Recent advances in materials, fabrication strategies and device designs for flexible and stretchable electronics and sensors make it possible to envision a not-too-distant future where ultra-thin, flexible circuits based on inorganic semiconductors can be wrapped and attached to any imaginable surface, including body parts and even internal organs. Robotic technologies will also benefit as it becomes possible to fabricate 'electronic skin' that, for instance, could allow surgical robots to interact, in a soft contacting mode, with their surroundings through touch. Researchers have now demonstrated that they can integrate high-quality silicon and other semiconductor devices on thin, stretchable sheets, to make systems that not only match the mechanics of the epidermis, but which take the full three dimensional shapes of the fingertip - and, by extension, other appendages or even internal organs, such as the heart.
Printed electronics has emerged as a key research field to meet the requirements of large area and cost-efficient production. The field of modern electronics is very general and includes not only printable interconnects, but also optoelectronics and magnetoelectronics. In this respect, cost-efficient versatile electronic building blocks, such as transistors, diodes and resistors, are already available as printed counterparts of conventional semiconductor elements. However, the element responding to a magnetic field, which is highly demanded for printable electronics, has not yet been realized and printable electronic sensors and contactless switches operating in combination with magnetic fields have not been reported so far. In new work, researchers in Germany have successfully overcome most of these issues. Researchers have now fabricated the first printable magnetic sensor that relies on the giant magnetoresistance (GMR) effect. The developed magneto-sensitive ink can be painted on any substrate - such as paper, polymers, ceramics, and glass - and retains a GMR ratio of up to 8% at ambient conditions. This value is beyond the state of the art.
It has been known for some time that graphene can be used for detection of individual gas molecules adsorbed on its surface - a graphene sensor can detect just a single molecule of a toxic gas. However, the extremely high sensitivity of graphene does not necessarily translate into its selectivity to various molecules. In other words, it can be detected that some molecules attached to the graphene surface change the resistivity of a graphene field-effect transistor but one cannot say what kind of a molecules have attached. Scientists have therefore thought that truly selective gas sensing with graphene devices requires the functionalization of graphene surface with some agents specific for different gas molecules. In new research, though, scientists have now found that chemical vapors change the noise spectra of graphene transistors. The noise signal for each gas is reproducible, opening the way for practical reliable and simple gas sensors made from graphene.
Graphene with its distinctive band structure and unique physiochemical properties - such as exceptionally low intrinsic electrical resistivity, high surface area, rapid electrode kinetics and good mechanical properties - is considered an attractive material for analytical electrochemistry. However, one of the key technical challenges for the use of graphene as functional material in device applications is the integration of nanoscale graphene onto micro- or millimeter sized sensing platforms. With a new methodology, a team from Florida International University was able to integrate graphene onto three-dimensional (3D) carbon microstructure arrays with good uniformity and controllable morphology.
Single-walled carbon nanotubes arguably are the ultimate biosensor among nanoscale semiconducting materials due to their high surface-to-volume ratio and unique electronic structure. After more than a decade of excitement though, more and more researchers in the nanotube field believe that pristine SWCNTs are very limited as a sensing material. Ironically the ultrahigh sensitivity of SWCNTs is easily compromised by various unintentional contaminants from the device fabrication process as well as the ambient environment. As a result, significant efforts have been focused on all kinds of ways to functionalize or decorate nanotubes with other species in order to improve their sensitivity. Researchers have now shown that applying continuous in situ ultraviolet light illumination during gas detection can enhance a SWCNT-sensor's performance by orders of magnitude under otherwise identical sensing conditions.
Early detection of pathogenic bacteria is critical to prevent disease outbreaks and preserve public health. This has led to urgent demands to develop highly efficient strategies for isolating and detecting this microorganism in connection to food safety, medical diagnostics, water quality, and counter-terrorism. A team of scientists has now developed a novel approach to interfacing passive, wireless graphene nanosensors onto biomaterials via silk bioresorption. The nanoscale nature of graphene allows for high adhesive conformality after biotransfer and highly sensitive detection. The team demonstrates their nanosensor by attaching it to a tooth for battery-free, remote monitoring of respiration and bacteria detection in saliva.
Optical fibers have revolutionized telecommunications by providing higher performance, more reliable telecommunication links with ever decreasing bandwidth cost. In parallel with these developments, fiber-optic sensor technology has been a major user of technologies associated with the optoelectronic and fiber optic communications industry. Today, with the rapid advance of communications and especially sensing applications, there is an ever increasing need for advanced performance and additional functionalities. This, however, is difficult to achieve without addressing fundamental fabrication issues related to the integration onto optical fibers of advanced functional materials at the micro- and nanoscale. Solving these technical problems will open up the possibility of developing multifunctional labs integrated onto a single optical fiber, exchanging information and combining sensorial data. This could result in auto diagnostic features as well as new photonic and electro-optic functionalities useful in many strategic sectors such as optical processing, environment, life science, safety and security.
Various types of nanostructures are used in the development of nanosensors: nanoparticles, nanotubes, nanorods, two-dimensional materials like graphene, embedded nanostructures, porous silicon, and self-assembled materials. For instance, gas sensors often operate by detecting the subtle changes that deposited gas molecules make in the way electricity moves through a surface layer. Researchers have fabricated gas sensors based on carbon nanotube-based field effect transistors, which can detect electrical potential changes around them. While these and related sensing schemes can be all-electronic - i.e., not requiring optical readout - they all require sophisticated nanolithographic techniques to isolate, identify, and integrate electrical contact to the active nanosensor. Researchers have now presented a nanoscale 3D architecture that can afford highly sensitive, room temperature, rapid response, and all-electronic chemical detection.