DNA-linked CdSe QDs/AGQDs "Z-scheme" system: Ultrasensitive and highly selective photoelectrochemical sensing platform with negative background signal

Depended on the target-induced formation of a DNA-linked CdSe quantum dots/amino-functionalized graphene quantum dots (denoted as CdSe QDs/AGQDs) "Z-scheme" system, an ultrasensitive and highly selective PEC sensing platform has been constructed for DNA assay. Firstly, the indium tin oxide (ITO) electrode was modified with the poly(diallyldimethylammonium chloride) (PDDA)-decorated reduced graphene oxide (PDDA-rGO) to fix and disperse CdSe QDs. The obtained ITO/PDDA-rGO/CdSe QDs electrode generated an anode photocurrent. After catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) processes triggered by target DNA (T-DNA), abundant and long double-strand DNA (dsDNA) were introduced to the sensing platform. And then, numerous AGQDs were intercalated into the dsDNA strands, resulting in the formation of DNA-linked CdSe QDs/AGQDs "Z-scheme" system and the change of the response signal from anodic to cathode photocurrents. Because of the negative background signal and DNA-based amplification strategy, T-DNA was detected sensitively (linear range, 1 aM - 100 pM; detectable limit, 0.1 aM). Importantly, the developed PEC sensing platform can avoid the effects of the initial signal and background noise, and has the enhanced sensitivity and anti-interference ability, which make it may have promising application in bioanalysis and disease diagnosis.