Food, especially fish meat, is extremely vulnerable to oxidation and microbiological deterioration. Therefore, effective analytical techniques for quality control and safety monitoring are required. Electrochemical biosensors have become reliable, rapid, and affordable devices for in-field and real-time food quality assessment. However, their application is often limited in point-of-need scenarios due to the requirement for intensive sample preparation. Here, we introduce a microneedle array (MNA)-based electrochemical biosensor, designed for direct food safety and quality analysis without the need for sample preparation. A gold (Au)-coated polymeric MNA was functionalized with a chitosan-gold nanoparticles (Ch-AuNP) nanocomposite and further modified by immobilizing xanthine oxidase (XO) for selective hypoxanthine (HX) detection. The MNA-based biosensor exhibited a linear range between 5 and 50 μM, and 50 to 200 μM, with a sensitivity of 0.024 μA/μM and a limit of detection (LOD) of 2.18 ± 0.75 μM for HX, with a response time of approximately 100 s. Furthermore, the MNA-based biosensor was successfully utilized for monitoring HX levels in fish tissue samples over 48 h, showing strong agreement with results obtained from a commercial Amplex Red assay kit. The technology can be used for real-time food quality assessment and food safety monitoring due to its high sensitivity, interference tolerance, and lack of requirement for sample preparation.

Wearable electrochemical biosensors offer a promising alternative to conventional invasive blood‐based methods for monitoring biomarkers in diagnostic or therapeutic applications. Microneedle (MN)‐based technology provides direct access to the skin's interstitial fluid (ISF), enabling real‐time monitoring of biomarkers. Nevertheless, current micro‐ and nanofabrication techniques do not adequately support the development of MN‐based wearable technology that can utilize soft hybrid conductive inks, limiting its use in transdermal biosensing. Herein, an MN‐based biosensing platform is developed by integrating 3D printing, soft lithography, and hybrid conductive ink technology, featuring a fenestrated MN shell (FMNS) that serves as a protective layer for the inner hybrid conductive ink coating and prevents delamination during skin application. This FMNS patch demonstrates a wide pH monitoring range, high selectivity and accurate detection of subtle ISF pH changes, safe integration of hybrid conductive inks, and reduced fabrication time and cost when compared to other microfabrication methods such as lithography and deep reactive ion etching. The biosensor excels in protecting the biosensing layer and demonstrates excellent analytical performance in monitoring changes in pH levels of the skin ISF. This micro‐ and nanofabrication approach has great potential in integrating hybrid conductive ink technology into transdermal wearable devices for health monitoring and diagnostics.

Microneedles (MNs) are emerging as versatile tools for both therapeutic drug delivery and diagnostic monitoring. Unlike hypodermic needles, MNs achieve these applications with minimal or no pain and customizable designs, making them suitable for personalized medicine. Understanding the key design parameters and the challenges during contact with biofluids is crucial to optimizing their use across applications. This review summarizes the current fabrication techniques and design considerations tailored to meet the distinct requirements for drug delivery and biosensing applications. We further underscore the current state of theranostic MNs that integrate drug delivery and biosensing and propose future directions for advancing MNs toward clinical use.

Microneedles (MNs) or microneedle arrays (MNAs) are critical components of minimally invasive devices comprised of a single or a series of micro‐scale projections. MNs can bypass the outermost layer of the skin and painlessly access microcirculation of the epidermis and dermis layers, attracting great interest in the development of personalized healthcare monitoring and diagnostic devices. However, MN technology has not yet reached its full potential since current micro‐ and nanofabrication methods do not address the need of fabricating MNs with complex surfaces to facilitate the development of clinically adequate devices. This work presents a new approach that combines 3D printing technology based on two‐photon polymerization with soft lithography for cost‐effective and time‐saving fabrication of complex MNAs. Specifically, this method relies on printing complex 3D objects efficiently replicated into polymeric substrates via soft lithography, resulting in a free‐standing polymeric lattice (PL) membrane that can be transferred onto gold‐coated MNs and used for electrochemical biosensing. This platform shows excellent electrochemical performance in detecting metabolite (glucose) and protein (insulin) biomarkers with a dynamic linear range sufficient for detecting biomarkers in healthy individuals and patients. The approach holds great potential for fabricating next‐generationMNs, including their transfer into clinically adequate devices.

Microneedle-based wearable electrochemical biosensors are the new frontier in personalized health monitoring and disease diagnostic devices that provide an alternative tool to traditional blood-based invasive techniques. Advancements in micro- and nanofabrication technologies enabled the fabrication of microneedles using different biomaterials and morphological features with the aim of overcoming existing challenges and enhancing sensing performance. In this work, we report a microneedle array featuring conductive recessed microcavities for monitoring urea levels in the interstitial fluid of the skin. Microcavities are small pockets on the tip of each microneedle that can accommodate the sensing layer, provide protection from delamination during skin insertion or removal, and position the sensing layer in a deep layer of the skin to reach the interstitial fluid. The wearable urea patch has shown to be highly sensitive and selective in monitoring urea, with a sensitivity of 2.5 mV mM-1 and a linear range of 3 to 18 mM making it suitable for monitoring urea levels in healthy individuals and patients. Our ex vivo experiments have shown that recessed microcavities can protect the sensing layer from delamination during skin insertion and monitor changing urea levels in interstitial fluid. This biocompatible platform provides alternative solutions to the critical issue of maintaining the performance of the biosensor upon skin insertion and holds great potential for advancing transdermal sensor technology.