Graphene

Polyurethane resin (99%, Henan DaKen Chemical Co., Ltd) was added into the dispersant of aromatic solvents (S150, 98%, Pengchen New Material Technology Co., Ltd) and ethylene glycol diglycidyl ether (99%, Hangzhou Dayangchem Co., Ltd). To fully dissolve the resin, the mixture was heated to 80°C for 2 h. Subsequently, graphene (Nanjing XFNANO Materials Tech Co., Ltd), superfine graphite (Wuxi Hengtai Metal Material Co., Ltd), carbon black (90%, Zhengzhou Blue Ribbon Industry Co., Ltd) and MnO₂ powder (99.9%, Beijing DK Nano Technology Co. Ltd) were put into the above resin solution with an intense stirring of 1500 r/min for 30 min. After the resultant precursor was repeatedly ground under a three-roll grinder, MnO₂ ink was achieved. The mass proportion of polyurethane resin: graphene: superfine graphite: carbon black: MnO₂ powder is 3: 1: 1: 3: 2. The graphene conductive ink was prepared using the same reagent and procedure with graphene nanosheets (lateral size of 5–10 μm, 3–6 layers, Fig. S9), except with no addition of MnO₂. The Zn ink was made by uniformly mixing the as-prepared conductive ink and zinc powder (6–9 μm, 97.5%, Alfa Aesar) with a weight ratio of 2:1, when it was used.

The following were used in this study: graphene (XFNANO, Nanjing China, with a diameter of 0.5 μm–5 μm, thickness of 0.8 nm, and purity of 99%), BSA (Sigma-Aldrich, Shanghai, China, product no. V900933), glutaraldehyde (GA, Sigma-Aldrich, Shanghai, China, no. G7776), N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide (EDC, Sigma-Aldrich, Shanghai, China, no. 03449), N-hydroxysuccinimide (NHS, Sigma-Aldrich, Shanghai, China, no. 130672), 2-(N-morpholino)ethanesulfonic acid (MES, Sigma-Aldrich, Shanghai, China, no. M3671), ethanolamine (MEA, Aladin, Shanghai, China, E103810), anti-CA19-9 antibody (GeneTex, Irvine, CA, USA, GTX635391), CA19-9 protein (Fitzgerald, Louisville, KY, USA, 30-AC15), normal human serum (Solarbio, Beijing, China, SL010), a CA19-9 ELISA test kit (Bio-Swarmp, Beijing, China, HM10541), transmission electron microscopy (TEM) (JEOL JEM-2100Plus, Tokyo, Japan), and scanning electron microscopy (SEM) (TESCAN MAIA3 LMH, Brno, Czech Republic). All electrochemical measurements were performed using an electrochemical workstation (Metrohm Dropsens STAT-I 400, Asturias, Spain).

Porous titanium alloys with external shapes of 8 mm × 4 mm × 3 mm and 4 mm × 4 mm × 3 mm were designed by using CAD v23.0 (Materialise, Leuven, Belgium). The internal pore parameters were designed by taking a cube as the basic structural unit and the aperture size was designed as 550 μm. The porosity was ∼70%. The two sizes of porous titanium alloy scaffolds were prepared by SLM technology. The scaffold was connected with wires after pretreatment and placed into the prepared electrolyte as required. The graphite plate and the support were set as anode and cathode, and the corresponding electrolyte group was divided into 4 g/L graphene (Nanjing XFNANO Materials Tech Co. Ltd., China) and 5 g/L EDTA (Wujiang Aobang Chemical Co. Ltd., China). Oxidation treatment was performed under constant current (2 A/dm² mode for 30 min) and the preparation of graphene coating was completed by MAO. The surface morphology of Ti and Gr-Ti obtained by micro-arc oxidation technology was observed by scanning electron microscopy (JSM-TM3000, Japan).