Determination of size and concentration of gold and silica nanoparticles from absorption and turbidity spectra Nikolai Khlebtsov Institute of Biochemistry and Physiology of Plants and Microorganisms (IBPPM), Russian Academy of Sciences Saratov State University, Saratov, Russia
IBPPM gallery of plasmonic nanoparticles, hybrid multifunctional nanostructures and atomic clusters
Paracelsius (1493-1541) M. Faraday (1791-1867) R. Zsigmondy (1865-1929. NP 1925) Lord Rayleigh (1842-1919 NP 1904) T. Svedberg (1884-1971 NP 1926) G. Mie (1868-1957)
Gold nanospheres: Founding Fathers and basic properties 60 20 80 100 120 Abs 10 500 600 700 Wavelength M. Faraday G. Mie R. Zsigmondy 20 nm 50 nm
The average Au particle size is determined by the spectral position of plasmonic peak. The particle concentration can be determined from the absorption in the short wavelength part of spectrum (e.g., at 400-450 nm) independently on the particle size.
Anal. Chem. 2007 These plots represent schematic fits of experimental data
In Situ Determination of Colloidal Gold Concentrations with UV Vis Spectroscopy: Limitations and Perspectives Thomas Hendel, et al. Anal. Chem. 2014
max [nm] 580 Sp2-0 560 0 10 20 5 Sp3-0 540 520 Sp2-1 Sp1-0 Sp1-1 - 1-2 - 3-4 500 0 40 80 120 Equivolume diameter [nm] Mie theory vs experiment
The calculated Mie data are affected by: The input optical constants, that can be size-dependent! The particle-size distribution The particle shape is not regular or spherical 2.0 Re(n) a 8 Im(n) b 1.5 1.0 0.5 1 Schulz 2 Irani 3 Hageman 4 Canifeld 5 Otter 6 John.-Chr. 7 Weaver 6 4 1 2 3 4 5 6 7 50 nm 2 0.0 300 500 700 900 300 500 700 900 Wavelength [nm] Wavelength [nm]
-5 4 3+7.5 10 X, X 23 d= [ X 17 1]/ 0.06, X 23 X 500 max Eq.(15) fit:
Deviations of the extinction peak positions of Au nanorods from Mie theory as a function of the particle aspect ratio. The inset shows the initial part of the curves together with the experimental points 120 Mie max max max [nm] 80 20 10 max 60 0 1.0 1.2 1.4 e 20 b d ev =60 50 (b) a 40 40 20 30 0 1.0 1.2 1.4 1.6 1.8 2.0 Aspect ratio e=a/b
Calculated ratios of the extinction ratio of Au nanorods depending on their equivolume diameter and aspect ratio 1, 1.2, and 1.4. The inset shows linear fits for the logarithmic abscissa. A max /A 450 2.5 1.0 1.2 1.4 e=a/b b a 2 1.5 2.5 2.0 1.5 1 1.0 1 3 10 30 100 0 10 20 30 40 50 60 Equivolume diameter [nm]
Effects of polydispersity on the extinction position and peak value. Experimental points for citrate Au spherical particles were taken from Khlebtsov(1996), Haiss (2007), and Njoki (2007). max [nm] (a) A max (b) 580 W i 1 =0.5 =0 1.6 =0 0.1 560 0.5 0.1 0 d/d av 0 1 2 0.1 1.2 A max /A 450 =0.5 540 520 =0.5 0.8 2 =0.5 d av 1 0 50 100 500 0 40 80 120 Equivolume diameter [nm] 0.4 20 40 60 80 100 Equivolume diameter [nm]
Main conclusions : 1. Extinction spectra can be used for a simple and cheap in situ estimation of Au particle size and concentration. 2. Expected errors can be about 15-20%, except for very fine particles with diameters less than 3-5 nm where the bulk optical constants of Au become quite questionable. 3. Most critical factors affecting the method accuracy are the particle nonspherical shape, the size polydispersity, and uncertain optical constants of ligand-stabilized particles. TOC graph created by Thomas Hendel et al, 2014.
1 2 3 4 l 2 2.3 A/ l NCsca ( x, m) N ( d / 2) Qsca ( x, m) Three unknown parameters: N, d, m x= d/ is the diffraction parameter
Large-scale high-quality 2D silica crystals: Formation and decoration with gold nanorods and nanospheres for SERS analysis V. Khanadeev, B. Khlebtsov, S. Klimova et al., Nanotechnology, 2014. Enhancement Factor = 5000=10*Enh. Factor of Au Nanorods
Solution STER 1 Determination of the particle refractive index by using ethanol/dmso immersion media <n> =1.475 0.005 1 (a) 1 (b) Extinction ratio, A(n m )/A(n m0 ) 0.8 0.6 0.4 0.2 n=1.46 1.47 1.48 1.49 1.50 d=90nm =100 n m0 =1.364 =400, 500nm Extinction ratio, A(n m )/A(n m0 ) 0.8 0.6 0.4 0.2 n=1.46 1.47 1.48 1.49 1.50 d=215nm =100 n m0 =1.364 =400, 500nm 0 1.36 1.38 1.4 1.42 1.44 1.46 Refractive index n m 0 1.36 1.38 1.4 1.42 1.44 1.46 Refractive index n m
Solution STER 1 Determination of the particle refractive index by using ethanol/dmso immersion media <n> =1.475 0.005
Solution STER 2 Measuring the absorption spectra at several wavelength to redefine the solution w log / log Wavelength exponent is a function of the particle size
Example1: Mie calibration plots for a polydisperse silica spheres Average diameter d av [ m] 0 5 10 15 20 25 1E+008 4 <C sca > Q sca 1E+006 Q sca, w 2 0 w 1E+004 1E+002 1E+000 <C sca > [nm 2 ] -2 0 10 20 30 Size parameter, x= d av n m / 1E-002
Final STER 3 Determination of the particle size and concentration directly from extinction spectrum
Example 2: Determination the silica particle size and concentration by different methods (TEM, DLS, AFM, STT)
Example 3: Test of the method for 5 polystyrene latexes (90-220 nm)
Main conclusions : 1. Extinction spectra can be used for a simple and cheap in situ estimation of Silica particle size (50-1000 nm) and concentration. 2. We propose an optical method and provide experimental data on a direct determination of the refractive index of silica particles n=1.475±0.005. 3. Finally, we exemplify our method by determining the particle size and concentration for 10 samples to show good agreement with TEM, AFM, and dynamic light scattering data. 4. Most critical factor affecting the method accuracy is the accuracy in determination of the wavelength exponent. Typically, variations in w are about 0.01 thus leading to 10-15% errors in the average particle size (compared to TEM).
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