Chapter 2.1 - Wearable Bio and Chemical Sensors

Wearable sensors can be used to monitor many interesting parameters about the wearer’s physiology and environment, with important applications in personal health and well-being, sports performance and personal safety. Wearable chemical sensors can monitor the status of the wearer by accessing body fluids, such as sweat, in an unobtrusive manner. They can also be used to protect the wearer from hazards in the environment by sampling potentially harmful gas emissions, such as carbon monoxide. Integrating chemical sensors into textile structures is a challenging and complex task. Issues which must be considered include sample collection, calibration, waste handling, fouling and reliability. Sensors must also be durable and comfortable to wear. Here, we present examples of wearable chemical sensors that monitor the person and also his/her environment. We also discuss the issues involved in developing wearable chemical sensors and strategies for sensor design and textile integration.

In recent years much progress has been made in the integration of physical transducers into clothing e.g. breathing rate, heart rate and temperature [1]. The integration of chemical sensing into textiles adds a new dimension to the field of smart clothing. Wearable chemical sensors may be used to provide valuable information about the wearer’s health, monitoring the wearer during their daily routine within their natural environment. In addition to physiological measurements chemical sensors may also be used to monitor the wearer’s surrounding environment, identifying safety concerns and detecting threats. Whether the clothes are looking into the wearer’s personal health status or looking out into the surroundings, chemical sensing calls for a novel approach to sensor and textile integration. In contrast to physical sensors, chemical sensors and biosensors depend on selective reactions happening at an active surface which must be directly exposed to a sample. Therefore issues of fluid handling, calibration and safety must be considered. This paper discusses the constraints in integrating chemical sensors into a textile substrate. Methods of fluid control using inherently conducting polymers (ICPs) are discussed and a pH textile sensor is presented. This sensor uses colorimetric techniques using LEDs controlled by a wireless platform. Some of the potential applications of wearable chemical sensors are discussed.

A wireless potentiostat for mobile chemical sensing and biosensing

This year, the European Conference on Optical Chemical Sensors and Biosensors (Europt(r)ode) celebrated its 10th anniversary. The Europt(r)ode series was initiated by Otto S. Wolfbeis in 1992 and over the last two decades has realized his vision of providing researchers working on various types of optical chemical and biological sensors with a specialized conference to foster development in the field and to promote international collaboration. After the success of Europt(r)ode I in Graz in 1992, Europt(r)ode has continued as a biennial conference in Florence (chaired by A. M. Scheggi), Zurich (chaired by U. Spichiger-Keller), Munster (chaired by K. Camman), Lyon (chaired by P. R. Coulet), Manchester (chaired by R. Narayanaswamy), Madrid (chaired by G. Orellana), Tuebingen (chaired by G. Gauglitz) and Dublin (chaired by B. D. MacCraith and C. McDonagh). In 2010, Europt(r)ode X was held in Prague, 28–31 March, and attracted more than 250 participants from 27 countries. During the almost two decades of its existence, Europt(r)ode has become a major scientific meeting on optical chemical sensors and biosensors attracting scientists not only from Europe, but from across the globe. Because of the multidisciplinary nature of the field, Europt(r)ode has always brought together a diverse audience including scientists and engineers in physics, chemistry and biology. Their engaging discussions have stimulated interdisciplinary and international collaborations and helped to shape scientific schools from which several generations of PhD students have graduated. The scientific program of Europt(r)ode X comprised a total of 230 scientific presentations covering various aspects of research and development of optical chemical sensors and biosensors. These presentations included 5 plenary lectures, 10 invited lectures, 34 contributed oral presentations and 181 poster presentations. The plenary lectures were given by Maria C. Moreno Bondi (University Complutense, Spain), Andrew deMello (Imperial College, UK), Teri W. Odom (Northwestern University, USA), Michael J. Sailor (University of California, USA) and Otto S. Wolfbeis (University of Regensburg, Germany). The plenary and invited lectures were selected to cover traditional topics as well as emerging areas, such as optofluidics for chemical analysis, nanoparticles and nanostructures for optical biosensing, silicon photonics biosensors, photonic fibres for label-free biosensing, artificial receptors and polymers for label-free biosensing in complex media. The oral and poster presentations fell into six main thematic areas. The largest number of presentations (nearly 25%) were concerned with the topic Optical platforms and methods for sensing. This high percentage documents the pivotal role that optics plays today in optical chemical sensing and biosensing and a high number of new original developments realized in the last few years. Moreover, new optical solutions to sensing were also presented under the thematic area Multisensors and sensor arrays, which accounted for 8% of the presentations. Advances in the development of new receptors were less represented at Europt(r)ode X with less than 5% of presentations submitted for the thematic area Biological and synthetic receptors. Europt(r)ode X testified to the growing importance of nanophotonics and nanomaterials in optical sensing with nearly 17% of the presentations submitted to Published in the special issue Optical biochemical and chemical sensors (Europtrode X) with Guest Editor Jiři Homola.

Wireless smart tag with on-board conductometric chemical sensor

Nano-materials and chemical bio-sensors are two new substances in different areas of the last century. The researchers combine them with clever links and add new vitality to both substances. Due to the plasticity and specificity of nano-materials, as well as the characteristics of simple chemical sensor preparation, low cost and fast detection speed, it has become a hot spot in the field of scientific research to fix different nano-materials and functional nano-materials in chemical bio-sensors. In the past 20 years, semiconductor nano-titanium dioxide (TiO2) is widely used in the field of optoelectronic materials, chemical sensors and carriers and other important fields. It has the advantages of large surface area, surface activity, corrosion resistance, high catalytic activity, oxidation capacity and good stability. Multi-walled Carbon Nanotubes (MWNTs) have many unique chemical and physical properties, which is a good conductive materials and catalyst carriers. Meanwhile, it also has catalytic activity. Chitosan (CS) is a product of chitosan removed of part of the acetyl. It has excellent film-forming, adsorption, permeability and permeability. In addition, it is rich in amino and hydroxy and it is also used as a film-forming material in the preparation of the chemical sensor. However, CS is prone to swelling, and it is capable of sliding off the electrode surface. Based on this, it becomes a hot spot for modifying CS to enhance its film forming. Platinum is a rare precious metal with high corrosion resistance and high catalytic performance, which has a wild application in many field such as petrochemical, electrochemical and pharmaceutical industries and so on.

Des dispositifs et des procedes micro-electromecaniques souples (Soft-MEMS) sont necessaires pour le diagnostic medical et pour des mesures physiologiques. Plusieurs types de detecteurs chimiques portables formes de dispositifs micro-electromecaniques souples ont ete construits par des techniques de microfabrication sur des films de polymeres fonctionnels, pour doser des substances biochimiques. Le detecteur d'oxygene portable (epaisseur : 84 μm) a ete etalonne pour l'oxygene dissous entre 0 et 80 mg/l, et a ete utilise avec succes pour suivre la pression d'oxygene transcutanee en appliquant le dispositif sur la peau de l'avant-bras. La conductivite du liquide lacrymal a pu etre mesuree en appliquant un detecteur portable sur le cul-de-sac temporal inferieur d'un sujet humain, ce qui a permis de mesurer la concentration en electrolytes et la vitesse de renouvellement dans les larmes pour des volontaires sains normaux et pour des patients souffrant de secheresse oculaire. Pour une approche douce et non-invasive, des detecteurs biochimiques de gaz (bio-sniffers) pour l'ethanol et l'acetaldehyde en phase gazeuse ont ete developpes en utilisant une membrane a enzyme immobilisee et une cellule de reaction comportant des compartiments pour les phases gazeuse et liquide separes par un diaphragme a membrane poreuse. La monooxygenase a flavine (FMO, une des enzymzes de metabolisation des drogues) a aussi ete utilisee pour construire des dispositifs a biodetecteurs de gaz pour la trimethylamine, le methylmercaptan, etc, pour des mesures douces (non-invasives). Les changements de concentration de l'ethanol dans l'haleine apres ingestion ont pu etre mesures par un biodetecteur de gaz de type baguette. La technique des biodetecteurs de gaz devrait contribuer au developpement d'un systeme de nez intelligent.

In this modern era, wearable biosensors have emerged as a significant innovation in specialized personal healthcare. While smartphones and smartwatches today can easily measure vital signs and mobility, a new generation of wearable technology quickly emerges, allowing users to monitor their health metrics at the molecular level. Wearable electrochemical microneedle biosensors show the capability of detecting analytes and metabolites in interstitial fluid with minimal invasiveness. The use of microneedle sensing technology revolutionises biosensing techniques and opens new avenues for advancing current biosensors. In situ extraction, monitoring, and painless injection become possible through microneedle biosensors. However, there remains a need for improvement in detection accuracy and accessibility. This review begins with a discussion on the introduction and a comprehensive background of microneedle technology. It then explores different types of microneedles and fabrication methods. Various sensing modalities for microneedle biosensors, such as electrical, electrochemical, Raman, and colorimetric methods, are also discussed. Finally, the practical applications of wearable microneedle biosensors in various fields are examined, followed by a comprehensive conclusion and prospects.

An overview is given on work by the author's group on integrated optical (IO) sensors. The sensors make use of guided waves or modes in optical waveguides, in particular of the orthogonally polarized TE 0 and TM 0 modes in very thin planar waveguides of high refractive index. The principle of all direct (bio)chemical waveguide or IO sensors is as follows. A chemically selective coating on the waveguide surface binds the analyte molecules contained in the gaseous or liquid sample. Thus, the refractive index of the medium near the waveguide surface (more precisely, within the penetration depth Δz of the evanescent field of the guided wave) is changed. This effect in turn induces changes ΔN TE 0 and ΔN TM 0 of the effective refractive indices N TE 0 and N TM 0 of the guided modes. for example, in biochemical affinity sensors the chemically selective coating contains receptor molecules that specifically or selectively bind certain ligands as analyte molecules; in particular, in immunosensors or immunoassays the receptors are antibodies (or antigens, respectively) and the analyte molecules are the corresponding antigens (or antibodies). These ‘direct’ affinity of immunosensors eliminate the use of (e.g., fluorescently) labelled reagents. Effective refractive-index changes ΔN can also be induced by two other effects; namely by unspecific adsorption of molecules on the (uncoated) waveguide surface (or in pores of a waveguiding film F itself if it is microporous) and by refractive-index changes Δn C of the liquid sample. In the latter case the IO sensors work as refractometers. The effective refractive indices N give the phase velocity ν ph = c / N of the guided modes, where c is the velocity of light in vacuum. This means that the effective refractive-index changes ΔN can be measured by various optical means. Consequently, a number of different types of IO sensors can be used, in particular, grating couplers and interferometers. In the paper, I report on our own work on IO sensors including: the discovery of the basic sensor effect with grating couplers as sensors for relative-humidity changes, the theory of the sensor sensitivities, and experimental results obtained with three different types of IO sensors developed in our laboratory, namely input grating couplers, output grating couplers and the difference or polarimetric interferometer. The experiments have been performed with dip-coated SiO 2 TiO 2 waveguiding films of refractive index n F ≈ 1.75–1.88, on glass, silica and silicon wafers with oxidized buffer layers as substrates. The sensors working as refractometers are tested, for example, with glucose solutions of different concentrations. The adsorption of proteins (h-IgG, BSA, protein A, avidin) is monitored in real time. Not only the surface concentration Γ, with a resolution of a few pg mm −2 , but also the thickness d F′ and the refractive index n F′ of the adsorbing (mono)layers are determined as functions of time. Also immunoreactions (e.g., between h-IgG and anti-h-IgG, and between IgGs and protein A) and affinity reactions (between avidin and biotinylated proteins, such as biotin BSA) are observed in real time. The feasibility of IO immunosensors or affinity sensors or immunoassays with sub-nanomolar detection limits is demonstrated.

In recent years, the field of wearable sensors has undergone significant evolution, emerging as a pivotal topic of research due to the capacity of such sensors to gather physiological data during various human activities. Transitioning from basic fitness trackers, these sensors are continuously being improved, with the ultimate objective to make compact, sophisticated, highly integrated, and adaptable multi-functional devices that seamlessly connect to clothing or the body, and continuously monitor bodily signals without impeding the wearer's comfort or well-being. Potentiometric sensors, leveraging a range of different solid contact materials, have emerged as a preferred choice for wearable chemical or biological sensors. Nanomaterials play a pivotal role, offering unique properties, such as high conductivity and surface-to-volume ratios. This article provides a review of recent advancements in wearable potentiometric sensors utilizing various solid contacts, with a particular emphasis on nanomaterials. These sensors are employed for precise ion concentration determinations, notably sodium, potassium, calcium, magnesium, ammonium, and chloride, in human biological fluids. This review highlights two primary applications, that is, (1) the enhancement of athletic performance by continuous monitoring of ion levels in sweat to gauge the athlete's health status, and (2) the facilitation of clinical diagnosis and preventive healthcare by monitoring the health status of patients, in particular to detect early signs of dehydration, fatigue, and muscle spasms.

Chemical biosensors are an increasingly ubiquitous part of our lives. Beyond enzyme-coupled assays, recent synthetic biology advances now allow us to hijack more complex biosensing systems to respond to difficult to detect analytes, such as chemical small molecules. Here, we briefly overview recent advances in the biosensing of small molecules, including nucleic acid aptamers, allosteric transcription factors, and two-component systems. We then look more closely at a recently developed chemical sensing system, G protein-coupled receptor (GPCR)-based sensors. Finally, we consider the chemical sensing capabilities of the largest GPCR subfamily, olfactory receptors (ORs). We examine ORs' role in nature, their potential as a biomedical target, and their ability to detect compounds not amenable for detection using other biological scaffolds. We conclude by evaluating the current challenges, opportunities, and future applications of GPCR- and OR-based sensors.

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.

Wearable humidity sensors based on bar-printed poly(ionic liquid) for real-time humidity monitoring systems

Emerging plant diseases, caused by pathogens, pests, and climate change, are critical threats to not only the natural ecosystem but also human life. To mitigate crop loss due to various biotic and abiotic stresses, new sensor technologies to monitor plant health, predict, and track plant diseases in real time are desired. Wearable electronics have recently been developed for human health monitoring. However, the application of wearable electronics to agriculture and plant science is in its infancy. Wearable technologies mean that the sensors will be directly placed on the surfaces of plant organs such as leaves and stems. The sensors are designed to detect the status of plant health by profiling various trait biomarkers and microenvironmental parameters, transducing bio‐signals to electric readout for data analytics. In this perspective, the recent progress in wearable plant sensors is summarized and they are categorized by the functionality, namely plant growth sensors, physiology, and microclimate sensors, chemical sensors, and multifunctional sensors. The design and mechanism of each type of wearable sensors are discussed and their applications to address the current challenges of precision agriculture are highlighted. Finally, challenges and perspectives for the future development of wearable plant sensors are presented.

Surface-engineered natural fibers: Emerging alternative substrates for chemical sensor applications: A review