A novel approach to the investigation of colloidal aggregation in experiments performed at microscopic particle levels by means of artificially induced particle collisions with the aid of optical tweezers is proposed. A physical model describing the artificially induced collisions was suggested. The stability ratios for different electrolyte concentrations (NaCl) are estimated by dividing the total number of particle collisions by the number of collisions leading to permanent doublets. The experimental results under different electrolyte concentrations are compared with zeta potentials and turbidity measurements. In regards to fully dispersed or rapid-coagulated systems, this approach can conveniently provide an accurate judgment of the system's stability. For general slow-coagulated systems, when the stability ratio is greater than 1.8, our data are in agreement with those obtained from the turbidity measurements. When the stability ratio is less than 1.8, the accuracy of the approach is limited due to the possibility of the imprecise control of the short duration during which the particle pair is held in the optical trap for the induced collisions. (C) 2003 American Institute of Physics.