398 ± 0.298 1,561 ± 259 3.444 ± 0.411 1,611 ± 362 SPEG 4,600 6.017 ± 0.368 4,621 ± 537 6.096 ± 0.349 4,736 ± 515 SPEG 8,000 8.086 ± 0.279 8,096 ± 532 7.974 ± 0.397 7,893 ± 747 SPEG 10,000 9.903 ± 0.432 11,919 ± 989 10.032 ± 0.387 12,212 ± 897 Conclusions In summary, a unique colorimetric method was developed to determine the MW of PEG, based on the steric stabilization of PEG-coated AuNPs. Using the ordinary UV–vis spectrophotometry technique, the MW of the PEG samples can be calculated by the absorbance values of the PEG-coated AuNP solutions, after adding salt to screen the electrostatic repulsion between nanoparticles. This strategy offers operational advantages (simplicity, convenience,

and sensitivity) Selleckchem GANT61 over many existing methodologies, which has important implications for the development of nanomaterial-based determination methods. In the future, this colorimetric method can be applied to the MW determination of other soluble macromolecules. This strategy would provide a great advantage to current research areas in polymer science, materials science, and biology. Authors’ information KL and HJ Blebbistatin mouse are Ph.D. holders, and QZ is a professor. All authors are from the Key Laboratory of ABT888 Biomedical Material of Tianjin, Institute of Biomedical Engineering, Chinese Academy of Medical Sciences & Peking Union Medical College,

Tianjin 300192, People’s Republic of China. Acknowledgements We are grateful for the financial support of Major Research Plan of NSFC (90923042, 913231004), NSFC (31271023), and Graduate Innovation Fund of PUMC (2011-1001-024). Electronic supplementary material Additional file 1: Supplementary information of a colorimetric method for the molecular weight determination of polyethylene glycol. Correlation between 〈h 2〉1/2 and M w of PEG (Figure S1). TEM images of as-prepared AuNPs (Figure S2). Plot of energy vs interparticular distance (H) for steric stabilization (Figure S3). Normalized absorption

spectra of PEG (SPEG 1,450 SDHB to 10,000)-coated AuNPs in the presence of 10.0% (w/v) NaCl solution (Figure S4). Calculation of surface area of 16-nm AuNP availability for PEG adsorption (Table S1). Calculation of surface area of 26-nm AuNP availability for PEG adsorption (Table S2). (PDF 240 KB) References 1. Knop K, Hoogenboom R, Fischer D, Schubert US: Poly(ethylene glycol) in drug delivery: pros and cons as well as potential alternatives. Angew Chem Int Ed 2010, 49:6288–6308.CrossRef 2. Kou D, Manius G, Zhan S, Chokshi HP: Size exclusion chromatography with Corona charged aerosol detector for the analysis of polyethylene glycol polymer. J Chromatogr A 2009, 1216:5424–5428.CrossRef 3. Daou TJ, Li L, Reiss P, Josserand V, Texier I: Effect of poly(ethylene glycol) length on the in vivo behavior of coated quantum dots. Langmuir 2009, 25:3040–3044.CrossRef 4.