Microneedles have emerged as a versatile technology for biosensing across biomedical domains and are increasingly being explored for other applications like agriculture. This review highlights recent advancements in the development of microneedle-based biosensors in novel areas. Biomedical applications include continuous glucose monitoring, multiplexed biomarker detection beyond glucose, and numerous recent works presenting fully integrated systems comprising microneedle arrays alongside miniaturized wearable electronics. Agricultural applications largely focus on the detection of plant growth markers, hormones, and nutrient levels. Despite significant progress, challenges remain in overcoming biofouling and electrode degradation, optimizing electrode longevity for long-term (weeks to months) in situ monitoring, and creating scalable sensor fabrication processes. Additionally, there is a need for standardized mechanical and electrical testing protocols, and guidelines specifying critical performance metrics that should be reported to facilitate accurate literature comparisons. The review concludes by outlining key opportunities for future research to address these persisting challenges.

Microneedles are a promising technology for pain-free and efficient pharmaceutical delivery. However, their clinical translation is currently limited by the absence of standardized testing methods for critical quality attributes (CQAs), such as mechanical robustness, which are essential for demonstrating safety and efficacy during regulatory review. A key aspect of mechanical robustness is transverse load capacity, which is currently assessed using diverse, non-standardized methods, which have limited capability to measure transverse failure forces at different heights along a microneedle. This is critical for understanding mechanics of potential failure modes during insertion after skin penetration. In this work we utilize a wire bond shear tester, a piece of test equipment widely used in the semiconductor industry, to measure the transverse load capacities of various microneedle designs. This approach is compatible with diverse microneedle types, geometries, and materials, and offers high-throughput and automated testing capabilities with high precision. We measure transverse failure loads with micron-scale control over the test height and have established comprehensive profiles of mechanical robustness along the length of different microneedle designs, which is a capability not previously demonstrated in literature for polymeric and metal microneedles. Transverse failure forces were 10 ± 0.3 gf–128 ± 12 gf for wire bonded gold and silver microneedles, 11 ± 0.7 gf–480 ± 69 gf for conical and pyramidal polymeric microneedles, and 206 ± 80 gf–381 ± 1 gf for 3D printed conical stainless steel microneedles. Additionally, we present standardized definitions for microneedle structural failure modes resulting from transverse loads, which can facilitate root cause failure analysis and defect detection during design and manufacturing, and aid in risk assessment of microneedle products. This work establishes a standardized approach to evaluating a significant CQA of microneedle products, which is a critical step towards expediting their clinical adoption.

This work reports a rapid, cleanroom-free route for fabricating three-electrode microneedle electrochemical biosensors by repurposing the high speed wire bonding technique from the semiconductor industry. The 50 µm diameter Au, Pt, and 30 µm Ag wires were bonded to commercial printed circuit boards (PCBs) to produce freestanding microneedles (MNs) that served as working (WE), counter (CE), and reference (RE) electrodes. Ag MNs were galvanostatically chlorinated to form Ag/AgCl reference electrodes with low drift, −3 ± 0.3 mV over 24 h in phosphate-buffered saline. Au MNs were coated with PEDOT:PSS/glucose oxidase for amperometric glucose sensing from 5–25 mM (sensitivity = 0.37 µA mM-1, +0.50 V working voltage), covering the physiologic range for diabetes management. Platform versatility was demonstrated by nanomolar-range detection after the addition of an aptamer self-assembled monolayer on wire bonded Au MNs. This fully automated, additive wire bonding process provides submillimetre electrode spacing, < US$2 materials cost per trielectrode array, and seamless integration with external sensing hardware for wearable applications owing to the PCB-substrate based approach. We demonstrate a scalable pathway toward multiplexed MN patches for continuous interstitial fluid monitoring and other microneedle-based minimally invasive biosensing applications.