Advances in Microneedle Biosensing Technology For Minimally Invasive Wearable Health Monitoring

1. Overview

Microneedles (MNs) are minimally invasive microscale skin-interfacing devices that painlessly penetrate the stratum corneum. They are widely adopted for transdermal drug delivery and dermal interstitial fluid (ISF) extraction. As the largest human organ, the skin retains abundant metabolites, proteins, ions and pathogenic biomarkers in interstitial fluid, which can accurately reflect physiological and pathological status and support disease prognosis, dynamic monitoring and pharmacodynamic evaluation. Compared with conventional venous blood collection and fingertip testing, microneedle technology features minimal invasiveness, pain-free operation, easy handling and long-term continuous monitoring capability, making it ideal for chronic disease management, home healthcare and real-time therapeutic monitoring.

Traditionally, microneedles served primarily as transdermal delivery carriers for drugs and vaccines. In recent years, the field has witnessed a significant paradigm shift: microneedles are increasingly developed as high-performance biosensing platforms for high-throughput, rapid and precise disease diagnosis and health surveillance. Advanced sensing modalities and structural optimization have substantially improved the accuracy, precision and sensitivity of MN-based biosensors, providing a novel technical pathway for personalized medicine, point-of-care testing and remote health management.

On September 26, 2023, the research team led by Professor Ryan F. Donnell from Queen's University Belfast published a comprehensive review titled Microneedle-based biosensing in Nature Reviews Bioengineering, with Dr. Lalitkumar K. Vora as the first author. This landmark work systematically elaborated the technical classification, sensing mechanisms, clinical scenarios and translational barriers of microneedle biosensing, establishing authoritative theoretical guidance for technological iteration and industrial translation.

2. Classification and Working Mechanisms of Biosensing Microneedles

Microneedles create transient microchannels on the skin surface to enable systemic transdermal delivery of drugs and vaccines, extract dermal interstitial fluid and trace blood, or act as in-situ skin electrodes for real-time biosignal detection. They can be applied as adhesive patches for long-term monitoring or used with handheld applicators for rapid sampling and administration. According to material properties, structural design and sensing principles, six mainstream microneedle types are widely applied in biosensing with differentiated performances and application scenarios.

2.1 Solid Microneedles

As the earliest developed microneedle type, solid microneedles are mainly fabricated from stainless steel or titanium via etching or laser cutting, featuring simple structure and high mechanical stability. They adopt a two-step sampling strategy: microneedles penetrate the skin to form microchannels and are then removed, followed by ISF collection through negative pressure or absorbent membranes. Despite mature fabrication and low cost, their relatively low sampling efficiency limits their application in high-precision multi-biomarker detection.

2.2 Coated Microneedles

Coated microneedles are functional upgraded versions of solid microneedles. Substrates include stainless steel, silicon and polymers such as polycarbonate and PLA. Functional coatings with metal nanoparticles or specific biorecognition molecules are modified on needle surfaces to serve as electrochemical electrodes. They enable targeted detection of glucose, renal function markers, peripheral arterial disease biomarkers and tumor indicators for chronic disease monitoring and tumor screening. Nevertheless, biocompatibility risks and coating detachment under long-term skin adhesion require further material optimization.

2.3 Porous Microneedles

Porous microneedles are a specialized subtype of solid microneedles fabricated by micro-molding with porogens incorporated into polymer matrices. Common materials include photocurable methacrylate resin, cellulose acetate and biodegradable PLGA. The porous microstructure enhances capillary action and accelerates ISF absorption without additional vacuum equipment. They are widely applied in electrochemical glucose monitoring and skin physiological parameter evaluation, combining high sampling efficiency, favorable biocompatibility and biodegradability.

2.4 Hollow Microneedles

Hollow microneedles are one of the most clinically mature types, made of metal, silicon or acrylate resin with central microchannels. They extract ISF and trace blood via capillary force or negative pressure, achieving larger sample volume and higher stability than solid microneedles. Suitable for high-precision medical monitoring and therapeutic drug detection, they require prolonged vacuum assistance for large-volume sampling, leading to relatively long detection cycles.

2.5 Hydrogel Microneedles

Fabricated from cross-linked hydrophilic polymers, hydrogel microneedles possess excellent liquid absorption and retention capacity. After skin insertion, they rapidly absorb interstitial fluid and form stable in-situ hydrogel systems for high-volume sample collection and long-term monitoring. However, interactions between certain metabolites and hydrogel matrices may cause biomarker loss and detection deviation, requiring complex pre-treatment procedures before ex-vivo analysis.

2.6 Dissolvable Microneedles

Dissolvable microneedles are prepared from biocompatible polymers including hyaluronic acid and PVP. They dissolve completely after penetrating the stratum corneum without residual wounds, achieving ultra-safe non-invasive sampling and drug delivery. Ideal for children, sensitive skin and home self-monitoring scenarios, they are a key research direction for next-generation minimally invasive biosensing.

3. Integrated Biosensing Technologies of Microneedle Platforms

Advanced microneedle biosensing relies on the deep integration of diversified microneedle structures and sensing modalities to construct in-situ, real-time and high-throughput detection systems. Four mainstream sensing technologies are widely adopted to support single-target precise detection and multi-target parallel analysis.

3.1 Electronic Sensing

Electronic sensing is commonly combined with hydrogel, porous and hollow microneedles to monitor ISF components, skin barrier function and electrolyte balance. Analytes are enriched on electrode surfaces via reverse iontophoresis for ex-vivo quantitative analysis or optimized for in-situ real-time detection. Leveraging the natural conductivity of human skin to form stable closed circuits, this technology serves as the fundamental framework for wearable microneedle sensing devices.

3.2 Electrochemical Sensing

As the most mature and mainstream modality, electrochemical sensing modifies microneedle electrodes with functional coatings. Specific biochemical reactions between coatings and biomarkers induce potential or current changes for quantitative detection of glucose, lactic acid, drug concentration and ions. It boasts fast response, high sensitivity and excellent portability for clinical point-of-care monitoring.

3.3 Optical Sensing

Optical sensing is mostly integrated with hollow microneedles to construct optofluidic detection systems. Ultra-micro ISF samples support high-precision analysis for therapeutic drug monitoring. Covering refractive index, fluorescence, absorption and polarization detection mechanisms, this technology features wide detection range, high specificity and anti-electromagnetic interference capability for high-precision non-invasive testing.

3.4 Raman Sensing

Based on surface-enhanced Raman spectroscopy (SERS), Raman sensing modifies microneedles with silver nanoparticles, gold nanoflowers and specific recognition probes to amplify signal intensity. It enables in-situ real-time monitoring of glucose, metabolites and trace drugs on the skin, with outstanding specificity and anti-interference performance for high-sensitivity micro-sample detection.

4. Core Clinical Applications

With the advantages of minimal invasiveness, real-time continuity and portability, microneedle biosensors have been widely applied in chronic disease management, tumor diagnosis, infectious disease screening, drug monitoring and emergency detection, empowering personalized medicine and remote healthcare.

4.1 Multi-layer Non-Invasive Body Fluid Sensing

Microneedles accurately extract superficial and deep dermal ISF and trace blood, replacing invasive venipuncture. They are maturely applied in dynamic blood glucose management for diabetes, providing continuous and stable data support with minimal pain and high repeatability.

4.2 Rapid Diagnosis of Tumors and Infectious Diseases

Microneedles precisely target tumor microenvironments and local infection lesions to capture specific biomarkers, including tyrosinase for melanoma, lactic acid for skin cancer and antibodies for COVID-19. They enable rapid and accurate early screening and therapeutic evaluation.

4.3 Therapeutic Drug Monitoring and Precision Medication

This technology dynamically monitors the concentration of antibiotics, anti-chronic disease drugs and levodopa in ISF, evaluates pharmacodynamic effects in real time and guides individualized dosage adjustment, effectively avoiding insufficient efficacy or drug overdose and improving clinical medication safety.

4.4 Long-Term Continuous Physiological and Pathological Monitoring

For diabetic patients and postoperative rehabilitation populations, microneedle biosensors achieve all-weather continuous monitoring of glucose, electrolytes and metabolites, capturing subtle disease fluctuations and supporting long-term disease management and prognosis assessment.

4.5 Wearable Intelligent Health Monitoring

Multiple wearable microneedle sensing prototypes have been developed for real-time monitoring of glucose, lactic acid and alcohol. Wireless data transmission synchronizes health indicators to smartphone terminals, realizing home independent monitoring and remote doctor follow-up.

4.6 Emergency Detection of Substance Overdose

With ultra-high sensitivity, microneedle biosensors support early rapid screening of opioids and neurotoxic agents, providing technical support for early intervention of substance abuse and public health risk control.

5. Translational and Commercialization Considerations

Despite great clinical potential, the industrial translation of microneedle biosensing faces multiple technical, clinical, regulatory and engineering barriers.

5.1 Clinical Performance Verification for Continuous Monitoring

Different from commercially available long-implantable CGM devices, novel hollow microneedle amperometric sensors have completed clinical trials in 10 diabetic patients, achieving 72-hour clinically accurate glucose monitoring with favorable patient tolerance, verifying the long-term clinical reliability of MN sensing systems.

5.2 Empowerment of Distributed Telemedicine

Wearable microneedle devices support remote home monitoring and wireless data transmission, optimizing medical resource allocation and adapting to grassroots medical care and remote health services, accelerating industry-university-research commercial cooperation.

5.3 Detection Range and Calibration Optimization

ISF sampling via microneedles avoids blood contamination and complex calibration problems. Current systems can detect more than 25 biomarkers within seconds to minutes, and five MN-based biosensors have entered clinical trials. Continuous optimization of ISF-blood biomarker correlation models further improves detection accuracy.

5.4 Energy Consumption and Data Security Management

High-precision devices equipped with pumps, optical and electronic components suffer from large size, high energy consumption and high production costs, limiting the popularization of disposable products. Meanwhile, standardized systems for health data collection, transmission, encryption and storage need further improvement to guarantee data privacy and security.

5.5 Patient Acceptance and Operational Adaptability

Commercial devices require simplified operation with minimal training for home use. Large-sample clinical studies are essential to verify device reliability and optimize skin adhesion and feedback mechanisms to improve user experience.

5.6 Biosafety Risk Prevention and Control

Although microneedle penetration temporarily disrupts the stratum corneum, the risk of microbial infection is extremely low due to minimal micro-wounds and skin immune defense. Standardized aseptic production processes are the core focus for industrial upgrading.

5.7 Regulatory System Improvement

No dedicated regulatory guidelines for microneedle biosensors have been released globally. FDA has issued regulatory considerations for cosmetic microneedle products, which will serve as important references for the approval of MN-based medical sensing devices, with industry standardization still in progress.

6. Future Development Trends and Prospects

Evolving from a single drug delivery tool, microneedle technology has developed into a multi-functional medical platform integrating drug delivery, sampling, sensing and monitoring. Measles and rubella microneedle patches have entered clinical trials, with equivalent immune efficacy to traditional subcutaneous injection and higher patient compliance. Leading global patch manufacturers have realized GMP-compliant large-scale production of microneedle devices.

The wearable biosensing market has exceeded 12 billion US dollars, and post-pandemic demand for home point-of-care testing and remote health monitoring continues to expand, bringing broad market prospects for microneedle biosensing. Currently, technological development is still dominated by academic research, with industrial translation lagging behind.

Future development focuses on five directions: miniaturization, lightweight and low-cost mass production; expansion of biomarker detection spectrum; integration with IoT, big data and AI algorithms to build closed-loop intelligent health management systems; improvement of long-term skin adhesion safety systems; and acceleration of clinical transformation and standardization via industry-university cooperation. With mature technology and regulatory systems, microneedle biosensing will become a core supporting technology for personalized medicine and smart home healthcare.