Fabrication of Strain Gauges via Contact Printing: A Simple Route to Healthcare Sensors Based on Cross-Linked Gold Nanoparticles

Abstract

In this study, we developed a novel and efficient process for the fabrication of resistive strain gauges for healthcare-related applications. First, 1,9-nonanedithiol cross-linked gold nanoparticle (GNP) films were prepared via layer-by-layer (LbL) spin-coating and subsequently transferred onto flexible polyimide foil by contact printing. Four-point bending tests revealed linear response characteristics with gauge factors of ∼14 for 4 nm GNPs and ∼26 for 7 nm GNPs. This dependency of strain sensitivity is attributed to the perturbation of charge carrier tunneling between neighboring GNPs, which becomes more efficient with increasing particle size. Fatigue tests revealed that the strain-resistance performance remained nearly the same after 10.000 strain/relaxation cycles. We demonstrate that these sensors are well suited to monitor muscle movements. Furthermore, we fabricated all-printed strain sensors by directly transferring cross-linked GNP films onto soft PDMS sheets equipped with interdigitated electrodes. Due to the low elastic modulus of poly­(dimethylsiloxane) (PDMS), these sensors are easily deformed and, therefore, they respond sensitively to faint forces. When taped onto the skin above the radial artery, they enable the well-resolved and robust recording of pulse waves with diagnostically relevant details.

Cross‐Linked Gold Nanoparticle Composite Membranes as Highly Sensitive Pressure Sensors

“…This value is typical for disordered GNP films. [12,14] It is higher than the value of g = 7 roughly estimated in our previous study. [34] We attribute this deviation to the different experimental setup used in our earlier work, which only allowed a rough estimation of the membrane deflection and strain.…”

“…For the fabrication of device B a stamp-transfer process was used. [14,45] For this purpose, the membrane was coated with a supporting PMMA layer and subsequently transferred from its original substrate to a polydimethylsiloxane (PDMS) stamp. [46] Afterward, the GNP film was stamped onto a microstructure and released from the PDMS stamp by applying a temperature cycle.…”

“…[11] Such linear relations are also commonly observed for disordered multilayer films of smaller GNPs. [12,14] Here, reorganization of GNPs upon the application of strain can additionally contribute to result in the observed linear behavior. In accordance with these earlier studies the resistance change of the GNP composites observed in this work is approximately linear and the strain sensitivity can be described by the gauge factor g.…”

“…The as-deposited GNP films had a thickness between 41 nm and 68 nm. GNP multilayer composites commonly show ohmic conduction [14,33,35,40,41] and their conductivity can be described following a thermally activated tunneling model. [42][43][44] The GNP films used for sensor fabrication showed ohmic conductivities between 1 and 3 Ω −1 m −1 , which is roughly one order of magnitude higher than values observed earlier for 9DT cross-linked GNP films consisting of significantly smaller particles.…”

Highly Sensitive Graphene/Polydimethylsiloxane Composite Films near the Threshold Concentration with Biaxial Stretching

“…In the application of graphene, some researchers, who studied graphene in combination with different substrates, found that the response of GNP/PDMS (polydimethylsiloxane) to electrical resistance was three or four orders of magnitude higher than that of GNP/Si, GNP/PET (polyethylene terephthalate) [23], and GNP/PU(polyurethane) [24]. The composite prepared by the combination of the elastic PDMS and the conductive graphene has been used to make stretch-sensitive strain sensors [25][26][27][28][29]. Dong et al found that the deformation range and resistance change rate of 5 wt.…”