Tuning the Photothermal Effect of Carboxylated-Coated Silver Nanoparticles through pH-Induced Reversible Aggregation

CATIVA, NANCY M.; DELL'ERBA, IGNACIO E.; WAIMAN, CAROLINA V; CEOLIN, MARCELO; GIOVANETTI, LISANDRO J; RAMALLO LÓPEZ, JOSÉ M.; ELIÇABE , GUILLERMO E.; HOPPE, CRISTINA E.

LANGMUIR

AMER CHEMICAL SOC

Lugar: Washington; Año: 2020

0743-7463

The photothermal response of mercaptoundecanoic acid (MUA)-coated Ag nanoparticles (Ag@MUA NPs) in both, aqueous dispersions and paper substrates, was determined as a function of pH when irradiated with a green laser or a blue LED source. Aqueous dispersions of Ag@MUA NPs showed an aggregation behavior by acidification that was used for the formation of NPs clusters of variable sizes. Aggregation was induced by changing pH across the apparent pKa of the acid, higher than pKa of the free acid. Formation of these aggregates was completely reversible allowing the returning to the well-dispersed initial state by simply increasing pH by addition of a base. Aggregation produced a shift of the plasmon band that changed the spectra of the dispersions and their ability to be remotely heated when irradiated with visible light. These aggregates could be transferred to paper by simple impregnation of the substrates with the dispersion. On the solid substrate, a higher photothermal response than in the liquid medium was observed. A high local increase of up to 75ºC could be recorded on paper after only 30 seconds of irradiation with a green laser, whereas a blue LED array was enough for inducing melting of a solid paraffin (Tm = 36-38ºC) deposited on it. This work demonstrates that photothermal heating can be controlled by reversible aggregation of NPs to induce different thermal responses in liquid and solid media.