Microneedle-Based Detection of Ketone Bodies along with Glucose and Lactate: Toward Real-Time Continuous Interstitial Fluid Monitoring of Diabetic Ketosis and Ketoacidosis

Lab under the Skin: Microneedle Based Wearable Devices

While the current smartwatches and cellphones can readily track mobility and vital signs, a new generation of wearable devices is rapidly developing to enable users to monitor their health parameters at the molecular level. Within this emerging class of wearables, microneedle-based transdermal sensors are in a prime position to play a key role in synergizing the significant advantages of dermal interstitial fluid (ISF) as a rich source of clinical indicators and painless skin pricking to allow the collection of real-time diagnostic information. While initial efforts of microneedle sensing focused on ISF extraction coupled with either on-chip analysis or off-chip instrumentation, the latest trend has been oriented toward assembling electrochemical biosensors on the tip of microneedles to allow direct continuous chemical measurements. In this context, significant advances have recently been made in exploiting microneedle-based devices for real-time monitoring of various metabolites, electrolytes, and therapeutics and toward the simultaneous multiplexed detection of key chemical markers; yet, there are several grand challenges that still exist. In this review, we outline current progress, recent trends, and new capabilities of microneedle-empowered sensors, along with the current unmet challenges and a future roadmap toward transforming the latest innovations in the field to commercial products.

Recent Advances in Microneedle-Based Sensors for Sampling, Diagnosis and Monitoring of Chronic Diseases

Chronic diseases (CDs) are noncommunicable illnesses with long-term symptoms accounting for ~70% of all deaths worldwide. For the diagnosis and prognosis of CDs, accurate biomarker detection is essential. Currently, the detection of CD-associated biomarkers is employed through complex platforms with certain limitations in their applicability and performance. There is hence unmet need to present innovative strategies that are applicable to the point-of-care (PoC) settings, and also, provide the precise detection of biomarkers. On the other hand, especially at PoC settings, microneedle (MN) technology, which comprises micron-size needles arranged on a miniature patch, has risen as a revolutionary approach in biosensing strategies, opening novel horizons to improve the existing PoC devices. Various MN-based platforms have been manufactured for distinctive purposes employing several techniques and materials. The development of MN-based biosensors for real-time monitoring of CD-associated biomarkers has garnered huge attention in recent years. Herein, we summarize basic concepts of MNs, including microfabrication techniques, design parameters, and their mechanism of action as a biosensing platform for CD diagnosis. Moreover, recent advances in the use of MNs for CD diagnosis are introduced and finally relevant clinical trials carried out using MNs as biosensing devices are highlighted. This review aims to address the potential use of MNs in CD diagnosis.

Type 1 diabetes glycemic management: Insulin therapy, glucose monitoring, and automation

Despite innovations in insulin therapy since its discovery, most patients living with type 1 diabetes do not achieve sufficient glycemic control to prevent complications, and they experience hypoglycemia, weight gain, and major self-care burden. Promising pharmacological advances in insulin therapy include the refinement of extremely rapid insulin analogs, alternate insulin-delivery routes, liver-selective insulins, add-on drugs that enhance insulin effect, and glucose-responsive insulin molecules. The greatest future impact will come from combining these pharmacological solutions with existing automated insulin delivery methods that integrate insulin pumps and glucose sensors. These systems will use algorithms enhanced by machine learning, supplemented by technologies that include activity monitors and sensors for other key metabolites such as ketones. The future challenges facing clinicians and researchers will be those of access and broad clinical implementation.

Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

The detection of glucose is crucial in the management of diabetes and other medical conditions but also crucial in a wide range of industries such as food and beverages. The development of glucose sensors in the past century has allowed diabetic patients to effectively manage their disease and has saved lives. First-generation glucose sensors have considerable limitations in sensitivity and selectivity which has spurred the development of more advanced approaches for both the medical and industrial sectors. The wide range of application areas has resulted in a range of materials and fabrication techniques to produce novel glucose sensors that have higher sensitivity and selectivity, lower cost, and are simpler to use. A major focus has been on the development of enzymatic electrochemical sensors, typically using glucose oxidase. However, non-enzymatic approaches using direct electrochemistry of glucose on noble metals are now a viable approach in glucose biosensor design. This review discusses the mechanisms of electrochemical glucose sensing with a focus on the different generations of enzymatic-based sensors, their recent advances, and provides an overview of the next generation of non-enzymatic sensors. Advancements in manufacturing techniques and materials are key in propelling the field of glucose sensing, however, significant limitations remain which are highlighted in this review and requires addressing to obtain a more stable, sensitive, selective, cost efficient, and real-time glucose sensor.

Enhanced extraction of skin interstitial fluid using a 3D printed device enabling tilted microneedle penetration

Interstitial fluid (ISF) is a body fluid that fills, surrounds cells and contains various biomarkers, but it has been challenging to extract ISF in a reliable and sufficient amount with high speed. To address the issues, we developed the tilted microneedle ISF collecting system (TMICS) fabricated by 3D printing. In this system, the microneedle (MN) was inserted at 66° to the skin by TMICS so that the MN length could be extended within a safe range of skin penetration. Moreover, TMICS incorporating three MN patches created reliable ISF collecting conditions by penetrating the skin at consistent angle and force, 4.9 N. Due to the MN length increase and the patch number expansion, the surface area of the penetrated tissue was increased, thereby confirming that ISF extraction efficiency was improved. Skin ISF was collected into the paper reservoir on the patch, and the absorbed area was converted into a volume. ISF extraction from the rat skin in vivo by TMICS was well tolerated, and the 2.9 μL of ISF was obtained within 30 s. Therefore, TMICS is promising to apply in the diagnosis of multiple biomarkers in ISF with high speed and stability.

Feasibility of Continuous Ketone Monitoring in Subcutaneous Tissue Using a Ketone Sensor

BACKGROUND

The feasibility of measuring β-hydroxybutyrate in ISF using a continuous ketone monitoring (CKM) sensor using a single calibration without further adjustments over 14 days is described.

METHODS

A CKM sensor was developed using wired enzyme technology with β-hydroxybutyrate dehydrogenase chemistry. In vitro characterization of the sensor was performed in phosphate buffered saline at 37°C. In vivo performance was evaluated in 12 healthy participants on low carbohydrate diets, who wore 3 ketone sensors on the back of their upper arms to continuously measure ketone levels over 14 days. Reference capillary ketone measurements were performed using Precision Xtra® test strips at least 8 times a day.

RESULTS

The sensor is stable over 14 days and has a linear response over the 0-8 mM range. The operational stability of the sensor is very good with a 2.1% signal change over 14 days. The first human study of the CKM sensor demonstrated that the sensor can continuously track ketones well through the entire 14 days of wear. The performance with a single retrospective calibration of the sensor showed 82.4% of data pairs within 0.225 mM/20% and 91.4% within 0.3 mM/30% of the capillary ketone reference (presented as mM at <1.5 mM and as percentage at or above 1.5 mM). This suggests that the sensor can be used with a single calibration for the 14 days of use.

CONCLUSIONS

Measuring ketones in ISF using a continuous ketone sensor is feasible. Additional studies are required to evaluate the performance in intended patient populations, including conditions of ketosis and diabetic ketoacidosis.

Aptamer-decorated porous microneedles arrays for extraction and detection of skin interstitial fluid biomarkers

The detection of biomarkers in body fluids plays a great role in the diagnosis, treatment, and prognosis of diseases. Here, we present novel aptamer-decorated porous microneedles (MNs) arrays to realize the extraction and detection of biomarkers in skin interstitial fluid (ISF) in situ. The porous MNs arrays are fabricated by replicating the negative molds comprising glass microspheres with a UV-curable ethoxylated trimethylolpropane triacrylate (ETPTA). As the MNs arrays combine the superiorities of porous structure and aptamers, their specific surface area increased significantly to 6.694 m²/g, thus vast of stable aptamer probes with a concentration of 0.9459 μM could be immobilized. In addition, the MNs arrays could extract skin ISF into their porous structure on the basis of the capillarity principle, and subsequently capture and detect skin ISF biomarkers without sample post-process. Taking advantage of these features, we further demonstrated a highly sensitive and rapid detection of ISF endotoxin in the concentration ranges of 0.0342 EU/mL to 8.2082 EU/mL from rats model injected with endotoxin via tail vein by using such aptamer-decorated porous MNs arrays, with the limit of detection (LOD) of 0.0064 EU/mL. These results indicated that the aptamer-decorated porous MNs arrays possess great potential for non-invasive extraction and detection of biomarkers in clinical applications.

Wearable and Mobile Sensors for Personalized Nutrition

While wearable and mobile chemical sensors have experienced tremendous growth over the past decade, their potential for tracking and guiding nutrition has emerged only over the past three years. Currently, guidelines from doctors and dietitians represent the most common approach for maintaining optimal nutrition status. However, such recommendations rely on population averages and do not take into account individual variability in responding to nutrients. Precision nutrition has recently emerged to address the large heterogeneity in individuals' responses to diet, by tailoring nutrition based on the specific requirements of each person. It aims at preventing and managing diseases by formulating personalized dietary interventions to individuals on the basis of their metabolic profile, background, and environmental exposure. Recent advances in digital nutrition technology, including calories-counting mobile apps and wearable motion tracking devices, lack the ability of monitoring nutrition at the molecular level. The realization of effective precision nutrition requires synergy from different sensor modalities in order to make timely reliable predictions and efficient feedback. This work reviews key opportunities and challenges toward the successful realization of effective wearable and mobile nutrition monitoring platforms. Non-invasive wearable and mobile electrochemical sensors, capable of monitoring temporal chemical variations upon the intake of food and supplements, are excellent candidates to bridge the gap between digital and biochemical analyses for a successful personalized nutrition approach. By providing timely (previously unavailable) dietary information, such wearable and mobile sensors offer the guidance necessary for supporting dietary behavior change toward a managed nutritional balance. Coupling of the rapidly emerging wearable chemical sensing devices-generating enormous dynamic analytical data-with efficient data-fusion and data-mining methods that identify patterns and make predictions is expected to revolutionize dietary decision-making toward effective precision nutrition.

Touch-Based Fingertip Blood-Free Reliable Glucose Monitoring: Personalized Data Processing for Predicting Blood Glucose Concentrations

Diabetes prevalence has been rising exponentially, increasing the need for reliable noninvasive approaches for glucose monitoring. Different biofluids have been explored recently for replacing current blood finger-stick glucose strips with noninvasive painless sensing devices. While sweat has received considerable attention, there are mixed reports on correlating the sweat results with blood glucose levels. Here, we demonstrate a new rapid and reliable approach that combines a simple touch-based fingertip sweat electrochemical sensor with a new algorithm that addresses for personal variations toward the accurate estimate of blood glucose concentrations. The new painless and simple glucose self-testing protocol leverages the fast sweat rate on the fingertip for rapid assays of natural perspiration, without any sweat stimulation, along with the personalized sweat-response-to-blood concentration translation. A reliable estimate of the blood glucose sensing concentrations can thus be realized through a simple one-time personal precalibration. Such system training leads to a substantially improved accuracy with a Pearson correlation coefficient higher than 0.95, along with an overall mean absolute relative difference of 7.79%, with 100% paired points residing in the A + B region of the Clarke error grid. The speed and simplicity of the touch-based blood-free fingertip sweat assay, and the elimination of periodic blood calibrations, should lead to frequent self-testing of glucose and enhanced patient compliance toward the improved management of diabetes.

A review of biomarkers in the context of type 1 diabetes: Biological sensing for enhanced glucose control

As wearable healthcare monitoring systems advance, there is immense potential for biological sensing to enhance the management of type 1 diabetes (T1D). The aim of this work is to describe the ongoing development of biomarker analytes in the context of T1D. Technological advances in transdermal biosensing offer remarkable opportunities to move from research laboratories to clinical point-of-care applications. In this review, a range of analytes, including glucose, insulin, glucagon, cortisol, lactate, epinephrine, and alcohol, as well as ketones such as beta-hydroxybutyrate, will be evaluated to determine the current status and research direction of those analytes specifically relevant to T1D management, using both in-vitro and on-body detection. Understanding state-of-the-art developments in biosensing technologies will aid in bridging the gap from bench-to-clinic T1D analyte measurement advancement.

Microneedle Arrays for Sampling and Sensing Skin Interstitial Fluid

Dermal interstitial fluid (ISF) is a novel source of biomarkers that can be considered as an alternative to blood sampling for disease diagnosis and treatment. Nevertheless, in vivo extraction and analysis of ISF are challenging. On the other hand, microneedle (MN) technology can address most of the challenges associated with dermal ISF extraction and is well suited for long-term, continuous ISF monitoring as well as in situ detection. In this review, we first briefly summarise the different dermal ISF collection methods and compare them with MN methods. Next, we elaborate on the design considerations and biocompatibility of MNs. Subsequently, the fabrication technologies of various MNs used for dermal ISF extraction, including solid MNs, hollow MNs, porous MNs, and hydrogel MNs, are thoroughly explained. In addition, different sensing mechanisms of ISF detection are discussed in detail. Subsequently, we identify the challenges and propose the possible solutions associated with ISF extraction. A detailed investigation is provided for the transport and sampling mechanism of ISF in vivo. Also, the current in vitro skin model integrated with the MN arrays is discussed. Finally, future directions to develop a point-of-care (POC) device to sample ISF are proposed.

New application of a traditional method: colorimetric sensor array for reducing sugars based on the in-situ formation of core-shell gold nanorod-coated silver nanoparticles by the traditional Tollens reaction

An effective and robust colorimetric sensor array for simultaneous detection and discrimination of five reducing sugars (i.e., glyceraldehyde (Gly), fructose (Fru), glucose (Glu), maltose (Mal), and ribose (Rib)) has been proposed. In the sensor array, two negatively charged polydielectrics (sodium polystyrenesulfonate (NaPSS) and sodium polymethacrylate (NaPMAA)), which served as the sensing elements, were individually absorbed on the surface of the cetyltrimethylammonium bromide (CTAB)-coated gold nanorods (AuNR) with positive charges through electrostatic action, forming the designed sensor units (NaPSS-AuNR and NaPMAA-AuNR). In the presence of Tollens reagent (Ag(NH₃)₂OH), Ag⁺ was absorbed on the surface of negatively charged NaPSS-AuNR and NaPMAA-AuNRs. When confronted with differential reducing sugars, different reducing sugars exhibited differential levels of deoxidizing abilities toward Ag⁺, thus Ag⁺ was reduced to diverse amounts of silver nanoparticles (AgNPs) in situ to form core-shell AuNR@AgNP by the traditional Tollens reaction method, leading to distinct colorimetric response patterns (value of A_S/A_L (the ratio of absorbance at 360 nm to that at 760 nm in Ag⁺-NaPMAA-AuNR, and the ratio of absorbance at 360 nm to that at 740 nm in Ag⁺-NaPSS-AuNR)). These response patterns are characteristic for each reducing sugar, and can be quantitatively distinguished by linear discriminant analysis (LDA) at concentrations as low as 10 nM with relative standard deviation (RSD) of 4.11% (n = 3). The practicability of this sensor array has been validated by recognition of reducing sugars in serum and urine samples. A colorimetric sensor array for reducing sugar discrimination based on the reduction of Ag⁺ and in situ formation of AuNR@AgNP.

Graphene nanocomposites for transdermal biosensing

Transdermal biosensors for the real-time and continuous detection and monitoring of target molecules represent an intriguing pathway for enhancing health outcomes in a cost-effective and non-invasive fashion. Many transdermal biosensor devices contain microneedles and other miniaturized components. There remains an unmet clinical need for microneedle transdermal biosensors to obtain a more accurate, rapid, and reliable insight into the real-time monitoring of disease. The ability to monitor biomarkers at an intradermal molecular level in a non-invasive manner remains the next technological gap to solve real-world clinical problems. The emergence of the two-dimensional material graphene with unique material properties and the ability to quantify analytes and physiological status can enable the detection of critical biomarkers indicative of human disease. The development of a user-friendly, affordable, and non-invasive transdermal biosensing device for continuous and personalized monitoring of target molecules could be beneficial for many patients. This focus article considers the use of graphene-based transdermal biosensors for health monitoring, evaluation of these sensors for glucose and hydrogen peroxide detection via in vitro, in vivo, and ex vivo studies, recent technological innovations, and potential challenges. This article is categorized under: Diagnostic Tools > Biosensing.

Hydrophilic and anti-adhesive modification of porous polymer microneedles for rapid dermal interstitial fluid extraction

Porous polymer microneedles (MNs) with interconnected structures demonstrate great potential in dermal interstitial fluid (ISF) extraction. However, the fluid extraction rate and the recovery of the extracted ISF by the porous MNs are limited by the poor hydrophilicity and the adhesion of porous MNs. Herein, we present a facile and mild polydopamine (PDA) and poly(ethylene glycol) (PEG) coating strategy for hydrophilic and anti-adhesive modification of porous polymer MNs from a phase inversion method. As a proof-of-concept, taking polysulfone (PSF) as an example, PDA and PEG-coated MNs (PSF@PDA@PEG) are fabricated through the self-polymerization of dopamine and PEG anchoring. Thanks to the hydrophilicity and anti-adhesion of PEG, the resulting PSF@PDA@PEG MNs demonstrate improved hydrophilicity, fast fluid extraction speed, and low target molecular adhesion. Besides, this method can be extended to hydrophobic polymers generally used in medical fields, including polylactic acid (PLA), polyvinylidene fluoride (PVDF), etc. This investigation provides a new road for MN-based off-line analysis in point-of-care testing (POCT).

Porous Platinum Black-Coated Minimally Invasive Microneedles for Non-Enzymatic Continuous Glucose Monitoring in Interstitial Fluid

Individuals with diabetes can benefit considerably from continuous blood glucose monitoring. To address this challenge, a proof-of-concept was performed for continuous glucose monitoring (CGM) based on an enzymeless porous nanomaterial (pNM)-modified microneedle electrode array (MNEA). The pNM sensing layer was electrochemically deposited on MNs by applying a fixed negative current of -2.5 mA cm^-2 for 400 s. The pNM-modified MNEA was packed using a biocompatible Nafion ionomer. The fabricated MNEAs were 600 × 100 × 150 µm in height, width, and thickness, respectively. The surfaces of the modified MNs were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The fabricated MNEAs showed a wide dynamic range (1-30 mM) in phosphate-buffered saline (PBS) and in artificial interstitial fluid (ISF), with good sensitivities (PBS: 1.792 ± 0.25 µA mM^-1 cm^-2, ISF: 0.957 ± 0.14 µA mM^-1 cm^-2) and low detection limits (PBS: 7.2 µM, ISF: 22 µM). The sensor also showed high stability (loss of 3.5% at the end of 16 days), selectivity, and reproducibility (Relative standard deviations (RSD) of 1.64% and 0.70% for intra- and inter-assay, respectively) and a good response time (2 s) with great glucose recovery rates in ISF (98.7-102%).

Non-Invasive Blood Glucose Monitoring Technology: A Review

In recent years, with the rise of global diabetes, a growing number of subjects are suffering from pain and infections caused by the invasive nature of mainstream commercial glucose meters. Non-invasive blood glucose monitoring technology has become an international research topic and a new method which could bring relief to a vast number of patients. This paper reviews the research progress and major challenges of non-invasive blood glucose detection technology in recent years, and divides it into three categories: optics, microwave and electrochemistry, based on the detection principle. The technology covers medical, materials, optics, electromagnetic wave, chemistry, biology, computational science and other related fields. The advantages and limitations of non-invasive and invasive technologies as well as electrochemistry and optics in non-invasives are compared horizontally in this paper. In addition, the current research achievements and limitations of non-invasive electrochemical glucose sensing systems in continuous monitoring, point-of-care and clinical settings are highlighted, so as to discuss the development tendency in future research. With the rapid development of wearable technology and transdermal biosensors, non-invasive blood glucose monitoring will become more efficient, affordable, robust, and more competitive on the market.

Textile sensors platform for the selective and simultaneous detection of chloride ion and pH in sweat

The development of wearable sensors, in particular fully-textile ones, is one of the most interesting open challenges in bioelectronics. Several and significant steps forward have been taken in the last decade in order to achieve a compact, lightweight, cost-effective, and easy to wear platform for healthcare and sport activities real-time monitoring. We have developed a fully textile, multi-thread biosensing platform that can detect different bioanalytes simultaneously without interference, and, as an example, we propose it for testing chloride ions (Cl^-) concentration and pH level. The textile sensors are simple threads, based on natural and synthetic fibers, coated with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and properly functionalized with either a nano-composite material or a chemical sensitive dye to obtain Cl^- and pH selective sensing functionality, respectively. The single-thread sensors show excellent sensitivity, reproducibility, selectivity, long term stability and the ability to work with small volumes of solution. The performance of the developed textile devices is demonstrated both in buffer solution and in artificial human perspiration to perform on-demand and point-of-care epidermal fluids analysis. The possibility to easily knit or sew the thread sensors into fabrics opens up a new vision for a textile wearable multi-sensing platform achievable in the near future.

Microneedle-based bioassays

Disease diagnosis and therapeutic efficacy can be monitored via a number of established bioassays that sample body fluids to assess and monitor health conditions. Traditional bioassays generally include several steps and start with invasive body fluid extraction procedures. These steps are painful and often require specialized techniques and tailored equipment, as well as the supervision of professional medical personnel. Innovations in engineering alternative bioassays to address these shortcomings are thus desired. Microneedles (MNs) represent promising tools to sample body fluids, in view of their minimal invasiveness, painlessness, and uncomplicated implementation. Recent progress in microfabrication and materials engineering, including the development of hollow and solid MNs with uniquely optimized architectures and multi-functional materials, has positioned MN-based platforms as prime candidates for bioassay solutions. In this minireview, we summarize the studies of MN-based platforms for detection and diagnosis. We categorize the platforms based on three different mechanisms: MNs as body fluid reservoirs, MNs integrated with electrochemical assays, and MNs engineered with colorimetric analyses. A discussion of design principles for MN-based bioassay platforms is presented. We also discuss the challenges and opportunities associated with MN-based bioassays in future clinical applications.

Electrochemical glucose sensors in diabetes management: an updated review (2010-2020)

While over half a century has passed since the introduction of enzyme glucose biosensors by Clark and Lyons, this important field has continued to be the focus of immense research activity. Extensive efforts during the past decade have led to major scientific and technological innovations towards tight monitoring of diabetes. Such continued progress toward advanced continuous glucose monitoring platforms, either minimal- or non-invasive, holds considerable promise for addressing the limitations of finger-prick blood testing toward tracking glucose trends over time, optimal therapeutic interventions, and improving the life of diabetes patients. However, despite these major developments, the field of glucose biosensors is still facing major challenges. The scope of this review is to present the key scientific and technological advances in electrochemical glucose biosensing over the past decade (2010-present), along with current obstacles and prospects towards the ultimate goal of highly stable and reliable real-time minimally-invasive or non-invasive glucose monitoring. After an introduction to electrochemical glucose biosensors, we highlight recent progress based on using advanced nanomaterials at the electrode-enzyme interface of three generations of glucose sensors. Subsequently, we cover recent activity and challenges towards next-generation wearable non-invasive glucose monitoring devices based on innovative sensing principles, alternative body fluids, advanced flexible materials, and novel platforms. This is followed by highlighting the latest progress in the field of minimally-invasive continuous glucose monitoring (CGM) which offers real-time information about interstitial glucose levels, by focusing on the challenges toward developing biocompatible membrane coatings to protect electrochemical glucose sensors against surface biofouling. Subsequent sections cover new analytical concepts of self-powered glucose sensors, paper-based glucose sensing and multiplexed detection of diabetes-related biomarkers. Finally, we will cover the latest advances in commercially available devices along with the upcoming future technologies.

Highly Stretchable Fiber-Based Potentiometric Ion Sensors for Multichannel Real-Time Analysis of Human Sweat

Wearable potentiometric ion sensors are attracting attention for real-time ion monitoring in biological fluids. One of the key challenges lies in keeping the analytical performances under a stretchable state. Herein, we report a highly stretchable fiber-based ion-selective electrode (ISE) prepared by coating an ion-selective membrane (ISM) on a stretchable gold fiber electrode. The fiber ISE ensures high stretchability up to 200% strain with only 2.1% increase in resistance of the fiber electrode. Owing to a strong attachment between the ISM and gold fiber electrode substrate, the ISE discloses favorable stability and potential repeatability. The Nernst slope of the ion response fluctuates from 59.2 to 57.4 mV/dec between 0 and 200% strain. Minor fluctuation of the intercept (E⁰) (±4.97 mV) also results. The ISE can endure 1000 cycles at the maximum stretch. Sodium, chloride, and pH fiber sensors were fabricated and integrated into a hairband for real-time analysis of human sweat. The result displays a high accuracy compared with ex situ analysis. The integrated sensors were calibrated before and just after on-body measurements, and they offer reliable results for sweat analysis.

Wearable Electrochemical Sensors for the Monitoring and Screening of Drugs

Wearable electrochemical sensors capable of noninvasive monitoring of chemical markers represent a rapidly emerging digital-health technology. Recent advances toward wearable continuous glucose monitoring (CGM) systems have ignited tremendous interest in expanding such sensor technology to other important fields. This article reviews for the first time wearable electrochemical sensors for monitoring therapeutic drugs and drugs of abuse. This rapidly emerging class of drug-sensing wearable devices addresses the growing demand for personalized medicine, toward improved therapeutic outcomes while minimizing the side effects of drugs and the related medical expenses. Continuous, noninvasive monitoring of therapeutic drugs within bodily fluids empowers clinicians and patients to correlate the pharmacokinetic properties with optimal outcomes by realizing patient-specific dose regulation and tracking dynamic changes in pharmacokinetics behavior while assuring the medication adherence of patients. Furthermore, wearable electrochemical drug monitoring devices can also serve as powerful screening tools in the hands of law enforcement agents to combat drug trafficking and support on-site forensic investigations. The review covers various wearable form factors developed for noninvasive monitoring of therapeutic drugs in different body fluids and toward on-site screening of drugs of abuse. The future prospects of such wearable drug monitoring devices are presented with the ultimate goals of introducing accurate real-time drug monitoring protocols and autonomous closed-loop platforms toward precise dose regulation and optimal therapeutic outcomes. Finally, current unmet challenges and existing gaps are discussed for motivating future technological innovations regarding personalized therapy. The current pace of developments and the tremendous market opportunities for such wearable drug monitoring platforms are expected to drive intense future research and commercialization efforts.

Nanophotonic-Carbohydrate Lab-on-a-Microneedle for Rapid Detection of Human Cystatin C in Finger-Prick Blood

Miniaturized total analysis systems, for the rapid detection of disease biomarkers, with features including high biomarker sensitivity, selectivity, biocompatibility, and disposability, all at low cost are of profound importance in the healthcare sector. Within this frame of reference, we developed a lab-on-a-carbohydrate-microneedle biodevice by integrating localized surface plasmon resonance (LSPR) paper-based substrates with biocompatible microneedles of high aspect ratio (>60:1 length:width). These microneedles are completely fabricated with carbohydrate (maltose) and further coated with poly lactic-co-glycolic acid (PLGA), which together serves the purpose of fluid channels. The porous nature of PLGA, in addition to drawing blood by capillary action, filters out the whole blood, allowing only the blood plasma to reach the biorecognition layer of the developed biodevice. While the use of maltose provides biocompatibility to the microneedle, the axial compression and transverse load analysis revealed desired mechanical strength of the microneedle, with mechanical failure occurring at 11N and 9 N respectively for the compressive and transverse load. For a proof-of-principle demonstration, the developed biodevice is validated for its operational features by direct detection of cystatin C in finger-prick blood and up to a concentration of 0.01 μg/mL in buffered conditions using the LSPR technique. Furthermore, by changing the biorecognition layer, the use of the developed needle can be extended to other disease biomarkers, and therefore the innovation presented in this work represents a hallmark in the state of the art of lab-on-a-chip biodevices.