Supplementary Figure S1. CV curves of gold wire and seamless solid/nanoporous Au electrodes in 0.5 M H 2 SO 4 solution at a scan rate of 100 mv S -1.

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1 Supplementary Figure S1. CV curves of gold wire and seamless solid/nanoporous Au electrodes in 0.5 M H 2 SO 4 solution at a scan rate of 100 mv S -1. The seamless solid/nanoporous Au electrode was obtained after 50 cycles for electrochemical alloying/dealloying at a scan rate of 10 mv s -1 and 120 C in the mixture of BA and 1.5 M ZnCl 2. Inset: An enlarged curve for solid gold wire.

Supplementary Figure S2. SEM images of S/NPG microwires fabricated by alloying/dealloying for 50 cycles at (a) 30 mv s -1 and (b) 50 mv s -1, respectively, in a mixed electrolyte of BA and 1.

2 Supplementary Figure S2. SEM images of S/NPG microwires fabricated by alloying/dealloying for 50 cycles at (a) 30 mv s -1 and (b) 50 mv s -1, respectively, in a mixed electrolyte of BA and 1.5 M ZnCl 2 solution at 120 C, and (c) their corresponding CV curves in 0.5 M H 2 SO 4 solution at a scan rate of 100 mv s -1. (d) CV curves of S/NPG/Co 3 O 4 microelectrodes constructed on S/NPG (fabricated at scan rates of 30 and 50 mv s -1 ) in 0.5 M KOH solution containing 10 mm glucose at a scan rate of 20 mv s -1.

Supplementary Figure S3. (a) SEM image of S/NPG microwire fabricated by alloying/dealloying for 20 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C.

3 Supplementary Figure S3. (a) SEM image of S/NPG microwire fabricated by alloying/dealloying for 20 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C. (b) CV curve of 20-cycle alloyed/dealloyed S/NPG microwire in 0.5 M H 2 SO 4 solution at a scan rate of 100 mv s -1. (c) CV curve of S/NPG/Co 3 O 4 microelectrode in 0.5 M KOH solution containing 10 mm glucose at a scan rate of 20 mv s -1.

Supplementary Figure S4. (a) SEM image of S/NPG microwire fabricated by alloying/dealloying for 50 cycles at a scan rate of 10 mv s -1 and 120 C in a mixed electrolyte of BA and 0.

4 Supplementary Figure S4. (a) SEM image of S/NPG microwire fabricated by alloying/dealloying for 50 cycles at a scan rate of 10 mv s -1 and 120 C in a mixed electrolyte of BA and 0.5 M ZnCl 2 solutions, and the corresponding CV curves in (b) 0.5 M H 2 SO 4 solution at a scan rate of 100 mv s -1, and (c) 0.5 M KOH solution containing 10 mm glucose at a scan rate of 20 mv s -1.

5 Supplementary Figure S5. (a) SEM image of S/NPG microwire fabricated by alloying/dealloying in a mixed electrolyte of BA and 1.5 M ZnCl 2 solution for 50 cycles with a scan rate of 10 mv s -1 at 60 C. The CV curves of this S/NPG/Co 3 O 4 microelectrode (b) in 0.5 M H 2 SO 4 solution at a scan rate of 100 mv s -1, and (c) in 0.5 M KOH solution containing 10 mm glucose at a scan rate of 20 mv s -1.

6 Supplementary Figure S6. Typical low-magnification top-view SEM image of seamless solid/nanoporous Au microwire that is fabricated by alloying/dealloying for 50 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C.

microwires that are fabricated at the conditions listed in Table S1.

7 Supplementary Figure S7. Diagrams showing the real surface areas of (a) the S/NPG and (b) the corresponding S/NPG/Co 3 O 4 microwires that are fabricated at the conditions listed in Table S1. Note that the real surface area of specimen No. 10 of S/NPG/Co 3 O 4 is probably underestimated according to the equation A = i/vc F with C F = 80 F cm -2 because the loading of Co 3 O 4 is too little.

8 Supplementary Figure S8. Comparison of SEM micrographs of S/NPG/Co 3 O 4 microwires synthesized by hydrothermal method at 180 C for 90 minutes in the solution containing (a) 9 mm, (b) 6 mm and (c) 3 mm Co(NO 3 ) 2, and (d) their corresponding CV curves in 0.5 M KOH and 10 mm glucose mixture at a scan rate of 20 mv s -1.

9 Supplementary Figure S9. Evolution of microstructure of S/NPG/Co 3 O 4 microwires synthesized at hydrothermal temperatures of (a) 260 C, (b) 180 C and (c) 100 C for 90 minutes in the 6 mm Co(NO 3 ) 2 solution. (d) CV curves of these S/NPG/Co 3 O 4 microelectrodes in 0.5 M KOH solution containing 10 mm glucose at a scan rate of 20 mv s -1.

10 Supplementary Figure S10. High-magnification SEM image and EDS spectrum (inset) of seamless solid/nanoporous Au/Co 3 O 4 hybrid microelectrode synthesized under the alloying/dealloying (50 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C) and hydrothermal (6 mm Co(NO 3 ) 2 and 180 C) conditions (the first one in Table S1).

11 Supplementary Figure S11. XRD pattern of seamless solid/nanoporous Au/Co 3 O 4 hybrid synthesized under the alloying/dealloying (50 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C) and hydrothermal (6 mm Co(NO 3 ) 2 and 180 C) conditions (the first one in Table S1).

12 Supplementary Figure S12. Photographs comparing the mechanical flexibility of (a) fragile NPG ribbon and (b) flexible seamless solid/nanoporous Au/Co 3 O 4 hybrid microwire.

Supplementary Figure S13. (a) SEM image and XRD pattern (inset) of Co 3 O 4 nanoparticles grown on ITO glass substrate. (b) CV curves of Co 3 O 4 nanoparticles in 0.

13 Supplementary Figure S13. (a) SEM image and XRD pattern (inset) of Co 3 O 4 nanoparticles grown on ITO glass substrate. (b) CV curves of Co 3 O 4 nanoparticles in 0.5 M KOH with (blue curve) and without (grey curve) 10 mm glucose at a scan rate of 20 mv s -1. (c) Chronoamperometry curve and (d) the corresponding calibration curves (current versus glucose concentration) of Co 3 O 4 nanoparticles with successive addition of glucose from 1 M to 10 mm in 0.5 M KOH solution at 0.26 V.

14 Supplementary Figure S14. (a) Chronoamperometry and (b) calibration curves, and (c) the corresponding concentration-dependent sensitivities of S/NPG/Co 3 O 4 hybrid microelectrodes with the S/NPG skeletons that are fabricated by the alloying/dealloying conditions listed in Table S1 (Nos. 2-6). (d) Chronoamperometry and (e) calibration curves, and (f) the corresponding concentration-dependent sensitivities of S/NPG/Co 3 O 4 hybrid microelectrodes synthesized by incorporating Co 3 O 4 onto the same S/NPG skeletons at various hydrothermal conditions (Nos in Table S1).

15 Supplementary Figure S15. (a) Maximum sensitivities as a linear function of surface area of S/NPG for S/NPG/Co 3 O 4 microelectrodes synthesized by incorporating Co 3 O 4 nanoparticles onto the different S/NPG microwires at the same hydrothermal conditions (Nos. 1-6 in Table S1). (b) Maximum sensitivities as a linear function of surface area of S/NPG/Co 3 O 4 microelectrodes that are fabricated by incorporating Co 3 O 4 into the same S/NPG skeleton at various hydrothermal conditions (Nos. 1 and 7-10 in Table S1).

16 Supplementary Figure S16. (a) Glucose response time as a function of concentration of added glucose. Glucose sensitivity of seamless solid/nanoporous Au/Co 3 O 4 hybrid microelectrode [synthesized under the alloying/dealloying (50 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C) and hydrothermal (6 mm Co(NO 3 ) 2 and 180 C) conditions (the first one in Table S1)] at different concentrations of added glucose: (b) 1 M, (c) 10 M, (d) 100 M, (e) 1 mm, and (f) 10 mm.

17 Supplementary Figure S17. Glucose sensitivity of seamless solid/nanoporous Au microwire (fabricated by alloying/dealloying for 50 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C) at different concentrations of added glucose: (a) 1 M, (b) 10 M, (c) 100 M, (d) 1 mm, and (e) 10 mm.

18 Supplementary Figure S18. Glucose sensitivity of Co 3 O 4 on ITO glass substrate at different concentrations of added glucose: (a) 1 M, (b) 10 M, (c) 100 M, and (d) 1 mm.

19 Supplementary Figure S19. UV-Visible spectra of the measurement solution of 0.5 M KOH and 10 mm glucose before and after test. The absorption peak occurring at about 264 nm is due to the production of gluconic acid during the test 43.

20 Supplementary Figure S20. The aging tolerance of S/NPG/Co 3 O 4 hybrid microelectrode over 15-day storage period. (a) Retention of current responses and (b) the corresponding current-time curves of S/NPG/Co 3 O 4 hybrid microelectrode for the addition of 1 mm glucose in the 0.5 M KOH at a potential of 0.26 V.

21 Supplementary Figure S21. SEM micrographs of (a) the microwire of S/NPG collected from S/NPG/Co 3 O 4 microelectrodes via chemical etching in 60% HNO 3 for 1 hour, and (b) the reconstructed S/NPG/Co 3 O 4 on this S/NPG skeleton by hydrothermal method.

22 Supplementary Figure S22. Glucose sensitivity of reconstructed S/NPG/Co 3 O 4 hybrid microelectrode on the basis of S/NPG microwire collected from the used S/NPG/Co 3 O 4 electrode at different glucose concentrations: (a) 1 M, (b) 10 M, (c) 100 M, (d) 1 mm, and (e) 10 mm.

23 Supplementary Figure S23. Glucose sensitivity of NPG film at different concentrations of added glucose: (a) 1 M, (b) 10 M, and (c) 100 M.

24 Supplementary Figure S24. The dependence of sensitivities of S/NPG/Co 3 O 4 hybrid electrodes on the NPG thickness of S/NPG microwires.

25 Supplementary Table S1. Alloying/dealloying conditions for the fabrication of S/NPG microwires and hydrothermal conditions for the synthesis of S/NPG/Co 3 O 4 microelectrodes. Condition Alloying/dealloying conditions Hydrothermal conditions No. Temperature ZnCl 2 concentration Scan rate Cycle number Co(NO 3 ) 2 concentration Hydrothermal temperature 1 10 mv s C 1.5 M 30 mv s cycles 6 mm 180 C 3 50 mv s C 1.5 M 10 mv s cycles 6 mm 180 C C 0.5 M 10 mv s cycles 6 mm 180 C 6 60 C 1.5 M 10 mv s cycles 6 mm 180 C C 1.5 M 10 mv s cycles 6 mm 260 C 100 C C 1.5 M 10 mv s cycles 9 mm 10 3 mm 180 C

26 Supplementary Table S2. Interfering currents of other sugars to electrochemical glucose sensing of S/NPG/Co 3 O 4 microelectrodes. Glucose: interferent molar ratio Current ratio (%) Fructose 10: Mannose 10: Maltose 10: Sucrose 10: Lactose 10: Supplementary Table S3. Comparison of glucose concentrations of diabetic patients measured by hospital and our sensors. Hospital (mm) Our sensors (mm) Patient No Patient No

27 Supplementary Note 1: The real surface areas of S/NPG microwires are evaluated through an in-situ method of oxygen adsorption of surface Au atoms on the basis of assumption that oxygen is chemisorbed in a monoatomic layer with a one-to-one correspondence with surface metal atoms 34. Therefore, the surface areas of S/NPG microwires are determined by measuring the charge from the oxide reduction peaks of their CV curves in 0.5 M H 2 SO 4 solution (Q O ) (Figs. S2c, S3b, S4b, S5b). The charge (Q S ) associated with a smooth Au surface is accepted to be 390 C cm The electrochemical surface areas (A) of S/NPG microwires are given by A = Q O /Q S. The real surface areas of S/NPG/Co 3 O 4 microelectrodes are determined by the method of capacitance measurement according to the equation A = i/vc 34,44 F. Here i is the capacitive current at a voltage of -0.1 V vs Ag/AgCl, v is the scan rate of cyclic voltammetry curves that are recorded in the 0.5 KOH electrolyte (10-50 mv s -1 ), C F 80 F cm -2 is the surface capacitance of Co 3 O 45 4.

28 Supplementary Note 2: Because the S/NPG microwires fabricated by alloying/dealloying for 20 and 50 cycles in a mixture of BA and 1.5 M ZnCl 2 at a scan rate of 10 mv s -1 and 120 C have NPG layers with the almost same characteristic length, their change of real surface areas is assumed to result from the variation of thickness of NPG layer. Therefore, the thickness of NPG layer on S/NPG microwire alloying/dealloying for 20 cycles is evaluated to be 570 nm according to the equation h 50 /h 20 Q 50 /Q 20, where Q 50, Q 20 are the charges associated with reduction of the Au oxide for S/NPG alloying/dealloying for 50 and 20 cycles, and h 50 1 m.

29 Supplementary References 43. Li, Y.X., Wang, J.X., Peng, S.Q., Lu, G.X. & Li, S.B. Photocatalytic hydrogen generation in the presence of glucose over ZnS-coated ZnIn 2 S 4 under visible light irradiation, Int. J. Hydrogen Energy 35, (2010). 44. Brezesinksi, T., Wang, J., Polleux, J., Dunn, B. & Tolbert, S.H. Templated nanocrystal-based porous TiO 2 films for next-generation electrochemical capacitors. J. Am. Chem. Soc. 131, (2009). 45. Boggio, R, Carugati, A. & Trasatti, S. Electrochemical surface properties of Co 3 O 4 electrodes, J. Appl. Electrochem. 17, (1987).