Imprinting Upconversion Nanoparticles by Means of Scanning Probe Microscopy

The authors consider using upconversion fluoride nanoparticles of NaYF₄ doped with Yb³⁺ and Er³⁺ ions as ordered non-invasive hidden labels. At the first stage the synthesized upconversion fluoride nanoparticles have been deposited from the suspension onto the substrate with mechanical scratches used as large-scale markers. The scanning probe microscope is then used to move individual upconversion nanoparticles macroscopically significant distances and deposit them in a controlled manner onto a clean surface, thereby imprinting nanoobjects. The displacement and deposition process has been monitored using a conventional optical microscope. Luminescent signals from regularly placed labels have been recorded in an optical confocal microscope.