Sub-femtomolar detection of HIV-1 gene using DNA immobilized on composite platform reinforced by a conductive polymer sandwiched between two nanostructured layers: A solid signal-amplification strategy.

This study introduces a signal amplification strategy rely on incorporating a specific polymer film between two typical nanostructured layers, aiming to improve the electrical properties of the platform to be able to transduce small binding event through sub-femtomolar detection of HIV-1 gene at the surface of the constructed biosensing device. The proposed composite was arrayed based on a conductive layer consist of p-aminobenzoic acid (PABA) sandwiched between the electrochemically reduced graphene oxide (ERGO) as the sub-layer, and the gold nanoparticles (AuNPs) as the interfacial layer. We computationally explored that how the use of such design enables the platform to transduce small changes in the interfacial properties of the biosensor, caused by low concentrations of HIV-1 gene, without needing any amplification strategy. Furthermore, it was found that the loin PABA conductive polymer sandwiched between two nanostructure layers play an artwork-ensemble role, which resulted in a good signal repeatability and stability during the relatively long successive incubation and detection procedures. The justification of using such an array of conductive layers was established on the attaining extra low-level of detection limit. The observed performance for probe-DNA immobilized on glassy carbon electrode (GC) modified with ERGO/PABA/AuNPs compared to the GC electrode modified with ERGO/AuNPs inspired us to perform computational calculations, a hybrid of ab-initio and semi-empirical quantum mechanics methods, to discover its probable molecular-scale reasons. A rapid single frequency impedance measurement (SFIM) was also employed to remarkably reduce the measurement time and diminish the probable nonspecific impedance changes. The proposed biosensor was used to evaluate the DNA target over an extremely wide concentration range from 0.1 fM to 10 nM, with a detection limit of 37 aM (S/N = 3).