Concentration-dependent thermophoretic accumulation for the detection of DNA using DNA-functionalized nanoparticles

Thermophoresis is a phenomenon about the migration of particles along a temperature gradient and is sensitive to the properties of particles and the surrounding medium. While a few studies have investigated its mechanisms and effects on particle motion in recent years, the applications of thermophoresis in biosensing has not been well explored. In this study, we demonstrate a thermophoresis-based method for detecting DNA. We use DNA-functionalized gold nanoparticles and fluorescent DNA probes to capture target DNA in free solution, and we demonstrate that the hybridization between the specially designed capture probes and the target DNA significantly changes the thermophoretic properties of the fluorescent probes. As a result, the target DNA can be specifically detected in serum-containing buffers based on the spatial distribution of the fluorescent probes in a laser-induced temperature gradient. The optical setup consists of only a laser and an epifluorescence microscope, and the detection does not rely on any micro- or nanofabricated devices. In addition, because the detection is based on the thermophoretic motion of molecules in free solution, no capture probes need to be immobilized on a fixed surface before detection, and no channels or pumps are needed for washing away unbound molecules. The thermophoresis-based biosensing method is found to be simple and effective for detecting DNA.