Abstract
We describe 3D single particle tracking of gold nanoparticles (AuNPs) moving along collagen fibers in aqueous environment with two-photon excitation conditions. The photoacoustic effect at the collagen fiber caused by the irradiation with ultrashort, near-infrared laser pulses propels the particles adsorbed to the surface of the collagen fibers. We report the tracking of individual AuNPs in three dimensions with high spatial and temporal resolution, of few nanometers and milliseconds, respectively. Due to the emission signal caused by the interaction between the AuNPs and the weak chromophores in the collagen fiber, the trajectories of individual AuNPs reveal the fiber topography with nanometric resolution. The intensity along the trajectory shows that we are sensitive to the distribution of the weak chromophores on the fiber.
Highlights
Collagen forms the structural network of the extracellular matrix in tissue and is the most abundant protein in vertebrates
The white dots are stationary AuNPs while the collagen fibers are visualized via the second-harmonic generation signal (SHG) occurring at the fibers
Based on the lack of motion at 4°C, we propose that the driving force of AuNPs stepping along a collagen fiber is due to photoacoustic effect (PA) effect which originates on the collagen fiber due to nearinfrared absorption of the excitation light that couples to the surrounding solvent
Summary
Collagen forms the structural network of the extracellular matrix in tissue and is the most abundant protein in vertebrates. Type I collagen consists of three lefthanded polypeptide strands twisted together into a rod-shaped, triple-helix tertiary conformation stabilized by numerous hydrogen bonds. Fibers are formed by bundles of the triple-helix basic element. Understanding both the structural and functional properties of fibrillar collagen type I is of considerable interest to many researchers, those in the medical field because the structural modifications of the fibrillar matrix are associated with various physiologic processes such as diabetes, aging, wound healing, and cancer [1,2,3]. Changes in the collagen nanostructure have been used to identify breast tissue malignancy [4]. Received 1 Nov 2010; revised 14 Jan 2011; accepted 4 Feb 2011; published 7 Feb 2011 1 March 2011 / Vol 2, No 3 / BIOMEDICAL OPTICS EXPRESS 512
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