Label-free and competitive aptamer cytosensor based on layer-by-layer assembly of DNA-platinum nanoparticles for ultrasensitive determination of tumor cells

A label-free and competitive electrochemical cytosensor based on layer-by-layer (LBL) assembly of DNA-platinum nanoparticles (DNA-PtNPs) for signal amplification was developed for the tumor cell determination. In this study, three different sizes of PtNPs were synthesized and successfully characterized. The PtNPs with the highest electrocatalytic activity were selected as nanocarriers. The thiolated TLS11a aptamer, with high affinity to human liver hepatocellular carcinoma (HepG2) cells, was covalently attached to the gold nanoparticles (AuNPs) deposited on indium tin oxide (ITO) glass. Meanwhile, nanoprobes were fabricated through ferrocene-labeled complementary DNA (cDNA-Fc) immobilized on the surfaces of the PtNPs. LBL technology could provide abundant signal tags and efficient signal amplifiers for electrochemical cytosensing. When the target cells competed with cDNA to bind with aptamer, double-stranded DNA was denatured and PtNPs-DNA bioconjugates were released from the ITO electrode, resulting in decreased current response. Thus the current change was related linearly to the logarithm of cell concentration from 50 to 1 × 106 cells mL−1 with a low detection limit of 15 cells mL−1, acceptable stability and reproducibility. Furthermore, the enzyme-free cytosensor could be regenerated through an electrochemical reductive desorption technique. The cytosensor possesses potential applications in early cancer diagnosis and treatment.