Reagents and equipments. All DNA sequences were all synthesized by Sangon

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1 Supporting Information Experimental Section Reagents and equipments. All DA sequences were all synthesized by Sangon (Shanghai, China). The sequences are as follows: DA-(AG 3 ): 5 - H -(CH ) 6 -AGGGTTAGGGTTAGGGTTAGGG-(CH ) 6 -SH-3 DA- (C-rich DA): 5 -CCCTAACCCTAACCCTAACCCT-3 DA-3 (Control): 5 -da -3 Tris-(-carbozyethyl) phosphine hydrochloride (TCEP) was purchased from Sigma- Aldrich (St. Louis, MO) and used without further purification. 6-Mercaptohexanol (MCH) was purchased from Fluka and used as received. Ferrocenecarboxylic acid (Fc), -ethyl-3-(3-dimethyl-aminopropyl) carbodiimide hydrochloride (EDC), and -hydroxysulfosuccinimide (Sulfo-HS) were purchased from Sigma-Aldrich. All aqueous solutions were prepared using ultra-pure water (8. MΩ, Milli-Q, Millipore). The metallo-supramolecular cylinder [i L 3 ]Cl was synthesized and purified as previously reported. The enantiomerically pure [i L 3 ]Cl was obtained by using a cellulose (~ μm, Aldrich) column and eluting with mm acl aqueous solution. The purity is more than 95%, which was determined by ESI-MS and elemental analysis. UV-vis spectroscopy was used to determine the enantiomer concentration. The samples of purified M- and P-enantiomer were collected and freeze-dried for future use. [,]

2 Labeling of Fc to H -Modified Oligonucleotides. The ferrocene (Fc) label was conjugated to the 5 -H -moiety of the oligonucleotide (DA-), using the succinimide coupling (EDC-HS) method. Briefly, μl of μmol DA- was mixed with μl of mm PBS (ph 7.) containing mmol of ferrocenecarboxylic acid (FcA), 5mM EDC, 5mM Sulfo-HS, followed by incubation for h at 37. The excessive ferrocenecarboxylic acid was subsequently dialyzed against mm PBS buffer through the molecularporous memebrane tubing (MWCO:, Spectrum Laboratories, Inc. US). The resulting DA solution was stored at for use. Electrode Cleaning and E-DA Sensor Preparation. The oligo modified sensor was fabricated by using gold disk electrodes (Φ = mm, CH Instruments, Austin, TX). The electrodes were prepared by polishing with.3 and.5 μm deagglomerated γ alumina (BUEHLER, UAS) suspensions followed by sonication in water and multiple steps of electrochemical cleaning before modification with the thiolated Fc-tagged probe DA. The clean gold surface was incubated with a. μm solution of thiolated Fc-labeled DA oligomer pretreated with TCEP in buffer ( mm Tris buffer,.5m LiCl, m M MgCl, ph 7.) for h at room temperature. The surface was then rinsed with buffer and subsequently passivated with 6-mercaptohexanol in the Tris buffer for h. Then, the electrodes were rinsed again with buffer ( mm Tris buffer, m M LiCl, ph 7.) and stored in the Tris buffer prior to measurements.

3 Electrochemical Measurements. Alternating current voltammetry (ACV) were performed with a CHI 66B electrostation in a standard cell with a platinum counter electrode and an Ag/AgCl reference electrode. The E-DA sensor measurements were conducted by monitoring the modified working electrode in Tris buffer ( mm Tris salt, mm LiCl, ph 7.) using ACV with a step potential of mv, amplitude of 5 mv, and a frequency of Hz. Electrochemical impedance spectroscopy (EIS) was performed using Solartron Instrument equipped with S87 electrochemical interface and S55 HF Frequency response analyzer in m M Tris buffer (m M LiCl, p H= 7.) as the supporting electrolyte. The impedance spectra were recorded at potential of.65v within the frequency range of Hz. The amplitude of the applied sine wave potential in each case was 5 mv. For all G-quadruplex ligands detection measurements, ligands were diluted with the aqueous Tris buffer, and then the modified electrodes were incubated in each sample containing different concentrations of ligands for min at room temperature except the time-course study. Prior to measurement, washing with the measured buffer is necessary. For the target hybridization measurements, the electrodes were incubated in μm complementary G-quadruplex DA or μm da oligomer solution for h, and the regeneration was done with a simple 3s ultrapure water rinse. The experimental temperature was controlled at 5. To measure the apparent electron transfer rates, we performed square wave voltammetry (SWV) after min of target binding. SWV measurement were conducted over a potential range of.7 to.v, using a mv step potential and 3

4 5mV amplitude at frequencies ranging from to Hz. At each SWV mearsurement frequency, we calculated the ratio between the Fc peak current and the frequency. This peak current-to-frequency ratio was normalized and plotted against the SWV measurement frequency. The apparent electron transfer rate was estimated from the critical frequency, which was defined as the normalized peak current maximum. [3,] UV Melting and Circular Dichroism Measurements. UV melting studies were carried out on JASCO V-55 UV-vis spectrophotometer, equipped with a Peltier temperature control accessory. CD spectra were measured on JASCO J-8 spectropolarimeter. The optical chamber of the CD spectrometer was deoxygenated with dry purified nitrogen (99.99%) for 5 min before use and kept the nitrogen atmosphere during experiments. Three scans were accumulated and automatically averaged.

5 L H 3 C CH 3 L 5 [i L 3 ] + -M [i L 3 ] + -P [i L 5 3 ]+ -M [i L 5 3 ]+ -P wavelength/nm wavelength/nm Supplementary Figure S. The structure of bis(pyridylimine) ligand L and L 5 with alkyl substituent.cd spectra of the M-enantiomer (black) and P-enantiomer (red) of [i L 3 ] + (left) and [i L 5 3] + (right). 5

6 Current/ A A Current / A R =.995 B E/V vs.ag/agcl Scan Rate (V/s) Supplementary Figure S. (A) A cyclic voltammogram of Fc-AG 3 -coated Au electrode in mm Tris buffer solution (mm Li +, ph=7.). Scan rate: mv/s. (B) The linear relationship between peak currents and scan rates confirms that the redox species is confined to the electrode surface. Signal decrease/% Time/min Supplementary Figure S3. Incubation time dependence. The signal response was measured after incubation in.5μm [i L 3 ] + -P solution with different time. P-cylinder facilitated the formation of intramolecular G-quadruplex structures within several minutes, and the signal decrease 9.6% after minutes. 6

7 6 5 Current/nA 3 ACV Frequency/Hz Supplementary Figure S. ACV frequency optimization. Sensor peak currents were measured using standard parameters at frequencies from Hz to Hz. The frequency is displayed in a logarithmic scale, and a plateau of Hz was chosen. 6 Current/nA Probe Density/pmol cm - Supplementary Figure S5. Optimization of the probe surface density of E-DA sensor. The probe surface density is controlled by adjusting the probe concentration (.,.,.5,.,.5, μm) employed during sensor fabrication and subsequently determined using a previously established relationship with ACV peak current [] described in Eq. : I avg (E )=nff tot [sinh(nfe ac /RT)]/[cosh(nFE ac /RT)+] [] In which I avg (E ) is the average peak current in the AC voltammograms, n is the number of electron transferred per redox event (with Fc label n=), f is the frequency of the applied ACV perturbation, F is the Faraday constant, tot is the number of 7

8 electroactive DA probe in moles, E ac is the peak amplitude (E ac =5 mv in experiment), R is the universal gas constant, and T is the temperature (T=88.5K). The apparent electrode area-measured from the gold oxide reduction peak area during gold working electrode cleaning in.5m H SO solution-was used to calculate the probe surface density from tot. The optimal modified probe concentration was. μm with a calculated surface density of 5.7 pmol/cm. Current / na buffer 5 regenerated i-motif Current/nA 3 buffer A E/V vs. Ag/AgCl E/V vs. Ag/AgCl Supplementary Figure S6. Alternating current (AC) voltammograms of the E-DA sensor in the present of the complementary C-rich DA (μm, left) and control strand da DA (μm, right). 8

9 5 Z im /k 5 A B C simulated A simulated B simulated C Z re /k Equivalent electronic circuit: Supplementary Figure S7. yquist plots in m M Tris buffer at.65v for (A) and (simulated A): Fc-AG 3 -modified Au electrode, (B) and (simulated B): Fc-AG 3 /MCH-modified Au electrode, (C) and (simulated C): After exposure of (B) into 5μM [i L 3 ] + -P solution. Frequency range: Hz; AC amplitude: 5m V. The equivalent electronic circuit was shown below. The ZSimpWin TM electrochemical impedance analysis software was used to deal with the EIS results. 9

10 Table S. EIS results obtained by fitting of experimental data to inset circuit of Figure S7. Each EIS data has been measured for four times. R e, C e/f, R e/f, C f, R f, Zw -5 Ωcm μf cm - Ωcm μf cm - kωcm A 8± ±.9.± ±6.9 3.± ±. B 978±..7± ± ±5. 5.5± ±.6 C 895±6.86±. 99±383..7± ±5.3.98±.8 The impedance data were analyzed on the basis of the Vorotyntsev theoretical model of a surface-confined redox system that takes into account the charge-transfer process at the film/electrolyte interface as well as charge diffusion through the film. [5] o significant difference was found in the solution resistance, R e. The combining [i L 3 ] + -P cause the redox label away from the electrode surface, leading to significant increase in the electron-transfer resistance as the electeolyte/film interface R e/f, in accord with the decreased signal of ACV. It also resulted in an increase in the interpolate spacing between the electrode surface and the redox active center, reflected as a decrease in C e/f (used as an constant phase element, CPE, to improve the fitting of the experimental data). At the same time, the film thickness increased must give a decreased film capacitance, C f. R f would be the resistance of the film, which increased slightly. The Warburg impedance Zw, was resulting from diffusion of the redox probe.

11 Abs at 95nm AG3+[i L 3 ] + -P AG3+[i L 3 ] + -M Temperature / C AG3 AG3+[i L 3 ] + -P AG3+[i L 3 ] + -M Wavelength/nm 5 AG3 AG3+TMPyP 5 AG3 AG3+TO Wavelength/nm Wavelength/nm Supplementary Figure S8. UV melting and CD spectra of AG 3 solution containing [i L 3 ] + -P, [i L 3 ] + -M, TMPyP and TO.

12 5 3 3 AG3 AG3+[i L 5 3 ]+ -P AG3 AG3+[i L 5 3 ]+ -P Wavelength/nm Wavelength/nm Supplementary Figure S9. CD spectra of AG 3 solution containing [i L 5 3] + -P and [i L 5 3] + -M. Current / na buffer TMPyP Current / na 5 3 buffer TO E/V vs.ag/agcl E/V vs.ag/agcl Supplementary Figure S. Alternating current (AC) voltammograms of the E-DA sensor after incubation with 5μM TMPyP (left) and TO (right) solutions.

13 Signal decrease/% M 5 M P- M- TMPyP TO Supplementary Figure S. E-DA sensor can readily discriminate between [i L 3 ] + -P, [i L 3 ] + -M, TMPyP, and TO at the same concentration of μm and 5μM. At the same concentration of 5 μm, the signal decrease was about 7% for P-enantiomer and only. % for M-enantiomer, with the value of (I -I ip )/(I -I im ) only about 3.. The enantioselective recognition ratio would be as high as 5 at the concentration of μm. Such a large difference in electrochemical signal change made this E-DA sensor practically useful for the enantioselective recognition of the metallo-supramolecular complex. Furthermore, both of the TMPyP and TO signal decreases were much smaller than [i L 3 ] + -P, comparable with [i L 3 ] + -M solution. References: [] H. J. Yu, X. H. Wang, M.L. Fu, J.S. Ren and X. G. Qu, ucleic Acids Res. 8, 36, [] C. Q. Zhao, J. Geng, L. Y. Feng, J. S. Ren and X. G. Qu, Chem. Eur. J., 7, [3] R. J. White and K. W. Plaxco, Anal. Chem., 8, [] K. Hsieh, R. J. White, B. S. Ferguson, K. W. Plaxco, Y. Xiao and H. T. Soh, Angew. Chem., Int. Ed., 5, [5] M. A. Vorotyntsev, L. I. Daikhin and M. D. Levi, J. Electroanal.Chem. 99, 36,