Supporting Information

Transcription

1 Supporting Information Gold Nanoparticle Dimers for Plasmon Sensing Yunan Cheng, 1,2,3 Mang Wang, 1 Gustaaf Borghs, * 2,3 Hongzheng Chen * 1 1. MOE Key Laboratory of Macromolecule Synthesis and Functionalization, State Key Laboratory of Silicon Materials, & Department of Polymer Science and Engineering, Zhejiang University, Hangzhou , P. R. China 2. IMEC, Kapeldreef 75, 3000 Leuven, Belgium 3. Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200, 3000 Leuven, Belgium * Corresponding authors: hzchen@zju.edu.cn (H.Chen), borghs@imec.be (G.Borghs) 1

2 Transistions of conducting polymer (CP). Figure S1. Protonation of CP with HCl or gold (Au) and deprotonation of CP by methanol. Surface chemistry of gold nanoparticles (GNP). The electrostatic attraction occurs between the positively charged Au surface and the negatively charged carbonxylic groups of CP (Figure S2). The hydrophilic substitutions of CP shell increases the dispersity of the composite nanoparticles in aqueous solutions. 2

3 Figure S2. Surface chemistry of GNP-CP core-shell nanoparticle. 3

4 Figure S3. Surface chemistry of GNP-CP assemblies in methanol. 4

5 Figure S4. Surface chemistry of GNP-CP dimer in aqueous buffers. Formation mechanism of GNP-CP dimers. Figure S5 shows the size and size distribution of A) GNP-CP core-shell nanoparticles, B) GNP-CP clusters in methanol, C) GNP-CP clusters in 0.01 M HCl and D) GNP-CP dimers in PBS buffer ph 7.0. Figure S6 shows the size and size distribution of centrifuged supernatants of GNP-CP in 0.01 M HCl. 5

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7 Figure S5. Size and size distribution of A) GNP-CP core-shell nanoparticles, B) GNP-CP clusters in methanol, C) GNP-CP clusters in 0.01 M HCl and D) GNP-CP dimers in PBS buffer ph 7.0. Figure S6. Size and size distribution of GNP-CP supernatants as centrifuged and resuspended in 0.01 M HCl. 7

8 With the above evidences, the three essential steps in the synthesis of GNP-CP dimers are defined with different functions. 1. The encapsulation of CP around GNP produces stabilizer of particles. 2. The solvent transfer of methanol helps to cluster particles with close proximity. 3. The wash by HCl is the one and only purification procedure. Therefore the dimer yield is estimated as a combined result of Figure S5-C and Figure S5-D. In Figure S5-C, more than 28% of particles (single particle) are removed by the following centrifugation. The purification efficiency is therefore about 70%. Combining the PdI (Figure S5-D) to be 0.108, the dimer yield is calculated as 70% * ( ) = 63%. Formation mechanism of kissing particles. Figure S7 shows the size and size distribution of GNP-CP as dispersed in methanol for different durations. The cluster forms from the following procedures. 1. Methanol removes the CP layer around GNP. 2. The bare GNP aggregate. 3. The CP molecules re-assembly around the GNP clusters as a monolayer. The procedures are schematically shown in Figure S8. It is noted that the CP may not be completely removed from the GNP surface (in procedure 1), so that an ultra-thin interlayer may be formed between particles inside a dimer. 8

9 Figure S7. Size and size distribution of GNP-CP clusters as dispersed in methanol for A) and B) during the first one minute and C) after about 1 minute. 9

10 Figure S8. Transformation of GNP-CP from single particle to particle clusters and dimers. Loading efficiency of IgG on GNP-CP dimers. As shown in Figure S9, the LSPR shift reaches saturation for h-igg concentration of 10 µg/ml. h-igg is a protein with molecular mass of 150 kda (data from Protein Data Bank), which is 2.5 E-19 g. 10 µg/ml h-igg would make 4.0 E13 /ml protein molecules. According to our previous reports, a solution of 20 nm GNP at O.D. 1.0 contains 7E11 /ml particles. Therefore we deduce the solution of 17 nm GNP at O.D 1.0 contains 11.4 E11 /ml particles. 10

11 The number of protein molecules bond to a sing 17 nm GNP is calculated as N protein / N GNP = 4.0 E13 / 11.4 E11 = There are 35.1 molecules of h-igg bond to a single 17 nm GNP. We additionally calculated the theoretical loading efficiency of h-igg on a 17 nm GNP as a full coverage. The diameter of h-igg is approximately 5 nm (Protein Data Bank). The calculation is therefore S GNP / S protein = 4π(R GNP ) 2 / π(r protein ) 2 = 4 * (17/5) 2 = 46.2, meaning there are 46.2 h-ig molecules bond to a 17 nm GNP as a full coverage. The loss of more than 9 molecules per particle is caused by the interconnection neck between two particles and therefore the loss of surface area. Figure S9. Longitudinal LSPR shift of GNP-CP dimer colloids as a function of h-igg concentration. The inserted drawing represents the protein binding on a GNP-CP dimer with high loading efficiency. 11

12 GNP-CP dimers-igg bio-conjugates upon the binding of pra. Upon the addition of small amount of pra, part of the GNP-CP dimer-igg conjugates immediately aggregates, as confirmed by the DLS results (Figure S10). The peak at 148 nm is correspondent to two or three conjugates combined together by pra. As such, the GNP-CP dimer-igg conjugates are proved to form small clusters with controllable size upon the adding of ultra-low-volume of pra. Figure S10. Size and size distribution of GNP-CP dimer-igg conjugates upon binding of 100 ng/ml pra. Due to the controllable size of GNP-CP dimer-igg clusters, the band at nm has still a maximum peak value when pra concentration is below 500 ng/ml (Figure S11-A). The intensity of organic absorption at 300 nm region is calculated as an average value of datas between 310 nm and

13 nm, as shown in Figure S11-B. Both of the above changes are plotted as a function of pra concentration (Figure S12). Figure S11. Assignments of A) near-infrared wavelength shift and B) intensity increase of organic absorption. 13

14 Figure S12. Optical changes of DGNP-IgG upon adding of pra. Figure S13. Optical changes of GNP-IgG upon adding of pra. The schematic insert described aggregation of GNP-CP-IgG upon adding pra. 14