Electrochemiluminescence Biosensor for the Detection of the Folate Receptor in HeLa Cells Based on Hyperbranched Rolling Circle Amplification and Terminal Protection

A highly sensitive homogeneous electrochemiluminescence (ECL) biosensor for folate receptor (FR) has been developed based on hyperbranched rolling circle amplification (HRCA) and terminal protection. FR was combined to folic acid modified single stranded DNA (FA-ssDNA) through the strong affinity between FA and FR, which prevented ssDNA from enzymolysis of exonuclease I (Exo I). The protected ssDNA was then applied as a template of padlock looping to trigger the HRCA proceeding. The products of HRCA contains large amount of double strand DNA (dsDNA), which provided excellent carries for Ru(phen)(3)(2+) intercalation. The extra free Ru(phen)(3)(2+) was removed by ultrafiltration and the Ru(phen)(3)(2+) embedded into dsDNA can act as a high-efficiency ECL indicator to quantify the FR concentration. The enhanced ECL intensity had a linear relationship with logarithm of FR concentration in the range of 4 fM to 120 pM with a correlation coefficient of 0.998. Furthermore, the proposed ECL biosensor has been applied to detect FR in Hela cells and showed a linear relationship with the logarithm of cell concentration ranging from 100-5000 cell/mL. Compared to other FR biosensors, the proposed ECL biosensor presents the merits of the simplicity, high sensitivity and specificity, which shows the great potential application in the field of early cancers diagnosis.