Recent advances in ZnO nanostructures and thin films for biosensor applications: review.

Advances in carbon nanotube based electrochemical sensors for bioanalytical applications.

Wearable digital health devices are dominantly found in rigid form factors such as bracelets and pucks. An adhesive radio-frequency identification (RFID) sensor bandage (patch) is reported, which can be made completely intimate with human skin, a distinct advantage for chronological monitoring of biomarkers in sweat. In this demonstration, a commercial RFID chip is adapted with minimum components to allow potentiometric sensing of solutes in sweat, and surface temperature, as read by an Android smartphone app with 96% accuracy at 50 mM Na
 +
 (in vitro tests). All circuitry is solder-reflow integrated on a standard Cu/polyimide flexible-electronic layer including an antenna, but while also allowing electroplating for simple integration of exotic metals for sensing electrodes. Optional paper microfluidics wick sweat from a sweat porous adhesive allowing flow to the sensor, or the sensor can be directly contacted to the skin. The wearability of the patch has been demonstrated for up to seven days, and includes a protective textile which provides a feel and appearance similar to a standard Band-Aid. Applications include hydration monitoring, but the basic capability is extendable to other mM ionic solutes in sweat (Cl
 -
, K
 +
, Mg
 2+
, NH
 4
 +
, and Zn
 2+
). The design and fabrication of the patch are provided in full detail, as the basic components could be useful in the design of other wearable sensors.

Adhesive RFID Sensor Patch for Monitoring of Sweat Electrolytes

Implantable medical devices have been implemented to provide treatment and to assess in vivo physiological information in humans as well as animal models for medical diagnosis and prognosis, therapeutic applications and biological science studies. The advances of micro/nanotechnology dovetailed with novel biomaterials have further enhanced biocompatibility, sensitivity, longevity and reliability in newly-emerged low-cost and compact devices. Close-loop systems with both sensing and treatment functions have also been developed to provide point-of-care and personalized medicine. Nevertheless, one of the remaining challenges is whether power can be supplied sufficiently and continuously for the operation of the entire system. This issue is becoming more and more critical to the increasing need of power for wireless communication in implanted devices towards the future healthcare infrastructure, namely mobile health (m-Health). In this review paper, methodologies to transfer and harvest energy in implantable medical devices are introduced and discussed to highlight the uses and significances of various potential power sources.

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Power Approaches for Implantable Medical Devices

Diameter-controlled Growth of Single-crystalline In2O3 Nanowires and Their Electronic Properties

Carbon nanotubes (CNTs) were functionalized and employed in an electrochemical cell to serve as a biosensor to specifically detect either lactate or pH in an electrolyte solution of artificial sweat. They were functionalized with the carboxyl group ( COOH) to detect pH and the enzyme lactate oxidase (LOX) to detect lactate. All CNT samples were characterized to compare the electrodes before and after functionalization. Fourier transform infrared spectroscopy (FTIR) was used to verify the attachment of both COOH and LOX to the respective carbon nanotubes samples. Scanning electron microscopy (SEM) was used to examine the structure of the CNT–lactate electrode. Square wave voltammetry proved to be the best template to use to sense these target analytes. The functionalized CNT–COOH electrode displayed a linear response to pH 1–10, with a negative voltage shift corresponding to an increase in pH. Two types of lactate sensors were fabricated, both of which exhibited an increase in current corresponding to an increase in lactate concentration. The functionalized CNT–LOX on a glassy carbon electrode displayed an amperometric response in the range of 1–4 mM lactate. The CNT–LOX on a silicon/indium tin oxide (Si/ITO) substrate displayed an amperometric response in the range of 0.01–0.05 M lactate.

Novel lactate and pH biosensor for skin and sweat analysis based on single walled carbon nanotubes

This review presents the advancement in synthesis and characterisation techniques of one-dimensional nanostructures (ODNS) as well as their potential for novel applications. In the first section of the review, the authors describe the synthesis techniques of one-dimensional nanostructures, i.e. template based synthesis, vapour phase growth, solution based growth and other innovative techniques. Various characterisation techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are described in detail, followed by a comprehensive review of the unique material properties of one-dimensional nanostructures. The final section of this paper presents current state of the art chemical and biological sensing applications as well as other potential technologies which may emerge due to the advantage nanomaterials have over their bulk counterparts.

One-dimensional nanostructures : fabrication, characterisation and applications

Electrochemical impedance-based DNA sensor using a modified single walled carbon nanotube electrode

ZnO nanowire arrays were grown on a Si (100) substrate using the vapor-liquid-solid (VLS) method. ZnO nanowires were characterized by XRD, SEM, bright field TEM, and EDS. They were found to have a preferential orientation along the c-axis. The as-prepared sample was functionalized with glucose oxidase by physical adsorption. FTIR was taken before and after functionalization to verify the presence of the attached enzyme. Electrochemical measurements were performed on the nanowire array by differential pulse voltammetry in the range of -0.6 to 0.4 V. The nanoarray sensor displayed high sensitivity to glucose in the range of 1.0 × 10-4 to 1.0 × 10-2 mol L-1.

/pdf/fabrication-and-characterization-of-zno-nanowire-arrays-with-4w6loo3yjn.pdf

Fabrication and characterization of ZnO nanowire arrays with an investigation into electrochemical sensing capabilities

We report room temperature detection of carbon monoxide (CO) below 100 parts per million in air using boron doped diamond films prepared by hot filament chemical vapor deposition method. Gas sensing characteristics are observed to be improved with larger grain size in the films. Sensing characteristics for 100 ppm CO with response time of 30 s and recovery times of ∼50 s at room temperature show the excellence of boron doped diamond as CO sensor material. The lowest values of response time ∼5 s and recovery time ∼20 s were observed for BDD with grain size of 1 μm for 1000 ppm of CO in air. The carbon monoxide sensing mechanism is attributed to electron donation to p-type boron doped diamond as a result of CO oxidation on its surface.

Jessica Weber

Papers

Novel lactate and pH biosensor for skin and sweat analysis based on single walled carbon nanotubes

One-dimensional nanostructures : fabrication, characterisation and applications

Electrochemical impedance-based DNA sensor using a modified single walled carbon nanotube electrode

Fabrication and characterization of ZnO nanowire arrays with an investigation into electrochemical sensing capabilities

Carbon monoxide sensing at room temperature via electron donation in boron doped diamond films