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Luo et al. Soft Sci 2024;4:7 https://dx.doi.org/10.20517/ss.2023.40 Page 3 of 12

thermodynamically favorable galvanic reaction between metallic Ga and Cu ions facilitates the direct
growth of Cu-based compounds on the Ga-LM surface [23-25] . Accordingly, herein, we propose a simple but
highly effective route to synthesize a Ga-LM electrode decorated with a 2D annealed Cu-Oxide (ACO)
surface layer for use in non-enzyme-based electrochemical glucose biosensors. By taking advantage of the
LM’s fluidity , a uniform and continuous Ga-LM film is printed on various substrates as the current
[26]
collector. Then, a high-quality ultrathin 2D ACO layer is grown successfully on the Ga-LM surface by
triggering a mild galvanic replacement reaction, which is followed by low-temperature thermal treatment.
In this manner, an integrated electrochemical electrode for glucose sensing is realized. This electrode
combines the electrochemical sensing capability of ACO, good conductivity of Ga-LM, and good interfacial
charge transfer between ACO and Ga-LM. The performance of the proposed glucose-sensing electrode is
evaluated using cyclic voltammetry (CV), linear sweep voltammetry, and amperometry, and it exhibits
satisfactory sensitivity (0.87 μA·mM ·cm ) and a wide linear detection range (1 μM ·mM). Furthermore,
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the proposed sensor exhibits impressive glucose selectivity, and it can exclude several interfering signals,
such as those of sucrose, uric acid (UA), ascorbic acid (AA), and NaCl.
EXPERIMENTAL
Materials
Gallium (bulk, 99.99%) was purchased from Shanghai Aladdin Biochemical Technology Co. Ltd. Copper
nitrate hydrate [Cu(NO ) ·xH O, 99.99%], UA (99%), and AA (99%) were obtained from Shanghai Macklin
2
3 2
Biochemical Co. Ltd. Ammonium hydroxide solution (NH OH, 25%) was purchased from Sinopharm
4
Chemical Reagent Co. Ltd. Potassium hydroxide pellets (KOH, 85%) and anhydrous sodium sulfate
(Na SO , 99.0%) were procured from Hunan Hui Hong. Ringer’s solution and simulated body fluid (SBF)
4
2
solution (pH 7.4) were purchased from Aladdin. Carbon black (Mw 12.011 g/mol) was purchased from
Sigma Aldrich. Flexible polyethylene (PE) and paper substrates were purchased from the market. Sodium
chloride (NaCl, AR) and glucose (AR) were purchased from Tianjin Kermel Chemical Reagent Co. Ltd.
Indium tin oxide (ITO) conductive glass (surface resistance: 6 Ω/sq, light transmittance: -84%) was obtained
from South China Science and Technology Co. Ltd. All reagents were used directly without further
purification.

Sample preparation
The ACO electrode preparation process started with the printing of the Ga-LM electrode. 0.1 g of pure
melted Ga was first extruded onto the ITO glass substrate, which resulted in the formation of a well-
dispersed liquid Ga layer on the ITO substrate. Then, the liquid Ga layer was subjected to a blade coating
process to achieve uniform layer thickness. A simple printing process that combines this coating step with a
customized mask can be used to print various conductive patterns as electrodes. The Ga surface is sensitive
to oxygen; therefore, a Ga-oxide layer was readily formed after the printing process. In this manner, a
GaO -Ga electrode was fabricated. The surface of the fabricated GaO -Ga electrode was quickly treated with
x
x
1 mL of 1 M KOH solution, followed by rinsing with deionized (DI) water. This step was essential for
removing the gallium oxide skin formed on the Ga surface. Immediately after this step, the samples were
soaked in a solution of 0.01 M Cu(NO ) and NH OH (adjusted pH ≈ 11) and allowed to react for 10 min.
3 2
4
Thereafter, they were cleaned thrice with DI water and anhydrous ethanol to obtain CuO -Ga electrodes.
x
Eventually, these electrodes were dried and annealed for 2 h in a tubular furnace at 200 °C to obtain the final
ACO electrode.
Performance measurement
The electrochemical parameters and other response parameters of the fabricated electrodes were measured
using a standard electrochemical workstation (CHI660D, Shanghai Chenhua) in the test process. A three-
electrode system consisting of the synthesized electrodes was used as the working electrode, a platinum