There is a general agreement that the most versatile, abundant, and effective raw material for sensing applications is pure carbon in the form of graphene.
Graphene-based sensors are carrying out incredible tasks and creating completely new fields of sensing in applications such as new drug discovery and biomonitoring in wearables, gene editing in DNA, and alternative applications based on advanced health-related data acquisition.
To further increase the chances of the widespread adoption of these high-performing sensors, the price of manufacturing these sensors is now in the ‘pennies per unit’ range.
A critical factor to consider regarding the performance and manufacture of graphene sensors is referred to as the ‘wetting transparency’ of graphene; the metallic film takes a particular form when deposited on graphene which is strongly related to the identity of the substrate supporting that graphene.
Managing this substrate allows a wider range of geometries to form, for example, closely packed nanocrystals, nanospheres, and formations similar to an island with controllable gaps as low as 3 nm.
The wider range of geometries permit various performance characteristics, manufacturing latitudes, and sensing modalities.
A Multifunctional, Multimodal Monolayer
Structures that are graphene-supported with metallic films can be moved to any surface and can perform as ultrasensitive mechanical signal transducers.
These transducers have a high-sensitivity and range (at least four orders of magnitude of strain) suited for applications in electronic skin, structural health monitoring, the measurement of cardiomyocyte contraction, and even as substrates for surface-enhanced Raman scattering (SERS), including on the tips of optical fibers.
These composite graphene-based films can be known as a platform technology for multimodal sensing. They are mechanically robust, semi-transparent, low profile, and have the capability for reproducible manufacturing over wide areas.
For use in designing functional nanocomposite thin films, graphene has many desirable characteristics.
It is stretchable compared to metallic films with strains of 5 to 6%, flexible, transparent, conductive, receptive to large-area growth, transferable to several substrates, and its crystalline grains can reach dimensions of up to 1 cm.
Graphene is the thinnest 2D material that can be acquired, giving rise to the phenomenon known as wetting transparency.
This phenomenon has mainly been investigated in liquids where characteristics such as contact angle are a strong function of the surface energy of the layer supporting the graphene, and this notion is similarly applicable to an evaporated flux of atoms.
For example, a metal or graphene bilayer can be utilized as a template for the self-assembly of nanoparticles of controllable and diverse morphologies; namely, nanocrystals, percolated networks, and nanospheres.
The availability of multiple configurations creates a large range of easy to manufacture, inexpensive, and high performing sensing options.
The sensors configured for applications with the highest demand for specifications, for example, life sciences, are now being produced on large-area plastic sheets at very small (even disposable) per-unit costs.
Transferability of Graphene Sensor Material to ‘Nearly Any Surface’
Graphene or nano-island (NI) films have enough robustness to be transferred to almost any surface.
They also exhibit features such as gaps approaching molecular dimensions and sharp tips that make them suited to the sensing of optical, mechanical, and chemical stimuli.
Metallic nano-islands deposited on the surface of graphene provide an advantageous platform system for multimodal sensing.
Compared to the films of metallic nanoparticles created by alternative procedures, graphene-supported nano-islands can be manipulated and easily transferred to almost any surface, meaning that a wide range of processes for their deposition and creation to desired target substrates are suitable.
The biocompatibility and sensitivity of these structures allow for the noninvasive measurement of the contractions of cardiomyocytes.
This could be an important tool for the functional characterization of stem-cell-derived cardiomyocytes, the multimodal screening of novel drug candidates for cardiovascular drug discovery and cardiotoxicity, and DNA sensing for gene editing.
There is an infinite range of potential for next-generation sensing because of the ability to transfer these multimodal sensors to any substrate.
Graphene Sensor Foundries
The life sciences appear to be one of the first advanced areas utilizing graphene and its corresponding 2D films for use in innovative sensor applications where a new ‘key enabler’ is required to unlock a pioneering field.
An appropriate example is the ‘Crispr Chip’ which utilizes graphene for DNA sensing to finish gene-editing work within hours. This would have previously taken a team of researchers months to accomplish.
Large area, single-layer graphene is now available in multiple cost-effective formats and is beginning to be more commonly employed in MEMS chip fabrication facilities to produce these sensing chips.
The next degree of commercialization beyond these chips is already taking place, with conversion of expensive silicon-based chips and packages using graphene as the key performance layer, to much lower cost ‘graphene chips on plastic sheets’ coming out of factories by the square meter at a cost sometimes 100x lower than that of the silicon based sensor chips.
Graphene Sensors on Plastic
One of these recent graphene sensor foundry producers is Grolltex, its name being a concise reference to graphene-rolling-technologies.
Along with being the biggest producer of electronics grade graphene material in North America, Grolltex has acquired several important patents in the production and design of multi-modal graphene sensors and the methods to produce them.
To dramatically decrease the manufacturing costs, the company is now delivering prototypes of advanced graphene sensors on plastic.
Produced from materials originally authored by Jeff Draa from Grolltex.
References and Further Reading
Some of this article is excerpted from “Metallic Nanoislands on Graphene as Highly Sensitive Transducers of Mechanical, Biological, and Optical Signals”, by Dr. Aliaksandr Zaretski, et. al, published January 8, 2016, in Nano Letters.
This information has been sourced, reviewed and adapted from materials provided by Grolltex Inc.
For more information on this source, please visit Grolltex Inc.