<p> Electronic Supplementary Material</p><p>Colorimetric determination of lysozyme based on the aggregation of gold nanoparticles controlled by a cationic polymer and an aptamer</p><p>Xin Yao • Xiangdong Ma • Chun Ding •Li Jia* Ministry of Education Key Laboratory of Laser Life Science & Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, China * To whom correspondence should be addressed, Tel: +86-20-85211543, Fax: +86-20- 85216052, Email: [email protected]</p><p>1. Dynamic light scattering experiment The dynamic light scattering analysis showed that the average size of AuNPs was 20.2 nm, as shown in Fig. S1. The Stokes-Einstein formula was used as the mathematical model for dynamic light scattering analysis.</p><p>1 Fig. S1 Size distribution of well-dispersed AuNPs. The average size of AuNPs is about 20.2 nm.</p><p>2. Optimization of experimental conditions The concentrations of PDDA and aptamer are critical factors to the performance of this biosensing LZ system. Therefore, the concentrations of PDDA and aptamer were optimized. At first, a PDDA concentration-dependent the absorbance ratio at 590 nm and 531 nm</p><p>(A590/A531) change of 0.365 nM AuNPs was recorded, as shown in Fig. S2. The A590/A531 value gradually boosted up along with the increase of PDDA concentration until reaching a plateau beyond 111.1 nM PDDA, which revealed that 111.1 nM PDDA was enough to aggregate AuNPs. Thus, 111.1 nM was chosen as the concentration of PDDA for the assay. Next, an aptamer concentration-dependent the absorbance ratio (A590/A531) change of 0.365 nM AuNPs in the presence of 111.1 nM PDDA was recorded. Fig. S3 demonstrates that the A590/A531 value gradually decreases along with the increase of aptamer concentration until reaching a plateau beyond 0.6 μM. Consequently, 0.6 μM aptamer was selected as the suitable concentration for the assay. Afterwards, an incubation time-dependent the absorbance ratio</p><p>(A590/A531) change of 0.365 nM AuNPs in the presence of 111.1 nM PDDA was recorded. As shown in Fig. S4, the absorbance ratio (A590/A531) increases along with the increase of incubation time until reaching a plateau beyond 60 s. Thus, the incubation time 60 s was used for subsequent experiments.</p><p>2 Fig. S2 The relationship of the absorbance ratio (A590/A531) of AuNP solution (0.365 nM) with the concentration of PDDA (n=3).</p><p>Fig. S3 The relationship of the absorbance ratio (A590/A531) of AuNP solution (0.365 nM) with the concentration of LZ aptamer in the presence of 111.1 nM PDDA (n=3). </p><p>3 Fig. S4 The relationship of the absorbance ratio (A590/A531) of AuNP solution (0.365 nM) with the incubation time after adding PDDA to the AuNP solution containing aptamer and LZ (n=3). Experimental conditions: 50 μL AuNPs (2.6 nM); 10 μL LZ aptamer (0.6 μM); 6 μL PDDA (111.1 nM); 290 μL 100 nM LZ.</p><p>Fig. S5 Absorption ratios (A590/A531) of AuNP solutions after addition of thiol compounds</p><p>4 (n=3). The concentration of each thiol was 100 nM, and LZ 100 nM.</p><p>Fig. S6 Absorption ratios (A590/A531) of AuNP solutions after adding different concentrations of L-cysteine or GSH to the LZ solutions (100 nM), respectively (n=3). Experimental conditions: 50 μL AuNPs (2.6 nM); 10 μL LZ aptamer (0.6 μM); 6 μL PDDA (111.1 nM); the concentration of L-cysteine or GSH from a to c, 22.3 nM, 44.5 nM, 89.0 nM, respectively.</p><p>5</p>