Optical concentration of gold nanoparticles as a new concept of analytical sensitivity

Abstract

Concentration procedures have always been implemented when trace analysis of compounds in real matrices is contemplated. A variety of concentration strategies have been reported aiming at decreasing the limits of detection (LODs). The optical concentration of the substance in solution is one of the novel concepts for the enhancement of the analytical sensitivity. In this study, the optical concentration has been measured by the trapping of gold nanoparticles ($100$ nm) dispersed in water at low-concentrations at the focal volume of the laser beam. The influence of factors such as the time of gold nanoparticle trapping, the size of the nanoparticles, the intensity of the laser beam, their solution concentration have been reported on the accumulation of gold nanoparticles in the solution. The results showed at different laser intensities, the capacity of the optical trap changed. At low concentrations of gold nanoparticles, the signal increased linearly with the concentration until the capacity of the optical trap was filled. Also, the best optical concentration efficiency was observed when the time of trapping increased to a period of 40 s. Under the optimum conditions, the relative concentration increase of gold nanoparticles was calculated across the range of $2\mathrm{ }$ to $25$ particles at the focal volume of the laser beam for the range from $7.20\times {10}^7\text{ to }5.8\times {10}^9$ particle/mL of gold nanoparticles in the solution at a laser intensity of $400$ mW. This approach may be used to quantitatively determine of gold nanoparticles, supermolecules, and other nanoparticles.

Keywords:

• Concentration
• gold nanoparticles
• optical traping

Acknowledgment

The authors are grateful for the support of the Research Council of Chemistry and Chemical Engineering Research Center of Iran and Sharif University of Technology.

Disclosure statement

The authors declare that they have no conflicts of interest.

Scheme 2. Schematic diagram of the evaluation of the optical concentration of the gold nanoparticles.

Scheme 1. Setup of the optical tweezers: OL1, OL2, objective lenses; L1, L2, L3, lenses; M1, M2, mirrors; DM1, DM2, dichroic mirrors; CCD, charge-coupled device; QPD, quadrant photodiode; d and Ic are the diameter and the confocal length of the excitation beam.