Simultaneous Optical Trapping and Electromagnetic Micromanipulation of Ferromagnetically Doped NaYF₄ Microparticles

Abstract

Optical trapping allows the trapping and manipulation of dielectric microparticles. However, full control over all six degrees of freedom of the trapped object is challenging. Here, we use ferromagnetic iron-doped upconversion microparticles for simultaneous optical trapping and magnetic micromanipulation that allows full control over all translational and rotational degrees of freedom. These microparticles have a low absorption that allows optical trapping and a high coercivity and saturation magnetization that allow magnetic manipulation. The particles will enable micromanipulation experiments, for example, in single-molecule biophysics.

Facets of optically and magnetically induced heating in ferromagnetically doped-NaYF4 particles

“…Although the extinction coefficient of Fe-30 NYF particles we report is less than that of gold (≈0.15 [44]) and other metallic particles under 975nm illumination, they show a very efficient photothermal conversion without relying on plasmonic effects [45]. The refractive index of Fe-30 NYF particles has been reported to be 1.478 ± 0.0029ι [21]. In this regard, we also envisage that the photothermal properties of our particles can be improvised further by introducing a core-shell configuration with metallic nano/microparticles.…”

“…We show that these have better efficiency at heat generation upon illumination with 980 nm Laser light than those without iron doping. At the same time, the presence of iron in the lattice makes the particles ferromagnetic with saturation magnetization values as high as 3 A m −1 [21]. We first show the heating effects of these iron-codoped UCPs (Fe-15 NYF and Fe-30 NYF) through multi-cycle hysteresis losses, at an applied field frequency of 50 Hz.…”

“…A basic hydrothermal method [32] is followed to prepare the Fe-doped NaYF 4 :Yb,Er upconverting particles [21,28]. To prepare 15 at% Fe doped NaYF 4 :Yb,Er (Fe-15 NYF), 0.126 M yttrium nitrate (Y(NO 3 ) 3 ,63 at% of Y) and 0.3 M of sodium citrate (Na 3 C 6 H 5 O 7 ) were mixed with 14 ml of water by vigorous stirring for 10 min.…”

“…NaYF 4 :Yb, Er, 30 at% (Fe-30 NYF) particles were also prepared by similar steps except for modification in the concentration of 0.06M of ferric nitrate (Fe(NO 3 ) 3 ,30 at% Fe) and 0.096 of ytterbium nitrate (Yb(NO 3 ) 3 , 48 at% of Yb). The physical and chemical properties of the particles are reported in our previous work [21].…”

“…In this work, we report application of NaYF 4 : Er 3+ , Yb 3+ based UCPs which are codoped with different concentrations of iron (Fe) towards photothermal and magnetothermal heating. These particles also have adequate refractive index values that enable optical trapping [21]. Earlier studies have shown the enhancement in emission as well as lattice heating of NaYF 4 , Er 3+ , Yb 3+ UCPs with Fe-doping [22,23].…”