Supporting Information For. Microelectrode mirna Sensors Enabled by Enzymeless Electrochemical Signal Amplification

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1 Supporting Information For Microelectrode mirna Sensors Enabled by Enzymeless Electrochemical Signal Amplification Tanyu Wang 1,2, Emilie Viennois 2,3, Didier Merlin 2,3 *, Gangli Wang 1 * 1 Department of Chemistry, Georgia State University, Atlanta, GA USA 2 Institute for Biomedical Sciences, Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA USA 3 Atlanta Veterans Affairs Medical Center, Decatur, USA *Corresponding author: glwang@gsu.edu Tel: (404) dmerlin@gsu.edu Tel: (404) Table of Content: Figure S1. Characterizations of a 25-µm-radius gold microelectrode. Figure S2. Electrochemical sensor responses at different fabrication steps monitored with CVs. Figure S3. CV responses of a DNA-modified electrode at different TCEP concentrations. Figure S4. Frequency dependence of SWV and peak current analysis. Figure S5. SWVs of DNA-sensor response at mir-122 concentrations from 10 fm to 0.5 nm. Figure S6. SWV responses at different mir-122 concentrations at a frequency of 1 KHz. Figure S7. The stability of the microelectrode sensors. Figure S8. Mismatch discrimination of the microelectrode sensors. S-1

2 Figure S1. Characterizations of a 25-µm-radius gold microelectrode in (A) 0.1 M H 2 SO 4 at a scan rate of 100 mv s -1 ; (B) 1 mm ferrocene solution at a scan rate of 100 mv s -1. S-2

3 Figure S2. Electrochemical sensor responses at different fabrication steps monitored with CVs in HB. A clean background was obtained after the 2 nd passivation was performed. S-3

4 Figure S3. CV responses of a DNA-modified electrode at different TCEP concentrations. Data at 40, 80, 120, and 160 um were recorded at a scan rate of 5 V s -1. S-4

5 Figure S4. Frequency dependence of SWV and peak current analysis. (A) SWVs of a microelectrode sensor after hybridization with 0.5 nm mirna-122 in the presence of 160 um TCEP were recorded at varied frequency ( scan rate). (B) The peak current shows linear correlation with frequency. Peak current at each frequency was read after baseline adjustment as shown in Fig 2B. S-5

6 Figure S5. SWVs of DNA-sensor response measured at 10 min at a frequency of 100 Hz for mir-122 concentrations from 10 fm to 0.5 nm. The background curve before each measurement were recorded for the same sensor and demonstrated excellent sensor recovery after simple wash with 4 M guanidine chloride (GHCl). S-6

7 Figure S6 SWV responses at different mir-122 concentrations at a frequency of 1 KHz. (A) SWV of a microelectrode sensor measured at 10 min at a frequency of 1000 Hz. Increase in mir-122 concentration results in a quantitative increasee in anodic current of methylene blue with TCEP amplification. (B) The calibration curve shows a qualitatively-similar trend as the one measured at 100 Hz (Figg 3C). S-7

8 Figure S7. The stability of the microelectrodee sensors. The sensors can be regenerated by washing with 4 M GHCl for 30 seconds. The sensor responsee exhibited clean baseline in HB prior to each measurement and regenerable signal in the presence of mir-122. The recovery CVs (after regeneration) were recorded in HB only at a scan rate of 5 V s -1. S-8

9 Figure S8. Mismatch discrimination of the microelectrode sensors. The results demonstrate excellent selectivity against 2-mismatch synthetic mirna strand (mir 22B) and biological-relevant mismatch RNA strand (mir-122-3p) in the presence of 160 um TCEP. S-9