A Gelated Colloidal Crystal Attached Lens for Noninvasive Continuous Monitoring of Tear Glucose

Tear-Based Ocular Wearable Biosensors for Human Health Monitoring

Wearable tear-based biosensors have garnered substantial interest for real time monitoring with an emphasis on personalized health care. These biosensors utilize major tear biomarkers such as proteins, lipids, metabolites, and electrolytes for the detection and recording of stable biological signals in a non-invasive manner. The present comprehensive review delves deep into the tear composition along with potential biomarkers that can identify, monitor, and predict certain ocular diseases such as dry eye disease, conjunctivitis, eye-related infections, as well as diabetes mellitus. Recent technologies in tear-based wearable point-of-care medical devices, specifically the state-of-the-art and prospects of glucose, pH, lactate, protein, lipid, and electrolyte sensing from tear are discussed. Finally, the review addresses the existing challenges associated with the widespread application of tear-based sensors, which will pave the way for advanced scientific research and development of such non-invasive health monitoring devices.

Smart Contact Lenses in Ophthalmology: Innovations, Applications, and Future Prospects

Smart contact lenses represent a breakthrough in the intersection of medical science and innovative technology, offering transformative potential in ophthalmology. This review article delves into the technological underpinnings of smart contact lenses, emphasizing the current landscape and advancements in biosensors, power supply, biomaterials, and the transmission of ocular information. This review further applies new innovations to their emerging role in the diagnosis, monitoring, and management of various ocular conditions. Moreover, we explore the impact of technical innovations on the application of smart contact lenses in monitoring glaucoma, managing postoperative care, and dry eye syndrome, further elucidating the non-invasive nature of these devices in continuous ocular health monitoring. The therapeutic potential of smart contact lenses such as treatment through targeted drug delivery and the monitoring of inflammatory biomarkers is also highlighted. Despite promising advancements, the implementation of smart contact lenses faces technical, regulatory, and patient compliance challenges. This review synthesizes the recent advances to provide an outlook on the state of smart contact lens technology. Furthermore, we discuss future directions, focusing on potential technological enhancements and new applications within ophthalmology.

Smart Contact Lenses for Healthcare Monitoring and Therapy

The eye contains a wealth of physiological information and offers a suitable environment for noninvasive monitoring of diseases via smart contact lens sensors. Although extensive research efforts recently have been undertaken to develop smart contact lens sensors, they are still in an early stage of being utilized as an intelligent wearable sensing platform for monitoring various biophysical/chemical conditions. In this review, we provide a general introduction to smart contact lenses that have been developed for disease monitoring and therapy. First, different disease biomarkers available from the ocular environment are summarized, including both physical and chemical biomarkers, followed by the commonly used materials, manufacturing processes, and characteristics of contact lenses. Smart contact lenses for eye-drug delivery with advancing technologies to achieve more efficient treatments are then introduced as well as the latest developments for disease diagnosis. Finally, sensor communication technologies and smart contact lenses for antimicrobial and other emerging bioapplications are also discussed as well as the challenges and prospects of the future development of smart contact lenses.

Angle-Independent Color Change in Thermoresponsive Gel-Immobilized Colloidal Amorphous Film Attached to PET Substrate

Gel-immobilized colloidal amorphous structures comprise short-range-ordered monodisperse submicrometer particles embedded into a soft polymer gel. They exhibit an angle-independent structural color that is tunable in response to external stimuli via a volume change in the gel, which has significant potential for the development of sensors that respond to stimuli via angle-independent color changes. In this study, the amorphous structure of a charged colloidal suspension in water was immobilized in a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) gel film and simultaneously attached to a polyethylene terephthalate (PET) substrate. The gel film exhibited a uniform angle-independent color that changed in response to changes in temperature (i.e., thermosensitivity). Attachment to the PET substrate suppressed changes in the gel film area and film distortion, despite significant volume changes in the gel. Consequently, the degree of thermosensitivity was enhanced. The PET-attached gel-immobilized colloidal amorphous film was easy to handle and had excellent flexibility, allowing it to wrap around the surfaces of curved objects. These features are advantageous for sensor applications.

Smart Contact Lenses as Wearable Ophthalmic Devices for Disease Monitoring and Health Management

The eye contains a complex network of physiological information and biomarkers for monitoring disease and managing health, and ocular devices can be used to effectively perform point-of-care diagnosis and disease management. This comprehensive review describes the target biomarkers and various diseases, including ophthalmic diseases, metabolic diseases, and neurological diseases, based on the physiological and anatomical background of the eye. This review also includes the recent technologies utilized in eye-wearable medical devices and the latest trends in wearable ophthalmic devices, specifically smart contact lenses for the purpose of disease management. After introducing other ocular devices such as the retinal prosthesis, we further discuss the current challenges and potential possibilities of smart contact lenses.

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

BACKGROUND

Numerous laboratory tests are used in the diagnosis and management of diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

APPROACH

An expert committee compiled evidence-based recommendations for laboratory analysis in screening, diagnosis, or monitoring of diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association for Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association.

CONTENT

Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (HbA1c) in the blood. Glycemic control is monitored by the people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring (CGM) devices and also by laboratory analysis of HbA1c. The potential roles of noninvasive glucose monitoring, genetic testing, and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed.

SUMMARY

The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Wearable sensor platforms for real-time monitoring and early warning of metabolic disorders in humans

Nowadays, the prevalence of metabolic syndromes (MSs) has attracted increasing concerns as it is closely related to overweight and obesity, physical inactivity and overconsumption of energy, making the diagnosis and real-time monitoring of the physiological range essential and necessary for avoiding illness due to defects in the human body such as higher risk of cardiovascular disease, diabetes, stroke and diseases related to artery walls. However, the current sensing techniques are inconvenient and do not continuously monitor the health status of humans. Alternatively, the use of recent wearable device technology is a preferable method for the prevention of these diseases. This can enable the monitoring of the health status of humans in different health domains, including environment and structure. The use wearable devices with the purpose of facilitating rapid treatment and real-time monitoring can decrease the prevalence of MS and long-time monitor the health status of patients. This review highlights the recent advances in wearable sensors toward continuous monitoring of blood pressure and blood glucose, and further details the monitoring of abnormal obesity, triglycerides and HDL. We also discuss the challenges and future prospective of monitoring MS in humans.

Development of corneal contact lens materials and current clinical application of contact lenses: A review

Unlike conventional glasses, corneal contact lenses (CLs) can directly contact the surface of the tear film through the application of biopolymer materials, to achieve therapeutic and cosmetic purposes. Since the advent of polymethylmethacrylate, a material that has gained widespread use and attention, statistically, there are now more than 150 × 106 people around the world who wear corneal contact lenses. However, the associated complications caused by the interaction of contact lenses with the ocular surface, tear film, endogenous and environmental microorganisms, and components of the solution affect nearly one-third of the wearer population. The application of corneal contact lenses in correcting vision and myopia control has been widely recognized. With the development of related materials, corneal contact lenses are applied to the treatment of ocular surface diseases, including corneal bandage lenses, drug-loaded corneal contact lenses, biosensors, and other new products, while minimizing the side effects associated with CL wear. This paper summarized the development history and material properties of CLs, focused on the current main clinical applications and mechanisms, as well as clarified the possible complications in wearing therapeutic contact lenses and the direction for improvement in the future.

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

BACKGROUND

Numerous laboratory tests are used in the diagnosis and management of diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

APPROACH

An expert committee compiled evidence-based recommendations for laboratory analysis in screening, diagnosis, or monitoring of diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association of Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association.

CONTENT

Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (Hb A1c) in the blood. Glycemic control is monitored by the people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring (CGM) devices and also by laboratory analysis of Hb A1c. The potential roles of noninvasive glucose monitoring, genetic testing, and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed.

SUMMARY

The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Recent Advancements in Physiological, Biochemical, and Multimodal Sensors Based on Flexible Substrates: Strategies, Technologies, and Integrations

Flexible wearable devices have been widely used in biomedical applications, the Internet of Things, and other fields, attracting the attention of many researchers. The physiological and biochemical information on the human body reflects various health states, providing essential data for human health examination and personalized medical treatment. Meanwhile, physiological and biochemical information reveals the moving state and position of the human body, and it is the data basis for realizing human-computer interactions. Flexible wearable physiological and biochemical sensors provide real-time, human-friendly monitoring because of their light weight, wearability, and high flexibility. This paper reviews the latest advancements, strategies, and technologies of flexibly wearable physiological and biochemical sensors (pressure, strain, humidity, saliva, sweat, and tears). Next, we systematically summarize the integration principles of flexible physiological and biochemical sensors with the current research progress. Finally, important directions and challenges of physiological, biochemical, and multimodal sensors are proposed to realize their potential applications for human movement, health monitoring, and personalized medicine.

Insight into continuous glucose monitoring: from medical basics to commercialized devices

According to the latest statistics, more than 537 million people around the world struggle with diabetes and its adverse consequences. As well as acute risks of hypo- or hyper- glycemia, long-term vascular complications may occur, including coronary heart disease or stroke, as well as diabetic nephropathy leading to end-stage disease, neuropathy or retinopathy. Therefore, there is an urgent need to improve diabetes management to reduce the risk of complications but also to improve patient's quality life. The impact of continuous glucose monitoring (CGM) is well recognized, in this regard. The current review aims at introducing the basic principles of glucose sensing, including electrochemical and optical detection, summarizing CGM technology, its requirements, advantages, and disadvantages. The role of CGM systems in the clinical diagnostics/personal testing, difficulties in their utilization, and recommendations are also discussed. In the end, challenges and prospects in future CGM systems are discussed and non-invasive, wearable glucose biosensors are introduced. Though the scope of this review is CGMs and provides information about medical issues and analytical principles, consideration of broader use will be critical in future if the right systems are to be selected for effective diabetes management.

Glucose sensing based on hydrogel grating incorporating phenylboronic acid groups

We proposed a hydrogel grating sensor functionalized with phenylboronic acid (PBA) group for glucose concentration detection. A PBA functionalized polyacrylamide hydrogel film was first prepared via ultraviolet polymerization. Then, the diffraction grating was written on the hydrogel film via the femto-second (fs) laser point-by-point direct inscription. Binding between the PBA groups in the hydrogel and glucose molecules would lead to the swelling of hydrogel and the thus grating structure, thus modifying the diffraction properties of the grating. We experimentally characterized the swelling and transmission of the grating with different glucose concentrations. Sensitivity of the sensor was defined as variations in relative diffraction efficiency in response to glucose concentration changes, and was experimentally found to 0.61%/mM. The proposed sensor showed fast response towards the presence of glucose, and its reusability and biocompatibility were also confirmed. The use of fs-laser inscription technique does not require a pre-fabricated template, and would allow to directly modify the fabrication parameters such as scanning speed, pulse energy and frequency. Therefore, one is able to conveniently optimize the grating structure and improve the inscription efficiency. The proposed hydrogel grating could be potentially fabricated into wearable sensors, namely, contact lenses, for continuous monitoring of tear glucose level with rapid response.

Research Advances in Mechanical Properties and Applications of Dual Network Hydrogels

Hydrogels with a three-dimensional network structure are particularly outstanding in water absorption and water retention because water exists stably in the interior, making the gel appear elastic and solid. Although traditional hydrogels have good water absorption and high water content, they have poor mechanical properties and are not strong enough to be applied in some scenarios today. The proposal of double-network hydrogels has dramatically improved the toughness and mechanical strength of hydrogels that can adapt to different environments. Based on ensuring the properties of hydrogels, they themselves will not be damaged by excessive pressure and tension. This review introduces preparation methods for double-network hydrogels and ways to improve the mechanical properties of three typical gels. In addition to improving the mechanical properties, the biocompatibility and swelling properties of hydrogels enable them to be applied in the fields of biomedicine, intelligent sensors, and ion adsorption.

A review of Optical Point-of-Care devices to Estimate the Technology Transfer of These Cutting-Edge Technologies

Despite the remarkable development related to Point-of-Care devices based on optical technology, their difficulties when used outside of research laboratories are notable. In this sense, it would be interesting to ask ourselves what the degree of transferability of the research work to the market is, for example, by analysing the relation between the scientific work developed and the registered one, through patent. In this work, we provide an overview of the state-of-the-art in the sector of optical Point-of-Care devices, not only in the research area but also regarding their transfer to market. To this end, we explored a methodology for searching articles and patents to obtain an indicator that relates to both. This figure of merit to estimate this transfer is based on classifying the relevant research articles in the area and the patents that have been generated from these ones. To delimit the scope of this study, we researched the results of a large enough number of publications in the period from 2015 to 2020, by using keywords "biosensor", "optic", and "device" to obtain the most representative articles from Web of Science and Scopus. Then, we classified them according to a particular classification of the optical PoC devices. Once we had this sampling frame, we defined a patent search strategy to cross-link the article with a registered patent (by surfing Google Patents) and classified them accordingly to the categories described. Finally, we proposed a relative figure called Index of Technology Transference (IoTT), which estimates to what extent our findings in science materialized in published articles are protected by patent.

Non-gelated polymeric photonic crystal films

A rapid curing method for the preparation of colloidal photonic crystal films is presented. Firstly, a colloidal crystal array template was prepared by self-assembly of nanospheres, and then a dilute polymer solution was poured into the gap of the template. Then the composite photonic film was obtained as the polymer solution was cured. Such films have good properties in mechanical strength, anti pH interference, rapid solvent response and are easy to preserve. The films show good linear response to ethanol aqueous solutions of different concentrations, and the response equilibrium takes less than 20 s. The films also show long-term stability and reusability, and further functionalization can make the films multi-sensitive.

The Development and Progression of Micro-Nano Optics

Micro-Nano optics is one of the most active frontiers in the current development of optics. It combines the cutting-edge achievements of photonics and nanotechnology, which can realize many brand-new functions on the basis of local electromagnetic interactions and become an indispensable key science and technology of the 21st century. Micro-Nano optics is also an important development direction of the new optoelectronics industry at present. It plays an irreplaceable role in optical communication, optical interconnection, optical storage, sensing imaging, sensing measurement, display, solid-state lighting, biomedicine, security, green energy, and other fields. In this paper, we will summarize the research status of micro-nano optics, and analyze it from four aspects: micro-nano luminescent materials and devices, micro-nano optical waveguide materials and devices, micro-nano photoelectric detection materials and devices, and micro-nano optical structures and devices. Finally, the future development of micro-nano optics will be prospected.

Current and Future Perspectives on Microfluidic Tear Analytic Devices

Most current invasive analytic devices for disease diagnosis and monitoring require the collection of blood, which causes great discomfort for patients and may potentially cause infection. This explains the great need for noninvasive devices that utilize other bodily fluids like sweat, saliva, tears, or urine. Among them, eye tears are easily accessible, less complex in composition, and less susceptible to dilution. Tears also contain valuable clinical information for the diagnosis of ocular and systemic diseases as the tear analyte level shows great correlation with the blood analyte level. These unique advantages make tears a promising platform for use in clinical settings. As the volume of tear film and the rate of tear flow are only microliters in size, the use of microfluidic technology in analytic devices allows minimal sample consumption. Hence, more and more microfluidic tear analytic devices have been proposed, and their working mechanisms can be broadly categorized into four main types: (a) electrochemical, (b) photonic crystals, (c) fluorescence, and (d) colorimetry. These devices are being developed toward the application of point-of-care tests with rapid yet accurate results. This review aims to provide a general overview of the recent developmental trend of microfluidic devices for tear analysis. Moreover, the fundamental principle behind each type of device along with their strengths and weaknesses will be discussed, especially in terms of their abilities and potential in being used in point-of-care settings.

The Current State of Optical Sensors in Medical Wearables

Optical sensors play an increasingly important role in the development of medical diagnostic devices. They can be very widely used to measure the physiology of the human body. Optical methods include PPG, radiation, biochemical, and optical fiber sensors. Optical sensors offer excellent metrological properties, immunity to electromagnetic interference, electrical safety, simple miniaturization, the ability to capture volumes of nanometers, and non-invasive examination. In addition, they are cheap and resistant to water and corrosion. The use of optical sensors can bring better methods of continuous diagnostics in the comfort of the home and the development of telemedicine in the 21st century. This article offers a large overview of optical wearable methods and their modern use with an insight into the future years of technology in this field.

Recent Advancement in Biofluid-Based Glucose Sensors Using Invasive, Minimally Invasive, and Non-Invasive Technologies: A Review

Biosensors have potentially revolutionized the biomedical field. Their portability, cost-effectiveness, and ease of operation have made the market for these biosensors to grow rapidly. Diabetes mellitus is the condition of having high glucose content in the body, and it has become one of the very common conditions that is leading to deaths worldwide. Although it still has no cure or prevention, if monitored and treated with appropriate medication, the complications can be hindered and mitigated. Glucose content in the body can be detected using various biological fluids, namely blood, sweat, urine, interstitial fluids, tears, breath, and saliva. In the past decade, there has been an influx of potential biosensor technologies for continuous glucose level estimation. This literature review provides a comprehensive update on the recent advances in the field of biofluid-based sensors for glucose level detection in terms of methods, methodology and materials used.

A photonic crystal material for the online detection of nonpolar hydrocarbon vapors

A modern level of nanotechnology allows us to create conceptually new test systems for chemical analyses and to develop sensitive and compact sensors for various types of substances. However, at present, there are very few commercially available compact sensors for the determination of toxic and carcinogenic substances, such as organic solvents that are used in some construction materials. This article contains an overview of how 3D photonic crystals are used for the creation of a new test system for nonpolar organic solvents. The morphology and structural parameters of the photonic crystals, based upon a crystalline colloidal array with a sensing matrix of polydimethylsiloxane, have been determined by using scanning electron microscopy and by the results of specular reflectance spectroscopy based on the Bragg-Snell law. A new approach has been proposed for the application of this sensor in chemical analysis for the qualitative detection of saturated vapors of volatile organic compounds due to configuration changes of the photonic bandgap, recorded by diffuse reflectance spectroscopy. The exposure of the sensor to aromatic (benzene, toluene and p-xylene) and aliphatic (n-pentane, n-heptane, n-octane and n-decane) hydrocarbons has been analyzed. The reconstitution of spectral parameters of the sensor during the periodic detection of saturated vapors of toluene has been evaluated.

Photonic Crystal-Embedded Molecularly Imprinted Contact Lenses for Controlled Drug Release

As a noninvasive eye disease detection and drug delivery device, contact lenses can improve eye bioavailability and enable continuous drug delivery. In order to monitor the release of drugs in real time, molecularly imprinted contact lenses (MICLs) based on photonic crystals (PCs) were prepared for the treatment of diabetes-related diseases. The specific adsorption of molecularly imprinted polymers on dexamethasone sodium phosphate (DSP) increased the drug loading and optimized the drug release behavior. At the same time, the drug release ensures the rapid color report during the loading and releasing of drugs due to the volume and refractive index change of the hydrogel matrix. The continuous and slow release of DSP by MICLs in artificial tears was successfully monitored through structural color changes, and the cytotoxicity test results showed that the MICL had good biocompatibility. Therefore, MICLs with a PC structure color have great biomedical potentiality in the future.

A Meta-Analysis of Wearable Contact Lenses for Medical Applications: Role of Electrospun Fiber for Drug Delivery

In recent years, wearable contact lenses for medical applications have attracted significant attention, as they enable continuous real-time recording of physiological information via active and noninvasive measurements. These devices play a vital role in continuous monitoring of intraocular pressure (IOP), noninvasive glucose monitoring in diabetes patients, drug delivery for the treatment of ocular illnesses, and colorblindness treatment. In specific, this class of medical devices is rapidly advancing in the area of drug loading and ocular drug release through incorporation of electrospun fibers. The electrospun fiber matrices offer a high surface area, controlled morphology, wettability, biocompatibility, and tunable porosity, which are highly desirable for controlled drug release. This article provides an overview of the advances of contact lens devices in medical applications with a focus on four main applications of these soft wearable devices: (i) IOP measurement and monitoring, (ii) glucose detection, (iii) ocular drug delivery, and (iv) colorblindness treatment. For each category and application, significant challenges and shortcomings of the current devices are thoroughly discussed, and new areas of opportunity are suggested. We also emphasize the role of electrospun fibers, their fabrication methods along with their characteristics, and the integration of diverse fiber types within the structure of the wearable contact lenses for efficient drug loading, in addition to controlled and sustained drug release. This review article also presents relevant statistics on the evolution of medical contact lenses over the last two decades, their strengths, and the future avenues for making the essential transition from clinical trials to real-world applications.

Applications of Advanced Materials for Non-Enzymatic Glucose Monitoring: From Invasive to the Wearable Device

Diabetes mellitus (DM) is a global health problem leading to many complications and disabilities in life adjusting activities and even dead. Monitoring glucose levels is a key factor in diagnosis and management of DM. Conventional glucose sensors consisted of immobilized enzymes, are so susceptible to environmental conditions. In this way, nonenzymatic biosensors have attracted extensive attentions in many clinical diagnostics applications. To date, the finger pricking test is a common enzyme-based glucometer that is an invasive and inconvenient and may lead to infections in the injection sites. So, working on the possibility of cutaneous or subcutaneous insertion of devices as a noninvasive or minimally-invasive systems for continuous glucose controlling approaches through human biofluids (blood, perspiration, tears, saliva, etc.) have stimulated growing interest. This review summarizes recent nonenzymatic and noninvasive biofluids glucose monitoring systems which are highly resilience and stretchable to continuously adapt to body movements during common physical activity. Sensors are based on their constituent materials including carbon-based, metal nanoparticles, polymer, and hydrogel systems are classified for electrochemical, and optical glucose detection. Finally, we address the drawbacks and challenges of enzyme-free sensors which are aroused sustaining research passion to be used in point-of-care medical diagnostics applications.

The Application of Wearable Glucose Sensors in Point-of-Care Testing

Diabetes and its complications have become a worldwide concern that influences human health negatively and even leads to death. The real-time and convenient glucose detection in biofluids is urgently needed. Traditional glucose testing is detecting glucose in blood and is invasive, which cannot be continuous and results in discomfort for the users. Consequently, wearable glucose sensors toward continuous point-of-care glucose testing in biofluids have attracted great attention, and the trend of glucose testing is from invasive to non-invasive. In this review, the wearable point-of-care glucose sensors for the detection of different biofluids including blood, sweat, saliva, tears, and interstitial fluid are discussed, and the future trend of development is prospected.

Ophthalmic sensing technologies for ocular disease diagnostics

Point-of-care diagnosis and personalized treatments are critical in ocular physiology and disease. Continuous sampling of tear fluid for ocular diagnosis is a need for further exploration. Several techniques have been developed for possible ophthalmological applications, from traditional spectroscopies to wearable sensors. Contact lenses are commonly used devices for vision correction, as well as for other therapeutic and cosmetic purposes. They are increasingly being developed into ocular sensors, being used to sense and monitor biochemical analytes in tear fluid, ocular surface temperature, intraocular pressure, and pH value. These sensors have had success in detecting ocular conditions, optimizing pharmaceutical treatments, and tracking treatment efficacy in point-of-care settings. However, there is a paucity of new and effective instrumentation reported in ophthalmology. Hence, this review will summarize the applied ophthalmic technologies for ocular diagnostics and tear monitoring, including both conventional and biosensing technologies. Besides applications of smart readout devices for continuous monitoring, targeted biomarkers are also discussed for the convenience of diagnosis of various ocular diseases. A further discussion is also provided for future aspects and market requirements related to the commercialization of novel types of contact lens sensors.

Ophthalmic Sensors and Drug Delivery

Advances in multifunctional materials and technologies have allowed contact lenses to serve as wearable devices for continuous monitoring of physiological parameters and delivering drugs for ocular diseases. Since the tear fluids comprise a library of biomarkers, direct measurement of different parameters such as concentration of glucose, urea, proteins, nitrite, and chloride ions, intraocular pressure (IOP), corneal temperature, and pH can be carried out non-invasively using contact lens sensors. Microfluidic contact lens sensor based colorimetric sensing and liquid control mechanisms enable the wearers to perform self-examinations at home using smartphones. Furthermore, drug-laden contact lenses have emerged as delivery platforms using a low dosage of drugs with extended residence time and increased ocular bioavailability. This review provides an overview of contact lenses for ocular diagnostics and drug delivery applications. The designs, working principles, and sensing mechanisms of sensors and drug delivery systems are reviewed. The potential applications of contact lenses in point-of-care diagnostics and personalized medicine, along with the significance of integrating multiplexed sensing units together with drug delivery systems, have also been discussed.

Recent progress on wearable point-of-care devices for ocular systems

The eye is a complex sensory organ that contains abundant information for specific diseases and pathological responses. It has emerged as a facile biological interface for wearable healthcare platforms because of its excellent accessibility. Recent advances in electronic devices have led to the extensive research of point-of-care (POC) systems for diagnosing and monitoring diseases by detecting the biomarkers within the eye. Among these systems, contact lenses, which make direct contact with the ocular surfaces, have been utilized as one of the promising candidates for non-invasive POC testing of various diseases. The continuous and long-term measurement from the sensor allows the patients to manage their symptoms in an effective and convenient way. Herein, we review the progress of contact lens sensors in terms of the materials, methodologies, device designs, and target biomarkers. The anatomical structure and biological mechanisms of the eye are also discussed to provide a comprehensive understanding of the principles of contact lens sensors. Intraocular pressure and glucose, which are the representative biomarkers found in the eyes, can be measured with the biosensors integrated with contact lenses for the diagnosis of glaucoma and diabetes. Furthermore, contact lens sensors for various general pathologies as well as other ocular diseases are also considered, thereby providing the prospects for further developments of smart contact lenses as a future POC system.

Integration of paper microfluidic sensors into contact lenses for tear fluid analysis

In this article, using the integration of paper microfluidics within laser-inscribed commercial contact lenses, we demonstrate the multiplexed detection of clinically relevant analytes including hydrogen ions, proteins, glucose, nitrites and l-ascorbic acid, all sampled directly from model tears. In vitro measurements involved the optimization of colorimetric assays, with readouts collected, stored and analyzed using a bespoke Tears Diagnostics smartphone application prototype. We demonstrate the potential of the device to perform discrete measurements either for medical diagnosis or disease screening in the clinic or at the point-of-care (PoC), with future applications including monitoring of ocular infections, uveitis, diabetes, keratopathies and assessing oxidative stress.

Optical Waveguides and Integrated Optical Devices for Medical Diagnosis, Health Monitoring and Light Therapies

Optical waveguides and integrated optical devices are promising solutions for many applications, such as medical diagnosis, health monitoring and light therapies. Despite the many existing reviews focusing on the materials that these devices are made from, a systematic review that relates these devices to the various materials, fabrication processes, sensing methods and medical applications is still seldom seen. This work is intended to link these multidisciplinary fields, and to provide a comprehensive review of the recent advances of these devices. Firstly, the optical and mechanical properties of optical waveguides based on glass, polymers and heterogeneous materials and fabricated via various processes are thoroughly discussed, together with their applications for medical purposes. Then, the fabrication processes and medical implementations of integrated passive and active optical devices with sensing modules are introduced, which can be used in many medical fields such as drug delivery and cardiovascular healthcare. Thirdly, wearable optical sensing devices based on light sensing methods such as colorimetry, fluorescence and luminescence are discussed. Additionally, the wearable optical devices for light therapies are introduced. The review concludes with a comprehensive summary of these optical devices, in terms of their forms, materials, light sources and applications.

Recent advances of electrochemical and optical enzyme-free glucose sensors operating at physiological conditions

Diabetes is a pathological condition that requires the continuous monitoring of glucose level in the blood. Its control has been tremendously improved by the application of point-of-care devices. Conventional enzyme-based sensors with electrochemical and optical transduction systems can successfully measure the glucose concentration in human blood, but they suffer from the low stability of the enzyme. Non-enzymatic wearable electrochemical and optical sensors, with low-cost, high stability, point-of-care testing and online monitoring of glucose levels in biological fluids, have recently been developed and can help to manage and control diabetes worldwide. Advances in nanoscience and nanotechnology have enabled the development of novel nanomaterials that can be implemented for the use in enzyme-free systems to detect glucose. This review summarizes recent developments of enzyme-free electrochemical and optical glucose sensors, as well as their respective wearable and commercially available devices, capable of detecting glucose at physiological pH conditions without the need to pretreat the biological fluids. Additionally, the evolution of electrochemical glucose sensor technology and a couple of widely used optical detection systems along with the glucose detection mechanism is also discussed. Finally, this review addresses limitations and challenges of current non-enzymatic electrochemical, optical, and wearable glucose sensor technologies and highlights opportunities for future research directions.

Hydrogel-Based Colloidal Photonic Crystal Devices for Glucose Sensing

Diabetes, a common epidemic disease, is increasingly hazardous to human health. Monitoring body glucose concentrations for the prevention and therapy of diabetes has become very important. Hydrogel-based responsive photonic crystal (PC) materials are noninvasive options for glucose detection. This article reviews glucose-sensing materials/devices composed of hydrogels and colloidal photonic crystals (CPCs), including the construction of 2D/3D CPCs and 2D/3D hydrogel-based CPCs (HCPCs). The development and mechanisms of glucose-responsive hydrogels and the achieved technologies of HCPC glucose sensors were also concluded. This review concludes by showing a perspective for the future design of CPC glucose biosensors with functional hydrogels.

Selective and Colorimetric Detection of p-Nitrophenol Based on Inverse Opal Polymeric Photonic Crystals

The detection of p-nitrophenol (PNP) is of great significance for assessment of environment pollution and potential health risks. In this study, based on inverse opal polymeric photonic crystals (IOPPCs), a selective and visual sensor for high-performance PNP detection is developed. Due to their unique optical properties, IOPPCs report events by change of color, which can easily be observed by the naked eye. Hydroxyethyl methacrylate (HEMA) was selected as the functional monomer with which to fabricate the IOPPCs. By precisely adjusting the molar ratio between the functional monomer and the crosslinker, the sensors were only able to be sensitive to a specific solution, thus realizing the visual, selective, and semi-quantitative detection of PNP. When the sensors were immersed in different concentrations of PNP solution, their Bragg diffraction wavelengths showed different redshifts. The color of the IOPPCs changed from green to red as the peak shift of Bragg diffraction occurred. In addition, the IOPPCs displayed good interference immunity and reusability.

Applications of Hydrogels with Special Physical Properties in Biomedicine

As a polymer matrix containing a large amount of water, hydrogels have been widely used in many fields such as biology and medicine due to its similarity to extracellular matrix components, and its contact with blood, body fluids, and human tissue does not affect the metabolic processes of living organisms. However, due to the lack of unique physical properties of traditional polymer hydrogels, its further application in the high-end field is limited. With the progress of study, a series of hydrogels with special structures, such as double network hydrogel, composite hydrogel, Tetra-PEG gel, and topological gel, have improved the situation to a large extent. At the same time, the progress of research on the biocompatibility and biodegradability of hydrogels, which are expected to be used in biomedical fields, is also worthy of attention. This review introduces four such types of high-strength polymeric hydrogels and the mechanisms for improving their mechanical strength. Moreover, a discussion will be made around specific methods for imparting special physical properties to hydrogels and applications in the field of biomedicine such as cell culture, medical surgery, tissue engineering, and biosensing. At the end of the review, the main reasons and contradictions for the limits of the current applications are explained. An outlook on the future research in related fields and the importance of carrying out research in this area to promote medical progress are emphasized.

Wearable and flexible electronics for continuous molecular monitoring

Wearable biosensors have received tremendous attention over the past decade owing to their great potential in predictive analytics and treatment toward personalized medicine. Flexible electronics could serve as an ideal platform for personalized wearable devices because of their unique properties such as light weight, low cost, high flexibility and great conformability. Unlike most reported flexible sensors that mainly track physical activities and vital signs, the new generation of wearable and flexible chemical sensors enables real-time, continuous and fast detection of accessible biomarkers from the human body, and allows for the collection of large-scale information about the individual's dynamic health status at the molecular level. In this article, we review and highlight recent advances in wearable and flexible sensors toward continuous and non-invasive molecular analysis in sweat, tears, saliva, interstitial fluid, blood, wound exudate as well as exhaled breath. The flexible platforms, sensing mechanisms, and device and system configurations employed for continuous monitoring are summarized. We also discuss the key challenges and opportunities of the wearable and flexible chemical sensors that lie ahead.

The Progress of Glucose Monitoring-A Review of Invasive to Minimally and Non-Invasive Techniques, Devices and Sensors

Current glucose monitoring methods for the ever-increasing number of diabetic people around the world are invasive, painful, time-consuming, and a constant burden for the household budget. The non-invasive glucose monitoring technology overcomes these limitations, for which this topic is significantly being researched and represents an exciting and highly sought after market for many companies. This review aims to offer an up-to-date report on the leading technologies for non-invasive (NI) and minimally-invasive (MI) glucose monitoring sensors, devices currently available in the market, regulatory framework for accuracy assessment, new approaches currently under study by representative groups and developers, and algorithm types for signal enhancement and value prediction. The review also discusses the future trend of glucose detection by analyzing the usage of the different bands in the electromagnetic spectrum. The review concludes that the adoption and use of new technologies for glucose detection is unavoidable and closer to become a reality.

Detecting Glucose Levels in Blood Plasma and Artificial Tear by Au(I) Complex on the Carbopol Polymer: A Microfluidic Paper-Based Method

We report on a selective paper-based method and a microfluidic paper-based analytical device (μPAD) for the detection of human plasma glucose and tear glucose using carbopol polymer-encapsulated Au(I) complex (AuC₂C₆H₄OMe)₂(Ph₂P(C₆H₄)₃PPh₂), (B5). To the best of our knowledge, this demonstrates for the first time the glucose sensing based on dual emission, i.e., fluorescence and phosphorescence, of a single type molecule on the carbopol polymer. Upon addition of human blood treated with anticoagulants to μPADs, plasma is separated from the blood and flows into the response region of the μPADs to react with carbopol polymer-encapsulated B5, in which the ratiometric luminescence is analyzed. The plasma glucose concentration can be quantitively detected at 1.0⁻50.0 mM on paper, and tear glucose can be detected at 0.1⁻4.0 mM on μPADs. Owing to the structural design, this device has superior ratiometric changes of dual emission over other Au(I) complexes for signal transduction. The encapsulation of carbopol polymer also offers long-term storage stability. In tear measurement, carbopol polymer is not only used to encapsulate enzyme to remain the enzyme's activity, but also played as a glue (or media) to connect microfluidic channel and response region. This further improves the sensitivity and limit of detection for glucose. Moreover, this sensor provides a faster response time, a wider range for glucose sensing than reported previously, and no statistical difference of the data from a commercial glucometer, allowing for practical diagnosis of diabetes and healthy individuals.

Contact-Lens Biosensors

Rapid diagnosis and screening of diseases have become increasingly important in predictive and preventive medicine as they improve patient treatment strategies and reduce cost as well as burden on our healthcare system. In this regard, wearable devices are emerging as effective and reliable point-of-care diagnostics that can allow users to monitor their health at home. These wrist-worn, head-mounted, smart-textile, or smart-patches devices can offer valuable information on the conditions of patients as a non-invasive form of monitoring. However, they are significantly limited in monitoring physiological signals and biomechanics, and, mostly, rely on the physical attributes. Recently, developed wearable devices utilize body fluids, such as sweat, saliva, or skin interstitial fluid, and electrochemical interactions to allow continuous physiological condition and disease monitoring for users. Among them, tear fluid has been widely utilized in the investigation of ocular diseases, diabetes, and even cancers, because of its easy accessibility, lower complexity, and minimal invasiveness. By determining the concentration change of analytes within the tear fluid, it would be possible to identify disease progression and allow patient-oriented therapies. Considering the emerging trend of tear-based biosensing technology, this review article aims to focus on an overview of the tear fluid as a detection medium for certain diseases, such as ocular disorders, diabetes, and cancer. In addition, the rise and application of minimally invasive detection and monitoring via integrated contact lens biosensors will also be addressed, in regards to their practicality and current developmental progress.

A Novel Glucose Biosensor Based on Hierarchically Porous Block Copolymer Film

Enzymatic biosensors are widely used in clinical diagnostics, and electrode materials are essential for both the efficient immobilization of enzyme and the fast electron transfer between the active sites of enzyme and electrode surface. Electrode materials with a hierarchically porous structure can not only increase the specific surface area but also promote the electron transfer, facilitating the catalysis reaction. Block copolymer is a good candidate for preparation of film with a hierarchically porous structure due to its unique characteristics of self-assembly and phase separation. In the current work, hierarchically porous block copolymer film containing both micropores and nanopores was prepared by spinodal decomposition induced phase separation. The resultant copolymer film was adopted as the electrode material to immobilize glucose oxidase (GOx) for construction of an enzyme biosensor. Scanning electron microscopy (SEM), contact angle (CA) measurements, and Fourier-transform infrared (FTIR) and electrochemical impendence spectroscopy (EIS) were adopted to investigate the microstructure of the as-developed biosensor. Results demonstrated that the hierarchically porous block copolymer film offered a favorable and biocompatible microenvironment for proteins. These as-prepared glucose biosensors possessed a wide linear range (10⁻4500 μM), a low detection limit (0.05 μM), quick response (2 s), excellent stability, and selectivity. This work demonstrates that hierarchically porous block copolymer film is a good matrix candidate for the immobilization of the enzyme and provides a potential electrode material to construct novel biosensors with excellent performance.

Synthesis of hydrogel-bearing phenylboronic acid moieties and their applications in glucose sensing and insulin delivery

In past few years, phenylboronic acids (PBAs) have attracted researcher's attention due to their unique responsiveness towards diol-containing molecules such as glucose. This property allows hydrogel-bearing PBAs potentially to serve as an alternative for glucose-sensing and insulin-delivery systems. This review provides an outlook on the binding mechanism of PBA moieties with diols and the approaches to increase their binding selectivity and response for glucose molecules. The preparation methods and strategies of hydrogel-bearing PBA moieties along with their properties are discussed. In the last section, their applications in glucose-sensing and insulin-regulatory systems are described.

2D Photonic Crystal Hydrogel Sensor for Tear Glucose Monitoring

Photonic crystal (PC) materials have huge potentials as sensors for noninvasive and real-time monitoring glucose in tears. We developed a glucose-sensitive PC material based on monolayered colloidal crystals (MCCs). Polystyrene nanoparticles were first self-assembled into a highly ordered MCC, and this two-dimensional (2D) template was then coated by a 4-boronobenzaldehyde-functionalized poly(vinyl alcohol) hydrogel. Such a sensor efficiently diffracts visible light, whose structural color could change from red through yellow to green, as the glucose concentration altered from 0 to 20 mM, covering both tears' and bloods' physiological ranges. The sensor also represents a rapid response within 180 s at each titration of glucose, combining the characteristics of high accuracy and sensitivity in detecting the glucose concentration in tears, and this intelligent sensing material presents certain possibility for the frontier point-of-care glucose monitoring.