Wenzhao Jia

Electrochemical tattoo biosensors for real-time noninvasive lactate monitoring in human perspiration.

The present work describes the first example of real-time noninvasive lactate sensing in human perspiration during exercise events using a flexible printed temporary-transfer tattoo electrochemical biosensor that conforms to the wearers skin. The new skin-worn enzymatic biosensor exhibits chemical selectivity toward lactate with linearity up to 20 mM and demonstrates resiliency against continuous mechanical deformation expected from epidermal wear. The device was applied successfully to human subjects for real-time continuous monitoring of sweat lactate dynamics during prolonged cycling exercise. The resulting temporal lactate profiles reflect changes in the production of sweat lactate upon varying the exercise intensity. Such skin-worn metabolite biosensors could lead to useful insights into physical performance and overall physiological status, hence offering considerable promise for diverse sport, military, and biomedical applications.

Tattoo-Based Noninvasive Glucose Monitoring: A Proof-of-Concept Study

We present a proof-of-concept demonstration of an all-printed temporary tattoo-based glucose sensor for noninvasive glycemic monitoring. The sensor represents the first example of an easy-to-wear flexible tattoo-based epidermal diagnostic device combining reverse iontophoretic extraction of interstitial glucose and an enzyme-based amperometric biosensor. In-vitro studies reveal the tattoo sensors linear response toward physiologically relevant glucose levels with negligible interferences from common coexisting electroactive species. The iontophoretic-biosensing tattoo platform is reduced to practice by applying the device on human subjects and monitoring variations in glycemic levels due to food consumption. Correlation of the sensor response with that of a commercial glucose meter underscores the promise of the tattoo sensor to detect glucose levels in a noninvasive fashion. Control on-body experiments demonstrate the importance of the reverse iontophoresis operation and validate the sensor specificity. This preliminary investigation indicates that the tattoo-based iontophoresis-sensor platform holds considerable promise for efficient diabetes management and can be extended toward noninvasive monitoring of other physiologically relevant analytes present in the interstitial fluid.

Epidermal Biofuel Cells: Energy Harvesting from Human Perspiration†

The healthcare industry has recently experienced a major paradigm shift towards wearable biomedical devices. Such devices have the ability to monitor vital physiological parameters, such as heart rate or blood pressure. Particular recent attention has been directed towards skin-worn electronic devices fabricated by novel hybrid techniques for the measurement of these vital signs. Despite dramatic technological advances, further progress in the arena of on-body biomedical devices has been hindered by the lack of effective wearable power sources able to scavenge sufficient energy from the wearer. Major efforts have thus been directed towards the identification of a suitable wearable power source that offers conformal integration with the wearer s body. This activity has resulted in the development of flexible thin-film batteries, piezoelectric nanogenerators, wearable solar cells, mircosupercapacitors, and endocochlear-potential-based biobatteries. Nevertheless, new body-worn conformal power sources able to extract biochemical energy from the wearer s body (and his/her epidermis, in particular) are still highly desired. Herein we demonstrate the ability to generate substantial levels of electrical power from human perspiration in a noninvasive and continuous fashion through the use of epidermal biofuel cells based on temporary transfer tattoos (tBFCs). Enzymatic BFCs have attracted considerable interest owing to their ability to generate power from the bioelectrocatalytic reaction of common chemicals and metabolites, such as glucose and alcohol, under physiological conditions. Recent efforts resulted in implantable glucose BFCs that can generate significant power densities in small animals, such as snails, insects, and rats. However, there are no reports on harvesting the chemical energy from a human in connection with the rapidly developing field of wearable electronics. The successful development of non-invasive tBFCs requires the judicious integration of new manufacturing processes and advanced surface functionalization for efficient power generation from lactate present in the wearer s perspiration. The development of the tBFC builds on our recent introduction of epidermal electrochemical sensors. The two electrode constituents of the new wearable tBFC were designed in the shape of “UC” (acronym for “University of California”; Figure 1; see Figure S1 in the Supporting

Highly ordered multilayered 3D graphene decorated with metal nanoparticles

Highly ordered multi-layered three-dimensional (3D) graphene structures decorated with Pd, Pt and Au metal nanoparticles are prepared and characterized. The ability to control the morphology, distribution and size of the metal nanoparticles on the 3D graphene support upon changing the electro- and electroless-deposition conditions is demonstrated. Tailor-made Pt nanostructures, with nanospike and nanoparticle shapes, are prepared using electroless deposition techniques. Au nanoflowers and nanoparticle structures and Pd nanocubes are obtained following electrodeposition onto the 3D graphene support. The deposition patterns and trends are characterized. The greatly enhanced electrocatalytic activity of the metal-NP–graphene surfaces has been illustrated in connection to voltammetric measurements of ORR and hydrogen peroxide at 3D-graphene coated with Pt and Pd nanoparticles, respectively. Such metal nanoparticles decorated multi-layer 3D graphene allows for high mass transport access and catalytic activity for a diverse range of applications, including sensor and fuel-cell technologies.

All-printed stretchable electrochemical devices.

The fabrication and characterization of all-printed, inexpensive, stretchable electrochemical devices is described. These devices are based on specially engineered inks that can withstand severe tensile strain, as high as 100%, without any significant effect on their electrochemical properties. Such stretchable electrochemical devices should be attractive for diverse sensing and energy applications.

Wearable textile biofuel cells for powering electronics

The fabrication and performance of a wearable biofuel cell printed directly onto textile substrates are reported. The textile biofuel cell utilizes physiologically produced sweat lactate as the fuel to generate electrical energy, producing up to 100 μW cm−2 at 0.34 V during in vitro experimentation, even after repeated bending stress. Furthermore, the wearable and flexible biofuel cell can be easily integrated with a portable energy storage device for on-demand powering of wearable electronics. To validate energy harvesting, the biofuel cell is integrated into a headband and a wristband, and with the help of an on-board DC/DC converter, extracts energy from perspiring human subjects for direct powering of an LED or a digital watch. Convenient incorporation and removal from a variety of garments are achieved by printing the biofuel cell on a detachable care label. Such textile-based non-invasive biofuel cells can be expected to serve in the future as the power unit for wearable electronics and biomedical devices.

An epidermal alkaline rechargeable Ag–Zn printable tattoo battery for wearable electronics

Herein we report for the first time the fabrication of a rechargeable, benign, skin-worn Ag–Zn tattoo battery using unconventional materials, such as screen printed electrodes, temporary tattoo paper, alkaline gel electrolytes and a PDMS cover for sealing the battery. The tattoo battery can be easily worn by a person for powering wearable devices. Detailed characterization of a typical Ag–Zn tattoo cell reveals a capacity density in the range 1.3–2.1 mA h cm−2 and stability up to 13 cycles. The tattoo cell exhibits a stable open circuit voltage of 1.5 V over a 5 days period and endures repeated stretching and bending strain cycles with minimal decrement in its performance. The lateral arrangement of the negative and positive electrodes allows the integration of several cells into a battery in series or parallel combination for tuning the discharge capacity and voltage to the desired values. The practical nature of the tattoo battery was illustrated by applying it to a human subjects skin followed by lighting a red LED. The epidermal tattoo battery thus meets the demands of wearable power sources, including mechanical compliance and tunable discharge capacity, to power body-worn electronic devices.