle (MN) platforms-encompassing geometry, material composition, penetration depth, sampling mechanism, and downstream analytical compatibility, becomes central to enabling reliable and repeatable ISF-based biomacromolecule diagnostic monitoring.

Existing reviews have addressed this field from complementary perspectives, including broad overviews of microneedle-based ISF sampling and biosensing, analyte-specific focus on nucleic acid detection, and physiological analyses of ISF transport and diagnostic relevance (Friedel et al., 2023; Liu et al., 2025; Saifullah and Faraji Rad, 2023; Wu et al., 2024; Zhou et al., 2023; Ma et al., 2023). In contrast, this mini review focuses specifically on biomacromolecule sampling using microneedles, adopting a mechanism- and transport-oriented framework to compare how different MN strategies influence recovery, representativeness, and analytical performance, thereby providing a more application-driven and translational perspective.

2 Physiological constraints on macromolecule access and representativeness of extracted ISF

Dermal ISF contains most blood-borne biomolecules, but the fraction that is practically accessible and the extent to which an extracted sample reflects physiological ISF depends strongly on skin microstructure and transport barrier (Friedel et al., 2023; Fogh-Andersen et al., 1995; Saifullah and Faraji Rad, 2023; Heikenfeld et al., 2019). The dermis behaves as a porous, hydrogel-like matrix, collagen and glycosaminoglycans bind water and create high hydraulic resistance, while simultaneously imposing size- and charge-dependent hindrance that disproportionately affects proteins, antibodies, nucleic acids, and vesicles compared with small molecules (Nyström and Bruckner-Tuderman, 2019; Walicka and Iwanowska-Chomiak, 2018). Even where ISF is abundant systemically, the accessible dermal ISF volume per unit area is small and its replenishment is slow, constrained by high dermal fluidic resistance and lymphatic clearance (Friedel et al., 2023). Consequently, bulk extraction approaches face a physiological “speed limit”: pulling fluid too quickly increases the risk that the collected material is no longer compositionally representative for larger biomolecules, particularly when compared with capillary blood volumes that can be obtained rapidly.

A key constraint is that dermal fluid is not fully “free”, rather a substantial fraction is bound water associated with ECM components and is not readily extractable. Because the ECM acts as a mesh-like barrier, forced/rapid extraction preferentially mobilizes water and small solutes, whereas macromolecules experience reduced convective transport and can be under-represented in collected samples. Finally, partitioning from blood to ISF is not uniform across analytes. Transport across continuous dermal capillaries is governed by endothelial junctions, glycocalyx charge effects, and vesicular transcytosis, so the ISF: blood ratio depends on size, charge, hydrophobicity, and protein-binding state (Pries et al., 2000; Levick and Michel, 2010). This is especially important for hormones/drugs that are highly protein-bound (sensors may reflect the free fraction), and for mid-to-large proteins (ranging from 3 kDa and as large as 1,000 kDa) that sit near size-selective thresholds.

3 Microneedle platforms as controlled interfaces to overcome dermal ISF sampling constraints

The physiological constraints outlined above define a narrow operating window for reliable biomacromolecule sampling from dermal interstitial fluid. MN platforms address these challenges by providing spatially controlled, minimally invasive access to the viable epidermis and superficial dermis while limiting vascular disruption and large-scale fluid shifts. Unlike conventional extraction techniques, MNs function as engineered interfacial systems: their geometry, insertion depth, material chemistry, and transport mechanism can be tuned to minimize dilution, reduce pressure-induced compositional artifacts, or enable selective enrichment via affinity capture or electro-assisted transport (Anbazhagan et al., 2023; Davis et al., 2004). In this way, MNs shift the sampling paradigm from bulk ISF removal toward controlled, mechanism-specific access to biomacromolecules. The following section examines how device architecture and transport principles govern biomacromolecule recovery and analytical performance.

4 Design principles and transport constraints governing microneedle-based sampling of biomacromolecules from dermal ISF

Effective microneedle-based biomacromolecule sampling is governed by two coupled determinants: device architecture and transport mechanism. Device geometry, material composition, and insertion depth define the physical interface with dermal tissue, while the chosen extraction strategy determines how macromolecules traverse the ECM and reach the analytical interface. Because dermal ISF transport is inherently constrained by ECM hindrance, limited accessible volume, and size-dependent partitioning (Section 2), MN design cannot be separated from transport physics. This section therefore first examines structural design parameters (Section 4.1) and then analyses how specific MN-enabled transport mechanisms shape biomacromolecule recovery, selectivity, and potential sampling bias (Section 4.2).

4.1 Device design principles: geometry, material, and architecture

Microneedle device architecture fundamentally governs tissue access, local ISF availability, and the efficiency of biomacromolecule sampling. Reported platforms employ either single microneedles or array configurations, with needle heights typically ranging from ∼250 to 1,000 µm (Table 1). Needles shorter than ∼300 µm primarily access the viable epidermis, whereas those in the 600–800 µm range more consistently penetrate into the superficial dermis, where ISF volume and vascular proximity are greater (Gill et al., 2008). However, increasing penetration depth does not necessarily translate to improved macromolecular recovery, as transport remains limited by extracellular matrix constraints. Moreover, deeper insertion increases the risk of nociceptor activation and potential blood mixture, complicating quantitative interpretation.

TABLE 1. Microneedle-based platforms for biomacromolecule analysis in dermal ISF.

4.2 Mechanisms of microneedle-enabled ISF collection and extraction in biomacromolecule studies

MN platforms access dermal ISF through a limited set of physical transport mechanisms. Table 1 captures several representative design classes, which differ not only in the driving force for fluid/analyte transport but also in the bias they impose on macromolecule recovery (e.g., selective partitioning, blood admixture risk, and pressure-dependent proteome shifts).

4.2.1 Passive bulk ISF withdrawal through hollow needles into microcapillaries

One of the most direct strategies uses hollow MN (or short hypodermic “pen” needles) as conduits that hydraulically connect the interstitial to an external collector. Tran et al. assembled an array of five 32G ultrafine nano pen needles in a 3D-printed holder and attached microcapillaries to each needle to collect small volumes of ISF from human forearm skin (Tran et al., 2018). Similar hollow-needle configurations, including multi-needle pen arrays and modified hypodermic assemblies coupled to external collectors, have been employed in other proteomic ISF studies to enable passive bulk withdrawal without integrated suction systems (Miller et al., 2018; Ribet et al., 2023). Mechanistically, flow is driven by a combination of local interstitial pressure, capillary forces in the collection tubing, and transient fluid redistribution following puncture. This approach yields “bulk” ISF suitable for downstream proteomics, but volumes are small (<20 µL in Tran et al.), necessitating high-sensitivity workflows and extensive fractionation.

Taken together, hollow microneedle systems provide the most direct route to bulk ISF collection and enable downstream quantitative proteomic analysis. However, their performance is fundamentally constrained by low accessible ISF volume and slow replenishment, resulting in limited yield and extended sampling times. In addition, pressure-driven withdrawal may introduce variability in sample composition, particularly for larger biomacromolecules that are transport-limited within the extracellular matrix.

4.2.2 Capillary-driven ISF extraction using porous MNs coupled to paper microfluidics

Bao et al. demonstrate a distinct mechanism: porous polylactic acid (PLA) microneedles fabricated from heat-bonded microspheres create interconnected micropores that wick ISF by capillary effect (Bao et al., 2022). Here, porous MNs act as both skin-penetrating access points and capillary pumps, moving ISF from tissue into the device without external actuation. Bao et al. further integrate this with a layered immunochromatographic strip where ISF is transported vertically and then laterally through the membrane stack by capillary action to enable rapid (minutes-scale) anti-COVID 19 IgG/IgM detection. Capillary-driven porous microneedle systems enable simple, equipment-free sampling and are well suited for point-of-care applications. However, transport through tortuous pores and paper matrices introduces size-dependent filtration and sensitivity to fluid viscosity and protein content, leading to flow variability. As a result, these systems may preferentially recover smaller or more mobile biomolecules, limiting their suitability for comprehensive biomacromolecule profiling.

4.2.3 Pressure-gradient–driven bulk extraction from puncture sites

Hung et al. describe a mechanistically defined extraction strategy termed Puncture-Out-and-Press (POP), grounded in Darcy’s law–governed fluid flow in porous media, where ISF flux is driven by a spatially engineered pressure gradient within the dermis (Hung et al., 2025). In this configuration, a solid microneedle array punctures the skin through aligned apertures in a collection plate. After needle removal, external compression is applied to the surrounding skin while leaving the puncture sites uncompressed. This generates a lateral pressure gradient that directs ISF toward the punctures, where it accumulates and is collected via surface tension. Under optimized conditions, POP enabled extraction of 15.5 ± 7 mg of ISF within 5 min in human participants, corresponding to microliter-scale sampling volumes. The recovered ISF was subjected to untargeted LC-MS/MS proteomic profiling, identifying a broad ISF proteome and enabling quantitative comparison with plasma. The authors further demonstrate that extraction efficiency and proteomic composition are sensitive to applied pressure distribution, with POP outperforming needle-in and vacuum-assisted variants in both yield and reproducibility (Hung et al., 2025).

Pressure-assisted extraction strategies can overcome diffusion limitations and enable significantly higher ISF yield compared to passive approaches. However, the imposed pressure gradients may alter local fluid composition and introduce sampling bias, particularly for macromolecules with restricted mobility, highlighting a trade-off between extraction efficiency and physiological representativeness.

4.2.4 Swelling hydrogel MNs: passive absorption driven by osmotic swelling and polymer network partitioning

Swelling hydrogel MNs absorb ISF into a polymer network after insertion. Laszlo et al. develop superabsorbent acrylate-based hydrogel MN patches that “collect up to 6 µL of dermal ISF in 10 min in vivo,” enabling proteomic analysis from swelling-based collection (Laszlo et al., 2021). Mechanistically, dry hydrogel needles rapidly hydrate; osmotic forces and polymer swelling draw water and solutes into the expanding network. Importantly, Laszlo et al. explicitly identify that the “extraction fingerprint is strongly dependent on the MN chemistry,” implying that hydrogel formulation does not merely collect ISF but selectively partitions biomolecules depending on polymer composition and interactions. Swelling MNs are attractive for proteomics because they can accumulate microliter volumes without pumps. But, swelling-driven uptake is inherently diffusion-limited and dependent on polymer chemistry, leading to potential dilution effects and selective partitioning of biomolecules. Consequently, these systems may not provide a compositionally representative ISF sample without careful material design and calibration.

4.2.5 Electro-assisted extraction and capture: reverse iontophoresis + hydrogel MN capture

For nucleic acids, Yang et al. implement a hybrid mechanism: reverse iontophoresis (electric field) + hydrogel microneedle capture to enrich negatively charged cfDNA toward the collection interface. The group frames this as an iontophoretic dual-extraction wearable patch and uses reverse iontophoresis conditions (10 V, 10 min) coupled with microneedle insertion (Yang et al., 2020). Unlike volumetric ISF withdrawal, this mechanism is molecule-directed transport, where electrophoretic migration and electroosmotic effects can dominate recovery of charged macromolecules. Electro-assisted extraction can overcome diffusion limitations for charged species (cfDNA). However, their dependence on external power, sensitivity to skin impedance, and the need for downstream amplification introduce additional system complexity, which may limit translation to simple point-of-care applications.

4.2.6 Affinity capture on MNs: selective binding rather than bulk ISF collection

Smith et al. developed a stellate silicon microneedle platform (“ExoPatch”) designed for in situ affinity capture of tumor-associated extracellular vesicles (EVs) directly from dermal interstitial fluid (Smith et al., 2025). The device consists of a 13 × 13 array of silicon microneedles, each approximately 600 µm in height, spaced at 500 µm intervals, and fabricated from a 1 mm thick silicon wafer. Unlike bulk ISF extraction systems, ExoPatch operates through a binding-mediated capture mechanism. The microneedles are coated with a thin (≤10 µm) alginate–polyvinyl alcohol (PVA) hydrogel layer functionalized with Annexin V (AV). Annexin V binds phosphatidylserine (PS), which is enriched on the membrane of tumor-derived exosomes. Thus, capture is driven by surface affinity interactions, not volumetric ISF withdrawal. The study reports sensitive detection of melanoma-associated exosomes in murine melanoma models and distinguishes tumor-bearing from healthy samples using the LFIA readout. However, the LFIA output is primarily qualitative or semi-quantitative (visual band intensity), and no absolute exosome concentration (e.g., particles/mL) is reported. The system does not provide a defined volumetric sampling metric, as capture efficiency is governed by binding kinetics and hydrogel surface chemistry rather than extracted ISF volume. This work represents a distinct class of MN-based ISF biomacromolecule sensing: a capture–release–detect workflow, where the limiting factor is surface binding capacity and affinity kinetics, rather than ISF volume yield. It highlights that, for nanoscale vesicles (30–150 nm), affinity-driven enrichment may be more effective than bulk convective extraction approaches.

Affinity-based microneedle systems represent a fundamentally different sampling paradigm, relying on selective binding rather than bulk ISF extraction. While this enables targeted detection of specific biomolecules such as extracellular vesicles or proteins, it introduces bias associated with binding kinetics and molecular specificity. As a result, these systems provide high selectivity but do not yield a comprehensive representation of ISF composition.

Across these microneedle platforms, a consistent set of design trade-offs emerges between sampling efficiency, selectivity, and system complexity. Passive approaches, including hydrogel and porous microneedles, offer simplicity and minimal invasiveness but are constrained by diffusion-limited transport and low recovery efficiency for biomacromolecules. In contrast, active strategies such as pressure-assisted and electrokinetic systems improve extraction rates and access to larger or low-abundance analytes but require external actuation and may perturb the local ISF environment. Affinity-based platforms avoid bulk fluid extraction entirely by selectively capturing target molecules, enabling high specificity at the expense of representativeness. As summarized in Table 1, no single platform currently achieves high-efficiency, unbiased, and fully integrated sampling and sensing, highlighting the need for hybrid approaches that balance these competing design requirements.

5 Analytical performance, quantification, and clinical translation

Across microneedle-based platforms, the key analytical challenge is not only whether biomacromolecules can be detected, but what type of measurement each platform fundamentally produces and how that relates to physiological ISF composition. Reported performance metrics are therefore not directly comparable across studies, as they reflect distinct sampling paradigms with different relationships to transport limitations, recovery efficiency, and sampling bias.

5.1 Quantification versus capture: What is being measured?

Microneedle-based platforms for dermal ISF biomacromolecule analysis do not all measure the same analytical quantity, even when they report detection of the same biomarker class. A central distinction across the field is whether the platform is designed to recover a defined amount of ISF for downstream analysis or to selectively capture target molecules at the microneedle interface without true volumetric sampling. This distinction is critical because it determines how signal should be interpreted and whether the reported output can be considered a concentration measurement, an enrichment readout, or a capture-dependent proxy.

In volumetric sampling approaches, the analytical objective is to obtain bulk ISF that can be processed using downstream assays such as proteomics, transcriptomics, or immunoassays. In principle, these systems are the most compatible with absolute or relative concentration measurements because they are based on physical fluid recovery. However, this advantage depends on whether extraction volume is sufficiently defined and whether the recovered sample remains compositionally representative of native ISF. For biomacromolecules, this is a substantial limitation because extracellular matrix hindrance, slow replenishment, and size-dependent transport can cause extracted fluid to differ from the in situ molecular environment, particularly when sampling is rapid or pressure-driven.

By contrast, capture-based systems do not primarily measure the composition of extracted ISF, but rather the extent to which target molecules reach and bind to a functionalized interface. Their output is therefore governed by local analyte flux, affinity interactions, binding capacity, and residence time rather than recovered fluid volume. This makes such systems highly attractive for selective detection of low-abundance or diagnostically specific targets, but it also means that the measured signal cannot be interpreted in the same way as a bulk concentration unless the capture process has been rigorously calibrated.

These two paradigms also differ in the type of bias they introduce. Volumetric sampling is more vulnerable to dilution effects, blood admixture, and pressure- or flow-dependent changes in sample composition. Capture-based platforms, on the other hand, are more vulnerable to kinetic bias, competitive binding, and selective enrichment of only those molecules that can efficiently access and interact with the sensing surface. As a result, neither approach is intrinsically superior; rather, each is suited to a different analytical goal. Bulk extraction is more appropriate when broader molecular profiling or downstream multianalyte analysis is desired, whereas capture-based systems are better suited to targeted detection when specificity is more important than representativeness.

5.2 Sensitivity, dynamic range, and matrix effects

Analytical performance in MN-based ISF biomacromolecule platforms is governed not only by the detection method, but by the underlying sampling mechanism. Reported sensitivity and detection limits therefore reflect combined effects of transport constraints, sampling efficiency, and analyte–matrix interactions, making direct comparison across platforms non-trivial. In volumetric sampling approaches, sensitivity is limited by low ISF volume and restricted transport of biomacromolecules, requiring high-sensitivity downstream assays. In contrast, capture-based and electro-assisted systems can enhance apparent sensitivity through selective enrichment, but the resulting signal reflects transport and binding efficiency rather than equilibrium concentration. Dynamic range is similarly constrained. Passive systems tend to favour higher-abundance and more mobile species, whereas active or affinity-based approaches may extend detection limits but often sacrifice linearity and direct physiological interpretability.

Matrix effects further complicate measurement. Variations in protein content, extracellular matrix interactions, and local tissue response influence both transport and detection. These effects are platform-dependent, with hydrogel systems introducing partitioning bias, porous systems showing flow variability, and pressure-driven methods potentially altering sample composition. Consequently, sensitivity and dynamic range should be interpreted as system-level properties rather than intrinsic assay performance, and must be evaluated in the context of the sampling mechanism and its associated biases.

5.3 Human validation and calibration challenges

A key limitation across MN-based ISF biomacromolecule platforms is the gap between analytical performance and clinical validation. While many systems demonstrate biomarker detection in controlled or preclinical settings, relatively few have been validated in humans using standardized protocols. Calibration between ISF and plasma remains a fundamental challenge. ISF:plasma relationships vary across analytes due to size-dependent transport, protein binding, and local tissue effects, complicating interpretation of measured signals.

In addition, device-specific factors—including insertion depth, sampling duration, and applied pressure—can influence local ISF composition, making it difficult to distinguish physiological variation from sampling-induced bias. The lack of standardized validation and calibration frameworks limits cross-study comparability and remains a major barrier to clinical translation.

6 Future directions: toward clinically robust ISF biomacromolecule sampling

Despite significant progress, MN-based ISF biomacromolecule platforms remain limited by the lack of convergence between efficient sampling, quantitative detection, and clinical validation. Future development should therefore focus on resolving these gaps through coordinated advances in device design, analytical integration, and validation frameworks. Key microneedle-specific engineering challenges include optimizing needle geometry and array density to balance penetration efficiency with minimal tissue damage, controlling insertion depth to ensure consistent access to dermal ISF without vascular disruption, and maintaining mechanical robustness during repeated or prolonged use. In addition, designing MN materials and surface chemistries that enable efficient biomacromolecule transport while minimizing adsorption losses and clogging remains a critical challenge. Integration of these features with scalable fabrication and reproducible device–skin interfacing will be essential for reliable clinical deployment. In addition, integration with wearable biosensing platforms remains a critical goal, requiring the development of low-power, miniaturized systems capable of continuous or repeated sampling with stable analytical performance.

Another critical priority is the establishment of standardized sampling and reporting protocols. Key parameters—including insertion depth, sampling duration, applied pressure, and transport mechanism—should be consistently reported to enable cross-study comparison and reproducibility. Without such standardization, differences in analytical performance cannot be reliably attributed to device design or sensing capability. Future work should clearly distinguish between representative ISF sampling and selective enrichment strategies. These approaches serve different diagnostic objectives and should not be evaluated using the same performance criteria. Establishing this distinction will improve interpretation of results and guide appropriate clinical applications.

A major unmet need is the integration of efficient biomacromolecule extraction with quantitative, on-device detection. Current platforms often optimize either sampling or sensing, but rarely both. Hybrid systems that combine active transport mechanisms with selective capture and robust analytical readouts represent a promising direction. Improved understanding of ISF–plasma relationships is essential for clinical translation. Future studies should focus on establishing analyte-specific calibration models and defining reference ranges, accounting for transport limitations and tissue-specific variability. Expanded human studies are required to evaluate performance under physiologically relevant conditions and across disease states. This includes assessing reproducibility, patient variability, and the impact of repeated or long-term use.

Future MN-based ISF devices will likely need to function as integrated systems that combine controlled sampling, minimal perturbation of the local microenvironment, and real-time or near-real-time quantitative detection within a compact, user-friendly format. Such devices should balance transport-driven efficiency with selective detection, while maintaining reproducibility across users and conditions.

Ultimately, the success of MN-based ISF biomacromolecule diagnostics will depend on aligning transport physics, device architecture, and analytical methodology with clinically meaningful interpretation. Progress in any single domain alone is unlikely to be sufficient without integrated, system-level optimization.

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Footnotes

Edited by: Wendel Andrade Alves, Federal University of ABC, Brazil

Reviewed by: Xue Jiang, Spear Bio, United States