Functional metal-based 3D-printed electronics engineering: Tunability and bio-recognition

Functional metal-based 3D-printed electronics engineering: Tunability and bio-recognition MUÑOZ MARTIN, J.; REDONDO NEGRETE, E.; PUMERA, M. Applied Materials Today Volume 28, August 2022, 101519, Pages 1-6 ISSN: 2352-9407 DOI: https://doi.org/10.1016/j.apmt.2022.101519 Accepted manuscript © 2022. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ dspace.vutbr.cz Functional Metal-based 3D-printed Electronics Engineering: Tunability and Bio-recognition Jose Muñoz,a Edurne Redondo,a Martin Pumeraa,b,c,d,* aFuture Energy and Innovation Laboratory, Central European Institute of Technology, Brno University of Technology (CEITEC-BUT), Purkyňova 123, 61200 Brno, Czech Republic bDepartment of Chemistry and Biochemistry, Mendel University in Brno, Zemedelska 1/1665, 613 00 Brno, Czech Republic cDepartment of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, SeodaemunGu, Seoul 03722, South Korea dDepartment of Medical Research, China Medical University Hospital, China Medical University, No. 91 Hsueh-Shih Road, Taichung 40402, Taiwan *E-mail: [email protected] Abstract 3D-printing technology has brought light to the large-scale and sustainable production of a wide range of low-cost electronic devices with custom forms on-demand. Despite the current availability of mainstream carbon-based nanocomposite filaments, 3D-printing of noble metals is nowadays a challenge. Herein, a one-step functionalization approach has been devised for the straightforward and low-cost manufacturing of functional metalbased 3D-printed electronics by galvanically replacing Cu-based 3D-printed (3D-Cu) electrodes with nobler metal counterparts, viz. Ag and Au. As a first demonstration of applicability, two appealing bio-electroanalytical approaches, such as the chiral discrimination of amino acids and the supramolecular determination of uranium have been considered —by taking advantage of the capability of noble metals to physically/chemically accommodate several molecular components—, reaching enhanced performances when compared with the pristine 3D-Cu counterpart. Consequently, this alchemy-inspired approach, which combines i) 3D-Cu electrodes as sacrificial platforms with ii) noble metals via a galvanic exchange reaction, provides a robust pathway to harbor molecular components in order to exploit metal-based 3Dprinted electronics in real tasks. Keywords: Cu/PLA electrodes; galvanic replacement; chiral biosensors; supramolecular chemistry; noble metals 1. Introduction 3D printing technology has become at the forefront of modern materials science and chemistry owing to its eco-friendly principle of layered manufacturing, in which different materials can be rapidly prototyped through a simple layer-by-layer process. This technology has led to the large-scale production of 3D-printed objects with free-form designs while minimizing waste [1],[2],[3],[4],[5],[6]. Among the different methods of 3D-printing, fused deposition modeling (FDM) is probably the most exploited one due to the current availability of extrudable polymer-based filaments with a variety of mechanical and electronic properties [7],[8],[9],[10],[11]. In particular, the commercialization of carbon-based nanocomposite filaments —made of an electrically conductive carbon filler (e.g., graphene or carbon black) dispersed within an insulating polymeric matrix like polylactic acid (PLA)— has revolutionized the way of producing 3D-printed electronic devices for specific electrochemical tasks, including: energy, electrocatalysis, switching memories and (bio)sensors [12],[13],[14],[15],[16],[17],[18],[19]. Beyond carbon-based 3D-printed composites, 3D-printing of different metals (e.g., iron, steel or aluminum) is also possible via selective laser melting (SLM) technology [20],[21],[22],[23]. However, since this technology requires more expensive equipment than the one used for polymer-based filaments (viz. FDM), 3D-printing of metals has been mainly camouflaged by mainstream carbon-based composite materials. Further, the electrical resistivity of as-printed metals is relatively high, being necessary tedious postprinting surface coatings with additional noble metals —commonly via electrodeposition of Au— for their exploitation as electrochemical transducers [24],[25],[26],[27]. Accordingly, new insights into simpler and cheaper processes to achieve efficient metalbased 3D-printed electronic devices is a must. Herein, we report an eco-friendly approach based on combining i) 3D-printing technology with ii) galvanic replacement for the straightforward and low-cost bespoke manufacturing of functional metal-based 3D-printed electronic devices. For this goal, 3DCu electrodes were first printed via FDM by employing a commercially available Cu/PLA composite filament, and then functionalized by immersed them in an aqueous solution containing the desired noble metal ion precursor (viz. Ag+ and Au3+), leading to the simple fabrication of two alternative noble metal-based electrodes —named as 3D-Ag and 3DAu— without the aid of an external reducing stimulus (see Scheme 1 for illustration). Herein, the functionalization approach relies on exploiting 3D-Cu electrodes as sacrificial platforms for the spontaneous adsorption and subsequently reduction of noble metal ions to undergo galvanic exchange with a nobler metal that recovers the 3D-Cu surface [28],[29],[30]. The driving force is the difference in reduction potential (E0) between the 3D-Cu surface (Cu2+ + 2e– → Cu0, E0(𝐶𝑢2+/𝐶𝑢0) = +0.34 V vs. SHE) and the nobler metals (E0(𝑀𝑛+/𝑀0) > E0(𝐶𝑢2+/𝐶𝑢0)), which makes this redox reaction thermodynamically stable [31]. As a first demonstration of applicability, the feasibility of the unconventional 3D-Ag and 3D-Au transducers in the field of bio-electroanalysis was elucidated by taking advantage of noble metals to physically/chemically accommodate a variety of bio-molecular components [32],[33]. Two appealing approaches, such as the enantiodiscrimination of chiral drugs (i.e., amino acids) and the supramolecular determination of environmental pollutants (i.e., uranium), have been considered [34],[35]. Importantly, the noble metalbased 3D-printed electronics exhibited enhanced bio-electroanalytical performances when compared with the pristine 3D-Cu counterpart. To the best of our knowledge, it is the first demonstration of tunability and applicability of 3D-Cu electrodes, reaching a new family of noble metal-based 3D-printed electrochemical bio-recognition systems with promising potential in the field of bio-sensors and beyond. Scheme 1. Illustration of the functionalization approach carried out for the development of functional metal-based 3D-printed electronics and their bio-recognition achievements. 3D-Cu devices were first printed via FMD and then immersed in an aqueous solution containing a noble metal ion precursor (Mn+ = Ag+ or Au3+) for the fabrication of 3D-Ag and 3D-Au devices, which were further functionalized with biomolecular and supramolecular components for bio-recognition approaches. 2. Results and Discussion 2.1. Fabrication and characterization of functional metal-based 3D-printed electronics Pendulum-like 3D-Cu electrodes (dimensions: length: 1.6 cm, wide: 0.6 cm and thickness: 0.3 mm; geometric area of the circular part: 0.28 cm2, see Figure S1 for illustration) were designed with Fusion 360 (Autodesk, USA). For the 3D printing, a commercially available Cu/PLA filament was used as the raw material. The filament was extruded down via FDM (Prusa I3 MK3 printer, Prusa Research, Czech Republic) through a nozzle (Olsson Ruby-tipped 0.6 mm, 3DVerkstan, Sweden) at 215 ºC, while the bed temperature was kept to 60 ºC. To improve the conductivity of the devices, the as-printed 3D-Cu electrodes were subsequently sintered at 1075 ºC under N2 gas flow [36]. After the thermal process, they were immersed into a 1 M HNO3 solution for 1 min to clean the surface. Afterwards, 3D-Cu electrodes were galvanically replaced by noble metals (i.e., Ag and Au) by taking advantage of the differences in E0 between Cu and the noble metals. When 3D-Cu electrodes (with a E0(𝐶𝑢2+/𝐶𝑢0) = +0.34 V) were immersed in a solution containing ions with a higher E0, the resulting ΔE0 becomes positive (ΔE0 > 0). This means that 3DCu electrodes can spontaneously provide the zero valent form of nobler metal since the redox reaction is thermodynamically stable. To do this, 3D-Cu electrodes were simply immersed into a vial filled with a 2.5 mM aqueous solution of either Ag+ (Ag+ + 1e– → Ag0, E0(𝐴𝑔+/𝐴𝑔0) = +0.80 V) or Au3+ (Au3+ + 3e– → Au0, E0(𝐴𝑢3+/𝐴𝑢0) = +1.50 V), and aged for 1h in order to promote the interfacial Cu displacement by following the equations Equation (1) and Equation (2), resulting in the functional 3D-Ag and 3D-Au electronic devices, respectively. As shown in Figure S2, the 3D-Cu surfaces became darker after galvanic replacement. Cu0 (s) + 2Ag+ (aq) → Cu2+ (aq) + 2Ag0 (s), ΔE0 = 0.46 V Equation (1) 3Cu0 (s) + 2Au3+ (aq) → 3Cu2+ (aq) + 2Au0 (s), ΔE0 = 1.16 V Equation (2) The morphological characteristics of the pristine 3D-Cu and functionalized 3D-Ag and 3D-Au electrodes were studied by means of scanning electron microscopy (SEM). As shown in Figure 1a-c, while 3D-Cu presented a mixture of both octahedral and rhombic dodecahedral structures [37], a dendritic-like growth was revealed after the galvanic exchange reactions, which is representative of non-equilibrium growth conditions [38]. Importantly, such modifications were found to be homogeneous along the whole device (see low magnifications from Figure 1d-f), evidencing an optimum functionalization of the 3D-Cu surfaces with both Ag and Au noble metals. Figure 1. Morphological characterization of the functional metal-based 3D-printed electronics. SEM images of (a-b) pristine 3D-Cu, (c-d) 3D-Ag and (e-f) 3D-Au substrates at high (top) and low (bottom) magnifications. In addition, the elemental composition of the 3D-Cu, 3D-Ag and 3D-Au substrates was studied by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The EDX spectra from Figure 2 revealed the presence of both Ag (28%) and Au (16%) —together with the remnant Cu— after incubating the 3D-Cu electrodes for 1 h with its corresponding metal ion precursor solution. These results are also in agreement with those obtained by XPS (see Figure S3 for wide-range and highresolution spectra), demonstrating that 3D-Cu substrates can be simply galvanically exchanged by nobler metals for the development of advanced noble metal-based 3Dprinted electronic devices. Figure 2. Elemental mapping of the functional metal-based 3D-printed electronics. EDX spectra of (a) 3D-Ag (inset: 3D-Cu as control) and (b) 3D-Au substrates. 2.2. Electrochemical bio-recognition achievements Having verified the successful fabrication of both 3D-Ag and 3D-Au electrodes, the next step was focused on studying their feasibility for bio-electroanalytical. Noble metals are known to easily interact with a variety of molecular components via physical/chemical interactions [39]. As a proof-of-concept, two appealing bio-recognition systems were considered: i) 3D-Ag substrates were physically biomodified with a chiral selector (i.e., L–amino acid oxidase, L–AAO) towards the enantiodiscrimination of amino acids, and ii) 3D-Au substrates were covalently tuned with a supramolecular moiety (i.e., cucurbit[6]uril, CB[6]) for the host-guest determination of uranium [40]. Chiral biorecognition of amino acids 3D-Ag electrodes have been biofunctionalized with a class-enzyme like the L–AAO, which is known to catalyze the oxidation of L–amino acids following the enantiospecific chemical reaction: L–amino acid + O2 𝐿–𝐴𝐴𝑂 → α-keto acid + H2O2 [41]. Thus, the 3D-Ag electrode was immersed into a vial containing a 5 mg·mL-1 of L–AAO (solvent: phosphate buffered solution (PBS), pH 7.2) for 12 h at 7 ºC in order to promote the physical immobilization of the enzyme upon the 3D-Ag surface [12], resulting in the L– AAO/3D-Ag electronic biorecognition system. Their potential towards the electrochemical enantiodiscrimination of amino acids was interrogated using valine enantiomers (L–Val and D–Val) as model chiral targets (Figure 3). Figure 3a shows the cyclic voltammograms (CV) of the 3D-Cu, 3D-Ag and L– AAO/3D-Ag electrodes. The intrinsic electrochemical characteristics of the pristine 3DCu electrode presented three main peaks. On one hand, two pairs of well-defined anodic peaks at –0.01 V and +0.17 V (vs. Ag/AgCl), which might be attributed to the formation of Cu2O and CuO, respectively. On the other hand, a main cathodic peak at –0.30 V related to the Cu2O/CuO reduction [42]. Importantly, a more intensive and wider peak around +0.23 V was observed after surface modification with Ag (3D-Ag electrode), which must correspond to the pair Ag+/Ag0 [43]. 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