Highly Stretchable Fully-Printed CNT-Based Electrochemical Sensors and Biofuel Cells: Combining Intrinsic and Design-Induced Stretchability

Abstract

We present the first example of an all-printed, inexpensive, highly stretchable CNT-based electrochemical sensor and biofuel cell array. The synergistic effect of utilizing specially tailored screen printable stretchable inks that combine the attractive electrical and mechanical properties of CNTs with the elastomeric properties of polyurethane as a binder along with a judiciously designed free-standing serpentine pattern enables the printed device to possess two degrees of stretchability. Owing to these synergistic design and nanomaterial-based ink effects, the device withstands extremely large levels of strains (upto 500% strain) with negligible effect on its structural integrity and performance. This represents the highest stretchability offered by a printed device reported to date. Extensive electrochemical characterization of the printed device reveal that repeated stretching, torsional twisting and indenting stress has negligible impact on its electrochemical properties. The wide-range applicability of this platform to realize highly stretchable CNT-based electrochemical sensors and biofuel cells has been demonstrated by fabricating and characterizing potentiometric ammonium sensor, amperometric enzyme-based glucose sensor, enzymatic glucose biofuel cell and self-powered biosensor. Highly stretchable printable multi-analyte sensor, multi-fuel biofuel cell or any combination thereof can thus be realized using the printed CNT array. Such combination of intrinsically-stretchable printed nanomaterial-based electrodes and strain-enduring design patterns holds considerable promise for creating an attractive class of inexpensive multi-functional, highly stretchable printed devices that satisfy the requirements of diverse healthcare and energy fields wherein resilience towards extreme mechanical deformations is mandatory.

Nanomaterial‐Enabled Wearable Sensors for Healthcare

“…[171] In detail, stretchable components such as PU, ecoflex, and stretchable resistive inks (CNT and Ag/AgCl ink) were printed in a serpentine design array on a textile substrate and modified with ion selective membranes (Figure 6c His team further built a CNT based electrochemical sensor and biofuel cell (BFC) that can endure strains as high as 500% with no effect on structural integrity and sensor performance (Figure 6d). [67] Electrochemical characterization of the device revealed that repeated strain (from 0% to 500%), torsional twisting (180° for 50 cycles) and indenting stress (5 mm depth for 50 repetitions) had negligible effect on its device properties as shown in Figure 6e. A CNT-based device functionalized with selective ionophores and enzymes was developed to realize a wide-range of applications toward potentiometric ammonium sensor ((0.1-100) × 10 −3 m), amperometric enzyme based glucose sensor ((0-10) × 10 −3 m), enzymatic glucose BFC and self-powered biosensor (Figure 6f).…”

“…Sensors in the form of a stretchable capacitor can sense the tensile stretching and normal pressure based on the dimensional change and sense the approaching of an object based on the disturbed fringing field, as shown in Figure 4d. [25,41,43,165] Resistive sensors that can detect various mechanical stimuli such as pressure, [67] Copyright 2016, American Chemical Society. g) Optical images of the integrated watch type gas monitor based on intensive pulsed laser reduced rGO (IPL-RGO) (left) and the resistance change of the rGO sensor when exposed to 20 ppm.…”

“…Integration of multiple electrochemical sensors into a textile substrate allows for detecting various biochemical parameters such as glucose, ammonium, sodium, and potassium in real time. [67,171] Jin et al integrated a type of self-healing polymer with a functionalized AuNP sensor array to detect VOCs in human breath or on skin and monitor heart beat and breath rate. [198] As illustrated in Figure 7g, AuNP films functionized by 5 kinds of ligands were used to detect 11 different kinds of VOCs emitted from breath or skin.…”

“…[5] The power can be harvested from various sources including temperature difference and mechanical sources such www.advancedsciencenews.com www.advhealthmat.de as body movements and vibrations. [66,67,75,131,133,162,200,201] In an effort toward self-powered sensors, a sensor structure shown in Figure 5d was used as a triboelectric nanogenerator (TENG). [131] Power can be generated from various mechanical stimuli such as pressing, stretching, twisting, and sound driven vibrations due to the change in the air gap.…”

“…Direct spinning of CNTs onto a substrate or into yarns [53][54][55] and electrospinning of nanofibers or NWs were reported to produce fiber-like nanomaterials. [56][57][58][59] In addition, novel direct printing or writing techniques [60,61] such as inkjet printing, [62] gravure printing, [63,64] screen printing, [65][66][67] nozzle jet printing, [26] and direct writing [68,69] enabled the fabrication of wearable sensors that possess complex patterns with high resolution.…”