Optical trapping for biosensing: materials and applications.

Since the 70's, when Arthur Ashkin and coworkers demonstrated that optical forces could displace and levitate microsized particles, optical trapping has seen a steady stream of developments and applications, particularly in the biological field. Since that demonstration, optical trapping has been especially exploited as a powerful tool for non-invasive sensitive measurements. The recent development of synthesis routes has further expanded the possibilities of optical trapping in the area of biosensing where new multifunctional particles are used as a single probe. The synergy between the development of new materials and experimental techniques has led to the appearance of numerous studies in which novel biosensing applications are demonstrated. The design of new materials and optical systems to face new challenges makes it necessary to have a clear idea about the latest developments achieved in the field. In this work, we summarize recent experimental advances in biosensing achieved by optical manipulation of micro- and nanoparticles providing a critical review on the state of the art and future prospects.

Assessing Single Upconverting Nanoparticle Luminescence by Optical Tweezers.

We report on stable, long-term immobilization and localization of a single colloidal Er(3+)/Yb(3+) codoped upconverting fluorescent nanoparticle (UCNP) by optical trapping with a single infrared laser beam. Contrary to expectations, the single UCNP emission differs from that generated by an assembly of UCNPs. The experimental data reveal that the differences can be explained in terms of modulations caused by radiation-trapping, a phenomenon not considered before but that this work reveals to be of great relevance.

Gold nanorod assisted intracellular optical manipulation of silica microspheres.

We report on the improvement of the infrared optical trapping efficiency of dielectric microspheres by the controlled adhesion of gold nanorods to their surface. When trapping wavelength was equal to the surface plasmon resonance wavelength of the gold nanorods (808 nm), a 7 times improvement in the optical force acting on the microspheres was obtained. Such a gold nanorod assisted enhancement of the optical trapping efficiency enabled the intracellular manipulation of the decorated dielectric microsphere by using a low power (22 mW) infrared optical trap.