Plasmon‐Induced Optothermal Manipulation of Colloidal Particles and Biological Entities Resilient to Saline Environments

Plasmon‐induced optothermal manipulation (PIOM) offers versatile strategies to trap and manipulate various colloidal particles and biological entities by utilizing a heat‐mediated force, known as thermophoresis. Yet, it has been challenging to employ PIOM in biological environments due to high salinity and limited tunability of environmental conditions. This study investigates the mechanism underlying the robust thermophoretic accumulation of Escherichia coli ( E. coli ) in biological media to offer a mechanistic basis for applying PIOM in biological environments. By comparing the thermophoretic responses of three distinct particles with different surface chemistries, it is revealed that the particle with high surface hydrophilicity exhibits strong thermophoretic attraction, as its dense hydration layer enhances the role of interfacial water molecules in determining thermophoretic mobility over other ionic effects. Additionally, the results elucidate that E. coli particularly sustains its thermophoretic mobility in high salinity because it maintains a sufficient level of surface potential despite strong ionic screening. Building on these findings and the demonstration of the swarm controllability of PIOM in saline environments, this study provides valuable insights for developing PIOM strategies resilient to saline environments, highlighting its potential for biomedical applications, including microbiological studies and targeted drug delivery.