Nanodiamond-Agarose Gels for Effective Photothermal Heating

Experimental investigation of the photothermal properties of carboxylated nanodiamond (ND) particles in agarose gel base medium over a range of very low particle concentrations from 6.55 x 10-5 to 2.29 x 10-2% v/v and two different sizes (35 and 160 nm) is carried out. Laser-induced spot heating of gels with trace amounts of ND particles lead to a very large increase in temperatures away from the spot compared to base gels. These increases are inconsistent with any thermal conductivity increases associated with the incorporation of particles. UV-visible and Raman spectroscopy investigation demonstrates that this photothermal phenomenon is attributed to particle concentrations and size-dependent changes in optical scattering/entrapment of nanoparticle-laden gels. Structural investigation of the gels suggests that ND particles associate with the agarose polymer structure which leads to increased optical scattering and entrapment in particle-laden gels. Collectively, it is concluded that combining trace amounts of nanodiamond particles in agarose gels dramatically affect the light scattering and entrapment properties of the nanoparticle-laden gels, subsequently influencing the photothermal conversion efficiency of the system. This effect arises from the synergistic modification of the gel by the nanodiamond particle addition, rather than the independent effects of nanoparticles or the gel alone. Nanodiamond (ND)-agarose gels exhibit photothermal dissipation when exposed to 785 nm laser light. The nanoparticles bind to the agarose polymer structure causing structural deformation and increased light scattering. This photothermal excitation causes efficient heating of the nanogel at ultralow ND concentrations. At higher ND concentrations, saturation of the structural deformation sets in and effectively limits the heat transfer capabilities.image