Determination Of Molar Concentrations Of Gold Nanoparticles By Resonance Light Scattering Correlation Spectroscopy And Its Applications

Gold nanoparticles?GNPs?are a kind of new and important nano optical probes.It has been widely used in chemistry,biology,pharmacology,clinical medicine and other fields due to its unique optical properties.However,the shortage of methods for quantification of GNPs limits its applications in bioassays and in vivo.In this paper,based on resonance light scattering correlation spectroscopy?RLSCS?technique,we established a new method for direct determination of GNPs concentration.Similar to single molecule fluorescence correlation spectroscopy?FCS?,RLSCS is obtained by measuring the resonance light scattering fluctuations in a confocal detection volume(less than 10^-15 L)due to Brownian motion of single nanoparticle and then autocorrelation function analysis on the fluctuation.In RLSCS,the particle numbers of GNPs?N?at the detection volume(V_eff)is equal to the reciprocal value of G?0?of RLSCS curve.As a result,the molar concentration of GNPs could be calculated on the basis of N and V_eff obtained by RLSCS measurements.Based on the principle of the RLSCS,we established a new method for detection of GNPs concentration in solution,and applied it for caspase 3activity and apoptosis detection.First of all,with 543.5 nm He-Ne laser as the excitation light source,we studied the relationship between N and the concentration of GNPs under defferent light intensity.It showed good linear relationships between N and GNPs concentrations at low illumination laser intensity.Furthermore,we investigated the effects of illumination laser intensity,and observed the concentration of GNPs obtained by RLSCS at low illumination laser intensity were in good agreement with that obtained by combining atom emission spectroscopy with transmission electron microscopy?AES-TEM?.Above all,we established a new method for determination of the GNPs concentration.Furthermore,we developed a sensitive microscale method for determination enzyme activity of caspase 3 using the new method of RLSCS technique with GNPs as labeling probes.The assay principle is based on measuring the change in the molar concentration of GNPs that the concentration of GNPs should increase with the enzyme cleavage reaction because the aggregated GNPs were cleaved into free GNPs.RLSCS can be used to detect the change in the molar concentration of GNPs.This method was successfully used for determination enzyme activity of caspase 3.Finally,we built a new method of apoptosis detection by analyzing the activity of caspase 3 that closely related to the cell apoptosis.Compared with traditional methods,the new method is simple,rapid,and more sensitive.