A hair-thin strand of glass may soon do what entire laboratories of equipment currently cannot: detect the molecular whispers that precede cancer, heart disease, and neurodegeneration within minutes, at the patient’s side, without a single fluorescent label. That is the central promise examined in a sweeping critical review published in the open-access journal Results in Optics, in which researchers from Universiti Malaysia Sarawak systematically assess how functionalised optical fibre sensors could reshape microRNA diagnostics. The work, led by Noor Azie Azura Mohd Arif with co-authors Nur Nadia Dzulkifli and Mackerina Awing Mamat, arrives at a moment when the scientific literature on fibre-based microRNA sensing is expanding rapidly yet remains fragmented, dominated by laboratory demonstrations that rarely survive contact with real clinical samples.

MicroRNAs are minute non-coding RNA molecules, typically 18 to 24 nucleotides long, that act as master regulators of gene expression. By binding to messenger RNAs and suppressing their translation, they govern immune responses, apoptosis, and cellular differentiation. Because specific microRNA signatures circulate in blood, serum, urine, and other body fluids in patterns that correlate with disease states, they have become some of the most intensely pursued biomarkers in modern medicine. The catch is that these molecules are extraordinarily short and present at vanishingly low concentrations, which makes them notoriously difficult to quantify reliably. The current gold standard, reverse transcription quantitative PCR, achieves impressive sensitivity and specificity but demands precise primer design, accurate reverse transcription, fluorescent labelling, thermal cycling instrumentation, and hours of skilled labour. A 2021 refinement of PCR for microRNA work, the review notes, still required costly reagents and elaborate sample processing, and none of these approaches is well suited to point-of-care use.

The Malaysian team’s bibliometric analysis underscores how fast interest is building. A Scopus search pairing the terms “microRNA” and “fibre optic sensor” returned 48 papers, with publication counts rising steeply between 2020 and 2024. China emerged as the top contributing nation, and the literature spans chemistry, biochemistry, engineering, and physics in nearly equal measure, a distribution that reflects how fundamentally interdisciplinary the field has become. Yet the authors argue that no previous review has critically synthesised the functionalisation chemistry, the surface engineering, and the performance data that together determine whether these devices will ever leave the laboratory. Their paper sets out to close that gap by comparing working principles, functionalisation strategies, and detection limits across the full spectrum of optical fibre architectures.

At the heart of the technology lie several distinct transduction mechanisms. Surface plasmon resonance sensors coat optical fibres with thin metallic films, usually gold, and monitor how the binding of target molecules at the surface shifts the resonance condition of evanescent light waves interacting with collective electron oscillations in the metal. Localised surface plasmon resonance variants use nanoscale metallic structures that generate intense local electromagnetic fields, making them exquisitely sensitive to surface-bound molecules while remaining relatively robust against bulk refractive index changes. Fibre Bragg gratings and microfiber Bragg gratings inscribe periodic refractive index modulations into the fibre core, reflecting specific wavelengths that shift as surface mass changes. Interferometric sensors, including Mach-Zehnder configurations, detect the minute phase shifts induced when microRNAs hybridise with immobilised probes; one such device achieved a detection limit of one femtomole per microlitre in clinical urine samples, while also supporting real-time, multiplexed readout.

The review pays particular attention to how sensor surfaces are chemically engineered, because functionalisation ultimately governs selectivity, probe density, and resistance to fouling. For plasmonic sensors, three strategies for anchoring gold nanoparticles emerge as representative. Silane coupling chemistry, built on self-assembled monolayers of molecules such as APTMS, forms strong covalent bonds but produces uneven nanoparticle distributions that generate signal irregularities. Polyelectrolyte layer-by-layer assembly improves surface coverage through controlled multilayer deposition, but its reliance on electrostatic interactions makes it vulnerable to the ionic strength fluctuations typical of serum and plasma. Block copolymer templating, using materials such as polystyrene-block-poly(4-vinylpyridine), delivers highly ordered monolayers with superior sensitivity and repeatability, achieving a refractive index sensitivity of 386.36 nanometres per refractive index unit in one demonstration, yet its synthesis complexity keeps it the least commercially scalable option. The authors suggest hybrid approaches, combining the adhesive strength of silanes with the uniform dispersion of polymeric templating, as the most promising route forward.

Nanomaterial integration extends well beyond gold nanoparticles. Graphene oxide, carbon nanotubes, quantum dots, and metal-organic frameworks each increase the available surface area for biomolecule attachment and amplify light-matter interactions. Silver-coated fibre nanoprobes, fabricated by pulling multimode fibres to nanoscale tips with a laser-based micropipette device, have even been inserted into the nuclei of individual breast cancer cells to quantify telomerase overexpression in living cells through a sandwich immunoassay with enzymatic signal amplification. On the photonic side, researchers have shown that exciting pure higher-order modes in optical fibres, via mode-selective couplers, boosts the optical power circulating in the cladding and thereby strengthens evanescent interactions with the metallic layer, raising sensor sensitivity by 330 to 360 percent relative to conventional fundamental-mode designs. Photonic crystal fibre platforms, modelled with full-vectorial finite element methods, have theoretically achieved sensitivities of 7142.86 nanometres per refractive index unit for cancer cell detection, though fabrication complexity and optical losses remain obstacles.

Against these fibre-based advances, the review measures a crowded field of competing technologies, each with well-documented shortcomings. Next-generation sequencing identifies novel microRNAs with single-nucleotide resolution without requiring prior knowledge of target sequences, but its cost, bioinformatics burden, and prolonged sample preparation confine it to discovery research. Microarrays offer high-throughput multiplexing yet suffer from probe cross-reactivity and poor detection of low-abundance targets. Isothermal amplification methods such as loop-mediated isothermal amplification and rolling circle amplification have pushed detection limits down to attomolar levels, with one RCA-LAMP system reaching 10 attomolar, but their reaction complexity and susceptibility to matrix interference limit real-world scalability. Electrochemical biosensors built on two-dimensional transition metal sulphides and DNAzyme cascades have reported detection limits as low as 0.03 femtomolar for microRNA-21, and CRISPR-powered platforms have progressed from femtomolar to near-zeptomolar sensitivity through graphdiyne functionalisation and DNA origami engineering, yet these systems still depend on sophisticated instrumentation, complex biochemical workflows, and limited clinical validation. Surface-enhanced Raman spectroscopy achieves single-molecule sensitivity through molecular fingerprinting but demands costly optics and intricate signal interpretation.

What emerges from this comparison is a consistent pattern: the most sensitive platforms are rarely the most practical, and the most practical are rarely sensitive enough for the circulating microRNA concentrations that matter clinically. Optical fibre sensors occupy a genuinely distinctive middle ground, offering label-free, real-time detection in a format that is inherently miniaturised, immune to electromagnetic interference, and compatible with remote interrogation at telecommunication wavelengths, as demonstrated by spectral interferometry sensors operating near 1550 nanometres. Their persistent enemies, however, are biofouling and non-specific adsorption in complex biological matrices. Serum, plasma, urine, saliva, and tissue extracts differ markedly in protein content, ionic strength, and pretreatment requirements, and most fibre sensors have been validated only with purified or spiked samples rather than raw clinical specimens. Signal drift, photobleaching, temperature sensitivity, and the absence of standardised fabrication protocols further complicate inter-laboratory comparison and regulatory approval.

The authors see artificial intelligence and machine learning as essential allies in overcoming these limitations. Neural networks trained on spectral data can suppress noise, compensate for environmental fluctuations, and isolate genuine microRNA signatures from background interference, improving quantification precision at low abundance while reducing false positives and negatives. They also envision wearable and implantable optical fibre platforms, integrated with flexible fibres and microfluidics, that would continuously monitor microRNA levels in sweat, saliva, or interstitial fluid for non-invasive disease tracking. Beyond human medicine, the review highlights veterinary and ecological applications, from cattle health management and species identification to wildlife monitoring, pointing to studies that profiled extracellular vesicle microRNAs in boar seminal plasma as fertility biomarkers.

The review’s conclusion is measured but optimistic. Functionalised optical fibre sensors are judged to be genuinely practical alternatives to conventional microRNA detection, capable of femtomolar to attomolar sensitivity in label-free, real-time formats, and their performance has been transformed by nanomaterial integration and plasmonic enhancement. But the path to the clinic runs through problems no amount of sensitivity can solve on its own: reproducible functionalisation, anti-fouling surface design, standardised fabrication guidelines, longitudinal validation across whole blood, serum, and tissue biopsies, and large-scale clinical trials. Achieving that will require sustained collaboration among clinical researchers, bioengineers, material scientists, and computational specialists. If those challenges are met, the authors argue, a strand of glass thinner than a human hair could become the foundation of next-generation molecular diagnostics, enabling early disease detection and continuous, real-time therapeutic monitoring in settings where today’s laboratories cannot reach.

Subject of Research: Functionalised optical fibre biosensors for label-free, real-time detection of microRNA biomarkers

Subject of Research: Technology and Engineering

Article Title: Functionalised optical fibre sensors for microRNA detection: a critical perspective

Article References: Arif, N. A. A. M., Dzulkifli, N. N., & Mamat, M. A. (2026). Functionalised optical fibre sensors for microRNA detection: a critical perspective. Results in Optics, 24, Article 101132. https://doi.org/10.1016/j.rio.2026.101132

Image Credits: AI Generated

DOI: 10.1016/j.rio.2026.101132

Keywords: microRNA detection, optical fibre sensors, biosensors, surface plasmon resonance, functionalisation, label-free diagnostics, point-of-care testing, nanomaterials, evanescent wave sensing, clinical biomarkers, artificial intelligence, photonic crystal fibre

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Juliet Wilcox. (September 4, 2026). Functionalised optical fibre sensors offer critical insights into microRNA detection. Scienmag. https://scienmag.com/functionalised-optical-fibre-sensors-offer-critical-insights-into-microrna-detection/

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