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. 2019 Jan 4;29(1):1804798.
doi: 10.1002/adfm.201804798. Epub 2018 Nov 9.

Autocatalytic Metallization of Fabrics Using Si Ink, for Biosensors, Batteries and Energy Harvesting

Max Grell  1 , Can Dincer  1   2 , Thao Le  3 , Alberto Lauri  4 , Estefania Nunez Bajo  1 , Michael Kasimatis  1 , Giandrin Barandun  1 , Stefan A Maier  4   5 , Anthony E G Cass  3 , Firat Güder  1
Affiliations

Autocatalytic Metallization of Fabrics Using Si Ink, for Biosensors, Batteries and Energy Harvesting

Max Grell et al. Adv Funct Mater. .

Abstract

Commercially available metal inks are mainly designed for planar substrates (for example, polyethylene terephthalate foils or ceramics), and they contain hydrophobic polymer binders that fill the pores in fabrics when printed, thus resulting in hydrophobic electrodes. Here, a low-cost binder-free method for the metallization of woven and nonwoven fabrics is presented that preserves the 3D structure and hydrophilicity of the substrate. Metals such as Au, Ag, and Pt are grown autocatalytically, using metal salts, inside the fibrous network of fabrics at room temperature in a two-step process, with a water-based silicon particle ink acting as precursor. Using this method, (patterned) metallized fabrics are being enabled to be produced with low electrical resistance (less than 3.5 Ω sq-1). In addition to fabrics, the method is also compatible with other 3D hydrophilic substrates such as nitrocellulose membranes. The versatility of this method is demonstrated by producing coil antennas for wireless energy harvesting, Ag-Zn batteries for energy storage, electrochemical biosensors for the detection of DNA/proteins, and as a substrate for optical sensing by surface enhanced Raman spectroscopy. In the future, this method of metallization may pave the way for new classes of high-performance devices using low-cost fabrics.

Keywords: energy harvesting and storage; fabrics; paper; sensing; textiles.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Metal fabrics are created by autocatalytic metallization of a Si precursor ink (SIAM). We processed Si micropowder into a precursor ink by ballmilling and ultrasonication until particle sizes match fabric pore sizes. To optimize for Whatman 4 paper, we used ballmilling to break large particles (from 1 mm diameter) and ultrasonication to reduce the median particle diameter to 2.5 µm, from 4.3 µm unprocessed. A) We then controlled viscosity by adding CMC. B) We inkjet printed wax barriers to confine the precursor ink to the required design on the fabric substrate. C) Next we placed the substrate in an autocatalyic bath containing HF and metal salts. D1) Metal+ ions are attracted to electrons in the Si valence band. D2) Electrons e− in the Si are attracted to the deposited metal nuclei, catalyzing further reduction of metal+ ions. Si is subsequently oxidized near the metal nuclei, forming SiO2 that is etched away by the HF solution. D3) Metal+ ions in solution deposit preferentially on metal nuclei, which grow accordingly. This creates conductive percolation pathways throughout the entire fabric structure, formed around Si particles that sit within the fibres.
Figure 2
Figure 2
A) SEM images show Ag metallization during SIAM of paper. Si microparticles (predeposition) catalyze Ag nanoparticle deposition (visible after 40 s), which eventually grow in an Ostwald ripening process until Ag completely covers the Si particles (after 20 min), and conductive pathways are formed. Optical characterisation shows metals have been deposited throughout fabric microstructures, with B) Au in paper and C) Ag in cotton textile. D‐left) Metal fabrics are extremely hydrophilic and binder‐free, D‐right) whereas commmerically available metal nanoparticle inks are hydrophobic and require a binder.
Figure 3
Figure 3
A) Sheet resistance R s decreases with deposition time t deposition, as metal crystals grow larger and form more percolation pathways in an Ostwald ripening process. B) Rather than increasing deposition times, conductance may be increased more rapidly by sintering at 200 °C, with subsequent crystal growth causing metal particles to coalesce over time t sintering. We also report the durability of metallic paper (Ag) under cyclic strain (distance = 8 mm, angle = 90°) over 1000 cycles. C) The resistance increases significantly during the first 30 cycles. Number of samples n = 7 for deposition and sinter time, while n = 4 for bending cycles. Error bars correspond to the standard error.
Figure 4
Figure 4
Fabric‐based electrochemical devices can be powered with batteries and/or embedded coil antennas fabricated by the SIAM method. A‐left) We have fabricated a Ag‐paper coil antenna, with metallization cost under $0.17, which was capable of harvesting 409.6 mW, based on a root‐mean‐squared voltage of 6.4 V harvested over a 100 Ω resistive load. A‐center) This was also sufficient to power a LED with a NFC enabled smartphone. The coil antenna was able to power an NFC integrated circuit to produce a regulated 3 V DC voltage (V out), intended for powering microcontrollers or sensors via NFC. A‐right) We compared this to a commerical etched antenna over a range of frequencies. Secondary metals may be deposited on top of SIAM fabrics by electroplating, enabling a variety of electrochemical cells such as Ag–Zn or Zn–Cu. B‐left) Wax printing provides a hydrophic barrier without hampering conductivity, enabling a contact point for the circuit. B‐right) We have fabricated Ag–Zn batteries capable of generating electromotive force (EMF) greater than 2 V from a single cell (shown here over 30 s discharge time t discharge), where controlling Zn electrodeposition time (Zn t dep) can tune the capacity. Error bars correspond to the standard error of measurements in 7 cells for each Zn deposition time.
Figure 5
Figure 5
A) We have constructed a µPAD using SIAM to fabricate Ag paper counter and working electrodes. We printed wax on top with a circular hole in the center, and then laminated the bottom with polythene in a heatpress, also with a hole in the center. We fabricated the reference electrode by printing Ag/AgCl ink on the bottom of a second paper substrate. We then attached this to the polythene layer in the heatpress, with the top side of the RE paper substrate acting as a barrier between the RE and other electrodes. B) The result is a circular area in the µPAD's center capable of hydrophobically confining the electrolyte. C) We demonstrated the redox reaction of MB, D) calibrated for MB concentrations 0, 0.05, 0.1, 0.25, 0.5, 1, and 2.5 mg mL−1, and E) plotted against normalized current intensity I p. We have then shown normalized peak current intensities from SWVs recorded in MB solutions using the DNA biosensor in the presence of noncomplementary ss‐DNA (control) and complementary ss‐DNA (target). F) The current intensity is normalized with respect to the area. Error bars correspond to the standard error of measurements in 5 devices.
Figure 6
Figure 6
SIAM‐produced Au paper, coated with streptavidin (by dipping in 200 µL of 1 × 10−6 m SA, in 5 × 10−3 m Borax buffer for 2 h), has successfully immobilized 50 × 10−9 m of biotinylated protein (HRP). A) CVs of Au paper electrodes in 2 × 10−3 m FCA in PBS, with scan rate 100 mV s−1, demonstrate a decrease in current upon coating with SA, and a further decrease upon binding with biotinylated‐HRP. After SA was immobilized on the surface, oxidation and reduction peaks were shifted from 0.438 to 0.532 V and from 0.288 to 0.219 V, respectively. Binding of the biotinylated‐HRP to the immobilized SA caused a further small drift in peak separation to 0.57 and 0.20 V. B) SWV scans with increasing concentrations of biotinylated‐HRP are shown. A concentration of 50 × 10−9 m decreases the peak current intensity I p by 45%, but higher concentrations did not lead to further drop in signal.
Figure 7
Figure 7
A) We have demonstrated that Au paper substrates produced by SIAM are an effective low‐cost substrate for SERS. After being functionalized with 4‐MBA (modified with a thiol ligand by submersing in a 0.1 m NaOH solution with 1 × 10−3 m 4‐MBA for 24 h), the characteristic peaks typical of its aromatic core are observed at 1100 and 1590 cm−1 in the Raman signal, using a 1.2 mW laser at 633 nm. This has been applied to pH measurements, with deprotonation of the carboxylic acid end group of 4‐MBA creating the characteristic peak at 1430 cm−1 for increasing pH. B) Solutions of varying pH were prepared using HCl and NaOH, in which the sample was submerged for deprotonation. Intensities of the pH‐dependent peak at 1430 cm−1 have been normalized with respect to the characteristic 4‐MBA peak at 1590 cm−1, showing a linear correlation between intensity and pH. Error bars are the standard error of measurements from 6 locations on the same sample.
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