title: Two-Photon Fluorescence Tracking of Colloidal Clusters.
abstract: In situ dynamics of colloidal cluster formation from nanoparticles is yet to be addressed. Using two-photon fluorescence (TPF) that has been amply used for single particle tracking, we demonstrate in situ measurement of effective three-dimensional optical trap stiffness of nanoparticles and their aggregates without using any position sensitive detector. Optical trap stiffness is an essential measure of the strength of an optical trap. TPF is a zero-background detection scheme and has excellent signal-to-noise-ratio, which can be easily extended to study the formation of colloidal cluster of nanospheres in the optical trapping regime. TPF tracking can successfully distinguish colloidal cluster from its monomer.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur, Uttar Pradesh, 208016, India.
authors.forename: Debjit
authors.initials: D
authors.lastname: Roy
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur, Uttar Pradesh, 208016, India.
authors.forename: Dipankar
authors.initials: D
authors.lastname: Mondal
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur, Uttar Pradesh, 208016, India. dgoswami@iitk.ac.in.
authors.forename: Debabrata
authors.initials: D
authors.lastname: Goswami
keywords: Fluorescence; Optical tweezers; Trapping