Electronic Supplementary Information

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1 Electronic Supplementary Material (ESI) for RSC Advances. This journal is The Royal Society of Chemistry 2016 Electronic Supplementary Information osinase-catalyzed polymerization of L-DPA (versus L- tyrosine and dopamine) to generate melanin-like biomaterials for immobilization of enzymes and amperometric biosensing Mengzhen Dai a, Ting Huang a, Long Chao a, Yueming Tan a, Chao Chen a,*, Wenhua Meng b, and Qingji Xie a,* a Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education), National & Local Joint Engineering Laboratory for New Petrochemical Materials and Fine Utilization of Resources, College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha , China b Hunan Normal University Hospital, Changsha , China * Corresponding author. Tel./Fax: chenchao840103@163.com (C. Chen), xieqj@hunnu.edu.cn (Q. Xie) S1

2 H H H 2 N R H 2 N R L-DPA Dopaquinone Intramolecular cyclization H R H R Dopachrome Leucodopachrome Isomerization Polymer H H R R Scheme S1. The possible pathways for -catalyzed oxidation and polymerization of L- DPA (R=CH) and DA (R=H). The denominations here are given for L-DPA only and those for DA can be inferred simply by using the phrase dopamine instead of the phrase dapa, e.g., from dopachromine to dopaminechromine. S2

3 H H 2 N CH L-tyrosine H H H 2 N CH H 2 N CH L-DPA Dopaquinone Intramolecular cyclizati H CH H CH Dopachrome Leucodopachrome Isomerization Poly(L-DPA) (PD) H H CH CH Scheme S2. The possible -catalyzed pathway for oxidation and polymerization of L- tyrosine. S3

4 Table S1. Catechol-biosensing performance of some enzyme electrodes reported in literatures and developed in this work Enzyme electrode S / ma LD LDR reference mm -1 cm -2 / M / M -PPy/GCE /Co 3 4 /GMC AuNC-(PSS-AuNC) MPA-AuNP-SPCE PD--MWCNTs/GCE this work PD--G/GCE this work CS-/GCE this work Nafion-/GCE this work PD C -/GCE this work PD-/GCE this work poly(l-tyrosine)-/gce this work PDA-/GCE this work PPY: polypyrrole; MEBCs: metal-organic coordination polymers-enzyme biocomposites; GMC: graphitized ordered mesoporous carbon; AuNC: gold nanocubes; SPCE: screen printed carbon electrode; PD C : chemical oxidative polymerization of L-DPA by using K 3 Fe(CN) 6 as an oxidant. S4

5 Table S2. Performance comparison among some typical glucose biosensors based on immobilized Gx Enzyme electrode Sensitivity / A mm -1 cm - 2 LD / M LDR / M reference Gx-PoAP/platinized GCE CS-Gx-AuNP/Au PDA-Gx/Au Pt/mesoporous carbon-gxgelatin/gce Au-PtNPs/CNTs/Gx/CS/GCE MWCNTs-CS-Gx/Au CS-Fc/MWCNTs/Gx/GCE PDA-Gx-Lac-MWCNTs /Pt PD-Gx-/Pt this work PD-Gx--G/Pt this work PD-Gx--MWCNTs /Pt this work poly(l-tyrosine)-gx-/pt this work PDA-Gx-/Pt this work PoAP: poly(o-aminophenol); PPY: polypyrrole; PtNPs: Pt nanoparticles; CNTs: carbon nanotubes. S5

6 Table S3. Results obtained in analysis of several human serum samples with the PD-Gx- /Pt electrode* Determined by Determined in hospital Bias (mm) Standard added Found (mm) Recovery biosensor (mm) (mm) (mm) * Fresh serum samples were first analyzed at Hunan Normal University Hospital with a Biochemical Analyzer (Mindray BS-300, Shenzhen Mindray Biomedical electronics Co., Ltd.) based on the well-known Gx-peroxidase spectrophotometric method. The samples were then analyzed at the PD-Gx-/Pt electrode. Serum sample (0.100 ml) was added into 10.0 ml PBS at ph 7.0, and the current response was recorded at 0.50 V vs. SCE for glucose analysis. S6

7 Fig. S1. Digital pictures of the surfaces of bare GCE (1), PD-/GCE (2), PDA-/GCE (3), and poly(l-tyrosine)-/gce (4) (left) as well as bare Pt (5), PD-/Pt (6), PDA-/Pt (7), and poly(l-tyrosine)-/pt (8) (right) after water rinse and drying. S7

8 j / A cm -2 A j / A cm -2 B c / mg ml ph Fig. S2. ptimization of concentration and biosensing solution ph on the stable current response at PD-/GCE in stirred PBS containing mm catechol. Applied potential: V vs. SCE. The responses here are discussed as follows. The current response notably increased with the increase of concentration from 0.2 to 1.0 mg ml 1, then decreased slightly with the further increase of concentration to 1.4 mg ml 1, so 1.0 mg ml 1 was used in subsequent experiments. In addition, the maximum response of the biosensor occurred at ph 7.0 that fits the enzyme activity, so 0.1 M PBS with ph 7.0 was selected for future experiments. S8

9 A B 30 b 30 b -i / A 20 a - i / A 20 a t / s c / mm Fig. S3. Time-dependent current response (A) to successive additions of catechol into stirred 0.1 M PBS (ph 7.0) under atmosphere and the calibration curves (B) at PD--G/GCE (a), PD--MWCNTs/GCE (b). Applied potential: -0.1 V vs. SCE. S9

10 Fig. S4. The digital pictures of 5 mm L-DPA + 1 mg ml -1 (1), 5 mm DA + 1 mg ml -1 (2), and 5 mm L-tyrosine + 1 mg ml -1 (3) after reactions for various time periods (2, 10, 20 or 30 min) and finally a centrifugation immediately after the 30-min reactions. S10

11 i / i t / day Fig. S5. The storage stability of PD-/GCE under storage condition (as a dry state in a refrigerator at 4 o C). S11

12 A 40 B 40 j / A cm j / A cm ph E / V vs SCE Fig. S6. Effects of solution ph (applied potential: 0.5 V vs. SCE) and applied potential (solution ph 7.0) on the stable current density response at PD-Gx-/Pt in stirred PBS containing 0.5 mm glucose. The responses here are discussed as follows. The maximum response of the biosensor occurred at ph 7.0 that fits the enzyme activity, so 0.1 M PBS with ph 7.0 was selected for future experiments. j increased rapidly with the change of applied potential from 0.30 to 0.50 V vs. SCE and then increased slowly from 0.50 to 0.8 V vs. SCE, due to the increased driving force for the fast oxidation of H 2 2 at the higher potential. To minimize interferences and current noise at high potentials, 0.50 V vs. SCE was selected as the applied potential for amperometric measurement. S12

13 i / A A a b i / A B a b t / s c / mm Fig. S7. Time-dependent current responses (A) to successive additions of glucose into stirred 0.1 M PBS (ph 7.0) and the calibration curves (B) at PD-Gx--G/Pt (a) and PD-Gx- -MWCNTs/Pt (b) electrodes. Applied potential: 0.50 V vs. SCE. S13

14 A 5 B AA UA 0.8 i / A 3 2 i / i glucose t / s t / day Fig. S8. (A) Amperometric response obtained at PD-Gx-Ty/Pt electrode in PBS (ph 7.0). The arrows show the moments of injections of 1 mm glucose, 0.2 mm ascorbic acid (AA), and 0.2 mm uric acid (UA). Applied potential: 0.5 V vs. SCE. The addition of AA or UA only yielded within 4% of the glucose response here. (B) The storage stability of PD-Gx- /Pt electrode under storage conditions (as a dry state in a refrigerator at 4 o C). S14

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