Wearable biosensors are garnering substantial interest due to their potential to provide continuous, real-time physiological information via dynamic, noninvasive measurements of biochemical markers in biofluids, such as sweat, tears, saliva and interstitial fluid. Recent developments have focused on electrochemical and optical biosensors, together with advances in the noninvasive monitoring of biomarkers including metabolites, bacteria and hormones. A combination of multiplexed biosensing, microfluidic sampling and transport systems have been integrated, miniaturized and combined with flexible materials for improved wearability and ease of operation. Although wearable biosensors hold promise, a better understanding of the correlations between analyte concentrations in the blood and noninvasive biofluids is needed to improve reliability. An expanded set of on-body bioaffinity assays and more sensing strategies are needed to make more biomarkers accessible to monitoring. Large-cohort validation studies of wearable biosensor performance will be needed to underpin clinical acceptance. Accurate and reliable real-time sensing of physiological information using wearable biosensor technologies would have a broad impact on our daily lives.

Wearable biosensors for healthcare monitoring.

Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

Monitoring of Vital Signs with Flexible and Wearable Medical Devices

Non-invasive wearable electrochemical sensors: a review

Direct interfacing of nanosensors onto biomaterials could impact health quality monitoring and adaptive threat detection. Graphene is capable of highly sensitive analyte detection due to its nanoscale nature. Here we show that graphene can be printed onto water-soluble silk. This in turn permits intimate biotransfer of graphene nanosensors onto biomaterials, including tooth enamel. The result is a fully biointerfaced sensing platform, which can be tuned to detect target analytes. For example, via self-assembly of antimicrobial peptides onto graphene, we show bioselective detection of bacteria at single-cell levels. Incorporation of a resonant coil eliminates the need for onboard power and external connections. Combining these elements yields two-tiered interfacing of peptide-graphene nanosensors with biomaterials. In particular, we demonstrate integration onto a tooth for remote monitoring of respiration and bacteria detection in saliva. Overall, this strategy of interfacing graphene nanosensors with biomaterials represents a versatile approach for ubiquitous detection of biochemical targets.

/pdf/graphene-based-wireless-bacteria-detection-on-tooth-enamel-3fqoibyb68.pdf

Graphene-based wireless bacteria detection on tooth enamel

Flexible and wearable electronics are attracting wide attention due to their potential applications in wearable human health monitoring and care systems. Carbon materials have combined superiorities such as good electrical conductivity, intrinsic and structural flexibility, light weight, high chemical and thermal stability, ease of chemical functionalization, as well as potential mass production, enabling them to be promising candidate materials for flexible and wearable electronics. Consequently, great efforts are devoted to the controlled fabrication of carbon materials with rationally designed structures for applications in next-generation electronics. Herein, the latest advances in the rational design and controlled fabrication of carbon materials toward applications in flexible and wearable electronics are reviewed. Various carbon materials (carbon nanotubes, graphene, natural-biomaterial-derived carbon, etc.) with controlled micro/nanostructures and designed macroscopic morphologies for high-performance flexible electronics are introduced. The fabrication strategies, working mechanism, performance, and applications of carbon-based flexible devices are reviewed and discussed, including strain/pressure sensors, temperature/humidity sensors, electrochemical sensors, flexible conductive electrodes/wires, and flexible power devices. Furthermore, the integration of multiple devices toward multifunctional wearable systems is briefly reviewed. Finally, the existing challenges and future opportunities in this field are summarized.

Advanced Carbon for Flexible and Wearable Electronics.

A contact lens with embedded sensor for monitoring tear glucose level

This paper presents a noninvasive wireless sensor platform for continuous health monitoring. The sensor system integrates a loop antenna, wireless sensor interface chip, and glucose sensor on a polymer substrate. The IC consists of power management, readout circuitry, wireless communication interface, LED driver, and energy storage capacitors in a 0.36-mm2 CMOS chip with no external components. The sensitivity of our glucose sensor is 0.18 μA·mm-2·mM-1. The system is wirelessly powered and achieves a measured glucose range of 0.05-1 mM with a sensitivity of 400 Hz/mM while consuming 3 μW from a regulated 1.2-V supply.

A 3- $\mu\hbox{W}$ CMOS Glucose Sensor for Wireless Contact-Lens Tear Glucose Monitoring

A contact lens having an integrated glucose sensor is provided. The contact lens includes an electrochemical sensor configured to measure the level of glucose in the tear fluid of the eye of the user wearing the contact lens. The electrochemical sensor is powered by radiation off-lens, through an RF antenna or a photovoltaic device mounted on the periphery of the contact lens. The power provided to the contact lens also enables transmission of data from the electrochemical sensor, for example by backscatter communications or optically by an LED mounted to the lens.

Wireless powered contact lens with glucose sensor

We present an integrated functional contact lens, composed of a differential glucose sensor module, metal interconnects, sensor read-out circuit, antenna and telecommunication circuit, to monitor tear glucose levels wirelessly, continuously and non-invasively. The electrochemical differential sensor module is based on immobilization of activated and de-activated glucose oxidase. We characterized the sensor on a model polymer eye and determined that it showed good repeatability, molecular interference rejection and linearity in the range of 0–2 mM glucose, covering normal tear glucose concentrations (0.1–0.6 mM). We also report the temperature, ageing and protein-fouling sensitivity of the sensor. We report the design and implementation of a low-power (3 µW) sensor read-out and telecommunication circuit to deliver wireless power and transmit data for the sensor module. Using this small chip (0.36 mm2), we produced an integrated contact lens with sensors and demonstrated wireless operation of the system and glucose read-out over the distance of several centimeters.

https://iopscience.iop.org/article/10.1088/0960-1317/22/7/075007/pdf

A contact lens with integrated telecommunication circuit and sensors for wireless and continuous tear glucose monitoring

The increase in the diabetes population makes glucose monitoring a pressing demand for clinical and continuous use. Non-invasive sensing would allow a painless, convenient solution compared to traditional skin-piercing glucose meters. Among various body fluids, tear fluid, which is correlated to the glucose concentration in blood [1], is directly accessible on the eye and can provide a unique opportunity to develop an interface between a sensor and the human body. The current technique is to collect tear fluid samples in capillary tubes and assay the samples for glucose ex situusing standard laboratory instrumentation. Integrating sensors into a contact lens would provide a way to continuously and reliably sense metabolites in tear fluids.

Huanfen Yao

Papers

A contact lens with embedded sensor for monitoring tear glucose level

A 3- $\mu\hbox{W}$ CMOS Glucose Sensor for Wireless Contact-Lens Tear Glucose Monitoring

Wireless powered contact lens with glucose sensor

A contact lens with integrated telecommunication circuit and sensors for wireless and continuous tear glucose monitoring

A 3μW wirelessly powered CMOS glucose sensor for an active contact lens