Laser manipulation and optical adhesion control of functional gel-microtool for on-chip cell manipulation

Optical adhesion control of a functional gel microtool, made of hydrophilic photo-crosslinkable resin, was developed for on-chip cell manipulation. The functional gel microtool used can be manipulated by optical tweezers and functionalized by spiropyran chromospheres, which is a photochromic polymer. Spiropyran chromospheres were used for temporal cell adhesion of the gel microtool. The adhesiveness of the gel microtools was controlled by photo irradiation. The gel microtools adhere to glass and other gel microtools, in an electrolyte solution of adjusted concentration, after ultraviolet (UV) illumination. By controlling the electrolyte concentration, the adhesion to cells can be selected as either permanent or temporal cell adhesions. UV illumination caused the cell to adhere to the gel microtool, while VIS illumination detached it from the gel-microtool. We also produced a pH sensing gel microtool by modifying the gel microtool with a pH indicator, bromothymol blue (BTB). The pH value was measured by detecting the color of the gel microtool with calibrated color information. Local measurements of the ambient pH value of a single yeast cell were performed by a ring shaped gel microtool and by immobilizing the cell on the surface of the pH sensing gel microtool.