Simple experimental procedures to distinguish photothermal from hot-carrier processes in plasmonics

Light absorption and scattering of plasmonic metal nanoparticles can lead to non-equilibrium charge carriers,intense electromagnetic near-fields,and heat generation,with promising applications in a vast range of fields,from chemical and physical sensing to nanomedicine and photocatalysis for the sustainable production of fuels and chemicals.Disentangling the relative contribution of thermal and non-thermal contributions in plasmon-driven processes is,however,difficult.Nanoscale temperature measurements are technically challenging,and macroscale experiments are often characterized by collective heating effects,which tend to make the actual temperature increase unpredictable.This work is intended to help the reader experimentally detect and quantify photothermal effects in plasmon-driven chemical reactions,to discriminate their contribution from that due to photochemical processes and to cast a critical eye on the current literature.To this aim,we review,and in some cases propose,seven simple experimental procedures that do not require the use of complex or expensive thermal microscopy techniques.These proposed procedures are adaptable to a wide range of experiments and fields of research where photothermal effects need to be assessed,such as plasmonic-assisted chemistry,heterogeneous catalysis,photovoltaics,biosensing,and enhanced molecular spectroscopy.

Ionic Species Affect the Self-Propulsion of Urease-Powered Micromotors

Enzyme-powered motors self-propel through the catalysis of in situ bioavailable fuels,which makes them excellent candidates for biomedical applications.However,fundamental issues like their motion in biological fluids and the understanding of the propulsion mechanism are critical aspects to be tackled before a future application in biomedicine.Herein,we investigated the physicochemical effects of ionic species on the self-propulsion of urease-powered micromotors.Results showed that the presence of PBS,NaOH,NaCl,and HEPES reduced self-propulsion of urease-powered micromotors pointing towards iondependent mechanisms of motion.We studied the 3D motion of urease micromotors using digital holographic microscopy to rule out any motor-surface interaction as the cause of motion decay when salts are present in the media.In order to protect and minimize the negative effect of ionic species on micromotors’performance,we coated the motors with methoxypolyethylene glycol amine(mPEG)showing higher speed compared to noncoated motors at intermediate ionic concentrations.These results provide new insights into the mechanism of urease-powered micromotors,study the effect of ionic media,and contribute with potential solutions to mitigate the reduction of mobility of enzyme-powered micromotors.

Unraveling the optomechanical nature of plasmonic trapping

Noninvasive and ultra-accurate optical manipulation of nanometer objects has recently gained interest as a powerful tool in nanotechnology and biophysics.Self-induced back-action(SIBA)trapping in nano-optical cavities has the unique potential for trapping and manipulating nanometer-sized objects under low optical intensities.However,thus far,the existence of the SIBA effect has been shown only indirectly via its enhanced trapping performances.In this article,we present the first time direct experimental evidence of the self-reconfiguration of the optical potential that is experienced by a nanoparticle trapped in a plasmonic nanocavity.Our observations enable us to gain further understanding of the SIBA mechanism and to determine the optimal conditions for boosting the performances of SIBA-based nano-optical tweezers.