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Different Roles of Surface Chemistry and Roughness of Laser-Induced Graphene: Implications for Tunable Wettability

“Different Roles of Surface Chemistry and Roughness of Laser-Induced Graphene: Implications for Tunable Wettability”

Dallinger, Alexander, Felix Steinwender, Matthias Gritzner, and Francesco Greco
Publication Date: July 10, 2023
https://doi.org/10.1021/acsanm.3c02066

Abstract

The control of surface wettability is a technological key aspect and usually poses considerable challenges connected to high cost, nanostructure, and durability, especially when aiming at surface patterning with high and extreme wettability contrast. This work shows a simple and scalable approach by using laser-induced graphene (LIG) and a locally inert atmosphere to continuously tune the wettability of a polyimide/LIG surface from hydrophilic to superhydrophobic (Φ ∼ 160°). This is related to the reduced amount of oxygen on the LIG surface, influenced by the local atmosphere. Furthermore, the influence of the roughness pattern of LIG on the wettability is investigated. Both approaches are combined, and the influence of surface chemistry and roughness is discussed. Measurements of the roll-off angle show that LIG scribed in an inert atmosphere with a low roughness has the highest droplet mobility with a roll-off angle of ΦRO = (1.7 ± 0.3)°. The superhydrophobic properties of the samples were maintained for over a year and showed no degradation after multiple uses. Applications of surfaces with extreme wettability contrast in millifluidics and fog basking are demonstrated. Overall, the proposed processing allows for the continuous tuning and patterning of the surface properties of LIG in a very accessible fashion useful for “lab-on-chip” applications.

 

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Emerging technologies in wearable sensors

” Emerging technologies in wearable sensors “

Greco, Francesco, Amay J. Bandodkar, and Arianna Menciassi. “Emerging Technologies in Wearable Sensors.” APL Bioengineering 7, no. 2 (May 31, 2023): 020401.
https://doi.org/10.1063/5.0153940.

Abstract

This Editorial highlights some current challenges and emerging solutions in wearable sensors, a maturing field where interdisciplinary crosstalk is of paramount importance. Currently, investigation efforts are aimed at expanding the application scenarios and at translating early developments from basic research to widespread adoption in personal health monitoring for diagnostic and therapeutic purposes. This translation requires addressing several old and new challenges that are summarized in this editorial. The special issue “Emerging technologies in wearable sensors” includes four selected contributions from leading researchers, exploring the topic from different perspectives. The aim is to provide the APL Bioengineering readers with a solid and timely overall vision of the field and with some recent examples of wearable sensors, exploring new research avenues.

 

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Paper on sweat analysis featured in a SciLight by AIP

AIP SciLight

The latest publication on “Sweat analysis with a wearable sensing platform based on laser-induced graphene” was featured in a AIP SciLight. From the AIP: “A Scilight, a science highlight, briefly summarizes newly published research, emphasizing its significance to a particular field. Scilights are written to ‘intrigue’ a  broad scientific audience showcasing what is new and important in the latest research.”
 
Find the article “Don’t sweat it: laser-induced graphene monitors analytes in sweat ” by  Ashley Piccone here: https://aip.scitation.org/doi/10.1063/10.0014459

Vivaldi, F., A. Dallinger, N. Poma, A. Bonini, D. Biagini, P. Salvo, F. Borghi, A. Tavanti, F. Greco, and F. Di Francesco
Publication Date: 19 September 2022
https://doi.org/10.1063/5.0093301

 

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Sweat analysis with a wearable sensing platform based on laser-induced graphene

“Sweat analysis with a wearable sensing platform based on laser-induced graphene”

Vivaldi, F., A. Dallinger, N. Poma, A. Bonini, D. Biagini, P. Salvo, F. Borghi, A. Tavanti, F. Greco, and F. Di Francesco
Publication Date: 19 September 2022
https://doi.org/10.1063/5.0093301

Abstract

The scientific community has shown increasing interest in laser scribing for the direct fabrication of conductive graphene-based tracks on different substrates. This can enable novel routes for the noninvasive analysis of biofluids (such as sweat or other noninvasive matrices), whose results can provide the rapid evaluation of a person’s health status. Here, we present a wearable sensing platform based on laser induced graphene (LIG) porous electrodes scribed on a flexible polyimide sheet, which samples sweat through a paper sampler. The device is fully laser manufactured and features a two layer design with LIG-based vertical interconnect accesses. A detailed characterization of the LIG electrodes including pore size, surface groups, surface area in comparison to electroactive surface area, and the reduction behavior of different LIG types was performed. The bare LIG electrodes can detect the electrochemical oxidation of both uric acid and tyrosine. Further modification of the surface of the LIG working electrode with an indoaniline derivative [4-((4-aminophenyl)imino)-2,6-dimethoxycyclohexa-2,5-dien-1-one] enables the voltammetric measurement of pH with an almost ideal sensitivity and without interference from other analytes. Finally, electrochemical impedance spectroscopy was used to measure the concentrations of ions through the analysis of the sweat impedance. The device was successfully tested in a real case scenario, worn on the skin during a sports session. In vitro tests proved the non-cytotoxic effect of the device on the A549 cell line.

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Published chapter in Nanoporous Carbons for Soft and Flexible Energy Devices

LAMPSe was invited to contribute a chapter to the book “Nanoporous Carbons for Soft and Flexible Energy Devices“.

The chapter with the name “Laser-Induced Graphene and Its Applications in Soft (Bio)Sensors” features an overview from formation of LIG, properties to the application in soft (bio)sensors.

Abstract

In recent years the technological importance of graphene increased significantly also in the field of soft, flexible and wearable electronics. In this chapter a simple one step process to create 3D porous graphene structures into flexible polymer films is highlighted. By laser scribing polymer precursor substrates with commercially available laser scribing setups the polymer is converted into so-called Laser-Induced Graphene (LIG) via a photothermal conversion. The properties of this material and the influence of different processing parameters on its composition and structure are introduced. Different transfer methods for stretchable applications are discussed. Three main application fields of LIG for soft (bio)sensors are identified: piezoresistive, electrophysiological and electrochemical sensors. Each of the application fields is highlighted more in detail and an overview of recent publications is given. Concluding with an outlook on the future of LIG – including improvement of patterning resolution and the use of renewable, bio-derived precursors – this chapter provides a broad overview of LIG for soft and flexible sensor devices.

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Third place at TU Graz SciPix audience vote

LAMPSe is proud to anounce that Francesco Greco and Matthias Gritzner won the third price in the audience vote of the photo competition held at TU Graz called TU Graz SciPix.

The photos show examples of the everyday research at TU Graz.

 

Francesco Greco was participating with a photo made by Matthias Gritzner during his bachelor thesis and shows UV ink contained in microfluidic channels made from hydrophilic and hydrophobic LIG.

Liquid Yin&Yang on laser induced graphene
A Yin&Yang symbol is formed by self-guidance and mixing of fluorescent dyes in water on top of a pattern of Laser Induced Graphene with tunable wettability (superhydrophilic/superhydrophobic).

Here you can see video of the microfluidics created with LIG. Fluorescent dyes are deposited on the LIG tracks and are guided down to the bottom because of the hydrophilic properties. At the bottom they come in contact with each other and form a Yin&Yang symbol. The liquid is confined by the hydrophobic LIG on the outside.

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News Publications

Paper on Printed and Laser-Scribed Stretchable Conductors on Thin Elastomers for Soft and Wearable Electronics

“Printed and Laser-Scribed Stretchable Conductors on Thin Elastomers for Soft and Wearable Electronics”

Kirill Keller, David Grafinger and Francesco Greco
Publication Date: August 12, 2021
https://doi.org/10.3389/fmats.2021.688133

 

Abstract

As printed electronics is evolving toward applications in biosensing and wearables, the need for novel routes to fabricate flat, lightweight, stretchable conductors is increasing in importance but still represents a challenge, limiting the actual adoption of ultrathin wearable devices in real scenarios. A suitable strategy for creating soft yet robust and stretchable interconnections in the aforementioned technological applications is to use print-related techniques to pattern conductors on top of elastomer substrates. In this study, some thin elastomeric sheets—two forms of medical grade thermoplastic polyurethanes and a medical grade silicone—are considered as suitable substrates. Their mechanical, surface, and moisture barrier properties—relevant for their application in soft and wearable electronics—are first investigated. Various approaches are tested to pattern conductors, based on screen printing of 1) conducting polymer [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)] or 2) stretchable Ag ink and 3) laser scribing of laser-induced graphene (LIG). The electromechanical properties of these materials are investigated by means of tensile testing and concurrent electrical measurements up to a maximum strain of 100%. Performance of the different stretchable conductors is compared and rationalized, evidencing the differences in onset and propagation of failure. LIG conductors embedded into MPU have shown the best compromise in terms of electromechanical performance for the envisioned application. LIG/MPU showed full recovery of initial resistance after multiple stretching up to 30% strain and recovery of functionality even after 100% stretch. These have been then used in a proof-of-concept application as connectors for a wearable tattoo biosensor, providing a stable and lightweight connection for external wiring.

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Paper on Capacitive Coupling of Conducting Polymer Tattoo Electrodes with the Skin

“Capacitive Coupling of Conducting Polymer Tattoo Electrodes with the Skin”

The skin and the electrode interface. a) Schematization of the skin layers. The epidermis, with the stratum corneum as top layer and the electrodes adopted in the study: tattoo and Ag/AgCl electrodes. The dermis, with sweat glands, nerve ending and blood vessels. The subcutaneous tissue, composed by the hypodermis and the muscle layer. On the top-right, the equivalent circuit is adopted to model the skin. b) The electrode/skin interface through Ag/AgCl (top) and tattoo electrode (down). The equivalent circuits are represented together with the physical mechanism leading to the biosignal transduction.

Laura M. Ferrari, Usein Ismailov, Francesco Greco, Esma Ismailova
Publication Date: July 10, 2021
https://onlinelibrary.wiley.com/doi/10.1002/admi.202100352

 

Abstract

Tattoo electronics is one of the emerging technologies in skin compliant biosensing. The growing interest in their large application in health monitoring raises several interrogations on how these sensors interface with the skin. In this paper, the bioimpedance at the interface of the skin and ultra-conformable tattoo electrodes made of conducting polymers are focused on. The electrochemical characteristics of these electrodes differ from traditional gelled Ag/AgCl electrodes. The modeling of equivalent circuits in different skin-electrode configurations proposes the explanation of the biopotentials transduction mechanism. The strong agreement between the circuit model and experimental values reveals the capacitive coupling of conducting polymer tattoo electrodes where circuit’s values reflect the electrodes’ and skin physical characteristics. Additional studies underline an enhanced signal stability in inter/intra-subject evaluations using dry tattoos beneficial for broad long-term recordings. This study provides a comprehensive explanation of the skin/tattoo electrode interface model. The understanding of this interface is essential when designing next generation wearable biomonitoring devices using imperceptible interfaces.

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News Publications

Review on Laser Induced Graphene and its use for Chemical Sensing – Open Access Paper

“Three-Dimensional (3D) Laser-Induced Graphene: Structure, Properties, and Application to Chemical Sensing“

LIG for Chemical sensors review summary

Federico Maria Vivaldi, Alexander Dallinger, Andrea Bonini, Noemi Poma, Lorenzo Sembranti, Denise Biagini, Pietro Salvo, Francesco Greco*, and Fabio Di Francesco*
Publication Date: June 24, 2021
https://pubs.acs.org/doi/10.1021/acsami.1c05614

Abstract

Notwithstanding its relatively recent discovery, graphene has gone through many evolution steps and inspired a multitude of applications in many fields, from electronics to life science. The recent advancements in graphene production and patterning, and the inclusion of two-dimensional (2D) graphenic materials in three-dimensional (3D) superstructures, further extended the number of potential applications. In this Review, we focus on laser-induced graphene (LIG), an intriguing 3D porous graphenic material produced by direct laser scribing of carbonaceous precursors, and on its applications in chemical sensors and biosensors. LIG can be shaped in different 3D forms with a high surface-to-volume ratio, which is a valuable characteristic for sensors that typically rely on phenomena occurring at surfaces and interfaces. Herein, an overview of LIG, including synthesis from various precursors, structure, and characteristic properties, is first provided. The discussion focuses especially on transport and surface properties, and on how these can be controlled by tuning the laser processing. Progresses and trends in LIG-based chemical sensors are then reviewed, discussing the various transduction mechanisms and different LIG functionalization procedures for chemical sensing. A comparative evaluation of sensors performance is then provided. Finally, sensors for glucose detection are reviewed in more detail, since they represent the vast majority of LIG-based chemical sensors.

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Paper on Printed Tattoo Organic Photodiode in ACS Applied Electronic Materials + Journal Front Cover

“Temporary Tattoo Approach for a Transferable Printed Organic Photodiode“

Tattoo Photodiode_ToC

Bernhard Burtscher, Günther Leising, Francesco Greco
Publication Date: June 10, 2021
https://doi.org/10.1021/acsaelm.1c00249

Abstract

Generation of ultrathin, transferable, and imperceptible electronic devices [e.g., organic photodiode (OPD)] for multiple applications, such as personalized health monitors and wearables, is emerging due to the continuous development of materials and manufacturing processes. For such devices, the choice of a suitable substrate is of utmost importance. A water decal transfer from a temporary tattoo paper is adopted here as a substrate for ultrathin and conformable organic components because of easy and reliable transfer of a ≈600 nm robust and transparent polymer nanofilm of ethyl cellulose. Strategies for the fabrication of a transferable OPD on a temporary tattoo are investigated. A device with an overall thickness <1 μm and its performance after transfer are demonstrated. Then, efforts are put into fabricating an OPD by inkjet printing with a water-soluble active layer consisting of polythiophene and fullerene derivatives to aid cost- and material-efficient, large-scale production possibilities. Additionally, a second semitransparent electrode made of printed aluminum-doped zinc oxide and silver nanowires is used to allow usage from both sides to enhance the application potential. Both OPD examples presented here need improvement of the device performance but permitted us to highlight the versatility and application potential of temporary tattoos for transferable components. Target surfaces for the final application after transfer include artificial (flat and smooth, e.g., glass, or even complex and rough, e.g., concrete, paper, and so forth) as well as natural ones.

Featured in Journal Front COVER of June 2021 Issue

Front cover_ACS Appl Electron Mater June 21_Tattoo photodiode
A temporary tattoo printed organic photodiode (OPD) transferred onto a maple leaf. With an overall device thickness <1 μm, the tattoo OPD is able to achieve stable conformal adhesion on a variety of uneven target surfaces.