Facile Preparation of High-Quantum-Yield Gold Nanoclusters: Application to Probing Mercuric Ions and Biothiols Heng-Chia Chang 1, Ying-Feng Chang 2, Nien-Chu Fan 2 and Ja-an Annie Ho 1,2 * 1 Department of Chemistry, National Tsing Hua University, No. 101, Sec. 2, Kua`ng-Fu Road, Hsinchu, 30013 Taiwan 2 BioAnalytical Chemistry and Nanobiomedicine Laboratory, Department of Biochemical Science and Technology, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 20617 Taiwan *Corresponding author: Prof. Ja-an Annie Ho, e-mail: jaho@ntu.edu.tw Supplementary Information Determination of Quantum Yield Fluorescence quantum yield is defined as the numbers of emitted photons per number of absorbed photons. Quantum yields can be characteristically measured by a relative comparison method. s1 Absorption and fluorescence spectra of concentration series of the test sample and a reference sample (with known quantum yield) were acquired before determination of quantum yield. To avoid inner filter effects, the optical density of tested solutions must be below 0.1 at the excitation wavelength. Rhodamine 6G dissolved in ethanol (Q=0.95) was used herein as reference sample. Fluorescent gold nanoclusters (MUA-AuNC607, 754, 814) dispersed in methanol were used. For each sample and concentration, the absorption (optical density) at 330 nm using Varian Cary 300, and the corresponding photoluminescence spectra using Varian Cary Eclipse were recorded. The intensity versus absorption gradients of each sample was linearly fitted. After correction with the refractive index of solvent, the quantum yield of the test sample could be determined with the formula below. The quantum yield of fluorescent gold nanoclusters was determined as ca. 13% in methanol. QY = QYref x ( I/Iref) x (Aref/A) x (η 2 /ηref 2 ) I = integrated luminescence intensity of AuNCs; A = absorption at 330 nm η = the refractive index of the solvent Through comparison with rhodamine 6G (QY = 95%, in EtOH), we determined the QY of the AuNCs (MUA- AuNCs607) to be ca. 13%, a great improvement, by at least 8 orders of magnitude, relative to that of bulk gold (QY = 10 8 %) and approximately 1-2 orders of magnitude higher than the quantum S1
yield of Au NCs derived with other synthesis routes. Same comparison protocol was used to evaluate the QY of MUA-AuNCs754 and MUA-AuNCs814, they were determined to be 0.6% and 0.2%, respectively. Table S1 Comparison of the present sensing probe with other AuNPs- and AuNC-based assays AuNPs/ AuNCs Ligands on surface of AuNPs/AuNCs Detection method Masking Agent LOD (nm) Real sample tested? Reference AuNPs single-strand DNA absorption no 100 no s2 AuNPs MPA absorption no 100 no s3 AuNPs MPA/HCys absorption PDCA 25 no s4 AuNPs MPA/AMP/R6G FRET no 50 Yes, urine sample AuNPs peptide absorption no 26 no s6 AuNPs single-strand DNA absorption no 1000 no s7 AuNPs single-strand DNA Silver enhance -ment no 10 Yes, lake s8 AuNPs single-strand DNA SPR PDCA 300 no s9 AuNPs tween 20 absorption NaCl 100 Yes, drinking s10 AuNPs single-strand DNA/ OliGreen FRET no 25 Yes, pond AuNPs oligopeptides absorption no 10 no s12 AuNPs quaternary ammonium groupterminated thiols absorption no 30 Yes, drinking s13 AuNCs MUA Fluorescence PDCA 5 Yes, pond s14 AuNCs BSA Fluorescence no 0.5 no s15 AuNCs BSA Fluorescence no 80 Yes, river, tap and mineral s16 AuNCs Lysozyme type VI Fluorescence no 0.003 Yes, pond AuNCs MUA Fluorescence PDCA 0.45 Yes, lake s5 s11 s17 This study S2
Figure S1. Time evolution of the photoemission spectrum (excitation wavelength: 330 nm) for the reaction process of MUA AuNCs607. S3
(A) (B) (C) (D) Figure S2. (A, B) Absorbance spectra of (A) MUA AuNCs754 and (B) MUA AuNCs814 (insets: photographs of MUA AuNCs solution in room light). (C, D) Normalized fluorescence excitation (grey line) and emission (black line) spectra of (C) MUA AuNCs754 and (D) MUA AuNCs814 (insets: photographs of MUA AuNCs solution under a hand-held UV lamp, with excitation at 365 nm). S4
Figure S3. Fluorescence emission spectra of MUA AuNCs607 before (black line) and after (grey line) adding excess NaBH4. The fluorescence was excited at 330 nm. S5
(A) (B) Figure S4. HRTEM images of (A) MUA AuNCs754 and (B) MUA AuNCs814 (scale bar: 5 nm). S6
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