High-Performance Flexible Graphene Aptasensor for Mercury Detection in Mussels

Transcription

1 Supporting Information for: High-Performance Flexible Graphene Aptasensor for Mercury Detection in Mussels Ji Hyun An, ζ Seon Joo Park, ζ Oh Seok Kwon, ζ,ξ Joonwon Bae, and Jyongsik Jang ζ,* ζ World Class University (WCU) Program of Chemical Convergence for Energy & Environment (C 2 E 2 ), School of Chemical and Biological Engineering, Seoul National University, Seoul , Korea ξ Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA Department of Applied Chemistry, Dongduk Women s University, Seoul, Republic of Korea Corresponding Authors: Tel: ; Fax: ; * jsjang@plaza.snu.ac.kr The concentration of immobilized aptamer on modified graphene surface (Figure S1)... 2 Current-voltage (I V) curves of the graphene aptasensor before and after the introduction of Hg 2+ ions (Figure S2) 4 Selective responses of the aptasensor towards target metal ions (Figure S3)..6 Inductively Coupled Plasma-Atomic Emission Spectrometer (ICPE) analysis for mussels (Table S1)...7 1

2 The concentration of immobilized aptamer on modified graphene surface Figure S1. The absorbance of immobilized aptamer on modified graphene surface before and after washing. NanoDrop 2000/2000c spectrophotometer was used to measure the concentration of immobilized aptamer on the graphene surface.the spectrophotometer is stored in memory as an array of light intensities by wavelength. The sample intensities along with the reference intensities are used to calculate the sample absorbance according to the following equation: Absorbance = log[intensity sample /Intensity reference ] The spectrophotometer used the Beer-Lambert equation to correlate the calculated absorbance with concentration. TE buffer solution as solvent of aptamer was used for the reference solution. To calculate the amount of aptamer attached on the surface of graphene, we compared the aptamer concentrations before and after the immobilization of aptamer on the surface. The solution of 10 nm aptamer was measured before introduction to the graphene surface as standard curve (Figure S1, black-line). Then, the modified graphene using 0.02 M DAN and 2% GA was treated with the solution of 10 nm aptamer for 6 h. Consecutively, the aptamer-immobilized graphene were washed with 1 ml TE buffer solution, which was collected as the washing sample (Figure S1, red-line). Each concentration of standard and washing samples was 1.8 ng/µl and 0.2 ng/µl. As a result, 1.6 ng/µl of aptamer was immobilized on 2

3 the modified graphene surface. The results showed that 88.8 % of aptamer remained on the graphene surface after washed by PBS buffer solution. 3

4 Current-voltage (I V) curves of the graphene aptasensor before and after the introduction of Hg 2+ ions Figure S2. (a) Current-voltage (I V) curves of the graphene aptasensor before, after the immobilization of aptamer and after the introduction of 10 pm Hg 2+ ions as target metal ions (V ds : -2 to 2 V in a step of 40 mv). (b) I ds V ds relationships before and after the introduction of 10pM and 10nM Hg 2+ ions under a liquid-ion gated FET geometry (V ds : -2 to 2 V in a step of 40 mv and V g : 0 V) and (c) enlarged the relationships of (b) in the range of V 0 V. To confirm the interaction of the aptamer and target ions, we measured I V curves of the graphene aptasensor before and after the immobilization of aptamer. As you requested, we added the I V curve 4

5 after the introduction of target ions (Hg 2+, 10pM) as shown in Figure S2 (a). A di/dv value decreased with decreasing current from to after the introduction of Hg 2+. Increasing surface roughness (the attachment of Hg 2+ ) and resistance (charge-transfer) resulted in the decreased di/dv value. Although di/dv value decreased following the attachment of the aptamer and Hg 2+ ions, the I V relation remained linear, indicating that highly stable electrical properties is preserved after introducing the aptamer and Hg 2+ ions. Furthermore, to confirm clearly the interaction of the aptamer and target ions, a liquid-ion gated FET geometry, which is introduced for real-time response system, was constructed (V g = 0 V). A di ds /dv ds value slightly increased with following introduction of 10 pm Hg 2+ ions ( to ). Moreover, when the 10 nm Hg 2+ ion was dropped in the FET geometry, the I ds V ds value increased from to in comparison with 10 pm Hg 2+ ion (Figure S2 (b)) owing to the gating effect induced from the aptamer/hg 2+ ions interaction. The graphene aptasensor showed predominant p-type (hole-transporting) electrical behavior in the FET device. The aptamer/hg 2+ ions interaction accumulated holes as majority positive charge carriers forming a p-type FET on the graphene surface. Therefore, adding Hg 2+ ions resulted in an increase in the drain-to-source current (I ds ). Figure S2 (c) displayed enlarged I ds V ds curves in the range of -0.5 V 0 V, which shows significant difference after the introduction of Hg 2+ ions. 5

6 Selective responses of the aptasensor towards target metal ions Figure S3. (a) Selective responses of the aptasensor towards target metal ion (Hg 2+, 10 pm) and non-target metal ions (Cd 2+, Co 2+, Ni 2+, Na +, Pb 2+, Sr 2+, Li 2+ and Zn 2+, 10 mm ). (b) to (i) originate from (a) and show the magnified fragment of times orders by 100 seconds. ( SNR indicates signal-to-noise ratio). Figure S3, originated from Figure 5c, showed the magnified fragment by time. In case of non-target metal ions: Cd 2+, Co 2+, Ni 2+, Na +, Pb 2+, Sr 2+, Li +, and Zn 2+, no measureable change was observed in I ds (signal-to-noise < 0.168). However, significant signal changes in I ds occurred upon addition of Hg 2+ ions, which is clearly meaningful (signal-to-noise: ). 6

7 Inductively Coupled Plasma-Atomic Emission Spectrometer (ICPE) analysis for mussels Table S1. Inductively Coupled Plasma-Atomic Emission Spectrometer (ICPE) analysis for mussels. Metal ions Weight concentration (mg/l) Mole concentration (mole/l) Hg Pb Cd Li Ni Co Sr